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Illumination and the adsorption of xanthate in the flotation of galena and marmatite Guarnaschelli, Claudio 1968-12-31

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ILLUMINATION,AND THE ADSORPTION OF XANTHATE IN THE FLOTATION OF GALENA AND MARMATITE .by  CLAUDIO GUARNASCKELLI B.Sc., University o f Alberta, 1961 M.Sc, University of Alberta, 1965  A thesis submitted i n p a r t i a l f u l f i l m e n t o f the requirements f o r the degree o f DOCTOR OF PHILOSOPHY in the Department of Mineral . Engineering  We accept t h i s thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA November, 196 8  In p r e s e n t i n g an  this  thesis  in partial  f u l f i l m e n t of the requirements f o r  advanced degree a t t h e U n i v e r s i t y o f B r i t i s h  the  Library  I further for  shall  make i t f r e e l y  agree that  permission  available  Columbia,  I agree  that  f o r r e f e r e n c e and S t u d y .  for extensive  copying of this  thesis  s c h o l a r l y p u r p o s e s may be g r a n t e d b y t h e Head o f my D e p a r t m e n t o r  by  his  representatives.  of  this  written  thes.is f o r f i n a n c i a l  gain  permission.  Department o f  Mineral Engineering  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, Canada  Date  I t i s understood  December 24, 1968  Columbia  shall  that  copying or p u b l i c a t i o n  n o t be a l l o w e d w i t h o u t  my  ABSTRACT  The changes i n the adsorption c h a r a c t e r i s t i c s of potassium ethyl xanthate (KEtX) on galena (PbS) and marmatite [(Zn,Fe)S] due to i l l u m i n a t i o n have been investigated. Studies by others have indicated that:  (1)  the amount of surfactant adsorbed by a semiconductor depends on i t s n-type or p-type character, (2) copper activation of sphalerite (ZnS) i s required f o r f l o t a t i o n , (3)  sphalerite i s a semiconductor with an energy gap of  3.6 eV whereas galena i s a semiconductor with an energy gap of 0.3 7 eV. The amount of xanthate adsorbed from aqueous solution on galena and marmatite was found to depend on both the intensity and photon energy (0.5 to 3.5 eV) of the incident l i g h t .  In the galena system, increasing the  l i g h t photon energy above the energy gap value increased adsorption of xanthate.  The amount of xanthate adsorbed  by the p-type galena was three times the amount adsorbed by the n-type galena.  This suggested that the reaction  may i n v o l v e the t r a n s f e r o f an e l e c t r o n from the adsorbate t o t h e adsorbent.  The e f f e c t o f the presence o f an oxide  f i l m on the s u r f a c e s o f galenas was a l s o i n v e s t i g a t e d and appeared t o be l e s s s i g n i f i c a n t than the type o f charge c a r r i e r o r i g i n a l l y dominant i n the m i n e r a l . When c o p p e r - a c t i v a t e d marmatite by l i g h t with photon  was i l l u m i n a t e d  e n e r g i e s lower than the i n t r i n s i c gap  (3.6 e V ) , a d s o r p t i o n o f xanthate was l e s s than when the m i n e r a l was kept In darkness.  S i m i l a r "photodesorption"  e f f e c t s have been r e p o r t e d i n the l i t e r a t u r e .  These were  e x p l a i n e d by e x c i t a t i o n o f e l e c t r o n s from t r a p s t o the conduction band and subsequent In the v a l e n c e band.  recombination w i t h h o l e s  Fewer charge c a r r i e r s would then  have been a v a i l a b l e to p a r t i c i p a t e i n the a d s o r p t i o n reactions.  F l o t a t i o n experiments  r e s u l t s above. dropped  agreed with the a d s o r p t i  F l o t a t i o n recovery o f activated  marmatite  c a . 10% when the m i n e r a l was i l l u m i n a t e d with  a h i g h i n t e n s i t y o f 0.6 eV photons  as compared to the  recovery i n daylight. A model t h a t takes i n t o account the s u r f a c e conc e n t r a t i o n o f e l e c t r o n s and the type and c o n c e n t r a t i o n o f impurities i s discussed.  The a c t i v i t y and s e l e c t i v i t y  o f s u r f a c e r e a c t i o n s a r e e x p l a i n e d i n terms o f the e l e c t r o c h e m i c a l p o t e n t i a l , i . e . the Fermi energy  level,  iv  the a c t u a l affected  position  and/or displacement  by t h e i m p u r i t i e s  present.  o f which i s  TABLE OF CONTENTS  ABSTRACT .  i i  LIST OF TABLES  viii  LIST OF FIGURES  x  ACKNOWLEDGEMENT  xiv  CHAPTER 1  -  INTRODUCTION  1  CHAPTER 2  -  LITERATURE REVIEW  4  2.1  Introduction  4  2.2  Solid Semiconductors  4  2.3  Recent Approaches to Flotation  2.4  Illumination  2.5  Sources of Radiant Energy  CHAPTER 3 -  11 .13 19  EXPERIMENTAL METHODS  23  3.1  General Approach.  23  3.2  Materials  24  (a)  Marmatite C(Zn,Fe)S]  24  (b)  Galenas [PbS and (Pb,Ag)S]  26  Cc)  Potassium Ethyl Xanthate (KEtX)  26  (d)  Water  27  (e)  Copper Sulphate (CuS0 .5H 0) 4  2  27  vi  3.3  Surface Area Measurements  27  3.4  E l e c t r i c a l Conductivity and Hall E f f e c t  28  3.5  Seebeck Voltage Measurements  32  3.6  Oxidation of Galena Powders  HI  3.7  Adsorption from Solution  42  (a)  Apparatus  42  (b)  Typical Adsorption Procedure  48  (c)  A n a l y t i c a l Procedure  52  (d)  Reproducibility  55  3.8  Flotation  CHAPTER 4  -  56  EXPERIMENTAL RESULTS  59  4.1  Surface Area Measurements. .  59  4.2  Effects of Illumination  63  4.3  Effect of Oxidation on Adsorption  71  4.4  E f f e c t o f Surface Characteristics on Adsorption.  76  4.5  Effect of Illumination  77  4.6  Copper Activation.  81  4.7  Electrophysical Measurements  86  4.8  Correlation of Adsorption Results  4.9  Flotation Experiments  CHAPTER 5  -  Intensity on Adsorption .  DISCUSSION OF RESULTS  5.1  Adsorption  5.2  Photochemical  5.3  Carrier Behaviour  5.4  Impurities and Reaction Mechanism  .  88 92 96 96  Effects  99 . 101 103  vii  CHAPTER 6  -  SUMMARY AND CONCLUSIONS  106  SUGGESTIONS FOR FURTHER WORK  10 9  REFERENCES  110  APPENDICES . A  Hall C o e f f i c i e n t :  Conversion of cgs Units to  P r a c t i c a l Units  114  B  Beer's Law for KEtX  115  C  Reproducibility of Results  116  D  Detailed Calculation o f the BET Isotherm for Marmatite  120  E  Oxidation of Galena Samples  12 3  F  Sample Calculation ,of the Fermi Energy Level from Thermoelectric Power Detailed Calculation of the H a l l C o e f f i c i e n t , Carrier Concentration and Mobility Calculation of C a r r i e r Concentration i n PbS Using Thermoelectric Data Calculation of the Proportionality Factor to Correlate the Number of P a r t i c l e s to Their Weight f o r Galena and Marmatite  G H I  J  Preliminary  K  Tabulation  Flotation Tests of Adsorption Tests  12 7 12 8 130 131 . .133 137  LIST OF TABLES Page TABLE I  Electromagnetic Spectrum  19  TABLE II  Analysis of Marmatite Sample  25  TABLE I I I  Analysis of Galena Sample  26  TABLE IV  BET Areas of Powders (100/150 mesh). . . .  62  TABLE V  Calculated Surface Areas of Screened Fractions of Marmatite  62  Electrophysical Characteristics of Activated Marmatite after Adsorption of EtX~as a Function of Illumination Intensity  80  TABLE VII  Adsorption of Copper on Marmatite  85  TABLE VIII  Changes in the Electrophysical Characteristics of (Zn,Fe|S_ on Addition of Various Cu Concentrations  85  Electrophysical Characteristics of Solid Specimen  87  Seebeck E f f e c t of Solid and Powder Specimens  87  TABLE VI  TABLE IX TABLE X TABLE XI  Adsorption Results in Terms of Xanthate Coverage  90  TABLE XII  Summary of Flotation Results  94  TABLE XIII  Oxidation of of Galena (Cominco) in the Rates Presence Water Vapour . . . . 124  TABLE XIV  Oxidation Rates of Argentiferous Galena i n the Presence o f Water Vapour . . . . 125  ix  TABLE XV TABLE XVI  TABLE XVII  Oxidation Rates o f Galena i n a Dry Atmosphere o f Oxygen.  12 6  Flotation of Galena (100/150 mesh) in Daylight Using KEtX and Dowfroth 250  134  Flotation of Activated Marmatite (15 0/20 0 mesh) i n Daylight Using KEtX and Dowfroth 25 0  135  TABLE XVIII Flotation of Activated Marmatite (150/200 mesh) Using KEtX, Dowfroth 250 and Light of 2.5 Microns. . . . . . 136  LIST OF FIGURES Page Figure 1  Figure 2  Figure 3  Distribution function and electron and hole population f o r impurity semiconductors  6  Tentative energy l e v e l diagram f o r the excitation and emission t r a n s i t i o n s in ZnS phosphors.  9  Models of luminescence according t o : (a) Schon-Klasen; (b) Lambe-Klick; (c) Prener-Williams  18  Figure 4  Emission  18  Figure 5  Relative spectral energy d i s t r i b u t i o n of the black body r a d i a t o r normalized at ^ = 560 millimicrons  Figure 6 Figure 7  spectra of luminescence i n ZnS. . .  Spectral transmittances of absorption filters  21 21  Schematic diagram of the apparatus f o r surface area measurements  29  Figure 8  Schematic diagram of the Hall e f f e c t . . . .  31  Figure 9  Ohmic connections to marmatite specimens . .  33  Figure 10 Figure 11  Ohmic contacts to galena specimens . . . . . Origin of ohmic voltage drop due to misalignment when measuring the Hall c o e f f i c i e n t  34 35  Figure 12  Schematic diagram of the Seebeck e f f e c t . . .  37  Figure 13  Origin of the P e l t i e r e f f e c t f o r an n-type.  37  Schematic diagram of the apparatus f o r the measurement o f the Seebeck voltage  39  Figure 14  xi Page Figure 15  Figure 16 Figure 17  Figure 18  Apparatus for the measurement of the Seebeck voltage rearranged outside the Faraday cage. Schematic diagram of the adsorption apparatus Adsorption apparatus complete with accessories and a semi-micro flotation c e l l .  Figure 21 Figure 22 Figure 23  Figure 24  3  4  1 + 4  Characteristics of the Sylvania Quartz-Iodine lamps  Figure 19 Measured transmittance of Corning Glass f i l t e r s Figure 20  ^0  Adsorption on apparatus and decomposition of KEtX Schematic diagram of the f l o t a t i o n arrangement BET plot for 100/150 mesh mineral powders  4  9  5 4  " 61  Adsorption of EtX" from a solution of KEtX (9xlO- M) on activated (Zn,Fe)S (100/150 mesh) at 20°C and natural pH ( 6.5) under controlled illumination.  . 64  Adsorption of EtX" from a solution of KEtX (9xlO M) on activated (Zn,Fe)S (100/150 mesh) at 20°C and.natural pH (6.5) under controlled illumination  65  Adsorption of EtX" from a solution o f KEtX (9xlO" M) on PbS (100/150 mesh) at 20°C and natural pH under controlled illumination  69  Adsorption o f EtX" from a solution of KEtX (5xlO" M) on (Pb,Ag)S (100/150 mesh) at 20°C and natural pH under controlled i l l u m i n a t i o n  70  Oxidation rates of galena i n oxygen i n the presence of water vapour  73  5  _5  Figure 25  Figure 26  5  5  Figure 2 7  xii Page Figure 2 8 Oxidation rates of galena i n a dry atmosphere of oxygen Figure 2 9  Figure 30  Figure 31  Figure 32  Figure 33  .  74  Adsorption of EtX~ on freshly prepared surfaces of galena (100/150 mesh) from a solution of KEtX i n a helium atmosphere at 20°C, natural pH and constant wavelength (. 340-. 380 microns)  75  Adsorption of EtX~ on activated (Zn,Fe)S (150/200 mesh) at 20°C and natural pH using various i n t e n s i t i e s of i l l u m i n a t i o n at a constant wavelength (.340-.380 microns) from a 400 W7QI lamp . ,  78  Variation on the amount ."of :EtX~ . adsorbed as a function of l i g h t i n t e n s i t y f o r a constant energy (3.6-3.3 eV) at 10 min .,  79  The e f f e c t of copper a c t i v a t i o n on the adsorption of EtX" from a solution • of KEtX (5X10-5M) on (Zn,Fe)S (65/100 mesh) at 20°C and natural pK, illuminated with l i g h t of 3.6-3.3 eV.  83  ,  The effect of washing the marmatite after copper a c t i v a t i o n , lOg of (Zn,Fe)S (65/100 mesh) with 100 ml. of a 0.996xlO M solution of CuSO 4» 5H 0 on subsequent adsorption of EtX" at 20°C and natural pH, illuminated with l i g h t of 3.4-3.3 eV. -3  2  84  Figure 34  Beer's law for potassium ethyl xanthate using a 1 cm quartz c e l l  Figure 35  Reproducibility of testing procedure using marmatite.Test conditions: daylight, lOg of activated (Zn,Fe)S (65/100 mesh), 20°C, pH=6.5, 1000 ml.  117  Reproducibility of testing procedure using galena. Test conditions: 400 W-QI Lamp, 20g of PbS (100/150 mesh), 20°C, 600 ml. . .  118  Figure 36  ,  115  xiii Page Figure 37  Figure 38  Reproducibility of testing procedures using galena. Test conditions: 500 W-QI Lamp, 20g of PbS (100/150 mesh), 20°C, 600 ml  119  Electronic integrator areas of volumes of nitrogen injected  122  ACKNOWLEDGEMENT  I wish to express my deep gratitude and sincere appreciation to Dr. J . Leja f o r h i s guidance and useful c r i t i c i s m throughout the course o f t h i s investigation. My thanks are also due to a l l the members of the Department of Mineral Engineering, i n p a r t i c u l a r to Dr. G.W. Poling and Dr. H. Majima and a l l the graduate students for t h e i r useful suggestions  and discussions.  I wish also to thank Mr. M. Clegg for spending many hours i n technical discussions and meticulous proofreading of the manuscript. Unlimited appreciation goes to my wife who, during a l l my university years, displayed a great deal of patience and tolerance while accepting the major r e s p o n s i b i l i t y of bringing up a family. I am indebted to Syncrude of Canada Limited, and the National Research Council of Canada f o r t h e i r f i n a n c i a l support without which t h i s study would have not been possible.  CHAPTER 1 INTRODUCTION  The primary requirement for the successful f l o t a t i o n of a hydrophilic mineral i s the adsorption  of a  surfactant at the s o l i d / l i q u i d interface i n a form that w i l l lead to a subsequent particle-bubble  attachment.  While the fundamental mechanism of adsorption further elucidation, the role of the substrate  still  requires  i n adsorption  i s becoming increasingly apparent as some investigators  * '  have found that i r r a d i a t i o n may be used successfully to increase the recoveries o f the minerals floated. In general, solid-state photochemistry has not received the amount of quantitative e f f o r t dedicated to l i q u i d and gaseous systems because o f the inherent c u l t i e s peculiar to the s o l i d system.  diffi-  These include  profound differences i n chemical behaviour as a r e s u l t of c r y s t a l defects  (impurities, l a t t i c e imperfections, ion  vacancies), non-homogeneous absorption change i n the adsorption species on illumination.  of l i g h t and a  c h a r a c t e r i s t i c s of the adsorbing These changes may r e s u l t i n  either photodesorption or photoadsorption.  Cadmium  sulphide  shows less a f f i n i t y for phenolphthalein when i r r a d i a t e d i n  2 an aqueous solution of ethanol than when not exposed to i l l u m i n a t i o n ^ ' , whereas the red form of mercuric shows the reverse e f f e c t .  sulphide  As a d i r e c t consequence, the  results of studies o f a given system by d i f f e r e n t i n v e s t i gators are often i n direct disagreement. In an attempt to correlate the energy structure of minerals with t h e i r f l o t a t i o n properties,Plaksin et al^  y  considered the electrophysical properties of the  s o l i d phase as a base on which to construct theory of the f l o t a t i o n process.  a satisfactory  These authors showed  that the f l o t a t i o n recovery of zircon i s strongly affected by exposure of the s o l i d s to y-radiation.  In another work  Plaksin and Shafeev^) analyzed the e f f e c t of l i g h t from a 175 watt bulb on the adsorption  c h a r a c t e r i s t i c s of o l e i c  acid on ilmenite and found that the f l o t a t i o n recovery increased by 12%.  Since the photoelectric e f f e c t i n semi-  conductors i s well known^ *^'^' and a l l sulphide minerals 4  are semiconductors  v  , i t i s conceivable that a photon  energy of a few electron volts could cause the necessary electronic t r a n s i t i o n s that may enhance or retard the adsorption of surfactants. The purpose o f the present research  was to  investigate the e f f e c t s o f photon energies of 0.5 to 3.5 eV on the adsorption  of xanthate on copper activated  marmatite and on both p-type and n-type galena.  A further  objective was to correlate the electrophysical properties  3  of the substrate with the adsorption of xanthate at a constant illumination l e v e l .  In order to achieve these  objectives, electrophysical as well as adsorption ments were required.  experi-  The physical c h a r a c t e r i s t i c s given  by the H a l l c o e f f i c i e n t on s o l i d samples were supplemented by measurements of the thermoelectric power on p e l l e t i z e d powders.  Kinetic measurements of the adsorbed  quantities  of xanthate were obtained by c i r c u l a t i n g a xanthate solution i n a closed  system with the powder retained  f r i t t e d discs.  The  between  adsorption c h a r a c t e r i s t i c s of  two  the  xanthate on the various sulphides are presented as a function of the energy of illumination, illumination i n t e n s i ty, added impurities, oxidation  and f l o t a t i o n .  The  resulting  effects are further correlated in terms of the measured surface area. The  adsorption c h a r a c t e r i s t i c s of galena and  marmatite depend strongly on the electronic d i s t r i b u t i o n in the substrate.  The n-type or p-type character dominates  the adsorption behaviour more so than the e f f e c t of i l l u m i nation.  The l a t t e r i s readily detectable by k i n e t i c  measurements but i s not so evident under normal f l o t a t i o n conditions.  CHAPTER 2 LITERATURE REVIEW  2.1  Introduction Xanthate anions chemisorb readily on most sulphide (8  minerals  9)  '  but the r e l a t i v e amounts adsorbed vary de-  pending on the individual c h a r a c t e r i s t i c s o f the s o l i d substrate.  Since a l l sulphide minerals are semiconductors^  the effects of illumination on the adsorption o f xanthate at a s o l i d / l i q u i d interface  involve both an a p r i o r i know-  ledge of the electrophysical  c h a r a c t e r i s t i c s of the semi-  conductor and an understanding  of the changes i n the  electronic d i s t r i b u t i o n caused by the absorption o f photons. It i s this change i n the electronic d i s t r i b u t i o n that has been u t i l i z e d i n the most recent developments i n f l o t a t i o n recovery. 2,2  Solid Semiconductors The c r y s t a l structure of semiconductors i s cur-  rently described i n terms of the band theory of s o l i d s . In t h i s theory  the l a t t i c e ions are considered to  affect the movement of electrons only by causing exclusion  o f bands (energy gaps, E ) from t h e p o s s i b l e e l e c t r o n i c g  s t a t e s o f motion.  The d e n s i t y o f charge c a r r i e r s  (-lO^/cc)  12 i s lower than t h a t  f o r metals (^10  /cc) hence e l e c t r i c  f i e l d s i n the surface plane caused by s u r f a c e  dipoles  extend f o r a d i s t a n c e o f many atomic l a y e r s i n t o the bulk m a t e r i a l , forming a space charge r e g i o n  below the  surface.  The depth o f the e f f e c t i v e space charge l a y e r , o r the Debye l e n g t h , can be as great  as 10,0 00 A f o r semiconductors.  U s u a l l y semiconductors a r e c l a s s i f i e d as n-type o r p-type depending on whether the charge c a r r i e r s are e l e c t r o n s o r f r e e quantum s t a t e s ( h o l e s ) .  F i g . 1 shows the b a s i c  s t r u c t u r e o f both n-type and p-type semiconductors with p a r t i c u l a r emphasis on the form o f the Fermi d i s t r i b u t i o n f u n c t i o n [ f ( E ) 3 as i m p u r i t i e s a r e added t o the e x i s t i n g structure.  In F i g . l a i f an e l e c t r o n i s e x c i t e d from a  donor l e v e l i n t o the conduction band, the semiconductor behaves as a m e t a l .  In t h i s case, the e l e c t r i c a l  v i t y i s due to the f r e e movement o f e l e c t r o n s conductance).  A p-type conductance  (n-type  i s shown i n F i g . l b  when an e l e c t r o n i s moved i n t o an a c c e p t o r l e v e l behind a h o l e f r e e t o m i g r a t e .  conducti-  leaving  I f both donor and a c c e p t o r  l e v e l s are p r e s e n t then the semiconductor i s o f the mixed type.  Pure s p h a l e r i t e i s r e p o r t e d  t o be an n-type  semi-  conductor while galena can have e i t h e r p o r n-type  j  properties'^"'. The semiconducting p r o p e r t i e s o f pure s p h a l e r i t e  Density of states / g<>  (a) N - TYPE  E  c  Probability f of electron occup ation  Q  Product f ( E ) g ( E ) 0  c  DONOR LEVEL I n t r i n s i c Fermi Level Probability l - f of hole occupation Q  Product [ l - f ( E ) ] g ( E ) 0  v  (b) P - TYPE  Electrons  I n t r i n s i c Fermi Level ACCEPTOR LEVEL Holes Valence band F i g . 1 - D i s t r i b u t i o n function and electron and hole population f o r impurity semiconductors (after McKelvey ). 4  are well known even though at the standard conditions of temperature and pressure the mineral i s a non-conductor. To promote conducting properties, a suitable amount of energy must be supplied to transfer electrons from the (12) valence band to the conduction band.  Gudden and Pohl  measured the photoconductivity of sphalerite and showed that the absorption peak corresponds to a photon energy of approximately  3.7 eV i n agreement with the fundamental  absorption edge.  Cheroff and K e l l e r ^ ' attributed the 1 3  photoconductivity e f f e c t at longer wavelengths to the presence of impurities i n the c r y s t a l l a t t i c e . (14) Low and Weger i n sphalerite.  investigated the e f f e c t of iron  For an iron content as low as 0.03%  recorded three strong peaks at approximately  they  7,000 A (1.8  and a strong absorption band at 3 microns (0.4 eV).  eV)  The (15)  effect of manganese has been investigated by McClure who noted a number of peaks i n the 3,900-5,000 A region. The absorption below these regions increased steadily c u l minating i n what i s commonly referred to as the fundamental absorption edge.  Because of the gradual increase in ab-  sorption there i s a discrepancy i n the assignment of a particular wavelength to the fundamental frequency. and Goldsmith^**' and C u r i e a s  Beun  well as most of the  other investigators, agree that the absorption edge l i e s in the 3,400 A region and that i t i s a measure of the energy gap.  Thus, f o r sphalerite, the photon energy of  8 the forbidden gap i s of the order of 3.6 eV equivalent to 8 3 Kcal/mole.  Bube  v x o /  investigated the ZnS phosphors at  room temperature and proposed a tentative energy l e v e l diagram for the measured e l e c t r o n i c transitions involving absorption, e x c i t a t i o n , emission, trapping and photocond u c t i v i t y processes.  The materials studied included pure  ZnS, ZnS with Cu and ZnS with Ag as added impurities, together with other impurities, including Mn, Mg and Na.  The  author showed that there were f i v e major trapping l e v e l s common to a l l ZnS phosphors regardless of the impurity. Fig, 2 shows the proposed energy l e v e l diagram for e x c i tation and emission t r a n s i t i o n s .  Optical trap emptying by  v i s i b l e l i g h t , l i k e thermal trap emptying, involves a process of stimulation i n which trapped electrons are raised into the conduction band before returning to luminescence centers to produce emission. Natural galena i s normally an n-type semiconductor with an energy gap of the order of 0.37  eV or 8.5 Kcal/mole.  Amphoteric properties have been a t t r i b u t e d e i t h e r to impuries or to non-stoichiometric proportions o f Pb and S i n c r y s t a l s , both n-type and p-type being the object of more recent investigations. In general, the e l e c t r i c a l properties of p a r t i a l l y i o n i c semiconductors may  be attributed  to the presence of donor and acceptor l e v e l s produced e i t h e r by foreign atoms or by deviations from stoichiometric proportions.  The c r y s t a l can exist as a single phase over  EXCITATION  EMISSION  w +J  rH O >  c 2  2 o  0) H W  o L  F i g . 2 - T e n t a t i v e energy l e v e l diagram f o r the e x c i t a t i o n and e m i s s i o n t r a n s i t i o n s i n ZnS phosphors ( a f t e r BubelS).  J  a range of composition  through the inclusion of i n t e r -  s t i t i a l atoms and/or vacant l a t t i c e s i t e s .  Wide variations  in the absorption c h a r a c t e r i s t i c s of various samples of galena have been observed by Paul and J o n e s ^ ^ ' even though the impurity content was too small to be detected (21) by normal chemical procedures.  Brebrick and  Scaulon  investigated the e l e c t r i c a l properties of galena of near s t o i chiometric composition prepared  by c o n t r o l l i n g the tempe-  rature and vapour pressure of sulphur.  The impurity energy  gap that they calculated from t h e i r experimental ,was  0.03  eV f o r an n-type c r y s t a l and 0.001  results  eV f o r a p-type  crystal. The fact that galena does not show a sharp (22) absorption edge i s attributed by Gibson of radiation with energy l e s s than 0.37  to the absorption eV r e s u l t i n g i n an  electronic t r a n s i t i o n within the conduction band. In a recent study on the photoconductivity of (23) lead sulphide f i l m s , Fleming and Alberg  proposed that  t h e i r films were composed of both n-type and p-type material, the p-type regions c o n s i s t i n g of the i n t e r c r y s t a l l i n e layers and the outer portions of the c r y s t a l l i t e s which had become oxidized during the preparation of the f i l m . Plaksin and Shafeev^ ' described the action of oxygen as 24  the take-up of electrons during i o n i z a t i o n of the adsorbed oxygen molecules.  This resulted i n a lowering of the height  of the p o t e n t i a l b a r r i e r at the mineral surface.  The  11 chemical potential gradually f e l l o f f and the p r o b a b i l i t y of the xanthate anions overcoming the potential b a r r i e r gradually increased.  2.3  Recent Approaches to Flotation ( 25 ) As early as 1959, Plaksin  emphasized the role  of oxygen and other gases i n f l o t a t i o n .  According to t h i s  author, oxygen promotes dehydration of the mineral surface and f a c i l i t a t e s the penetration of xanthate groups thus assisting their fixation.  Using an i n f r a r e d multiple re(26)  flectance technique, Poling and Leja  found no i n t e r -  action between galena and xanthate ions solutions i n the (27) absence of oxygen.  Tolun and Kitchener  confirmed these  results and suggested that oxygen not only reacts with the galena surface forming a thin layer of basic thiosulphate, which i n turn reacts with xanthate to form lead xanthate, but also raises the electrochemical potential of galena modifying i t s form from n-type to p-type.  These suggestions  support the l a t e s t theory proposed by Plaksin and co-workers^ who  invoked semiconductor p r i n c i p l e s to explain the xanthate-  sulphide interactions. semiconductors  Since a l l sulphide minerals are  with electronic and hole conductivity, a  strong chemical bond w i l l r e s u l t from the t r a n s i t i o n of an anion electron to a free (anodic) vacant s i t e .  They proposed  that the separation o f sulphide minerals from non-sulphide  12 ones i s based on the following p r i n c i p l e s :  a) potential  energy of the surface and b) energy necessary to create an adsorption bond between a surfactant and the mineral surface.  The mosaic d i s t r i b u t i o n o f reagents on the surface  i s t h e o r e t i c a l l y explained by the non-uniform p o t e n t i a l of the surface and experimentally proven by radiographic studies of minerals treated with radioactive surfactants. According to these authors, the surface properties of mineral p a r t i c l e s can be modified by e i t h e r changing the oxidation-reduction p o t e n t i a l of the medium o r by the addition of ions that behave as donors o r acceptors. Natural sphalerite does not f l o a t when short chain xanthates are used as c o l l e c t o r s , but f l o t a t i o n i s f i r s t achieved with amyl xanthate and continues with higher chain homologues  (8 )  • A short chain xanthate can be used  e f f e c t i v e l y to c o l l e c t sphalerite i f the mineral has been e f f e c t i v e l y activated with copper. (28) Yonezawa  s  In a recent review  ' found a consistency between the extraction of  copper ions by sphalerite and the subsequent adsorption of xanthate.  From experimental  data of xanthate and copper  abstraction from solution, the surface area of the ground 2 sphalerite, the parking area o f a copper atom (10.4 A )  o  and the cross sectional area o f the xanthate r a d i c a l (25 A ), t h i s author showed that the ratio o f copper to xanthate ions adsorbed was close to the r a t i o of t h e i r respective cross sectional areas when the surface coverage o f copper  13 (v 2 9 )  ions i s about 100 per cent.  Gaudin e t a l  investigated  the activation o f sphalerite with Cu64 and described the activation as a rapid chemical exchange of C u u n t i l three layers of Z n  + +  + +  for Zn  + +  have been replaced.  The f l o t a t i o n of galena with potassium ethyl xanthate i s well known, 25 mg/1 being s u f f i c i e n t f o r c o l l e c t i o n up to a c r i t i c a l pH value of 10.4 where f l o t a t i o n c e a s e s ^ K l a s s e n and Mokrousov^ ^ indicate that only 20 1  to 40 percent coverage i s required to f l o a t the mineral. Obviously these values can only indicate a trend since they are based on a hypothetical uniform d i s t r i b u t i o n and v e r t i c a l orientation o f the c o l l e c t o r on the surface. (2) Plaksin and Shafeev  made an unusual c o n t r i -  bution to f l o t a t i o n by c o r r e l a t i n g absorption of photons and c o l l e c t i o n .  Illumination of ilmenite with a common  l i g h t bulb increased the mineral recovery by 12%. Y-irradiation Plaksin et a l ^ ^  Using  e f f e c t i v e l y separated  zircon from pyrochlore i n a f l o t a t i o n system, thus i n d i c a t ing the improved technology resulting, from the change of the r a t i o of electron concentrations and electron vacancies i n the mineral. 2.4  Illumination The e f f e c t of illumination i s to change the  electronic d i s t r i b u t i o n and thus to change the Fermi energy  14 level^ '. 4  Of p a r t i c u l a r importance i s the number of  electrons i n the conduction band because these electrons can d i r e c t l y p a r t i c i p a t e i n the formation of a chemical bond. Their d i s t r i b u t i o n i s given by:  f(E) N(E) dE  n =  (2.4-1)  where f(E) i s the Fermi d i s t r i b u t i o n function and N(E) dE the density of energy l e v e l s i n the energy range dE.  The  integration i s c a r r i e d out over the lower part of the conduction band.  The density of states, that i s the number  of energy states per unit volume l y i n g between E and E+dE taking into account the states f o r both spins i s :  dN = 4ir/h ( 2 m * ) 3  3/2  E  1 / 2  dE (2.4-2)  = N(E) dE where m* i s the e f f e c t i v e mass of the electron.  By sub-  (31) s t i t u t i n g and integrating Many et a l following  obtained the  N  expression: n = 2(2Trm*kT/h ) 2  3/2  exp(E -E )/kT F  c  (2.4-3)  or n * N  c  exp(E -E )/kT F  c  (2.4-3a)  15 i s the density of states, E Q the energy value of  where  the conduction band and Ep the Fermi energy l e v e l .  A  similar equation can be derived f o r holes. It i s t h i s e l e c t r o n i c density that can be modif i e d by providing the reactants with the necessary quanta of electromagnetic energy. ing from 1,000  In general, wavelengths vary-  to 10,000 A or, i n terms of energy of quanta,  from about 1 eV to 10 eV (23 to 2 30 Kcal per mole), are s u f f i c i e n t to cause the necessary e l e c t r o n i c transitions or recombinations between the valence band and conduction band.  Since these energies are of the same order of  magnitude as those of chemical bonds, d e f i n i t e e f f e c t s can be expected from the absorption of these photons. Absorption of l i g h t by an atom i n the l i n e spectrum region results i n an excited atom whereas i n the continuum i t produces a d i s s o c i a t i o n (an ion plus an electron).  These transitions occur i n accord with the  Frank-Condon p r i n c i p l e that e l e c t r o n i c excitations occur without a f f e c t i n g the positions of the n u c l e i . In this way, l i g h t absorption may cause the exc i t e d molecule to follow one of these a l t e r n a t i v e s : a)  Re-emission of a quantum of the same or d i f f e r e n t frequency (luminescence).  b)  C o l l i s i o n with another molecule e i t h e r transf e r r i n g energy to cause a reaction i n the other molecule or degrading the energy into heat.  16 c)  Reaction with another molecule.  d)  Spontaneous decomposition (predissociation). The phenomenon of luminescence i s well known i n  the case of sphalerite.  Luminescent s o l i d s have been  c l a s s i f i e d as pure and impurity activated. i s a t y p i c a l impurity activated s o l i d .  Zinc sulphide  Pure sphalerite  displays no luminescence but, i f the material i s heated, a dissociation takes place and there i s an excess of zinc atoms i n t e r s t i t i a l l y dissolved i n the zinc sulphide matrix. When t h i s material i s illuminated with l i g h t of wavelength approximately 3,400 A, phosphorescence i s displayed and the s o l i d becomes a better conductor of e l e c t r i c i t y (photoconductivity),  A simple explanation consists of the ab-  sorption of a quantum of radiation s u f f i c i e n t to drive an electron from the valence band to the conduction band leaving a hole behind.  In pure zinc sulphide the electron  and the positive hole w i l l recombine without the emission of l i g h t but with dissipation of heat.  In the impurity  activated zinc sulphide, the impurity centers provide a mechanism by which the excitation energy can be re-emitted as l i g h t .  Electron traps, from which t r a n s i t i o n s to the  ground state are forbidden, are present i n both pure and impurity activated sphalerite.  Thus when thermal energy  i s supplied an electron can move back to the conduction band and eventually emit the phosphorescent radiation by f a l l i n g to a lower energy,level.  A t r a n s i t i o n model of luminescence  was f i r s t  proposed by Schon^ ' and l a t e r modified by K l a s e n s ^ ^ . 32  33  According to these authors the luminescence  i s caused by  an electronic t r a n s i t i o n from the conduction band to a l o c a l i z e d l e v e l above the valence band ( F i g . 3a). The Lambe and K l i c k ^ ' model attributes the 3 4  luminescence  to a hole t r a n s i t i o n from the valence band  to a l e v e l located below the conduction band to account f o r the different value of the decay constant between photoconductivity and luminescence, the l a t t e r being the smaller of the two ( F i g . 3b). ( 35 ) Prener and Williams  considered necessary the  association of acceptors of group l b (Cu, Ag, Au) and donors of Group V l l b (CI, Br, I) o r I l l b ( A l , Ga, In) f o r the appearance of luminescence  thus proposing that the  t r a n s i t i o n takes place from the excited state o f the donor to the ground state of the acceptor i n an associated pair (Fig. 3c). In actual fact, luminescence  i s f a r more compli-  cated than these simple models describe, being affected by other factors such as Impurities, defects, thermoluminescence decay and o p t i c a l stimulation. Of p a r t i c u l a r interest i s the case when impurity cations are present i n the c r y s t a l l a t t i c e . spectra of the luminescence  The emission  i n sphalerite when other cations  are present i n the c r y s t a l l a t t i c e have been investigated Me)  by Shionoya et a l  .  F i g . 4, abstracted from t h e i r work,  18  CONDUCTION BAND  VALENCE BAND Cc) F i g . 3 - Models o f luminescence according to: (a) SchonKlasen; (b) Lambe-Klick; (c) Prener-Williams.  F i g . 4 - Emission spectra o f luminescence i n ZnS (after Shionoya et a l ^6)  19 c l e a r l y indicates that the presence of copper alone gives a peak at 1.7 7 eV while the copper-aluminum  produces a  s h i f t i n the peak which now rests at 2.41 eV.  2.5. Sources of Radiant Energy The electromagnetic spectrum of interest to t h i s study can be a r b i t r a r i l y divided into three regions: u l t r a v i o l e t , v i s i b l e and infrared.  The conventional wave-  length range of each of these regions i s given i n the following t a b l e  ( 3 7 5  :  TABLE I - ELECTROMAGNETIC SPECTRUM (After S t r o n g ) 37  Spectral Region  Wavelength Limits  Extreme UV  .050 to .200 microns  UV  .200 to .400 microns  Visible  .400 to .720 microns  Near IR  0.72 to 2 0 microns  Intermediate IR  20 to 40 microns  Far IR  40 to 400 microns  The most important natural source of continuous radiant energy i s the sun. Many spectroradiometric measurements have been made by various investigators but, because  20  of  instrumental problems and varying atmospheric conditions,  only a f a i r agreement exists between the spectral energy d i s t r i b u t i o n s reported. In general the luminous e f f i c i e n c y of the sun i s equivalent to that of a lamp with an output of 80 lumens/watt. The energy d i s t r i b u t i o n i n the solar spectrum i s c l o s e l y approximated by that of a black body at 5,U00°K.  A black  body, sometimes c a l l e d a f u l l radiator, i s an imaginary object that, when heated, emits radiation i n the form of a continuous spectrum.  At room temperature radiation i s  in the i n v i s i b l e infrared region, but at higher temperatures the  radiation frequency increases and covers the v i s i b l e  regions.  As i l l u s t r a t e d i n F i g . 5, black body colour i s  precisely related to temperature i n degrees K e l v i n ^ \ 3 8  The e f f i c i e n c y of a tungsten lamp i s approximately 11 lumens/watt and i t s spectrum i s limited by the transmission of glass, namely from 0.31 microns to 3 microns f o r a thickness of 0.25 mm.  F i g . 6 shows the transmittance  l i m i t s o f some glasses and water.  I f a tungsten l i g h t i s  provided with a quartz bulb (50 amp tungsten at 3,400°K) the  spectrum e a s i l y extends into the u l t r a v i o l e t . Addition o f iodine to the f i l l i n g gas of a  tungsten lamp s t a r t s a regenerative iodine cycle and the new lamp i s properly c a l l e d quartz iodine.  The evaporated  tungsten i s deposited on the walls of the lamp and converted into a v o l a t i l e iodide which, i n turn, i s decomposed  21  900  >o u  200  100  400  500 600 WAVELENGTH  F i g . 5 - Relative spectral energy d i s t r i b u t i o n of the black body radiator normalized at A=56 0 m i l l i microns (after Wyszecki ^). 3  Fig. 6 - Spectral transmittances of absorption f i l t e r s ( a f t e r Wyszecki ). 38  22  by the high temperature of the filament and thus completes the cycle.  Since a l l of the tungsten i s returned to the  filament, i t i s possible to increase the operating temperature and the lamp e f f i c i e n c y . Mercury arcs give several strong l i n e s i n the v i s i b l e , u l t r a v i o l e t and infrared region but lack a good spectrum continuity.  CHAPTER 3 EXPERIMENTAL METHODS  3.1  General Approach The materials used i n t h i s study were PbS,  (Pb,Ag)S and copper activated (Zn,Fe)S.  The o r i g i n a l  samples were crushed, ground, sized, cleaned and stored in a desiccator.  The surface areas of the powders were  evaluated from measurements of nitrogen adsorption by a continuous flow method.  Further characterization of the  materials included measurements of the Hall voltage f o r s o l i d specimens and of the Seebeck e f f e c t for p e l l e t i z e d powders. The k i n e t i c s of adsorption of high purity KEtX on the individual solids under various conditions of illuminat i o n were measured by determining the difference between the i n i t i a l concentration and the concentration at time t . Samples of solution were removed at predetermined f o r U.V.  spectroscopic analysis and immediately  to the c i r c u l a t i n g system.  intervals returned  The adsorption apparatus  normally contained 600 ml of solution at 20+0.1°C.  The  solution was c i r c u l a t e d once every 30 seconds through a  24 f l u i d i z e d bed of 10 or 20 g of powders. The major portion of the experimental work was completed on 100/150 mesh powders.  In the case of  (Zn,Fe)S  other size fractions had to be used because of the limited amount of material available;  some tests were carried out  on a 65/100 mesh f r a c t i o n whilst a l l of the f l o t a t i o n experiments were performed on a 150/200 mesh f r a c t i o n .  3.2  Materials (a)  Marmatite  [(Zn,Fe)S3.  Various screened  fractions of the mineral were prepared from a selected sample received from The Zinc Corporation Limited, Broken H i l l , Australia.  The o r i g i n a l material was crushed i n a  mortar and pestle and screened on a c a r e f u l l y cleaned set of  stainless steel Tyler Sieves.  A l l traces of free  pyrrhotite were then removed from each f r a c t i o n with a hand magnet p r i o r to a f i n a l cleaning i n a Frantz Isodynamic Magnetic Separator.  Each f r a c t i o n was subsequently washed  with d i s t i l l e d water on the largest retaining screen to remove the fines attached to the larger p a r t i c l e s .  After  a f i n a l rinse with doubly d i s t i l l e d water, the sample was dried i n a vacuum desiccator, thoroughly mixed, and stored under nitrogen.  An analysis of the major and minor con-  stituents of the marmatite sample i s reported i n Table I I .  25 TABLE II - ANALYSIS OF MARMATITE SAMPLE (by Coast Eldridge, Vancouver,  Chemical Analysis of major constituents-% Zn: S: Fe: Cu: Cd: Mn: Insol.:  54.05 33.46 11.63 0.31 0.18 0.14 0.15  B.C.)  Spectrographic Analysis of minor elements-% Co: Mo: Ca: . Mg: Si: Mn:  0. 01 0.003 0.003 0.0005 0.03 0.2  99.92  Pure zinc sulphide  consists of 67.09% zinc and 32.91%  sulphur. Copper activated marmatite was prepared by immers_14  ing the mineral for 45 minutes i n a 9.97x10 solution at room temperature. l i q u i d was 1 to 10.  M copper sulphate  The weight r a t i o of s o l i d to  Since the uptake of copper ions was  almost instantaneous^ ', the time selected to reach equi9  librium  was more than ample.  A separate investigation of  the e f f e c t of varying i n i t i a l concentrations on the t o t a l amount of copper abstracted was also carried out and w i l l be described with the adsorption r e s u l t s .  Further prepa-  ration of the activated powders included repeated washing with doubly d i s t i l l e d water, f i l t e r i n g , drying and storing under nitrogen.  (b)  Galenas [(PbS) and  (Pb,Ag)S3.  A high purity  sample of galena from Pine Point (N.W.T.) was a v a i l a b l e i n t h i s Department.  This was  re-screened p r i o r to storage  in a desiccator.  A complete analysis i s presented i n  Table I I I .  TABLE III - ANALYSIS OF GALENA SAMPLE  Chemical Analysis of major constituents-% (by Cominco) Pb: S: Zn: Fe:  84.7 14.1 0.7 0.4 99.9  Spectrographic Analysis of minor constituents-% (by Coast Eldridge) Si: Ca: Fe: Cu: Mg: Au,Ag:  0.05 0.001 0. 003 0.0005 0.0007 traces  The t h e o r e t i c a l contents of PbS are 86.6%  lead and  13.4%  sulphur. Another sample of galena containing 0.2 8 oz/ton of s i l v e r [hereafter referred to as argentiferous galena, (Pb,Ag)Sl was  crushed in a porcelain mortar and pestle and  screened for immediate use i n a series of t e s t s where excessive oxidation of the surface was (c)  to be avoided.  Potassium ethyl xanthate (KEtX).  sample of potassium ethyl xanthate was series of experiments.  A fresh  prepared for t h i s  R e d i s t i l l e d ethyl alcohol was mixed  with pure potassium hydroxide (Fisher C e r t i f i e d Reagent) to  which carbon disulphide (Fisher C e r t i f i e d Reagent-Infrared Spectranalyzed) was added slowly at low temperature to avoid decomposition of the mixture.  The product was then re-  c r y s t a l l i z e d from acetone f i v e times and stored i n a vacuum desiccator.  At weekly i n t e r v a l s , the xanthate was washed  several times with ether to remove any dixanthogen formed on oxidation. (d)  Water.  Low conductivity d o u b l y - d i s t i l l e d  water was used i n a l l experiments.  Typical values of the  s p e c i f i c conductance taken from the storage pyrex bottles G —6 —1 —1 ranged between 0.9xl0~ and 1.0x10 ohms cm (e)  Copper Sulphate (CuSO^.5H 0).  Certified  2  ACS reagent grade copper sulphate supplied by Fisher S c i e n t i f i c Company of Vancouver was used f o r a l l experiments.  3.3  Surface Area Measurements The surface areas of the 100/150 mesh size o f  the three powders have been measured by a continuous flow method^ '. 39  Nitrogen was adsorbed by the sample at l i q u i d  nitrogen temperature from a gas stream o f nitrogen and helium and eluted upon warming the sample.  The nitrogen  liberated i s measured by thermal conductivity.  With t h i s  method, materials of low s p e c i f i c area (well below one square meter per gram) can be measured with a precision of + one  28  per cent at the 95 per cent confidence l e v e l Fig. 7 shows a schematic diagram of the apparatus for surface area measurements made available by the Department of Chemical Engineering. The experimental procedure was i n i t i a t e d with the introduction o f a known weight (approximately l g ) of sample to a U-tube.  The sample tube was then placed i n the c i r c u i t  as indicated i n F i g . 7.  When a l l the a i r was flushed out  by the mixture of nitrogen and helium (5, 10 or 15% N ) 2  the thermal conductivity detector was switched on and the bridge balanced to zero output.  The sample was then cooled  slowly i n the l i q u i d nitrogen and at the same time the adsorption peak was recorded.  In order to take advantage o f  the f u l l range of the recorder scale, the p o l a r i t y switch was reversed p r i o r to desorption o f nitrogen.  Desorption  was achieved by rapid immersion o f the U-tube i n warm water. The complete sequence o f adsorption was repeated three times to show consistency o f r e s u l t s .  In addition, a c a l i b r a t i o n  of the volumes eluted was achieved by i n j e c t i n g known volumes of p u r i f i e d nitrogen into the system.  3.4  E l e c t r i c a l Conductivity and the H a l l E f f e c t The electrophysical c h a r a c t e r i s t i c s o f the s o l i d  specimens have been investigated by the Hall e f f e c t .  The  H a l l c o e f f i c i e n t i s given by the transverse voltage produced  Nitrogen Thermometer Probes QJ •M Q)  12V Power Source Sample Tubes  He-N2 Mixture  > u  <u w CD  C^SESE  £  PS  J  w  CO  c <D  Dewar  Thermoconductivity Cell To M i l l i v o l t Recorder  O C nJ  bO  0 ...  Flask  U  •ri  Liquid  N  ». •  U O  Vap  Back Pressure Manometer  6  u  •H O  2  JCSl Oil  Nitrogen Thermometer  Filled  Syringe Caps f o r Calibration P u r i f i e d N2  Fig.  Exhaust  7 - Schematic diagram of the apparatus f o r surface area measurements (courtesy of Mr. R. O r r ) . 1 to  when a current i s passed through a conductor l y i n g in a magnetic f i e l d at right angles to the current.  The  sign  of  voltage produced depends on the material under  investigation.  This voltage i s proportional to the current (I) in amperes, to the magnetic f i e l d (H) i n oersteds and  inversely  pro-  portional to the thickness (t) i n cm measured i n the direction of the magnetic f i e l d .  The  proportionality  constant (R=l/nqc) i s c a l l e d the H a l l c o e f f i c i e n t :  V = R. IH/t  = IH/nqct  (3.4-1)  where n i s the number of c a r r i e r s , £_ t h e i r charge and the velocity of l i g h t .  A schematic diagram of the  e f f e c t i s presented in F i g . 8. units and  substituting  V = 10""  8  c  Hall  Converting to p r a c t i c a l  the value of c (see Appendix A):  IH/nqt = R  H  10"  8  IH/t  (3.4-2)  indicating that the p r a c t i c a l Hall c o e f f i c i e n t , R^,  is  equal to  R  H  = + 1/nq  (3.4-3)  the plus or minus sign indicating hole or electron ductivity. the mobility  con-  From a knowledge of the conductivity (a = (u) can now  be readily calculated  ing the Hall c o e f f i c i e n t by the  conductivity:  nqu)  by multiply-  31  + ( p-type ) - ( n-type ) IT  a  - ( n-type ) + ( p-type )  F i g . 8 - Schematic diagram of the Hall e f f e c t .  32 u = a R  (3.4-4)  R  The samples o f galena and sphalerite used i n the measurements of the Hall c o e f f i c i e n t s were prepared from representative samples o f s o l i d specimens by (1) cutting thin sections with a diamond saw, (2) reducing the sections to the required size with a high speed carborundum wheel, and  (3) mounting on p l a s t i c as shown i n F i g . 9 and 10. The  three-points voltage pick up i s commonly used to avoid an ohmic voltage drop.  When the p o t e n t i a l contacts are not  p e r f e c t l y aligned and do not coincide with an equipotential l i n e , i n the absence o f a s t a t i c magnetic f i e l d an ohmic voltage drop proportional to the steady current w i l l be measured i n addition to the Hall voltage.  F i g . 11 shows  the o r i g i n of t h i s ohmic voltage drop. A l l measurements were made at room temperature using the f a c i l i t i e s made available by the Physics Department of The University o f B r i t i s h Columbia.  3.5  Seebeck Voltage Measurements The  Seebeck e f f e c t i s a simple and e f f i c i e n t  method for determining  the conductivity type o f a semi-  conductor from the sign of the p o t e n t i a l produced.  It i s  p a r t i c u l a r l y useful for low mobility materials and f o r powder specimens where the Hall effect i s d i f f i c u l t to  a) P r e s s u r e  contacts  1  /  j  b)  Indium  Ohmic c o n n e c t i o n s t o m a r m a t i t e  contacts  specimens.  Fig.  10 - Ohmic c o n t a c t s  to g a l e n a specimens.  35  Current lead  Voltage Misalignment  lead  X  Fig.  11 - O r i g i n o f ohmic v o l t a g e d r o p due t o m i s a l i g n m e n t when m e a s u r i n g coefficient..  the  Hall  measure '. 5  A s c h e m a t i c d i a g r a m o f t h e measurement o f  t h e r m o e l e c t r i c power i s shown i n F i g . 12.  The  indicates  gradient  the  that  when, t h e r e i s a t e m p e r a t u r e  ends o f a s p e c i m e n ,  an  emf  o f QAT  this  diagram between  in millivolts  is  produced  where Q r e p r e s e n t s t h e t h e r m o e l e c t r i c power i n  units of  millivolts/degree. The  Peltier effect  which  Seebeck e f f e c t ,  arises  semiconductor:  the heat absorbed  conductor-metal  junction  Peltier  a t one  i s liberated  an n - t y p e  an e l e c t r o n  metal  entering  an e n e r g y but  no  f l o w from  f l o w from the  left  levels right  heat t r a n s f e r the cold  mobile charge junction  re-  heat  U n d e r an  Electrons  from l e f t  diffuse  imparting a potential  re-  from  must  and  (E^-Ep)  semiconductor  are e a s i l y  added  to r i g h t .  This  effect  since  from t h e hot t o the o f the  the  possess  barrier  the b a s i s o f the P e l t i e r  carriers  coulomb  physical  from t h e l e f t  i s p r e s e n t a t the r i g h t ,  forms  per  to l e f t corresponding  to r i g h t .  semiconductor  the metal t r a n s f e r r i n g  The  slope to the r i g h t  e l e c t r o n s with e x c e s s i v e thermal energy to  The  equal o r g r e a t e r than the energy  barrier  semi-  i n terms o f energy l e v e l s f o r  the energy  i n a current  a  i s e x p r e s s e d as  s e m i c o n d u c t o r i s shown i n F i g . 13.  applied potential, sulting  end o f a  heat absorbed o r l i b e r a t e d  effect  through  at the other.  charge p a s s i n g through the j u n c t i o n .  presentation of this  to  when a c u r r e n t i s p a s s e d  TT i n u n i t s o f v o l t s  coefficient  joules of reversible of  i s the i n v e r s e o f the  same s i g n  as  37  -  (p-type)  +  (p-type)  +  (n-type)  -  (n-type)  Q AT  (millivolts)  HOT JUNCTION  COLD JUNCTION  [Z  A AT (°K) Fig.  12 - S c h e m a t i c d i a g r a m ( a f t e r Hannay^).  o f t h e Seebeck  Fig.  13 - O r i g i n o f t h e P e l t i e r e f f e c t . f o r s e m i c o n d u c t o r ( a f t e r HannayS).  effect  an  n-type  38 the c a r r i e r s to the c o l d j u n c t i o n as i n d i c a t e d i n F i g . 12. The energy t r a n s f e r r e d t h e r e f o r e i s the energy r e q u i r e d to overcome the energy b a r r i e r CCE^-Ep) f o r an n-type  semi-  conductor] p l u s a term f o r the k i n e t i c energy t r a n s p o r t e d by the c a r r i e r s , o r :  qiT = qQT  = (E^-Ep) + 2kT  (3.5-1)  T h i s equation i n d i c a t e s t h a t the p o t e n t i a l Q i s r e l a t e d to the p o s i t i o n o f the Fermi l e v e l and by s u b s t i t u t i n g i n equation  (2.4-3):  n - p = 2(2Trm*kT/h ) 2  the number o f e l e c t r o n s  3/2  exp(E -E )/kT p  c  (3.5-2)  (n) o r h o l e s (p) can be c a l c u l a t e d .  A simple apparatus designed to i n v e s t i g a t e the type o f semiconduction i n low m o b i l i t y m a t e r i a l s i s shown i n F i g . 14.  A photograph o f the apparatus i s shown i n F i g . 15.  Solid  specimens as w e l l as p e l l e t i z e d d i s c s , made  by compressing powders i n a standard p r e s s at 65,000 p s i , were p l a c e d between the two constant temperature.  copper d i s c s maintained at  The v o l t a g e produced was measured  by a K e i t h l e y E l e c t r o m e t e r (Model 610B).  Fig.  14 - S c h e m a t i c d i a g r a m o f t h e a p p a r a t u s f o r t h e measurement o f t h e Seebeck v o l t a g e .  F i g . 15 - Apparatus f o r the measurements o f the Seebeck v o l t a g e r e a r r a n g e d o u t s i d e the Faraday cage.  41 3.6  Oxidation of Galena Powders The role of oxygen i n xanthate adsorption on  sulphide minerals i s well documented.  Some i n v e s t i g a t o r s ^ ^ 3  propose that penetration o f oxygen into the surface layer of the mineral weakens the surface bonds and increases the (25 3 0) chemical a c t i v i t y of the surface.  Others  *  describe  the effect o f oxygen adsorption as one o f surface dehydration that allows the subsequent penetration o f surfactants. experimenters^ ^ 4  Other  postulate electrophysical changes from an  n-type s o l i d to a p-type through adsorption of oxygen. In t h i s case, the p-type s o l i d i s described as being more susceptible to anionic adsorption.  A fourth p o s s i b i l i t y  i s the oxidation of xanthate anions to dixanthogen^ '^ ^. 9  6  Since no complete agreement has been reached, i t was decided to investigate the r e l a t i v e oxidation rates o f . the two galenas i n order to d i f f e r e n t i a t e between the effect of surface products, i f any, and the bulk characteri s t i c s i n subsequent adsorption t e s t s . The r e l a t i v e rates of oxidation o f the two galena .samples were analyzed with a Cahn RH Electrobalance made available by the Faculty o f Forestry of The University o f B r i t i s h Columbia. crushing  The galena powders were prepared by  large specimens i n a porcelain mortar and pestle  followed by screening the 100/150 mesh f r a c t i o n i n a dry box f i l l e d with p u r i f i e d premium nitrogen.  The sealed  t e s t tubes c o n t a i n i n g the powders were then t r a n s f e r r e d to the dry box p r o t e c t i n g the e l e c t r o b a l a n c e .  For the  t e s t s without water vapour, the dry box was r e p e a t e d l y evacuated and f i l l e d with helium.  The remaining water  vapour was then removed by d r i e r i t e and sodium  hydroxide.  Approximately t h r e e grams o f galena were removed from the t e s t tube, p l a c e d on the balance and e q u i l i b r a t e d by the a d d i t i o n o f the a p p r o p r i a t e weight to the o t h e r pan. r e c o r d e r was  The  then a l l o w e d to run f o r a few minutes to  establish a baseline. as the oxygen was  The dry box was  then evacuated and  admitted the c h a r t r e c o r d e r was  switched  on s i m u l t a n e o u s l y to measure the weight i n c r e a s e .  For the  t e s t s with water vapour the same procedure was used but the d e s i c c a n t s were r e p l a c e d by a beaker o f water.  3.7  A d s o r p t i o n from (a)  Solution  Apparatus.  The a d s o r p t i o n apparatus  was  designed to i n v e s t i g a t e the r a t e o f a d s o r p t i o n o f xanthate on d i f f e r e n t n-type and p-type m i n e r a l s by c o n t i n u o u s l y c i r c u l a t i n g the s o l u t i o n c o n t a i n i n g the s u r f a c t a n t through the s o l i d s i n a c l o s e d system.  The most c r i t i c a l  features  to be c o n t r o l l e d we're the energy o f i l l u m i n a t i o n , the i n e r t n e s s o f the c o n s t r u c t i o n m a t e r i a l and the presence o f atmospheric oxygen. The apparatus presented i n F i g s . 16 and 17, i s  0>  LEGEND: (c) a) l i g h t  source  b) t h e r m o s t a t i c c)  bath  thermometer  d) sample  chamber  e) heat  excharigers  f)  meter  flow  (g)  (a)  n  g) r e c e i v i n g v e s s e l h) c i r c u l a t i n g  (f)  (d)  pump  15  (e) (b)  Fig,  16 - S c h e m a t i c  (h)  diagram o f the adsorption  apparatus.  Fig.  17  - A d s o r p t i o n apparatus complete with a c c e s s o r i e s and a s e m i - m i c r o f l o t a t i o n cell.  an improved v e r s i o n o f t h a t used by the a u t h o r ^ D previous  in a  study. The main f e a t u r e s o f the apparatus i n c l u d e :  (1)  l o c a l i z e d i l l u m i n a t i o n w i t h i n an energy range o f 0 . 5 - 3 . 5 eV, (2) a b i l i t y to handle d i f f e r e n t different  volumes o f s o l u t i o n ,  amounts o f s o l i d s and (3) f l u i d i z e d m i x i n g o f  s o l i d s to reduce t h e p r o d u c t i o n o f f i n e s and, changes i n s u r f a c e a r e a , during sampling, pump l i n e r ,  consequently,  (4) e l i m i n a t i o n o f f i n e s  removal  (5) e l i m i n a t i o n o f s o l i d a b r a s i o n o f  (6) a b i l i t y t o c a r r y out t e s t s i n  s i m p l i c i t y and r e l i a b i l i t y o f  system  versatility,  design.  Two S y l v a n i a Q u a r t z - I o d i n e  Lamps (No. 40 0 T4Q/C1/F  and No. 500 T3 Q/CL/U) were used as a l i g h t s o u r c e . characteristics  are presented i n F i g . 18.  lamp used i n any one experiment  the  inert  atmospheres, (7) a b i l i t y to c l e a n , wash and d r y the w i t h o u t d i s m a n t l i n g t h e components, and (9)  the  The  Their  particular  was encased i n a m e t a l  box  open a t both v e r t i c a l ends to a l l o w f o r the d i s s i p a t i o n o f heat.  A p r o t r u d i n g c o l l i m a t o r was used to support  the  c o l o u r e d g l a s s f i l t e r s at a r e a s o n a b l e d i s t a n c e t o a v o i d absorption of heat.  The nominal r a t i n g s o f the lamps were  g i v e n as 7,500 and 10,500 lumens f o r an approximate  colour  t e m p e r a t u r e o f 3,0 00°K. Temperature c o n t r o l o f the  s o l u t i o n at  2 0°C was  achieved w i t h a C o l o r a Ultra-Thermostat  B a t h , Type NB,  having a s p e c i f i e d accuracy o f +0.01°C.  A precision  thermometer with a range o f -1 to +51°C i n subdivisions of 1/10°C indicated that a constant temperature within 1/10°C was attained within the sample chamber. The sample chamber was constructed from a Buchner f r i t t e d glass (Pyrex) funnel of coarse porosity (60 microns). To provide illumination from a l l sides a U-type aluminum r e f l e c t o r (not shown i n Fig. 17) was placed around the sample chamber. The heat exchangers, the main receiving vessel and the flow meter (supplied by Manostat Corporation, New York) were a l l made of Pyrex Brand Glass. A standard rheostat and an ammeter were used to control the speed of the c i r c u l a t i n g pump (Vanton Flex-I Liner) which was supplied by Vanton Pump and Equipment Corp., H i l l s i d e , N.J.  The pump was equipped with a Kel-F  l i n e r (a polymonochlorotrifluoroethylene  fluorocarbon)  encased i n a s o l i d block o f t e f l o n (a p o l y t e t r a f l u o r o ethylene fluorocarbon). A l l mechanical connections  were made by squeezing  a t e f l o n gasket sheath between the tapered ends of QVF glass tubing [QVF Glass (Canada) Limited, Scarborough, Ontario], a b o r o s i l i c a t e glass with the following t y p i c a l Silica  80.60%  (Si0 ) 2  composition:  Boric Oxide ( B 0 ) 2  3  12.60%  Sodium Oxide (Na 0)  4.15%  Calcium Oxide (CaO)  Aluminum Oxide  2.20%  Magnesium Oxide (MgO) 0.05%  0.04%  Chlorine (CI)  2  (Al 0g) 2  Iron Oxide ( F e 0 O 0  0.10%  0.10%  48 The t r a n s m i s s i o n curves f o r QVF g l a s s i n the ultraviolet  and v i s i b l e r e g i o n s o f the spectrum, as s u p p l i e d  by the manufacturer, correspond t o t h a t o f Dense F l i n t G l a s s shown i n F i g . 6. In  the present work the s e l e c t i o n o f s p e c t r a l  e n e r g i e s was achieved u s i n g c o l o u r g l a s s f i l t e r s  5-8 3,  5-7 5 and 7-86 manufactured by Corning G l a s s Works o f New York.  The t r a n s m i t t a n c e curves f o r the f i l t e r s  i n question  were determined on a Model 4 50 P e r k i n - E l m e r Spectrophotometer for  the u l t r a v i o l e t and v i s i b l e r e g i o n s and on a Model 521  Perkin-Elmer Spectrophotometer f o r the i n f r a r e d (Fig.  19).  These narrow band f i l t e r s  region  were s e l e c t e d so that  they cover approximately the same range o f photon energy i n d i f f e r e n t r e g i o n s o f the spectrum. the  The  range o f 0.340-0.380 microns (3.6-3.3  5-83 f i l t e r covers eV), the 5-75  f i l t e r extends from 0.44 0 t o 0.4 90 microns (2.9-2.6 while the 7-86 f i l t e r  eV)  covers the 1.5-2.75 microns range  (0.8-0.5 eV). A n c i l l a r y equipment  i n c l u d e d a Beckman Zeromatic  II pH Meter and a Cenco Hyvac 7 Vacuum Pump (from C e n t r a l S c i e n t i f i c Company, Chicago, 111.). (b)  T y p i c a l A d s o r p t i o n Procedure.  The f o l l o w i n g  procedure used f o r the a d s o r p t i o n o f xanthate on lOg o f PbS at  constant i l l u m i n a t i o n i s t y p i c a l f o r a l l  systems.  b a s i c d i f f e r e n c e s l i e i n the type and amount o f s o l i d  The  Fig. 19 - Measured transmittance of Corning Glass F i l t e r s .  m a t e r i a l used i n the t e s t , the i n i t i a l c o n c e n t r a t i o n and volume of xanthate s o l u t i o n and the i l l u m i n a t i o n  conditions.  To minimize the v a r i a t i o n s i n s u r f a c e area caused  by  weighing, lOg o f PbS were weighed, a f t e r coning and on a M e t t l e r H15 to  parting,  baldnce to w i t h i n +0.001 g which corresponded  an accuracy o f s u r f a c e area o f +1.8  cm /10g. 2  was t r a n s f e r r e d to the a d s o r p t i o n c e l l ,  The  material  a l l s e a l s were  c a r e f u l l y t i g h t e n e d and the whole system evacuated. same time the a p p r o p r i a t e g l a s s f i l t e r was  At the  p l a c e d i n the  c o l l i m a t o r and the r e f l e c t o r p o s i t i o n e d around the  cell.  Complete removal o f i n t e r f e r i n g e x t e r n a l i r r a d i a t i o n achieved by darkening the a d s o r p t i o n assembly cloth.  The l i g h t  with a b l a c k  source and the t h e r m o s t a t i c bath were  then switched on.  While the s o l i d s were being i r r a d i a t e d ,  600 ml of approximately 10  M s o l u t i o n o f KEtX were prepared  and the exact c o n c e n t r a t i o n determined 450  was  Spectrophotometer.  The  by a P e r k i n Elmer  s o l u t i o n was  transferred to  the evacuated apparatus while the c i r c u l a t i n g pump  was  operating.  within  the f i r s t  Thermal  e q u i l i b r i u m was  e a s i l y reached  two minutes, the maximum i n i t i a l d e v i a t i o n  exceeding +2°C.  never  At s e l e c t e d time i n t e r v a l s , 4 ml o f  s o l u t i o n s were removed t o r e c o r d the xanthate c o n c e n t r a t i o n and immediately r e t u r n e d t o the c i r c u l a t i n g system.  The  d i f f e r e n c e s i n c o n c e n t r a t i o n r e p r e s e n t e d the amount o f xanthate a b s t r a c t e d by the m i n e r a l sample t o g e t h e r w i t h l o s s e s due to  decomposition.  In  connection w i t h o x i d a t i o n s t u d i e s i t was  n e c e s s a r y to c a r r y out a d s o r p t i o n t e s t s i n an i n e r t atmosphere.  In t h i s case oxygen contamination had t o be avoided  i n the p r e p a r a t i o n o f m a t e r i a l s as w e l l as d u r i n g adsorption.  The powders were crushed i n a p o r c e l a i n mortar  and p e s t l e and screened i n a dry box c o n t a i n i n g p u r i f i e d premium n i t r o g e n .  Ten grams o f m a t e r i a l were then weighed  i n the same dry box and t r a n s f e r r e d t o the a d s o r p t i o n c e l l the ends o f which were s e a l e d o f f with removable discs.  The s e a l e d chamber was  apparatus which was seals.  teflon  reconnected t o the main  subsequently evacuated up t o the t e f l o n  These s e a l s were removed w h i l e f l u s h i n g the loosened  connection with helium from the p r e v i o u s l y evacuated The whole apparatus was  then evacuated.  the xanthate s o l u t i o n was  side.  In the meantime  prepared by adding deaerated  doubly d i s t i l l e d water to the proper weight o f xanthate i n a v o l u m e t r i c f l a s k , the procedure c a r r i e d out i n a p o r t a b l e dry to  box f i l l e d w i t h helium.  T h i s s o l u t i o n was  the evacuated apparatus which was  helium to atmospheric p r e s s u r e .  slowly added  then p r e s s u r i z e d w i t h  Before s t a r t i n g the  c i r c u l a t i n g pump, o t h e r c o n d i t i o n s being s e l e c t e d , milliliters t e s t was  four  o f s o l u t i o n were removed f o r UV a n a l y s i s .  The  c a r r i e d to completion i n the manner p r e v i o u s l y  d e s c r i b e d , except t h a t the samples removed f o r UV were not r e t u r n e d t o the system.  analysis  (c)  A n a l y t i c a l Procedure.  In order to r e t a i n  the constancy o f c i r c u l a t i n g volume, a f a s t and p h y s i c a l method of a n a l y s i s was  reliable  p r e f e r r e d to a chemical  one.  U l t r a v i o l e t spectroscopy o f f e r s these advantages s i n c e KEtX d i s p l a y s a good spectrum with a sharp a b s o r p t i o n culminates at 301 my. 3 01 my  The  absorption  o f r a d i a n t energy at  f o l l o w s the well known Beer-Lambert Absorption  T h i s law  Law.  s t a t e s that the amount o f energy absorbed by  e x c i t e d i o n s i s p r o p o r t i o n a l to the t h i c k n e s s o f medium t r a v e r s e d ,  and q u a l i t y  = al  (3.7-1)  where I_ i s the i n t e n s i t y o f l i g h t , x a d i s t a n c e medium, and a the a b s o r p t i o n the boundary c o n d i t i o n s  coefficient.  (I = I  •I = I  o  Q  when X = 0)  c o f the  1=1 In t h i s equation the  o  gives:  exp(-ax)  (3.7-2) proportional  solute, therefore, rewriting:  exp(-ecx)  (3.7-2a)  symbol £ i s known as the molar e x t i n c t i o n  c o e f f i c i e n t , an i n t r i n s i c p r o p e r t y substance.  i n t o the  I n t e g r a t i o n at  Beer showed t h a t t h e c o e f f i c i e n t a was  to the c o n c e n t r a t i o n  the  or:  -dl/dx  In 1852  peak t h a t  t h a t c h a r a c t e r i z e s each  In the case o f potassium e t h y l xanthate,  the  molar e x t i n c t i o n c o e f f i c i e n t used by Pomianowski and Leja^  '  (43) was 17,750, the value g i v e n by Majima suming that these d i s c r e p a n c i e s may  was 17,460.  As-  be caused by instrument-  a l c a l i b r a t i o n , an independent d e t e r m i n a t i o n o f the molar e x t i n c t i o n c o e f f i c i e n t was  c a r r i e d out f o r the p a r t i c u l a r  sample o f KEtX used i n these experiments (Appendix B). The e x t i n c t i o n c o e f f i c i e n t c a l c u l a t e d from these data i s equal to 17,500. One o f the major o b j e c t i o n s t o the assumption that a l l o f the reagent t h a t d i s a p p e a r s from s o l u t i o n i s a c t u a l l y adsorbed by the m i n e r a l s u r f a c e i s that no cons i d e r a t i o n i s g i v e n to the amount o f s u r f a c t a n t decomposed o r evaporated from s o l u t i o n .  precipitated,  In o r d e r t o  circumvent such a d i f f i c u l t y a number o f curves l a b e l l e d "Adsorption on Apparatus and Decomposition o f Potassium E t h y l Xanthate" have been r e c o r d e d to account, at l e a s t i n p a r t , f o r these e f f e c t s .  The curves are p l o t t e d i n F i g . 20  and have been used to c o r r e c t a l l subsequent measurements open to atmospheric oxygen.  adsorption  I t should a l s o  be noted t h a t the c o r r e c t i o n s apply to the t o t a l amount o f s o l i d s present.  For example, i n the case o f 2 0g o f PbS,  the c o r r e c t i o n i s l e s s than 4% a t 10 minutes and 13% a t 300 minutes. was  The change i n volume from 1,000  ml. to 600  i n t r o d u c e d a f t e r the p r e l i m i n a r y experiments to i n -  crease the s e p a r a t i o n o f the xanthate a b s o r p t i o n l i n e s on the UV r e c o r d e r .  I t i s most i n t e r e s t i n g to observe t h a t  ml.  20  Time - m i n u t e s Fig.  20 - A d s o r p t i o n on a p p a r a t u s and d e c o m p o s i t i o n o f x a n t h a t e . T e s t c o n d i t i o n s : K E t X (10-4M), 2 0 ° C , i l l u m i n a t e d w i t h a 400W Q/I lamp.  cn  when the o r d i n a t e i s changed to read i n micromoles/1, the two  l i n e s o f F i g . 20 d i s p l a y almost a p e r f e c t c o i n c i d e n c e .  This suggests that t h e m a j o r i t y o f the c o r r e c t i o n can be a t t r i b u t e d t o decomposition s i n c e t h e i n t e r n a l s u r f a c e  area  of the apparatus was a constant. (d)  Reproducibility.  A major concern o f a l l  experimenters i s t o a t t a i n good r e p r o d u c i b i l i t y o f r e s u l t s . To e s t a b l i s h the degree o f r e p r o d u c i b i l i t y r e l a t i v e l y  coarse  marmatite (65/100 mesh) was s e l e c t e d f o r t h e t e s t s u s i n g 1,000 ml volumes whereas galena  was used f o r the t e s t s  using 600 ml volumes (Appendix C ) .  The s l i g h t  departure  o f the l i n e s d i s p l a y e d by t h e marmatite sample can be a t t r i b u t e d to v a r y i n g l i g h t c o n d i t i o n s and/or sample d e v i a t i o n s from s t o i c h i o m e t r y . was obtained  A more remarkable r e p r o d u c i b i l i t y  with the galena  samples i r r a d i a t e d by a 4 00  W/QI lamp and by a 500 W/QI lamp.  The c h o i c e o f a 500 W/QI  lamp f o r the l a s t experiments emerged from n e c e s s i t y when the burnt out 400 W/QI lamp proved to be one o f the f i r s t prototypes p r e s e n t l y out o f p r o d u c t i o n .  In the r e p r o d u c i b i -  l i t y t e s t s as w e l l as most o f the subsequent experiments, _4 the i n i t i a l  c o n c e n t r a t i o n o f xanthate was 10  M.  In the  case o f marmatite, the maximum e r r o r , a t the beginning o f 2  10  the a d s o r p t i o n , was 0.08 moles/cm x l O  .  To a s s i s t  i n the  l o g a r i t h m i c p r e s e n t a t i o n , times o f l e s s than 10 minutes were omitted  from the graphs.  The l i n e a r i t y o f a d s o r p t i o n  i n the 1 t o 10 minute r e g i o n was w e l l demonstrated i n (41) previous work  and i s shown f o r two t e s t s from the  present s e r i e s i n F i g . 34.  A d s o r p t i o n r e s u l t s below the  one minute l i m i t a r e not r e l i a b l e w i t h the p r e s e n t apparatus s i n c e i t takes t h i r t y  seconds f o r the s o l u t i o n t o c i r c u l a t e  once through the m i n e r a l bed.  A d s o r p t i o n below t h i s  was i n v e s t i g a t e d by s e v e r a l a u t h o r s ^ ' . 3 0  limit  In the case o f  galena, they observed that the a d s o r p t i o n on the a c t i v e s i t e s o c c u r r e d w i t h i n the f i r s t  s i x t y seconds, a slower ad-  s o r p t i o n proceeding subsequently.  In the p r e s e n t study  the a d s o r p t i o n a t times g r e a t e r than one minute,  was i n -  v e s t i g a t e d by changing the s u r f a c e c h a r a c t e r i s t i c s o f the m i n e r a l s u r f a c e with i l l u m i n a t i o n . s e l e c t e d because  Such a range  was  i t i s more c l o s e l y r e l a t e d to the a c t u a l  f l o t a t i o n conditions i n a plant operation. 3.8  Flotation F l o t a t i o n o f the v a r i o u s m i n e r a l s was i n v e s t i g a t e d  u s i n g a semi-micro the a u t h o r ^ ' . 4 4  tube  ( 4 5  '  4 5  f l o t a t i o n technique p r e v i o u s l y used by  T h i s method was p r e f e r r e d to the Hallimond  ' and to the c e l l d e v i s e d by P u r c e l l  ( 4 7 )  f o r the  ready a d a p t a b i l i t y o f the design t o the l i g h t  attachment  used i n the a d s o r p t i o n t e s t s .  flotation  cell,  The semi-micro  handmade from a Pyrex G l a s s f r i t t e d  microns p o r o s i t y , i s shown i n F i g . 21.  funnel o f 6 0  57  LEGEND: (a) Pyrex semi-microflotation c e l l (capacity: 150 ml; porosity: 60 microns) (b) Mercury manometer (c) Needle valve bleed o f f Cd) Constant pressure d i s t r i b u t i o n chamber (e) Gas cylinder  Fig. 21 - Schematic diagram of the f l o t a t i o n  arrangement.  58 The p r e v i o u s l y cleaned c e l l of  doubly d i s t i l l e d  was f i l l e d w i t h 150 ml  water while s u f f i c i e n t back p r e s s u r e o f  n i t r o g e n was maintained t o a v o i d p e r c o l a t i o n through the fritted  disc.  A t y p i c a l charge o f 2g o f c l o s e l y  sized  s o l i d s [150/200 mesh i n the case o f (Zn,Fe)S] was  weighed,  a f t e r coning and p a r t i n g , and added t o the c e l l .  Potassium  e t h y l xanthate was then added to g i v e a t y p i c a l c o n c e n t r a t i o n o f 2.5x10 Syringe. mg/1  M/l (0.04 mg/1)  u s i n g an A g l a Micrometer  F o l l o w i n g a c o n d i t i o n i n g time o f 3 0 seconds,  0.02  o f e t h y l a l c o h o l were added as a f r o t h e r and the n i t r o g e n  pressure a d j u s t e d t o 2 0.5 cm o f Hg t o produce not  violent agitation.  for  3 minutes.  i n t e n s e but  The f r o t h product was c o l l e c t e d  Both product and t a i l i n g  were d r i e d and  t h e i r r e s p e c t i v e weights used t o c a l c u l a t e the m e t a l l u r g i c a l r e c o v e r i e s under c o n d i t i o n s o f normal d a y l i g h t In the  the case where s e l e c t e d wavelengths were used,  procedure was e s s e n t i a l l y the same but more a t t e n t i o n  was focused on t h e p r e p a r a t i o n o f s o l i d s .  A l l s o l i d s were  weighed i n numbered beakers and kept i n t o t a l overnight. the  illumination.  light  They were then added  darkness  i n d i v i d u a l l y to the c e l l ,  source t u r n e d on and the s o l i d s i l l u m i n a t e d f o r  15 minutes p r i o r t o a d d i t i o n o f the xanthate. steps were e x a c t l y the same as d e s c r i b e d  above.  Subsequent  CHAPTER 4 EXPERIMENTAL RESULTS  The adsorption r e s u l t s are presented as the t o t a l amount adsorbed versus tine.  Such a presentation i s pre-  ferred to the conventional equilibrium method because f l o t a t i o n per se i s a non-equilibrium system and more information can be obtained at selected time i n t e r v a l s . A detailed analysis of the rate constant, reaction order, activation energies and entropies of a c t i v a t i o n f o r a similar system has been presented by Guarnaschelli and Leja i n a previous p u b l i c a t i o n ^ ^ " \ 4  According to t h i s ,  the reaction for the adsorption o f xanthate i s o f the f i r s t order with an activation energy of about 18 Kcal/mole.  This  high value indicates strong chemisorption. In the present work the r e s u l t s are discussed i n terms of surface area  4.1  coverages.  Surface Area Measurements The physical adsorption o f nitrogen on mineral  surfaces can best be represented by the Brunauer, Emmett (48) and T e l l e r (BET) equation* :  60 P/Vad(P -P) = [(C-1)/Vm C]  (P/P )+l/VmC  Q  where:  P P  (4.1-1)  o  p a r t i a l pressure of nitrogen s a t u r a t e d pressure o f n i t r o g e n at temperature o f l i q u i d n i t r o g e n used t o t a l volume o f gas adsorbed monolayer volume o f gas adsorbed constant  o  Vad Vm C  T h i s i s the equation of a s t r a i g h t l i n e having as o r d i n a t e and P/P  Q  as a b s c i s s a .  slope o f t h i s l i n e and 1/VmC BET p l o t , the value o f P/P  Q  P/Vad(P -P) Q  Then (C-l)/VmC i s the  the i n t e r c e p t .  For a l i n e a r  should l i e between 0.05  and  0.35.  In o r d e r to work w i t h i n these l i m i t s , mixtures o f n o m i n a l l y 5, 15 and  25 per cent n i t r o g e n i n helium were used.  q u a n t i t y Vm and  f o r each powder was  c a l c u l a t e d from the  i n t e r c e p t o f the l i n e s o f F i g . 22.  The slope  In t h i s f i g u r e  every  p o i n t r e p r e s e n t s the a r i t h m e t i c average o f three independent measurements.  The main parameters and  s u r f a c e areas o f the  three samples are summarized i n Table IV.  A detailed  cal-  c u l a t i o n o f the s u r f a c e area o f marmatite i s presented i n Appendix D.  The l a r g e s u r f a c e area o f the marmatite, f o u r  times the area r e p o r t e d f o r a s i m i l a r s i z e i s the consequence o f the presence  fraction^ ^, 9  o f porous o x i d a t i o n  products due to the h i g h Iron content o f the sample the presence  of inevitable fines  and  (slimes).  From a knowledge o f the measured s u r f a c e area o f the 100/150 mesh marmatite the areas o f o t h e r  screened  f r a c t i o n s can be o b t a i n e d from t h e i r average screen  size.  10  ©  -O  (Zn,Fe)S  •+  (Pb,Ag)S  -©  PbS  a. i o a. a.  P/P  Fig.  22 - BET p l o t s  Q  x 10-  2  f o r 100/150 mesh m i n e r a l  powders,  62  TABLE IV - BET AREAS OF POWDERSQ00/150 MESH)  o  Sample  Size-g  Slope  (Zn,Fe)S  0.4600  25.4  0.4  0.0388  3675*400  (Pb,Ag)S  1.5751  21.3  0.4  0.0460  1270*200  PbS  1.0983  21.5  0.1  0.04 64  1850*200  Intercept  Vm-ml  Area-cm /g  TABLE V - CALCULATED SURFACE AREAS OF SCREENED FRACTIONS OF MARMATITE  Me sh Size  Average Screen Size (microns)  65/100  177  100/150  125  150/200  88  BET Area of (Zn,Fe)S cmVg —  3675 —  Calculated Area cm^/g 2600 —  5200  These calculated areas are shown i n Table V. In addition the number of xanthate molecules and 2 the equivalent i n moles/cm required to form a c l o s e l y packed monolayer can be calculated i n terms of the estimated 2 (9) parking area of 2 9A f o r the xanthate r a d i c a l . The number of xanthate r a d i c a l s per cm 2 i s 10 16 A 2 /2 9 A 2 = 13 = 34.5x10  which divided by Avogadro's Number y i e l d s  -10 5.7x10  2 moles/cm .  This monolayer coverage i s included  i n each of the adsorption figures. 4.2  Effects of Illumination The results of the adsorption of xanthate on  copper activated marmatite as a function of varying radiant energy are presented i n Figs. 2 3 and 24.  In F i g . 2 3 the  amounts of xanthate adsorbed increased as higher energy was supplied to the system.  F i g . 24 shows that  marmatite  adsorbed less xanthate when illuminated with 0.6 eV than when not illuminated.  In the case of illumination with  0.6 eV there was a decrease i n both the amount adsorbed at 10 minutes and the t o t a l amount adsorbed compared to the case of no illumination.  This same trend towards a de-  creased adsorption i s observed i f the test with 2.9 eV illumination i s compared to the test i n darkness ( F i g . 23 vs. F i g . 24). The l a s t e f f e c t can be explained i n terms of  ( Monolayer coverage at 5.7 moles/cm^ x 1 0  1 U  — o-  — — —  )  -o-  -o-  o  o-o  °  Light energy: 3.6-3.3 eV 2.9-2.6 eV 0.8-0.5 eV  0  20  30  40  _L  _L  50  60  J_  J  80  I  L  100  200  300  400 500  TIME - minutes -5 F i g . 23 - Adsorption of EtX from a solution of KEtX (9x10 M) on activated (Zn,Fe)S (100/150 mesh) at 20°C and natural pH (6.5) under controlled i l l u m i n a t i o n . (20g).  ( Monolayer coverage at 5.7 moles/cm  2  x 10  Light  1 0  )  conditions: Mercury vapour lamp Darkness 0.8 - 0.5 eV  LO  20  30  40  X  X  50  60  X  80  100  200  3000  H00  500  TIME - minutes F i g . 24 - A d s o r p t i o n o f EtX from a s o l u t i o n o f KEtX (9xlO" M) on a c t i v a t e d (Zn Fe)S (100/150 mesh) a t 20°C and n a t u r a l pH (6.5) under c o n t r o l l e d i l l u m i n a t i o n .ummation, (20g). 5  66 e l e c t r o n - h o l e recombination by t r a p p i n g .  The  traps,  commonly a s s o c i a t e d with i m p u r i t i e s and s t r u c t u r a l  defects,  provide l o c a l i z e d energy l e v e l s l y i n g deep w i t h i n the f o r b i d d e n energy gap  (See F i g . 2).  l e s s than the energy gap value may  The a d d i t i o n o f energy be s u f f i c i e n t to r a i s e  the e l e c t r o n from a t r a p i n t o the conduction band from which i t can then recombine with a h o l e i n the valence band.  T h e r e f o r e the f u n c t i o n o f energy l e s s - t h a n - t h e -  energy-gap value i s to promote these recombinations by supplying the r e q u i r e d t r a n s i t i o n e n e r g i e s t o the  system.  The net e f f e c t i s to a n n i h i l a t e an e l e c t r o n - h o l e p a i r and consequently to decrease c h e m i s o r p t i o n . w i l l be reached when the energy  A limiting  s t a t e <..  s u p p l i e d has promoted a l l  the e l e c t r o n s from the t r a p s to the conduction band. the r e s u l t s o f the present i n v e s t i g a t i o n i t may cluded that an energy o f 0.6  be  From  con-  eV i s s u f f i c i e n t to r a i s e  an e l e c t r o n from the t r a p to the conduction band, and t h a t 2.9 eV i s s u f f i c i e n t to r a i s e e l e c t r o n s from the valence band i n t o the t r a p s .  The  former p r o c e s s r e s u l t s i n a  combination and removal o f h o l e s and the l a t t e r  results  i n both c r e a t i o n o f e l e c t r o n - h o l e p a i r s and r e c o m b i n a t i o n . An energy o f 3.4  eV appears t o be s u f f i c i e n t t o promote  e l e c t r o n s from the valence band t o the conduction band thus creating electron-hole  pairs.  The e x i s t e n c e o f d i f f e r e n t e q u i l i b r i u m a d s o r p t i o n v a l u e s a f t e r about two  hours i s somewhat d i s c o n c e r t i n g .  67 The  a t o m i s t i c approach with i t s " d a n g l i n g  o r a c t i v e s i t e s has experimental  valence  bonds"  been q u i t e u s e f u l i n e x p l a i n i n g s i m i l a r  r e s u l t s up to a monolayer v a l u e .  Preferential  a d s o r p t i o n on s u r f a c e s o f d i f f e r e n t c r y s t a l l o g r a p h i c o r i e n t a t i o n would be d i f f i c u l t  to measure i n the case o f  the m i n e r a l powders used i n the present more a d s o r p t i o n difficult bonds.  study.  Further-  s l i g h t l y above the monolayer value i s  to v i s u a l i z e from the concept o f d a n g l i n g  The  photoactive  valence  f u n c t i o n o f i l l u m i n a t i o n i s to produce more sites, resulting in different equilibrium  adsorption values.  In the o n l y case where the  results  i n d i c a t e d a d s o r p t i o n g r e a t e r than the monolayer -value, t h a t o f the p-type galena, the s t r o n g a t t r a c t i o n  of  xanthate c o u l d be a t t r i b u t e d to the l a r g e r number o f  strong  (23) l y anodic  sites  .  However the r a t e o f a d s o r p t i o n would  be expected to decrease at the monolayer coverage.  In  view of the f a c t t h a t the i n d i c a t e d s u r f a c e coverage not much g r e a t e r than a monolayer, t h i s excess c o u l d , the o t h e r hand, a r i s e from the experimental s u r f a c e area measurement.  was on  e r r o r o f the  I f the s u r f a c e area i s assumed  to  be c o r r e c t , then the most s a t i s f a c t o r y a l t e r n a t i v e i s  to  d e s c r i b e the experimental  r e s u l t s i n terms o f the.  p o s i t i o n o f the Fermi l e v e l . When a semiconductor i s i n thermal e q u i l i b r i u m , the Fermi energy l e v e l assumes a c e r t a i n v a l u e . i l l u m i n a t i o n , the quasi-Fermi  Upon  l e v e l s f o r e l e c t r o n and  holes  68 depend on the amount o f photon energy s u p p l i e d to the system.  The h i g h e r the l i g h t i n t e n s i t y , the g r e a t e r t h e ,  p r o b a b i l i t y o f f i n d i n g an e l e c t r o n i n a s u r f a c e t r a p and a l o c a l i z e d hole i n the depletion.: l a y e r . favours the chemisorption  This condition  o f xanthate anions.  charge d e n s i t y extends i n t o the s u b s t r a t e , values  Since the  adsorption  s l i g h t l y l a r g e r than a monolayer can be accommodated.  While t h i s e x p l a n a t i o n may not o f f e r an exact d e s c r i p t i o n o f the system, these c o n s i d e r a t i o n s , l i k e many o t h e r s , a r e i n a d i r e c t i o n to f i l l the chemisorption  a d e f i c i e n c y i n the understanding  of  process.  When higher-than-the-energy-gap values o f r a d i a n t energy a r e used i n the t e s t s , l e s s d i f f i c u l t i e s are encountered in. the i n t e r p r e t a t i o n o f the r e s u l t s . galena,  In the case o f  i n c r e a s i n g e n e r g i e s always i n c r e a s e the amounts  o f xanthate adsorbed. c a t e d i n F i g . 25.  T h i s constant  Somewhat  by the a r g e n t i f e r o u s galena a d s o r p t i o n values  trend i s c l e a r l y  indi-  less regularity i s displayed i n F i g . 26.  In t h i s graph, the  f o r the darkness and t h e one o b t a i n e d  0.5 eV are superimposed suggesting f o r the s o l i d i n q u e s t i o n .  a minimum  with  adsorption  A sudden i n c r e a s e i n the amount  adsorbed i s d i s p l a y e d when 3.4 eV are used. two e f f e c t s must be taken i n t o c o n s i d e r a t i o n :  In t h i s case the o r i g i n a l  d i s t r i b u t i o n o f e l e c t r o n s i n the s u b s t r a t e and the h i g h j  energy value o f i l l u m i n a t i o n .  Since the (Pb,Ag)S i s p r e -  dominantly an n-type semiconductor, l e s s a d s o r p t i o n o f  40  30 o o  Light  r-i X 20  —  6 o  P - TYPE  conditions: 3.6 - 3.3 eV 2.9 - 2.6 eV 0.8 - 0.5 eV Darkness  ID <D •H O  e  o II  8 7 6  Monolayer  10  20  30  ±40  50  60  J 80  L L 100  l  200  300  400  500  TIME - minutes .-5. from a s o l u t i o n o f KEtX (9xl0~ M) on PbS F i g . 25 - Adsorption EtX 20°C and n a t u r a l pH under c o n t r o l l e d i l l u m i n a t i o n ; 20g.  (100/150 mesh) at  U3  10  N - TYPE  Light J  i  10  20  30  40  J  conditions 3.6 - 3.3 eV 2.9 - 2.6 eV 0.8 - O.tS.eV and darkness  L  50 60 80 100 TIME - minutes  X  200  300  X  400,  ,-5, F i g . 26 - A d s o r p t i o n o f EtX from a s o l u t i o n o f KEtX (5xl0~ M) on a r g e n t i f e r o u s galena (100/150 mesh) at 20°C and n a t u r a l pH under c o n t r o l l e d i l l u m i n a t i o n ; 20g.  500  71 xanthate anions i s to be expected, as w i l l be subsequently.  The  discussed  e f f e c t o f i l l u m i n a t i o n i s then to change  d r a s t i c a l l y the e l e c t r o n - h o l e d i s t r i b u t i o n r e s u l t i n g i n p r e - • ferential  adsorption. A comparison between F i g . 2 5 and  2 6 shows a two-  f o l d d i f f e r e n c e i n the amount o f xanthate a b s t r a c t e d the two  samples o f galena.  T h i s e f f e c t may  by  be a t t r i b u t e d  to e i t h e r o x i d a t i o n o r to the e l e c t r o p h y s i c a l c h a r a c t e r ^ i s t i c s of the o r i g i n a l these  4.3  samples and  w i l l be d i s c u s s e d  under  headings.  E f f e c t o f O x i d a t i o n on The  Adsorption  r e s u l t s presented  i n the p r e v i o u s  suggest t h a t xanthate a d s o r p t i o n may  section  be i n f l u e n c e d e i t h e r  by the e l e c t r o p h y s i c a l c h a r a c t e r i s t i c s o f the  original  s u r f a c e o r by the presence o f an o x i d a t i o n product mineral  surface.  Two  on  the  s e t s o f experiments were c a r r i e d  out  i n o r d e r to d i f f e r e n t i a t e between the two a l t e r n a t i v e s . The  experiments were: (1) o x i d a t i o n r a t e s o f galena  surfaces  and  (2) a d s o r p t i o n o f xanthate on unexposed s u r f a c e s i n  the absence o f oxygen. In the f i r s t of the two  galena  case the r e l a t i v e r a t e o f o x i d a t i o n  samples i s expected to i n d i c a t e which  sample i s the most l i k e l y to form a t h i c k e r l a y e r o f  oxides  and,  the  by comparison to the p r e v i o u s a d s o r p t i o n t e s t s ,  i n f l u e n c e o f t h i s l a y e r on the f i x a t i o n o f xanthate The  anions.  t e s t r e s u l t s are summarized i n T a b l e s X I I I , XIV and  XV (Appendix E ) .  In these  t a b l e s a column has been added  to i n d i c a t e the amount o f oxygen uptake i n terms o f u n i t area.  In t h e f i r s t  the experimental  two t a b l e s d u p l i c a t e runs prove t h a t  procedure i s q u i t e r e p r o d u c i b l e .  This  can be seen i n the g r a p h i c a l r e p r e s e n t a t i o n o f F i g . 2 7. A comparison between F i g . 27 and F i g . 28 shows the e f f e c t o f water vapour on the weight i n c r e a s e .  Regardless  atmosphere, t h e weight g a i n o f the a r g e n t i f e r o u s (n-type) i s approximately  o f the  galena  double t h a t o f the p-type  galena  at the a r b i t r a r y value o f 30 minutes. As d e s c r i b e d p r e v i o u s l y i n s e c t i o n 3.7b a d s o r p t i o n o f xanthate anions was s t u d i e d on two samples o f galena which were s p e c i a l l y prepared atmosphere.  and t e s t e d i n an i n e r t  These r e s u l t s are presented  i n F i g . 29.  t h i s graph the ranges o f t h e p r e v i o u s a d s o r p t i o n  In  results,  when samples and s o l u t i o n were exposed t o atmospheric oxygen, are shown as shaded areas.  The e f f e c t o f oxygen  i s q u i t e pronounced i n the case o f t h e a r g e n t i f e r o u s galena.  The i n c r e a s e i n a d s o r p t i o n due to o x i d a t i o n o f  the n-type galena was approximately  one h a l f o f the d i f f e r e n c e  i n a d s o r p t i o n o f p-type compared t o n-type galena.  This  f a c t c o r r e l a t e s q u i t e w e l l with the p r e v i o u s o x i d a t i o n j  experiments s i n c e the a r g e n t i f e r o u s galena o x i d i z e d more r e a d i l y .  i s the one t h a t  73 .400  360 h  x  80 *  40  r  30  60  90  TIME - m i n u t e s Fig.. 2 7 - O x i d a t i o n r a t e o f g a l e n a i n o x y g e n water vapour.  120  150  J  i n the p r e s e n c e o f  Fig.  28 - O x i d a t i o n oxygen.  rates o f galena  i n a d r y atmosphere  of  o  r-t O rH  p -  X  e o  TYPE PbS  10 |  "v.  wD C r-i  8  O  e  6 [  < .  o 1  3  o°  f-  1  » 2  I-cr  5 6 F  ig.  29 -  30 40 TIME - minutes  l e n g t h (.340-.380 microns, 3.6-3.3 e V ) .  50  ' "  a  eu 100  t  u  r  a  l  p  H  a  n  200  d  300 40  c o n s t a n t wave-  tn  76 4.4  E f f e c t o f Surface C h a r a c t e r i s t i c s on A d s o r p t i o n Apart from the e f f e c t s o f o x i d a t i o n and  nation there i s s t i l l  illumi-  a b a s i c d i f f e r e n c e i n the a d s o r p t i o n  behaviour between the p-type and n-type  samples.  This  behaviour can be analysed i n terms o f the e l e c t r o p h y s i c a l c h a r a c t e r i s t i c s o f the s o l i d s . Since t h e uptake o f an adsorbate i s a c c e l e r a t e d by the presence o f f r e e quantum s t a t e s ( h o l e s ) , a p-type s o l i d i s expected to favour the chemisorption o f xanthate. The r e v e r s e i s t r u e f o r a s o l i d o f the n-type.  Fig. 2 9  shows t h a t the o r d e r o f magnitude o f t h i s e f f e c t i s l a r g e r than that o f e i t h e r i l l u m i n a t i o n o r o x i d a t i o n .  In terms  o f surface coverage, the amount o f xanthate adsorbed i n the f i r s t 10 minutes  by the p-type galena reaches that o f a  monolayer whereas i n the case o f the n-type  s o l i d , the c o v e r -  age i s approximately one h a l f o f the monolayer v a l u e . To summarize, t h e combination o f the r a t e o f o x i d a t i o n and the presence o f o x i d a t i o n products on the a d s o r p t i o n o f xanthate anions l e a d s to some i n t e r e s t i n g conclusions.  Since (Pb,Ag)S o x i d i z e s more r a p i d l y than  PbS, the former should have changed to a p-type (24) conductor i n a r e l a t i v e l y  short p e r i o d  .  semi-  That  this  t r a n s i t i o n d i d not take p l a c e i s evidenced by the Seebeck Effect  ( n - t y p e ) , d i s c u s s e d subsequently i n s e c t i o n 4.7,  and  by the lower a f f i n i t y o f (Pb,Ag)S f o r EtX~ than that d i s -  77 played by PbS (p-type) i n the adsorption experiments. Without refuting the e f f e c t s of oxygen on adsorption, the present results strongly suggest that the o r i g i n a l n-type or p-type character of the solids i s the more  important  factor.  4.5  Effect o f Illumination Intensity on Adsorption The dependence of the adsorption on the i n t e n s i t y  of l i g h t of a constant wavelength i n the system  xanthate-  activated marmatite was investigated and results are shown i n Fig. 30. The system i s characterized by a strong photoadsorption e f f e c t which depends on the intensity of the light.  When the maximum intensity was i r r a d i a t e d on the  sample, the amount of xanthate adsorbed i n the f i r s t 10 minutes was twice the amount adsorbed by the sample kept i n t o t a l darkness.  These points as well as those f o r  intermediate i n t e n s i t i e s are presented  i n F i g . 31. In  these figures the l i g h t intensity was calculated using the mean emf of a c a l i b r a t e d thermopile* and the reading o f a high-impedance microvoltmeter  (Fluke, Model 845-AB). A l l  measurements refer to the l i g h t values after f i l t e r i n g as present at the outside walls of the adsorption chamber.  *  Eppley Thermopile S e r i a l No. 8 824, The Eppley Inc., Newport, R.I.  Laboratory  3 ( Monolayer coverage at 5.7 moles/cm x 1 0 ^ ) 2  Intensity o f illumination: « 275 vi watts/cm •O 180 y watts/cm © 80 y watts/cm •O 0 y watts/cm  2  2  2 2  J  10  20  30  40  I  I  I  50 60 80 100 TIME - minutes  200  300  Fig. 30 - Adsorption of EtX" on activated (Zn,Fe)S (150/200 mesh) at 20°C and natural pH using various i n t e n s i t i e s o f illumination at a constant wavelength (.340-. 380 microns) from a 400 W/QI lamp; lOg.  400 500 oo  1.0  0.8  o  I 0  i  : i  i  i  i  i  i  l  50  100  150  200  250  300  350  400  INTENSITY OF LIGHT Fag.  31 - V a r i a t i o n intensity  -  microwatts/cm  2  on t h e amount o f x a n t h a t e a d s o r b e d a s a f u n c t i o n o f l i g h t f o r a c o n s t a n t e n e r g y (3.6-3.3eV) a t 10 m i n u t e s .  ^  80  TABLE VI ELECTROPHYSICAL CHARACTERISTICS OF ACTIVATED MARMATITE AFTER ADSORPTION OF EtX~ AS A FUNCTION OF ILLUMINATION INTENSITY.  Light Intensity Vi watts/cm  2  Type of Sera i c o n due t o r  Thermoelectric Power WV/°C  Fermi Level (E -E ) eV C  F  0  P  34  0.97  80  P  21  0.58  180 :  P  24  0.67  275  P  26  0.73  81 The  electrophysical characteristics of pelletized  samples o f a c t i v a t e d marmatite a f t e r exposure t o i l l u m i n a t i o n and a d s o r p t i o n were determined as d e s c r i b e d p r e v i o u s l y . These are summarized i n Table VI. A sample c a l c u l a t i o n o f the Fermi energy l e v e l from t h e r m o e l e c t r i c power measurements i s presented  i n Appendix F.  In a l l cases, the Fermi  energy l e v e l was r a i s e d a f t e r a d s o r p t i o n o f the donor adsorbate ( E t X ~ ) .  4.6  Copper A c t i v a t i o n Copper a c t i v a t i o n o f marmatite i s normally r e -  quired f o r f l o t a t i o n .  The e f f e c t o f i n i t i a l  copper i o n  c o n c e n t r a t i o n on the a c t i v a t i o n o f marmatite and subsequent a d s o r p t i o n o f xanthate ions was i n v e s t i g a t e d u s i n g a constant  illumination.  Concentrations  The r e s u l t s are shown i n F i g . 32.  o f 1 0 " and 10~ M/1 o f copper sulphate had 4  3  a d e f i n i t e e f f e c t on the a d s o r p t i o n o f xanthate whereas a c o n c e n t r a t i o n o f 10~^M/1 showed but l i t t l e over the n o n - a c t i v a t e d marmatite. t i o n s o f copper sulphate was  improvement  At the h i g h e r  concentra-  the r a t e o f xanthate a d s o r p t i o n  o f the same o r d e r o f magnitude as i n the p r e v i o u s  tests.  A t the low c o n c e n t r a t i o n , xanthate a d s o r p t i o n appeared t o reach e q u i l i b r i u m a t a low surface coverage.  Coverages by  copper atoms were determined from t h e d i f f e r e n c e s between the i n i t i a l and f i n a l c o n c e n t r a t i o n o f copper i n s o l u t i o n  82 i n the a c t i v a t i o n  step, assuming the p a r k i n g area o f the  9 ( 28) copper atom t o be 10.4 k  l  .  A l l c o n c e n t r a t i o n s were  measured by an EEL Atomic Absorption  Spectrophotometer.  The r e s u l t s o f Table V I I together with F i g . 32 i n d i c a t e t h a t a c o n c e n t r a t i o n o f 14% o r more o f t h e monolayer value promotes a d s o r p t i o n o f xanthate, is insufficient.  whereas a coverage o f 2%  S t o i c h i o m e t r i c a l l y , the value o f 14%  i s i n e x c e l l e n t agreement with t h e c a l c u l a t e d coverage by xanthate  (13%) a f t e r t h e f i r s t 10 minutes, a common  r e t e n t i o n time used by f l o t a t i o n p l a n t s . The  e f f e c t s o f washing, non-washing and washing  followed o r not by d r y i n g on the a d s o r p t i o n o f xanthate on copper a c t i v a t e d marmatite a r e shown i n F i g . 33. r e s u l t s were obtained with o r without  Identical  d r y i n g o f t h e washed  marmatite p r i o r t o a d s o r p t i o n o f xanthate.  When t h e sample  was  In t h i s  not washed more xanthate  the high xanthate of  was adsorbed.  case  a b s t r a c t i o n was due t o t h e p r e c i p i t a t i o n  cuprous e t h y l xanthate.  In the absence o f washing e x t r a  copper was present In the system as an aqueous f i l m around each mineral  particle.  Table V I I I summarizes t h e e l e c t r o p h y s i c a l c h a r a c t e r i s t i c s o f the powders p r i o r to and a f t e r xanthate  adsorption.  I f the r e s u l t s a r e grouped i n p a i r s t h e c o r r e l a t i o n o f Table V I I I with F i g . 32 i s q u i t e e v i d e n t .  Following  acti-  v a t i o n i n low copper c o n c e n t r a t i o n s the r e s i s t a n c e stays  50  60  80  100  200  300  400 500  TIME - minutes Fig.  32 - The e f f e c t o f c o p p e r a c t i v a t i o n on the a d s o r p t i o n o f EtX~ from a s o l u t i o n o f KEtX (5xlO~ M) on ( Z n , F e ) S (65/100 mesh) a t 20°C and n a t u r a l pH, i l l u m i n a t e d w i t h l i g h t o f 3.6-3.3 eV;10g. 5  oo to  TIME - minutes Fig.  33 - The e f f e c t o f washing the marmatite a f t e r copper a c t i v a t i o n , lOg o f (Zn,Fe)S (65/100 mesh) with 100 ml o f a 0. 9 9 6 x l O M s o l u t i o n o f CuS0i|.5Ho0 on the subsequent a d s o r p t i o n o f EtX" a t 20°C and n a t u r a l pH, i l l u m i n a t e d w i t h l i g h t o f 3.6-3.3 eV. _3  85 TABLE V I I - ADSORPTION OF COPPER ON MARMATITE  Initial Concentration o f Copper x l O - M/1  (65/100 MESH)  Final Concentrat i o n of Copper x l 0 ~ M/1  5  Adsorbed Copper xlO-'M/l  5  0  0  0.996  0  0  traces  0.9  2  3. 95  6.0  14  43.7  105  9.96 99.6  Calculated Surface Coverage %  55. 9  TABLE VIII CHANGES IN THE ELECTROPHYSICAL CHARACTERISTICS OF (Zn,Fe)S ON ADDITION OF VARIOUS Cu  I n i t i a l Copper Concentrat i o n M/l 0 0.996xl0"  5  .  + +  CONCENTRATIONS  P r i o r EtX~ A d s o r p t i o n  A f t e r EtX" A d s o r p t i o n  Type o f Semic.  Type o f Semic.  u V/°C  P. cm  Vi V/°C  P. cm  P  174  2xl0  8  P  155  2x10  P  155  4xl0  8  P  139  2xl0  8  8  0.996xl0  -4  P  65  4xl0  6  P ..  66  4xl0  7  0.996xl0  -3  P  14  lxlO  6  P  46  2xl0  7  86 approximately (Table V I I I ) .  the same before and a f t e r  adsorption  T h i s e f f e c t i s p a r a l l e l e d by low  r a t e s of xanthate i n F i g . 32. copper c o n c e n t r a t i o n s  adsorption  F o l l o w i n g a c t i v a t i o n i n high  the r e s i s t a n c e o f the powders before  a d s o r p t i o n i s l e s s than i n the previous s l i g h t l y a f t e r adsorption  case and  (Table V I I I ) .  This trend i s  again c l e a r l y i n d i c a t e d i n F i g . 32 by the h i g h e r s o r p t i o n r a t e and  4.7  increases  ad-  t o t a l adsorption of t h i s p a i r .  E l e c t r o p h y s i c a l Measurements In the p r e v i o u s two  s e c t i o n s some p e r t i n e n t  e l e c t r o p h y s i c a l measurements were i n t r o d u c e d .  In t h i s  s e c t i o n , some b a s i c e l e c t r o p h y s i c a l c h a r a c t e r i s t i c s o f a s - r e c e i v e d s o l i d and powder specimens are These i n c l u d e a study o f c a r r i e r type and  presented. concentration,  from both the H a l l c o e f f i c i e n t and the Seebeck e f f e c t . Table IX shows the r e s u l t s obtained specimens by measuring the H a l l v o l t a g e . c a l c u l a t i o n o f one G.  on  solid  A detailed  o f the measurements i s shown i n Appendix  In the case o f galena r e l i a b l e r e s u l t s were o b t a i n e d  with pressure results.  contacts, solder contacts y i e l d i n g  similar  Since no measurement c o u l d be made on the ground  marmatite from Broken H i l l , Columbia s p h a l e r i t e was  a s o l i d sample o f  prepared  British  as a p o s s i b l e a l t e r n a t i v e .  Because o f i t s h i g h r e s i s t a n c e , measurements with e i t h e r  87  TABLE IX - ELECTROPHYSICAL CHARACTERISTICS OF SOLID SPECIMENS  Sample  Semic. Type  Resistivity J2 cm'  PbS  P  0.4  (Pb,Ag)S  n  1.3xl0""  7  Hall Carriers C o e f f . Concen|r*n cm /coul cm" 3  Mobility cm / / v o l t cm 2  280  2.2xl0  1 6  700  0. 013  6x10  17  10  5  TABLE X - SEEBECK EFFECT ON SOLID AND POWDER SPECIMENS  Sample PbS  Semiconductor Type  Q Millivolts/degree  Resistivity ft cm  P P  0.0018 0.0012  (Zn,Fe)S act .powd e r non act.powd er  p p  0.0028 0.0012  1x101  (Pb,Ag)S powder solid  n n  0.0031 0.0026  5xl0"c  powder solid  56 20  2x10°  2x10  88 p r e s s u r e o r indium s o l d e r c o n t a c t s were not f u r t h e r work was  s o l i d and  warranted on  successful.  t h i s p a r t i c u l a r sample.  Table X summarizes the r e s u l t s o b t a i n e d on  both  powder specimens.  the  c a r r i e r concentration  A sample c a l c u l a t i o n o f  i s presented i n Appendix H. 18  value o b t a i n e d , 5.1x10 the value p r e v i o u s l y  power data.  The  3 holes/cm , i s not  i n agreement with  c a l c u l a t e d from the H a l l  2.2x10-'-^, as i s commonly found when u s i n g S i m i l a r d i s c r e p a n c y has  and  voltage,  thermoelectric  been a t t r i b u t e d to  i n t e r a c t i o n between the a n i s o t r o p i c l a t t i c e to the thermal g r a d i e n t ,  The  c a r r i e r s are p r e f e r e n t i a l l y s c a t t e r e d toward the  end  o f the  the mobile charge c a r r i e r s ^  Appendix H the  \  has  been c o n f i n e d  been  been assumed to  Because o f these u n c e r t a i n t i e s , the  used  be  by  application  to the d i f f e r e n t i a t i o n  p-type specimens.  Correlation of Adsorption The  has  galena specimens and  Seebeck e f f e c t has  o f n-type and 4.8  Furthermore, i n  the mass o f the e l e c t r o n , a value p r e v i o u s l y  o f the  cold  e f f e c t i v e mass o f the e l e c t r o n has not  measured i n the  5 l  5 0  sample by the n o n - e q u i l i b r i u m phonon d i s t r i b u t i o n  thus enhancing the e l e c t r o s t a t i c f i e l d .  Slater^  an  vibrations,  due  0.3  No  Results  i n d i v i d u a l behaviour o f galena and  been c h a r a c t e r i z e d  by a d s o r p t i o n  measurements under v a r i o u s  conditions  and  marmatite  electrophysical  of i l l u m i n a t i o n .  To  89 be able to compare the a d s o r p t i o n e f f e c t s with each o t h e r , a common base had t o be s e l e c t e d . was  The most l o g i c a l c h o i c e  that o f percentage surface a r e a coverage.  Then the  surface covered by the s u r f a c t a n t c o u l d be used to r e p r e s e n t the tendency f o r the a d s o r p t i o n to take p l a c e .  This ten-  dency has been expressed as p e r c e n t o f monolayer  coverage.  Table XI i s a compendium o f s u r f a c e coverages f o r the v a r i o u s systems q u i t e apparent.  investigated.  The main t r e n d s are  Namely, the p-type galena adsorbs a mono-  l a y e r o f xanthate i n the f i r s t  10 minutes w h i l s t the n-type  galena adsorbs o n l y one h a l f o f i t s monolayer  value.  More-  over, t h e amount o f xanthate adsorbed by the two galenas d i f f e r s l a r g e l y from t h e amount o f xanthate a b s t r a c t e d by the marmatite.  The l a t t e r shows an a d s o r p t i o n t h a t never  exceeds an e q u i v a l e n t coverage o f 23% under t h e most f a v o u r able conditions. These t r e n d s s t r o n g l y i n d i c a t e that the e l e c t r o p h y s i c a l c h a r a c t e r i s t i c s o f the s u b s t r a t e are o f paramount importance i n a d s o r p t i o n .  Since the a d s o r p t i o n o f xanthate  i s a p-type r e a c t i o n i t i s a c c e l e r a t e d by f r e e quantum s t a t e s and the p-type galena i s expected t o adsorb a monol a y e r o f xanthate i n a r e l a t i v e l y short time.  When the  p-type galena i s compared to the p-type marmatite  the d i f -  f e r e n c e i n the a d s o r p t i o n c h a r a c t e r i s t i c s can be a t t r i b u t e d to the d i f f e r e n c e i n the energy gaps.  I f the t e s t s w i t h 0.6  are chosen i n each case, t h e r a t i o between t h e t h e o r e t i c a l  90  TABLE XI - ADSORPTION RESULTS IN TERMS OF XANTHATE COVERAGE  Monolayer Coverage-% Material (Zn,Fe)S u  ti ti it it II II II  ti ti n ti  PbS tt tt tt ti II  conditions t o r Adsorption Hg lamp Darkness  at 1 0 miri.  at e q u i l i b r i u m  23 14  31 30  22 17 12  30 26 24  7000 lumens 56 00 lumens 2 4 5 0 lumens Darkness  15 14 11 7  26 22 21 20  Cu -10- M/1 Cu -10- M/1 Cu +-10- M/1 Cu - 0 M/1  19 13 11 12  37 35 18 13  115 115 115 105 95 90  180 200 190 175 165 150  3.6-3.3 2.9-2.6 0.8-0.5  eV eV eV  + +  5  + +  4  +  3  4 0 0 W-QI 5 00 W-QI 3 . 6 - 3 . 3 eV 2 . 9 - 2 . 6 eV 0 . 8 - 0 . 5 eV  Darkness  PbS (Pb,Ag)S  U n o x - 3 . 4 eV U n o x - 3 . 4 eV  88 35  110 50  (Pb,Ag)S  3.6-3.3 2.9-2.6 0.8-0.5  62 53 44 44  120 72 63 63  n II  ti  eV eV eV  Darkness  91 values o f the energy gaps i s i n good agreement w i t h the r a t i o o f t h e i r surface coverages at the ten minute and a t e q u i l i b r i u m .  Namely, the t h e o r e t i c a l energy  value gap  r a t i o o f 10 compares f a v o u r a b l y with the r a t i o s o f 8 and 7 for  the experimental coverages.  The t e s t with 0.6 eV  has  been chosen because with t h i s energy the t r a p s are emptied and the marmatite more c l o s e l y resembles the semiconductor. to  intrinsic  Under these c o n d i t i o n s i t was a c c e p t a b l e  use as the t h e o r e t i c a l energy gap value the p u b l i s h e d  figure for sphalerite. The  same t r e n d towards Increased a d s o r p t i o n i s  observed when the u n o x i d i z e d forms o f galena are compared with the o x i d i z e d . 88% o f a monolayer monolayer. mately 1/4  The u n o x i d i z e d p-type galena adsorbs i n the f i r s t  10 minutes i n s t e a d o f a f u l l  The u n o x i d i z e d n-type galena adsorbs a p p r o x i o f a monolayer  r a t h e r than one h a l f o f a mono-  l a y e r d u r i n g the same p e r i o d o f time.  Thus a 5 0% d i f f e r e n c e  between the a d s o r p t i o n behaviour o f the two is  still  forms o f galena  apparent whether o r not they are o x i d i z e d . When the i n d i v i d u a l marmatite  systems are taken  i n t o c o n s i d e r a t i o n , i t i s noted t h a t i n the f i r s t t e n minutes the amount o f xanthate a d s o r p t i o n i n c r e a s e s as the i l l u m i n a t i o n energy, l i g h t i n t e n s i t y o r copper c o n c e n t r a t i o n increases.  At the e q u i l i b r i u m c o n d i t i o n s , a s i m i l a r i n -  crease i s observed but to a l e s s e r e x t e n t i n the case o f photoexcitation.  In the case o f copper a c t i v a t i o n a t  92 e q u i l i b r i u m c o n d i t i o n s a g r e a t e r a d s o r p t i o n o f xanthate was observed. The  e f f e c t o f i l l u m i n a t i o n on each v a r i e t y o f  galena was to i n c r e a s e a d s o r p t i o n .  However d u r i n g the  f i r s t 10 minutes, the amount o f xanthate adsorbed by PbS was enhanced by 25% w h i l s t the i n c r e a s e i n a d s o r p t i o n d i s p l a y e d by the (Pb,Ag)S was o n l y 18%. Thus the o r i g i n a l e l e c t r o p h y s i c a l c h a r a c t e r i s t i c s o f the s u b s t r a t e are more s i g n i f i c a n t than the e f f e c t s o f i l l u m i n a t i o n on the a d s o r p t i o n o f xanthate.  4.9  F l o t a t i o n Experiments The  d i f f e r e n c e s i n the a d s o r p t i o n r a t e s o f xanthate  anions on galena and marmatite suggest the p o s s i b i l i t y o f u t i l i z i n g c o n t r o l l e d i l l u m i n a t i o n i n the p r a c t i c a l t i o n o f the two m i n e r a l s .  separa-  The a c t u a l a p p l i c a t i o n has been  i n v e s t i g a t e d using a semi-micro f l o t a t i o n technique  describ-  ed i n s e c t i o n 3.8. At the beginning  i t was decided  to give the same  s t a t i s t i c a l p r o b a b i l i t y o f p a r t i c l e t o bubble attachment t o both m i n e r a l s  by u s i n g the same number o f p a r t i c l e s i n a l l  t e s t s (Appendix I ) . had it  been completed  As soon as the f i r s t  series of tests  (Appendix J ) , i t became apparent t h a t  was extremely d i f f i c u l t  to d e t e c t s i g n i f i c a n t d i f f e r e n c e s  between t e s t s o f v a r y i n g l i g h t e n e r g i e s  s i n c e comparable  high- r e c o v e r i e s were obtained  i n a l l tests.  To circumvent  t h i s d i f f i c u l t y , s t a r v a t i o n q u a n t i t i e s o f s u r f a c t a n t were c a l c u l a t e d as f o l l o w s .  Since o n l y 10% o f the surface o f  marmatite i s covered by xanthate  (present  work) i t i s not  necessary to have more than t h i s e q u i v a l e n t solution.  amount i n  In the case o f g a l e n a 20 to 40% coverage i s  required f o r f l o t a t i o n ^ ' . 3 0  Using 150 ml o f s o l u t i o n and  2g o f 150/200 mesh marmatite (5,200 cm /g), 0.04 mg/1 a r e 2  r e q u i r e d f o r a s u r f a c e coverage o f 9%. PbS, again fraction  In the case o f  using 150 ml o f s o l u t i o n and 2g o f 100/150 mesh 2  (1,850 cm / g ) , 0.08 mg/1 are r e q u i r e d  coverage o f 32%.  fora  surface  The f a c t that two d i f f e r e n t reagent con-  c e n t r a t i o n s were r e q u i r e d , n e c e s s i t a t e d an i n d i v i d u a l treatment o f the m i n e r a l s . A summary o f the f l o t a t i o n r e s u l t s i s presented i n Table X I I .  The data i n d i c a t e t h a t the f l o t a t i o n o f  g a l e n a was not s i g n i f i c a n t l y d i f f e r e n t when e i t h e r d a y l i g h t o r l i g h t o f 2.5 microns wavelength was used i n the e x p e r i ments.  A d e f i n i t e t r e n d towards lower r e c o v e r i e s  present  when marmatite was i n v e s t i g a t e d under  test conditions. 11%  The recovery  was  equivalent  o f marmatite decreased by  when i r r a d i a t e d w i t h l i g h t o f 2.5 microns wavelength  compared with t h a t i n d a y l i g h t . adsorption  The t r e n d o f the p r e v i o u s  experiments was thus confirmed even though a  p r a c t i c a l s e p a r a t i o n o f the mixed m i n e r a l s  would be e x t r e -  mely d i f f i c u l t to achieve s i n c e d i f f e r e n t I n i t i a l  concentra-  TABLE XII - SUMMARY OF FLOTATION RESULTS  FLOTATION CONDITIONS Sample  Light  KEtX mg/1  Ethanol mg/1  DISTRIBUTION ( A r i t h . Ave. of 5 tests)  Confidence L i m i t Standard  Float  Tails  Deviation  (68.27% l e v e l ) %  PbS (100/150)  Daylight  0. 08  0.03  37.0  63.0  3.0  37.0+3.0  PbS. (100/150)  2.5 u  0.08  0.03  39.7  60.3  2.7  39.7+2.7  (Zn,Fe)S (150.200)  Daylight  0.04  0.02  73.2  26.8  2.2  73.2+2.2  (Zn,Fe)S (150.200)  2.5 u  0. 04  0.02  62.2  37.8  3.3  62. 2+_3.3  (Zn,Fe)S (150/200)  150 W  0.04  0.02  72 .5  27.5  2.9  72.5+2.9  t i o n s o f xanthate were r e q u i r e d .  Furthermore, i n c o n c l u s i v e  r e s u l t s were o b t a i n e d with marmatite when t e s t s  conducted  i n d a y l i g h t were compared with t e s t s where a 150 watt bulb was used.  light  S i m i l a r r e c o v e r i e s suggest t h a t the o p t i c a l  e x c i t a t i o n was o f the same o r d e r o f magnitude i n both cases.  CHAPTER 5 DISCUSSION OF RESULTS  5.1  Adsorption In the p r e s e n t study two d i s t i n c t  stages can be i d e n t i f i e d :  adsorption  (a) a r a t e dependent stage  extends from 1 to approximately  that  100 minutes and, (b) a  stage above the 100 minutes where the r a t e i s g r e a t l y d i minished.  Another r e g i o n where a d s o r p t i o n takes p l a c e i n  l e s s than 1 minute has been p r e v i o u s l y d e s c r i b e d by o t h e r investigators^ ^. 3  No i n v e s t i g a t i o n o f the k i n e t i c s below  one minute c o u l d be made because o f t h e i n h e r e n t  limitations  o f the equipment used n e v e r t h e l e s s , a short d i s c u s s i o n must be i n c l u d e d s i n c e the mode o f a d s o r p t i o n i n t h i s r e g i o n c o n s t i t u t e s the b a s i s f o r subsequent  adsorption.  The k i n e t i c s o f a d s o r p t i o n below the one minute l e v e l vary depending on monolayer o r m u l t i l a y e r c o v e r a g e s ^ ^ ' 3  The  supporting data i n d i c a t e t h a t the r a t e o f c o l l e c t o r ad-  s o r p t i o n depends on the c o n c e n t r a t i o n o f reagent  i n solution.  These r e s u l t s with 50g/ton (=20 mg/1) agree with monolayer coverages whereas the r e s u l t s with lOOOg/ton (=3 00 mg/1) agree w i t h m u l t i l a y e r a d s o r p t i o n .  Presumably these  coverages  r e f e r to the h y p o t h e t i c a l o r d e r l y arrangement o f the f a c t a n t on the mineral  surface.  sur-  T h i s i s o f paramount  importance because the main i n d i c a t i o n o f m u l t i l a y e r  ad-  s o r p t i o n comes from the c a l c u l a t i o n o f the amount adsorbed on the u n i t area o f the mineral  surface.  Calculations of  m u l t i l a y e r coverages are not c o r r e c t because o f the nonuniform d i s t r i b u t i o n o f reagents on  the m i n e r a l  surface,  the d i f f e r e n c e between the uniform and non-uniform bution accounting s o r p t i o n at low seconds may  f o r the m u l t i l a y e r coverage.  concentrations  distri-  Thus  and w i t h i n the f i r s t  adsixty  be v i s u a l i z e d as a "monomolecular gaseous"  f i l m r e s i d i n g e n t i r e l y a t the a c t i v e s i t e s with random o r i e n t a t i o n of non-polar r a d i c a l s . ments m u l t i l a y e r a d s o r p t i o n the low c o n c e n t r a t i o n (=15  mg/1).  should  In the present  experi-  not have o c c u r r e d  of xanthate used f o r the  adsorption  These p r e d i c t i o n s were confirmed by the  ments where the c a l c u l a t e d monolayer values around the two  experi  appeared o n l y  hour l i m i t .  In the l-to-100-minute r e g i o n the r a t e o f s o r p t i o n was  with  found to vary a c c o r d i n g  mental c o n d i t i o n s .  to the  specific  A study o f these v a r i a t i o n s was  adexperi the  main o b j e c t i v e o f t h i s i n v e s t i g a t i o n s i n c e enhanced o r reduced a d s o r p t i o n d i s t r i b u t i o n o f the  r e s u l t e d on changing the substrate  electron-hole  with i l l u m i n a t i o n .  When more  a c t i v e s i t e s were induced i n the s u b s t r a t e more xanthate c o u l d be adsorbed by the i n c r e a s e d  electrostatic attraction  98  At t h i s stage  the molecules have a strong tendency to o r i e n t  themselves on the m i n e r a l a two dimensional  s u r f a c e forming  "liquid film".  the e q u i v a l e n t o f  Two e f f e c t s are apparent:  (1) i n c r e a s e d a d s o r p t i o n due to an i n c r e a s e i n t h e number o f surface s i t e s and/or an i n c r e a s e i n the e l e c t r o s t a t i c a t t r a c t i o n with more h o l e s l o c a l i z e d a t the a c t i v e s i t e s , and  (2) a d s o r p t i o n f a c i l i t a t e d by the a s s o c i a t i o n between  hydrocarbon c h a i n s .  Furthermore, m u l t i l a y e r formation i n  t h i s r e g i o n may be accompanied by a p h y s i c a l a d s o r p t i o n o f metal xanthate molecules and dixanthogen molecules p r e v i o u s l y formed i n the e l e c t r i c a l double l a y e r i n g the m i n e r a l p a r t i c l e s .  surround-  In t h i s case e x t e n s i v e ad-  s o r p t i o n o f n e u t r a l molecules would occur through i n t e r a c t i o n of hydrocarbon chains but without  electrostatic repulsion  s i n c e the p o l a r heads a r e uncharged. In the r e g i o n above 100 minutes the r e s u l t s i n d i c a t e that the a d s o r p t i o n r a t e i s n e g l i g i b l e . chemisorption  Because  i s r e s p o n s i b l e f o r the main a d s o r p t i o n o f  xanthate on galena, only p h y s i c a l a d s o r p t i o n may be operative i n t h i s region.  When chemisorption  usual f o r the s u r f a c t a n t to r e a c t completely solid  s u r f a c e becomes s a t u r a t e d .  u n l e s s the  I t i s d i f f i c u l t to  understand why t h i s does not occur i n the system.  occurs, i t i s  xanthate-galena  I t c o u l d be p o s t u l a t e d t h a t the r e a c t i o n i s very  slow a t a p a r t i c u l a r c o n c e n t r a t i o n o f xanthate but speeds up a t h i g h e r c o n c e n t r a t i o n being c o n t r o l l e d by a d i f f u s i o n  99  r a t e through a f i l m o f p r o d u c t s .  A l t e r n a t i v e l y the  r e a c t i o n c o u l d be due t o the presence o f a v e r y low c o n c e n t r a t i o n o f a n o t h e r r e a c t a n t which becomes exhausted diffuses  slowly through a continuous f i l m o f  x a n t h a t e ( i . e . oxygen i n s o l u t i o n ) .  or  adsorbed  I n e i t h e r case  the  r e s u l t i n g e f f e c t would be an e x t r e m e l y low a d s o r p t i o n , an e f f e c t  5.2  which was observed e x p e r i m e n t a l l y .  Photochemical E f f e c t s The c o n c e n t r a t i o n s  o f e l e c t r o n s and h o l e s  for  an i l l u m i n a t e d c r y s t a l vary from t h o s e o f a c r y s t a l k e p t i n t o t a l darkness.  The new d i s t r i b u t i o n i s expected  i n f l u e n c e the subsequent a d s o r p t i o n o f s u r f a c t a n t s . adsorption or photodesorption,  therefore,  to Photo-  may be o b s e r v e d  depending on t h e p o s i t i o n o f the Fermi l e v e l , presence o f impurities etc.  T h e o r e t i c a l l y , the presence  o f an a c c e p t o r  i m p u r i t y t h a t l o w e r s the Fermi l e v e l , o t h e r c o n d i t i o n s b e i n g equal, should r e s u l t i n  photoadsorption.  In the case o f g a l e n a , an e a s i l y o x i d i z e d m i n e r a l , t h e chemisorbed oxygen p r e s e n t a t the  s u r f a c e may  take p a r t i n an e l e c t r o n i c i n t e r a c t i o n by l o w e r i n g the e l e c t r o n i c energy b a r r i e r and t h u s r e d u c i n g t h e v a l u e o f the photon energy o f a c t i v a t i o n r e q u i r e d f o r t h e  adsorption  of xanthate.  The r e s u l t s o f F i g . 2 5 , 26, 29 c o n f i r m t h e s e  predictions.  F u r t h e r m o r e , o x i d a t i o n o f the n - t y p e  :  galena  i n c r e a s e d the a d s o r p t i o n o f x a n t h a t e by 50% ( F i g . 29) i n  c o n t r a s t w i t h the lower a d s o r p t i o n o f the p-type which was  galena  less readily oxidized. In the case o f marmatite a photon energy o f  0.6  eV i s capable of causing a captured e l e c t r o n to recombine with a hole i n the valence band but i s not s u f f i c i e n t to c r e a t e an e l e c t r o n - h o l e p a i r .  A depletion of electrons  and h o l e s r e s u l t s i n a lowering o f the amount o f reagent adsorbed,  an e f f e c t which i s r e a d i l y observed  Furthermore  i n F i g . 24.  the energy capable o f c a u s i n g these  recombina-  t i o n s i s of the same o r d e r o f magnitude as the Lambe and 17 K l i c k s t i m u l a t i o n band [quoted as 2.6 microns as p r e v i o u s l y i n d i c a t e d i n F i g . 3b.  (0.5 eV)  An a l t e r n a t i v e  ]  ex-  p l a n a t i o n o f t h i s e f f e c t i s an emission t r a n s i t i o n as p r o posed by Bube r e s u l t was  s  and p r e s e n t e d i n F i g . 2.  The  practical  an 11% r e d u c t i o n i n the f l o t a t i o n r e c o v e r y  (Table X I I ) , a r e s u l t which was p a r a l l e l e d by i n the f l o t a t i o n o f z i r c o n and p y r o c h l o r e ; the f l o t a t i o n o f p y r o c h l o r e was  on  o f the p r e s e n t study i n d i c a t e t h a t :  e f f e c t s , the r e s u l t s (1) p h o t o a d s o r p t i o n i s  the r e s u l t o f i l l u m i n a t i n g a semiconductor whilst  with  energy  (2) p h o t o d e s o r p t i o n i s  the r e s u l t o f i l l u m i n a t i n g the semiconductor lower-than-the-energy-gap.  irradiation,  reduced by 4 0%.  In terms o f photochemical  higher-than-the-energy-gap  Plaksin^  with  energy  101 5.3  Carrier  Behaviour  Measurements o f the H a l l c o e f f i c i e n t could o n l y be c a r r i e d out on galena specimens, the high r e s i s t a n c e o f the marmatite  being o u t s i d e the working l i m i t s o f the  a v a i l a b l e equipment.  These measurements and  are i n accord with the r e s u l t s of P u t l e y The work o f t h i s l a s t  limitations  (5 2)  and S a i t o  (53) .  investigator i s of particular  i n t e r e s t because h i s r e s u l t s i n d i c a t e t h a t the t r a n s i t i o n from n-type to p-type may  be f o l l o w e d through a change i n  r e s i s t a n c e , a r e l a t i v e l y simple measurement to c a r r y out. (6) Increased r e s i s t a n c e has been emphasized  a l s o by Mark  The tendency f o r the r e s i s t a n c e o f a c t i v a t e d marmatite  to  i n c r e a s e a f t e r a d s o r p t i o n i s e v i d e n t from Table V I I I . The Seebeck e f f e c t has been used  successfully  i n measuring the n-type o r p-type c h a r a c t e r o f the pressed powders.  The most important a p p l i c a t i o n i s presented i n  F i g . 29 where the amount o f xanthate anion adsorbed i s d r a s t i c a l l y reduced i n the case o f the n-type conductors.  semi-  Without the p o s s i b i l i t y o f measuring  the  e l e c t r o n i c c h a r a c t e r o f the powders, i t would have been impossible to i n t e r p r e t the experimental r e s u l t s . The p o s i t i o n o f the Fermi l e v e l w i t h i n a c r y s t a l and the degree o f c u r v a t u r e of the energy bands e s t a b l i s h the e l e c t r i c a l c o n d u c t i v i t y o f a semiconductor.  The  closer  the Fermi l e v e l i s to the c o n d u c t i o n band, the l a r g e r i s  the value o f the e l e c t r o n d e n s i t y and the more pronounced are the n-type c h a r a c t e r i s t i c s o f the semiconductor.  Thus  semiconductors a r e c l a s s i f i e d as n-type o r p-type when the hole component o r e l e c t r o n i c component r e s p e c t i v e l y i s negligible.  The c o n c e n t r a t i o n o f f r e e charge  carriers  t h a t take p a r t i n the r e a c t i o n must be r e s p o n s i b l e f o r the r e a c t i o n r a t e .  A p-type r e a c t i o n (donor) i s one which  i s a c c e l e r a t e d by f r e e quantum s t a t e s and an n-type r e a c t i o n (acceptor)  i s one which i s a c c e l e r a t e d by e l e c t r o n s .  Since  the measurements o f the H a l l c o e f f i c i e n t and the Seebeck e f f e c t i n d i c a t e t h a t the galena  i s a p-type  semiconductor,  the i n c r e a s e i n e l e c t r i c a l c o n d u c t i v i t y when the s o l i d i s i l l u m i n a t e d and a p a r a l l e l i n c r e a s e i n a d s o r p t i o n  rate  suggest t h a t the r e a c t i o n i s o f the p-type.  This i s i n  agreement with the s t r u c t u r e o f the n e g a t i v e  xanthate  anion  that r e q u i r e s a f r e e quantum s t a t e o r h o l e , and with the mechanism o f p h o t o c o n d u c t i v i t y Slater^^. i n the galena  o r i g i n a l l y d e s c r i b e d by  T h i s author r e c o g n i z e s  n and p-type  regions  s t r u c t u r e and the e x c i t a t i o n o f an e l e c t r o n  to the conduction  band when l i g h t i s absorbed anywhere i n  the c r y s t a l , l e a v i n g a hole i n the valence  band.  e l e c t r o n so i n t r o d u c e d  band w i l l now  tend to f a l l  i n t o the conduction  The  to t h e lowest p o s s i b l e energy, o r i n t o an  n-type r e g i o n , and a hole w i l l i n a s i m i l a r way f i n d i t s way i n t o a p-type r e g i o n .  The presence o f e x t r a e l e c t r o n s  i n the n-type r e g i o n , e x t r a h o l e s i n the p-type r e g i o n ,  will  103  neutralize some of the potential barriers. barriers w i l l be lowered and,  Thus the  in agreement with Plaksin  (7)  et a l  , the xanthate adsorption w i l l be enhanced.  This  fact has been demonstrated repeatedly i n the present work with the effect of illumination on adsorption, an e f f e c t that provides a good c o r r e l a t i o n between photoconductivity and adsorption. 5.4  Impurities and Reaction Mechanism In t h i s section emphasis i s placed on the  acti-  vation of marmatite, namely the role of copper i n adsorption. In general the amount and type of impurity, which govern the surface concentration of electrons, regulate also the amount of xanthate adsorbed by the substrate.  Any impurity  (dislo-  cations, vacancies, i n t e r s t i t i a l s and s u b s t i t u t i o n a l foreign atoms), depending on the type and concentration, displaces the Fermi l e v e l causing either an acceleration or a retardation of the adsorption reaction. Impurities, therefore, can be of two acceptors or donors.  Acceptor  types:  impurities always lower the  Fermi l e v e l , while donor impurities raise i t . In terms of n-type and p-type reactions, an acceptor reaction then w i l l be retarded by an acceptor impurity and accelerated by a donor impurity whereas a donor reaction w i l l be accelerated by an acceptor impurity and retarded by a donor  104  impurity. one  Thus a given impurity may  r e a c t i o n and  as a poison  shown i n the present  act as a promoter f o r  f o r another.  I t has  been  study t h a t marmatite a c t i v a t i o n by  copper i o n s r e s u l t s i n enhanced a d s o r p t i o n , t h a t i s , the a d s o r p t i o n r e a c t i o n i s promoted by copper.  T h i s may  be  caused by an increase i n c o n c e n t r a t i o n o f f r e e quantum s t a t e s (or h o l e s ) , a f a c t which i n d i c a t e s t h a t p a r t i c u l a r type o f impurity imparts to the m i n e r a l  surface.  this  acceptor p r o p e r t i e s  T h i s c o n c l u s i o n i s i n agreement  with the proposed energy l e v e l diagram o f Bube ( F i g . 2) and with P l a k s i n ^ ' who  o f f e r s an a d d i t i o n a l e x p l a n a t i o n  f o r the a c t i v a t i n g e f f e c t o f copper i o n s by d e s c r i b i n g a removal o f e l e c t r o n s from the s u r f a c e l a y e r as the copper i o n s d i f f u s e i n t o the Impurity  lattice.  c o n c e n t r a t i o n i s another  important  parameter t h a t r e g u l a t e s the p o s i t i o n o f the Fermi l e v e l . For an n-type semiconductor as the a c c e p t o r  impurity  c o n c e n t r a t i o n i n c r e a s e s , the n c h a r a c t e r i s d i m i n i s h e d u n t i l i t i s changed to a p-type, i n c r e a s i n g t h e r e a f t e r . For a donor r e a c t i o n (p-type) the net r e s u l t i s a increase i n the r e a c t i o n r a t e .  continuous  Thus, a g a i n , the p o s i t i o n  of the Fermi l e v e l u n i q u e l y d e s c r i b e s the p o i s o n i n g  or  promoting c h a r a c t e r i s t i c s o f a semiconductor on an  ad-  s o r p t i o n r e a c t i o n , the type o f i m p u r i t y being the cause o f the s h i f t o f the Fermi l e v e l . how  F i g . 32 and Table V I I I show  the a d s o r p t i o n o f xanthate i s a f f e c t e d by  different  l e v e l s o f c o p p e r a c t i v a t i o n , as w e l l concentration implies late  that  not o n l y  as t h e minimum  f o r a c t i v a t i o n o f xanthate adsorption. in a flotation  system  the r e a c t i o n r a t e  s e l e c t i v i t y o f the f l o a t of effective impurities.  i t i s possible  (activity)  by c o n t r o l l i n g t h e  copper This  to.regu-  but a l s o  the  concentration  CHAPTER 6 SUMMARY  AND CONCLUSIONS  The basic purpose o f t h i s investigation was to study the e f f e c t o f illumination on the adsorption o f xanthate on galena and marmatite and to present experimental evidence on the role o f the e l e c t r o n i c character of s o l i d s i n f l o t a t i o n . The experimental r e s u l t s indicate that:  1.  Absorption o f 0.6 eV photons by copperactivated marmatite causes a decrease i n the amount of xanthate adsorbed as well as a decrease i n the adsorption rate.  These e f f e c t s  can be explained by the e x c i t a t i o n o f electrons from traps to the conduction band and subsequent recombination with holes in the valence band. 2.  In the case of galena, illumination by energies higher than the energy gap (0.37 eV) Increases the amount adsorbed.  3.  At constant wavelength of i l l u m i n a t i o n , the  107 light intensity p e r cm  i s t o double the a d s o r p t i o n o f xanthate  on the a c t i v a t e d 4.  from darkness t o 275 microwatts  marmatite.  Under c o n d i t i o n s o f c o n s t a n t energy o f i l l u m i n a t i o n , temperature  and i n i t i a l  xanthate  concentration,  the amount o f xanthate adsorbed on the p-type g a l e n a i s t h r e e times the amount adsorbed on the n-type, s u g g e s t i n g t h a t the a d s o r p t i o n r e a c t i o n may depend on the t r a n s f e r o f an e l e c t r o n  from  the xanthate anion to the s u b s t r a t e . The r e s u l t s o f t r e a t i n g the p a r t i c u l a r marmatite with v a r i o u s copper s o l u t i o n s o f c o n c e n t r a t i o n s incremented by a f a c t o r o f 10 i n d i c a t e t h a t s o l u t i o n s o f 10~ M 4  produce  a pronounced I n c r e a s e i n both a d s o r p t i o n r a t e and amount o f xanthate adsorbed as compared TO the. a c t i v a t i o n w i t h a 10""°M copper s o l u t i o n . F l o t a t i o n t e s t s using starvation quantities of xanthate i n d i c a t e t h a t lower r e c o v e r i e s may be expected when marmatite i s i r r a d i a t e d w i t h l i g h t o f 0.6 eV compared with those i n d a y l i g h t . On t h e b a s i s o f the r e s u l t s d i s c u s s e d above i t i s suggested t h a t the e l e c t r o n i c d i s t r i b u t i o n substrate plays a v i t a l  i n the  role i n surface reactions.  It  i s p o s t u l a t e d t h a t the p o s i t i o n o f the Fermi l e v e l  may  c o n t r o l the a d s o r p t i o n rate and that t h i s c o u l d be m o d i f i e d  108  by  a judicious control o f the impurity  application  o f photo-induced  s y s t e m may be w a r r a n t e d  when h i g h  q u i r e d o r when s e l e c t i v i t y operation.  adsorption  concentration. to a  flotation  recoveries arer e -  i s t h e main o b j e c t i v e o f t h e  The  109  SUGGESTIONS FOR FURTHER WORK  An i n v e s t i g a t i o n o f the s u r f a c e charge and the f u n c t i o n o f donor and acceptor p a r t i c l e s would be of interest. served:  Experimentally,  two e f f e c t s c o u l d be ob-  (1) a change i n t h e work f u n c t i o n ; (2) a change  i n the e l e c t r i c a l c o n d u c t i v i t y . 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The f o l l o w i n g e q u a t i o n i s e x p r e s s e d i n cgs units:  v -  — t  nqc  Since:  1 e l e c t r o s t a t i c cgs u n i t = 300 v o l t s 9 1 amp = 3x10 e l e c t r o s t a t i c cgs u n i t s 9 1 coulomb = 3x10 e l e c t r o s t a t i c cgs u n i t s g V  300  V  (1x3x10 ) H n (qx3xlQ9) ( 3 x l 0 ) 1 0  1  = _i nq  -8 IH io — t  115 APPENDIX B  1.4  0  2  4  6 Concentration  Fig.  10  8  - xlO~^M  34 - B e e r ' s Law f o r p o t a s s i u m e t h y l u s i n g a 1 cm q u a r t z c e l l .  xanthate  12  116  APPENDIX  C  10 9  Monolayer  o° 2  _L  10  20  30  40  50  60  70  80  100  200  300  400  TIME - m i n u t e s Fig.  Test c o n d i t i o n s : 35 - R e p r o d u c i b i l i t y o f t e s t i n g p r o c e d u r e u s i n g m a r m a t i t e . ( Z n , F e ) S (65/100 mesh), 2 0 ° C , pH = 6.5, d a y l i g h t , lOg o f a c t i v a t e d 1000 ml o f 10~ M KEtX. 4  500  30  -  20  —  Monolayer 5 4  -  I 10  I 20  I 30  I 40  ! 50  I 60  I  I 80  I  I 100  | 200  I 300  I 400  500  400  V/ Q I  TIME - m i n u t e s Fig.  36 - R e p r o d u c i b i l i t y o f t e s t i n g p r o c e d u r e u s i n g lamp, 20g o f PbS (100/150 mesh), 2 0 ° C , 600  galena. Test c o n d i t i o n s : ml o f 10~ M KEtX. 4  30  -  20  -  Monolayer  5 — 41 10  l 20  ! 30  I 40  l 50  I 60  l  I 80  i  1  I 100  200  |  1  300  400  500  TIME - m i n u t e s Fig.  H  37 - R e p r o d u c i b i l i t y o f t e s t i n g p r o c e d u r e u s i n g g a l e n a . Test c o n d i t i o n s : lamp, 20g o f PbS (100/150 mesh) 2 0 ° C , 600 ml o f 1 0 M KEtX. _ 4  500  W/QI  *°  120  APPENDIX D  Detailed  calculation A plot  volumes i n j e c t e d  o f t h e BET i s o t h e r m  o f the e l e c t r o n i c  f o r marmatite  integration  i s shown i n F i g . 38.  Using  areas v s .  the d e s o r p t i o n  a r e a s o b t a i n e d i n each r u n , the e q u i v a l e n t volumes a d s o r b e d can  be r e a d  directly  For  V v  o  P/P  =  P/V™  a 5.05 8 5% n i t r o g e n  l l o P  T  p  r  n  r  n  (P -P) = 38.3/0.029 ml  a 15.5 9 8% n i t r o g e n  P P T = °  1  1  0  T,P 1 o  o  P/V m  a t STP  (955.4-38.3) =  2  1.44  0  For  P/P  o  = (0 . 0 5 0 5 8 5 x 7 5 7 . 4 ) / ( 7 5 7 . 4+198) = 4 . 0 1 x l 0 ~  m  V  mixture:  31x757.4x273 = — , = 2 9ul 295 .1x750 o  T  o  from the graph.  mixture:  43x757.4x273 =  = 40  u l a t STP  295.2x760  = (0.15598x757.4) (757.4+215)  = 12.15x10  (P -P) = 118/0.040(972.4-118) = 3.45 o  -2  121 For  a 25.3807% n i t r o g e n  V ^ T V  =  °  P/P  o  P/V m  43x754 . 8x273  L°L =  T,P 1 o  .  = 44 u l  _ 296.5x750  equal  Total  2  i s 25.4 a n d t h e i n t e r c e p t  t o 0.4 o r :  =  f o r V^:  1  and  V  surface area o f  0.4600 g  m  25.4 =  0.039mlx6.023.10 10  1 5  2 area  C-l  = 0.03 9 ml  = 169 0 cm Surface  = 19. 7 5 x l 0 ~  (P -P) = 191/0.044(969.8-191) = 5.57 o  0.4  solving  a t STP  = (0 . 253807x754 . 8)/(754 . 3 + 215)  From F i g . 22, t h e s l o p e is  mixture:  2 = 3675 cm /g  " molec/molexl6.2A  A / c n i x 2 2 4 1 4 .6 ml/mole 2  2  /molec  122  0  100  200  300  400  500  600  AREA Fig.  38  - Electronic  integrator  areas of  volumes o f  N2  injected.  12 3  APPENDIX E  124  TABLE XIII  OXIDATION RATES OF GALENA  (COMINCO)  IN THE PRESENCE OF WATER VAPOUR  Run No. 2  Run No. 1 TIME min.  Wt i n c r e a s e - u g =3.007535g)  Amt. Ads. g/cm x-10l0 2  Wt i n c r e a s e - u g (W =2.999612g) Q  Amt. Ads. g/cm xl0 2  0 2  46  83  48  86  , 4  64  115  65  117  6  73  131  73  131  3  79  142  77  138  10  84  151  81  145  12  88  158  85  153  14  91  163  88  158  16  93  167  92  166  13  95  171  95  171  20  97  174  99  178  30  107  192  110  198  60  115  206  115  209  150  112  201  1 0  125 TABLE XIV  OXIDATION RATES OF ARGENTIFEROUS  GALENA  IN THE PRESENCE OF WATER VAPOUR  Run No. 2  Run No. 1 TIME min.  Wt increase-ug =2.999466g) o  Amt. Ads. g/cm2 10l° x  Amt. Ads. Wt i n c r e a s e - y g (W = 2 .999148g) g / c m 2 1 0 10  Q  x  0 2  69  181  80  210  92  241  93  244 255  6  100  262  97  8  106  278  102  268  10  109  286  104  273  12  114  300  108  283  14  116  304  110  289  16  118  309  112  294.  18  120  ' 315  114  299  20  123  323  115  302  30  133  349  122  320  60  136  357  131  343  90  133  349  100  133  349  126 TABLE XV  OXIDATION RATES OF GALENA IN A DRY ATMOSPHERE OF OXYGEN PbS  Ag-PbS Wt i n c r e a s e - y g (W =2.983964g)  Amt. Ads. g/cm xl0  Wt increase-ug (W =3.001441g)  0  —  —  —  2  10  25  5  4  14  37  9  6  16  42  11  20  8  18  47  13  23  10  19  50  15  27  TIME min.  Q  2  1 0  Amt. Ads. g/ c m 2 1 0 10  x  .— 9 16  12  . 21  55  16  29  IH  24  63  18  32  16  26  69  20  36  18  27  71  22  40  20  28  74  23 .  41  30  35  92  29  52  60  44  116  29  52  90  50  132  28  51  100  52  137  250  64  169  300  65  171'  500  74  195  • •  ,i  127  APPENDIX  Sample C a l c u l a t i o n electric  o f the Fermi Energy L e v e l  (coul)  (Q)  • ,  to  = (E -E ) C  + 2kT  F  (millivolts/degree)  (degrees))=(E -Ep)+2kT c  electronvolts:  (1.6xl0~  1 9  )(10 )(300)(10 ) 3  2(1.38xl0~ )(300)  7  1 6  = 1.6xl0"  coul  volts degree  1 2  degree  for  F  Q = 0.0 34 m i l l i v o l t s / C 0  = 1.02  (E -Ep)  = 0.97 ev  C  c  F  1.6xl0~  E  p  = (Q m i l l i v o l t s / ° C )  (E -E )  P  F  erg ev _ ^ _ ^ ergs coul volt erg " C F degree  c  (E -E )  (E«-E )+ C  Q 30 = ( E - E )  C  f r o m Thermo-  Power  q QT  Changing  F  - 0.05  + 0.0517 ev  30-0.052  +  1 2  degree  ev ergs  APPENDIX  Detailed  Calculation  Concentration  and  o f the H a l l  G  Coefficient,  Mobility  Dimensions o f the galena specimen:  1 = 1.30 a  — R e s i s t a n c e o f t h e sample m e a s u r e d R = 19.54  Resistivity  Hall  0.2 5  cm  t = 0.10  cm  a t 10  mA:  + 0.01 ohms  = — = 0.280 + 0.005  Semiconductor type:  P (hole  ohms  conductivity)  coefficient.R„ i s : . V = 10  R.  -  cm  Rat 19.54x0.25x0.10 = p = —^~ = —— = 0.4 o:  Resistance  The H a l l  Carrier  8  -8  0.28x0.10x10  H  The number o f p o s i t i v e  8 = 280  cm  3  coulomb carriers i s :  129  1  1  n  =  R qH  Therefore  =  ]_s h o l e s  '280x1.6x10-19  =  *  2  2 x l  °  the m o b i l i t y y i s : -  1 H  1  nq  nqp cm  1  (2.2xl0  1 6  )  cm  (1.6xl0  2  - 1 9  )  (0.4) co.ul ohms cm  130  . APPENDIX H  Calculation electric  of Carrier  Concentration  i n PbS  Using  Thermo-  Data  From A p p e n d i x  B:  (E - E )  ,  = (millivolts/degree)  v  30-0.052  = 0.0030x30-0.052  = 0.038 eV  p  = 2  (  2TTm*kT 3 / 2 . ) exp ( E - E , . ) / k T ,'2 . J: V 0  P  h  s i n c e m*  = 0.3  m f o r galena:  —28 -16 6.28x2.74xl0~ gxl.38x10 erg/degreex300 P  = % (6.62xl0"  x exp  ) erg sec 2  2  (0.038/0.026)  p  , * = 2 (0.6x10  p  = 2 (0.6x10  p  =5.1  n  2 7  / 2,3/2 g/erg sec )  n  x 10  12  18  e  1.H6  2 2 2 3/2 g s e c /g cm sec ) ,x , .3 holes/cm  4.3  2  degree  -i3/ 2  APPENDIX I  Calculation Correlate Galena  o f the P r o p o r t i o n a l i t y  t h e Number o f P a r t i c l e s  Factor Required to t o t h e i r Weight f o r  and M a r m a t i t e  I (a)  I f s c r e e n e d m a t e r i a l s o f t h e same mesh s i z e a r e  available,  t h e i r weight i s : Wt = Vp  where V i s t h e volume a n d p t h e d e n s i t y . Using  the s u b s c r i p t s  W  but V  s  = V  g  t  g f o r g a l e n a a n d s_ f o r s p h a l e r i t e  g  =  V  Wt  g  W  Ws  '  = same number o f p a r t i c l e s  = wt 3  g  £ £ = wt  Ps  S  111 4.0  = 1.9 Wt g  are  P  = same volume  wt  (b)  g  s  I f s c r e e n e d m a t e r i a l s w i t h t h e f o l l o w i n g mesh s i z available:' PbS:  100/150*mesh ( a v e r a g e  diameter  = 0.125  mm)  ZnS:  150/200 mesh  diameter  = 0.088  mm)  (average  132 Assuming c u b i c Vt  g  particles: = Wt  s  Wt = 5.3  V p /V p g g s s H  K  (0.125) x7.5/(0.088) x4.0 3  Wt s  3  133  APPENDIX J  j  134  TABLE XVI  - F l o t a t i o n of Galena Daylight  (a)  KEtX  U s i n g KEtX and D o w f r o t h  = 30 mg/1 •  Dowfroth  250  = 130  mg/1  Test  1  Test 2  Recovery  •(b)  KEtX  (100/150 mesh) i n '  Recovery  Wt-g  %  Wt-g  %  Float  7.49  99.9  7.42  99.3  Tails  .01  .1  .05  .7  Total  7.50  100 .0  7.47  100 .0  = 130  mg/1  = 15  Dowfroth  mg/1 250  Test  Test  1  Recovery Wt-g  %  2  Recovery Wt-g  0. '0  Float  7.48  99. 8  7.45  99.5  Tails  .02  .2  .04  .5  Total  7.50  100.0  7.49  100,0  250.  135  TABLE XVII  - F l o t a t i o n o f A c t i v a t e d Marmatite mesh) i n D a y l i g h t  (a)  KEtX  =30  Dowfroth  2 50  = 130  mg/1  1  Test  Recovery  KEtX  and D o w f r o t h  mg/1  Test  (b)  U s i n g KEtX  2  Recovery  Wt-g  %  Wt-g  %  Float  3.95  99.1  3. 95  99.2  Tails  .04  .9  .03  .8  Total  4.00  = 15  Dowfroth  100.0  3.98  100.0  mg/1 250  = 13 0  Test  mg/1  Test  1  Recovery  2  Recovery  Wt-g  %  Wt-g  Float  3. 91  98.2  3.89  Tails  .07  1.8  .05  Total  3.98  100.0  (150/200  % 98. 7 1.3  3. 94 100.0  25 0  136  TABLE X V I I I - F l o t a t i o n o f A c t i v a t e d mesh) U s i n g KEtX, of  (a)  KEtX  = 15  Dowfroth  2.5  Marmatite  Dowfroth  250  Microns  mg/1 250  = 130  mg/1  Recovery  (b)  KEtX  = 5  Dowfroth  Wt-g  %  .Float  3.88  98.1  Tails  .07  1.9  Total  3.95  100 .0  mg/1' 250  = 130  mg/1  Recovery Wt-g  %  Float  3.89  9 8.2  Tails  .07  1.8  Total  3.96  100.0 J  (150/200  and  Light  137  APPENDIX K  }  138  Galena 20g o f 100/150 Temperature: Radiant  mesh 2 0°C  energy:  Reagent:  360-380  my  (500  W)  KEtX i n 60 0 ml  Abs.  Cone xl0~ M  Amt.Ads xl0~ M  1.54  8.80  --  —  10  0.55 .  3.14  . 56.6  55.1  20  0.43  2.46  6 3.4  61.3  1.84  9.9  30  0.35  2.00  68.0  65.5  1. 96  10.6  65  0.21  1.20  76.0  72.2  2.17  1U7  95  0.16  0.91  78. 9  74 5 6  2.24  12.1  170  0.11  0.63  81. 7  74.9  2.25  12.1  250  0.0 8  0.46  83.4  74.2  2.24  12.1  Time 0  b  6  Corr. Value  u mole g  moles/cm xlO"  —  --  .  1.65  8.9  139  Galena 20g o f 100/150 mesh Temperature:  2 0°C 360- 380 mu  Radiant energy: Reagent :  Time  KEtX i n  Abs.  (5 00 W)  600 ml  Cone. xl0- M 5  Amt.Ads X10-&M  —  Corr. Value  y mole . g  moles/i xlO-1  —  —  1.62 ,  9.24  10  0.66  3.77  54. 7  53.2  1.59  8.6  20  0.5 3  3.03  62.1  60.0  •. 1.80"  9.7  35  0.43  2.46 "  67.8 .  65.1  1.95  10. 5  60  0. 32  1.83  74.1  70. 5  2.11  11.4  105  0.22  1.26  79.8  74.8 .  2. 24  12.1  150  0.16  0.91  83.3  75.1  2.25  12.1  350  0.09  0. 51  87. 3  75.2  2.25  12.1  0.  mo  Argentiferous  galena  l O g o f 100/150 Temperature:  mesh 2 0°C  Radiant energy:  2-2.5y  (50 0 W)  R e a g e n t : ' KEtX i n 600 ml  Time 0  Abs  Cone. xlO~ M 5  Amt.Ads. xlO~ M  Corr. Value  6  —  y mole g  -  5 .42  --  10  0. 8 3  4. 74  6 .8  20  0.81  4.62  30  0. 79  . 4. 51  •"• 9.1  60  0.76  4.34  10.8  7.6  0.43  3.4  100  0.73  4.17  12.5  7.3  0.44  3.5 -  155  0.72  4.11  13.1  7.2  0.44  3.5  255  •• 0.68  3.88  15.4  '7.4  0.44  3.5  310  0.67  3.83  15.9  7.2  0.43  3.4  8.0  5.9 .  6. 6  0 .32 0.35 0. 39  •  1  0. 95  5. 3  __  moles/cm' xl0 __ 2.5 2.8 3.1  Q  141  Argentiferous lOg  o f 100/150  Temperature: Radiant  galena mesh 2 0°C  energy :  Reagent :  420-480 my  KEtX i n  (500  W)  600 ml  Abs.  Cone. xlO M  0  1.02  5.82  --  —  —  12  0.88  5.03  7.9  5. 3  0. 37  2.9  21  0.86  4.91  9.1  7.0  0.42  3.3  30  0.85  4.86  ' .9.6  7.1  0.43 •  3.4  60  0.82  4.69  11.3  7.7  0.46  3.6  100 •  0.79  4.51  13.1  8.3  0.50  4.0  160  0.76  4.34  14. 8  8. 3  0.50  4.0  3 00 .  0.72  4.11  17.1  8.3  0.50  4.0  Time  _ 5  Amt.Ads. xl0 M _ 6  Corr. Value  y mole g  moles, xl0~  —  142  Argentiferous  galena  l O g o f 100/150 mesh Temperature:  2 0°C  Radiant energy: Reagent:  Time  350-380 my  (500  W)  KEtX i n 60 0 ml  Abs  Cone. xlO M  Amt. A d s . xlO M  - 5  - 5  Corr. Value  —  u.:.mble g  moles/( xlO" ' 1  .—  —  0  0.95  5.42  . 10  0.81  4.62  8.0  6.5  0.39  3;1  20  . 0.76  4. 34  10. 8  8. 7  0. 52  4.1  30  0. 74  4.22  12.0  9.5  0.57  4.5  60  0.70  4.00  10.6  0. 64  110  0.65  3.71  12.1  0.73  5.8  185  0.59  3.37  20.5  13.5  0.81  6.4  375  0.51  2.91  25.1  13.4  0.81  6.4  •  14.2 .  17.1  '  5.1  2  14 3  Argentiferous lOg  galena  o f 100/150 mesh  Temperature:  20°C  Radiant.energy: Reagent:  Time  darkness  KEtX i n 60 0 ml  Abs  Cone. xl0" M 5  Amt.Ads xlO M - 6  0  0.93  5.32  —  . 10  0.81  4.63  6.9  20  0. 78  4.46  8.6  30  0.77  4.40  9.2 .  75  0.73  4.18  145  0. 69  300  0.63  Corr. Value  u mole g  —  —  '  5.4  .  moles/• xl0  - i  0. 32  2.5  6.5  0.39  3.1  6.7  0.40-  3.2  11.4  7.4  0.44  3.5  3.95  13.7  7.6  0.45  3.5  3.60  17.2  7.3  0.44  3.5  144  Galena 20g  o f 100/150  Temperature:  mesh 2 0°C  Radiant energy: Reagent:  360-380  my  KEtX i n 6 00 ml  I n e r t atmosphere: • h e l i u m  2 Time  Abs.  Cone. xlO" M  600  0. 0  1.57  8.95  596  1  1.15  6.57  2 3.8  0.71  3. 8  592  3  1.03  5.89  30.6  0.90  • 4.9  10  0.97  5.54  34.1  1. 00  5.4  584  20  0.91  5.20  37.5  1.10  5.9  580  40  0.87  4. 96  39.9  1.15  6.2  576  60.  0.84  4.80  41.5  1.19  6.4  Volume  5 88 •  •  :  5  :  Amt.Ads xlO~ M 5  y moles g  moles/cm xl0~ i O  572  100  0. 80  .4.57  43.8  1.24  6.7  564  200  0. 74  4.23  47.2  1.32  7.1  560  300  0.72  4.12  48.3  1.35  7.3  145  Argentiferous  Galena.  l O g o f 100/150 mesh Temperature: Radiant Reagent: Inert  'olume  2 0°C  energy:  360-380 my  KEtX i n 600 ml  atmosphere:  Time  helium  Abs.  Cone. xlO M - 5  Amt.Ads xlO' M 6  u mole g  moles/( xlO" ' 1  586  0  0. 865  4.94  —  —  —  583  2  0. 765  4.37  3.3  0.20  1.6  580  7  0. 745  4.26  3.9  0.24  1.9  577  10  0.740  4.23  4.1  0.25  2.0  574  20  0.725  4.14  . 4.6  0.27  2.1  571  30  0.720  4.11  4.7  0.28  2.2  568  60  0.705  4. 02  5.2  0.31  2.5  565  100  0.695  . 3.97  5.5  0.33  2.6  559  200  0.670  3.83  6.2  .0.37  2.9  556  330  0.665  3.79  6.4  ;  0. 38  3.0  146  Non-activated Marmatite l O g o f 65/100 mesh Temperature: Radiant  2 0°C  energy:  Reagent:  360.-38 0 my  KEtX i n 6 00 ml  Abs.  Cone. xlO" M  0  0.95  5.42  --  • 10 '  ' 0. 87  4.97  20  0.86  30 60  Time  5  Amt .Ads xlO" M 6  Corr. Value  y mole . g  moles/1 xlO - 1  --  —  4.5.'  3. 0  0.18  0.69  4.91  5.1  3.0  0.18  0.69  .0. 85  4.86. '  5.6  3.1  0.19  0.73  0.83  4.74  6.8  3.2  0.19  0.73  100  0. 81  4.63.  7.9  3.2  0.19  0.73  22 0  0.74  4.23  11.9  3.5  0.21  0. 81  147  A c t i v a t e d Marmatite l O g o f 65/100  mesh  Temperature:  2 0°C  Radiant  energy:  Reagent:  Time  ( 0 . 9 9 6 x l O ~ M Cu a  )  '  360-380  mu  KEtX i n 6 00 ml  Abs.  Cone. xlO" M  Amt. Ads xlO~ M  b  b  Corr. Value .  u mole g  moles/f xlO - 1 1  o  0. 95  5.43  —  —  —  —  10  0.88  5.03  4.0  2.6  0.15  0.58  20  0. 87  4.97  4.6  2.7  0.16  0.62  30  0. 85  4.86  5.7  3.2  0.19  0.73  100  - 0.80  "4.57  8.6  4.0  0.24  0. 92  150  0.77  4.40  10.3  4.2  0.25  0. 96  360  0.71  4.06  13.7  4.1  0.25  0.96  ;  '  148  A c t i v a t e d Marmatite (0.996x10" M 4  Cu  )  10 g o f 65/100 mesh Temperature:  20°G  Radiant energy: Reagent:  360-3 80 my  KEtX i n 600 ml  Time  Abs.  Cone. xlO M  -o  1.14  6.51  —  _i5  Amt.A ds xlO- M 6  Corr. Value  y mole . g  . --  --  moles/< xlO1  —•  10  .  1.05  6.04  4.7  3.2  0.19  20  .  1.03  5.88  6.3  4.2 .  0.25  0.96  5.76  7.5  5.0  0.30  1.15  5.48  10.3  6.7  0.40  1.54  0.50  30  1.01  60  0.96  100  0.91  5.20  13.1  8.4  165 ,  0.88  5.0 3  14.8  8.5  300  0.80  4.57  19.4  8.4  .  .  0.51 0.50  .  0.73  '  .1.92 1.96 1.92  149  Activated  Marmatite  ( 0 . 996xlO"" M Cu  F i l t e r e d but n e i t h e r  d r i e d n o r washed  lOg  o f 65/100  Temperature:  )  mesh 2 0°C  Radiant energy: Reagent:  d  360-380  my  KEtX i n 60 0.ml  y  mole g  moles/ xl0  Cone. xlO~ M  0  0.96  5.52  --  —  —  —  12  0.78  4.46  10.6  .. .9.1  0.55  2.02  20  0.76  11.8  9.6  0.58  2.2 3  30  0.74  4.23  12.9  10.4  0.63  2.42  65  0.69  3.95  15.7  12.1  0.73  2. 81  100  0.65  3.72  18.0  13.2  0.79  3 .04  175  • 0. 61  3.52  20.0  .. 13.3  0.79  . 3.04  200  0.59  3. 37  21.5  13.2  0.79  3.04  300  0.56  3.20  23.2  13.2  0.79  5  "4.34 •  Amt.Ads xlO M  Corr. Value  Abs.  Time  - 6  '  _ 1  . 3.04  150  A c t i v a t e d Marmatite l O g o f 65/100  mesh  Temperature:  20°C  Radiant  energy:  Reagent:  (0 . 9 9 6 x l O ~ M d  360-380  Cu)  mu  KEtX i n 600 ml  Abs.  Cone. xl0 M  •0.8 9  5.08  —  —  10  0.78  4.46  6.2  20  0.75  4. 34  30  0.73  "4.17  60  . 0.69.  100  Time  Amt. Ads xl0 M  - 5  - 6  Corr. Value  u mole g  moles/( xlO1 ,  —  —  4.7  0.28  1.08  7.4  5.3  0.32  1.23  9.1  6.4  0.38  3.94  11.4  7.8  0.47  1.81  0.66  3.77  13.1  8.6  0.52  2.00  165  0.63  3.60  14.8  8.8  0.53  2.04  310  0.58  3.31  17.7  8.7.  0.52  2.00  0  '  •  1.46  2  151  A c t i v a t e d Marmatite (0.996xlO"°M) l O g o f 65/100  mesh  Temperature:  2 0°C  Radiant energy: Reagent:  360-380  my  KEtX i n 6 00 ml  Abs.  Cone. xl0 M  0  1.18  6.75  —  —  .io  1. 08  6.17  5. 3  20  1.05  6.00  30  1.03  •" 5.88  70  0.98  5.60  150  0. 92  235 300  Time  - 5  Amt.Ads • xlO~ M 6  Corr. Value  y mole g  moles/cm ' xlO - 1 0  —  --  4.3  0.26  1.00  7.5  5.4  0. 32  1.2 3  8.7  6.2 '  0.37  1.42  11. 5  7.7  0.46  1.77  5.25  15.0  9. 0  0.54  .2.08  0.88  5.03  17.2  9.1  0.54  2.08  0. 85  4 . 86  18.9  9.0  0. 54  2.08  ;  .  2  152  Activated lOg  Marmatite  o f 150/200  Temperature:  mesh 20°C  Radiant energy: Intensity  360-380  of light:  mu  0 watts/cm  Abs .  Cone. xlO M  0  1.03  5.72  —  10  0.92  5.26  20  0. 89  30  Time  - 5  Corr. Value  Amt.Ads xl0~ M 6  u mole g  moles/< xlO"  —  —  —  4.6  3.6  0.22  0.42  5.09  6. 3  5.0  0.30  0.58  0.87  4.97  7.5  6.0  0.36  0. 69  60  0.82  4.6 9  10. 3  8.2  0.49  0. 94  100  0. 78  4.46  12.6  •9.7  0.58  1.12  150  0.74  4.23  14. 9  11.1  0.67  1.29  245  0. 71  4.06  16. 6  11.1  0.6 7  1.29  310  0.68  3.88  18.4  11.2  0.67  1.29  350  0.66  3. 77  • 19.5  11.0  0.66  1.2 8  ;  153  Activated lOg  Marmatite  o f 150/200  Temperature:  mesh 20°C  Radiant energy:  360-380  mu 2  Intensity of light:  80 u  watts/cm  moles/< xlO  —  —  Conc.xlO'^M  0  0.90  5.14  10  0.78  4.46  6. 8  5.8  3.35  0.67  20  0.76  4.34  8. 0  6.7  0.40  0.77  30  0. 74  4.23  9.1 '  7.6  0.46  0. 89  60  0.71  4.06  10. 8  8.7  0.52  1. 00  110  0.68  3.88  12.6  9.5  0.56  1.10  150  0.66  3. 77  13. 7  10.0  0.60  1.15  240  0.63  3.60  15.4  10. 0  0.60  . 1.15  300  0.61  3.49  • 16.5 '  10.0  0. 60  1.15  Amt.Ads xl0"°M  —  Corr. Value  U mole g  Abs.  Time  —  - 1  154  Activated lOg  Marmatite  o f 150/200  Temperature:  mesh 20°C  Radiant energy:  360-380  Intensity of light:  Time 0  my  180 y w a t t s / c m  2  Cone  Amt.Ads  Corr.  Abs.  xlO" M  xlO  Value  0.91  5.20  5  _ 6  M  —  y mole g  moles/cm xlO  —  --  10  0.77 . 4.40  8. 0  7.0  0.42  0. 81  20  0. 75  4.28  9.2  7.9  0.47  0.91  30  0.73  4.17  10. 3  8. 8  0.5 3  1.04  60  0. 69  3.94  12.6  10.5  0.63  1.21  100  0.67  3.8 3  13. 7  10. 8  0.65  1.25  160  0.63  3.63  15.7  11.7  0.70  1. 35  255  0.60  3.43  17.7  12.0  0.72  1. 38  320  0.58  3. 31  18.9  12.1  0. 72  1.38  •  y  - 1 0  155  A c t i v a t e d Marmatite lOg  o f 150/200  Temperature:  mesh 2 0°C  Radiant energy:  360-380  Reagent:  KEtX  Intensity  of Light:  i n 6 00 ml  Abs.  Cone. xlO" M  0  0.90  5.14  10  0.75  4.28  20  0. 71'  30  Time  mV  2 75 U w a t t s / c m  Amt.Ads xlO" M 6  5  Corr. Value  u  mole g  moles, xlO"  —  —  8.6  7.6  0.46  0.88  4.11  10. 3  9.0  0.54  1.04  0.69  3.90  12. 3  10.0  0.60  1.15  70  0.65  3.72  14.2  11.9  0.71  1. 37  100  0.64  3.65  14.9  12.0  0.72  1. 38  150  0.60  3.43  17.1  13.3 ;  0.80  1.54  245  0.56  3.25  18.9  13.4  0. 80  1.54  300  0. 56  3.20  19.4  13.1  0.79  1.52  400  0.53  3.03  21.1  13.5  0.81  1.56  .  Galena 20g o f 100/150 Temperature:  mesh 2 0°C  Radiant energy: Reagent:  360-3 80 my  KEtX i n '600 ml  Abs.  Cone. xlO~ M  0  1.68  9.60  --  —  10  0.86  4. 91  46.9  20  0.74  4.23  30  0.67  100  Time  5  Amt.Ads xlO M - 6  Co r r . Value  y mole g  moles/ xlO' ' 1  —  —  45. 5  1. 37  7.4  53.7  51.5  1.55  8.4  3.83-  57.7  55.2  1.66  9.0  0.44  2 .52  70.8  65.8  1.97  10.6  150  0. 38  2.17  74.3  6 7.8  2.03  11.0  215  0.30  1.71  78 .9  70.9 •  2.12  11. 5  300  0.24  1. 37  82.9  71.9  2 .21  12. 0  450  0.18  1.03  85.7  71.9  2.22  12.0  157  Galena 20g o f 100/150 Temperature:  mesh 2 0°C  Radiant energy: Reagent:  Time 0  435-480 mjj  KEtX i n 6 0 0. m l  Abs.  Cone. xlO~ M 5  1.80  10.28  Amt.Ads xl0~ M 6  —  Corr. Value  u mole g  —  —  (s  moles, xl0~  —  10  ' 1.10  6.28  4.0. 0  38.5  1.16  6.4  24  0.93  : 5.31  49.7  47.5  1.42  7.7  35  0.85  4.86  54.2  51.5  1.51  8.1  60  0.73  4.17  61.1  56.5  1.69  9.1  100  . 0.62 •  3.54  67.4  62.4  1.87  10.1  165  0.51  73. 7  66.7  2 .00  10. 8  220  0.45  2.57-  77.1 .  68.6  2.06  .11.1  295  0. 38  2.17  81.1  71.1  2.13  11. 5  470  0.29  1. 66  86.2  2.13  11.5  •  22.91  ' 71.0  J  m2  158  Galena 20g o f 100/150 mesh Temperature: Radiant  2 0°C  energy:  Reagent:  2-2.5 .u  KEtX i n 6 00 ml'  Abs.  Cone. xlO~ M  0  1.63  9. 30  11  0. 95  5.43  20  0.82 '  32  Time  5  Amt.Ads xlO M _ 6  Corr. Value  y mole .g  moles, xl0~  —  —  38 .3  37.7  1.13  6.1  4.74  45.6  43.5  1.27  6.9  0.77  4.40  49.0  46.4  1. 39  7.5  65  0.60  3.43 '  58. 7  55.0 ,  1.65  8.9  HQ  0.50  2.86  64.4  59.2  1.78  9.6  170  0.41  2 . 34  6-9.6  62.6  1. 88  10.4  220  0. 36  2.06  72.4  64 .2  1.93  10.5  300  0.30  1. 72  75.8 •  64.6  1. 94  10.5  490  0.22  80.4  65.0  1.95  10.6  •  1.26  —  ,  2  159  Galena 20g  o f 100/150  Temperature: Radiant  mesh 2 0°C  energy:  Reagent:  darkness  KEtX i n 500 ml  Cone. Time  Abs.  xlO~ M 5  Amt.Ads  Corr.  xlO" M  Value  6  y mole g  moles/cm' xlO  0  1.46  8.34  10  0.83  4.74  36.0  35.0  1.05  5.7  20  0.72  4.11  42.3  40.1  1.23  6.6  30  0. 66  3. 77-  45. 7  43. 2  1. 29  7.0  55  0.54  3.08  52.6  49,1  1.47  7,9  110  0.41  2.34  60.0  ' 55.0  1.65  8.9  150  0.37.  2.11  62.3  56.2  1.71  .9.2  220  0.30  1.71  66.3-  57.8  1.73  9.3  420  0.20  1.14  72.0  58.0  1.74  9.4  ..  - 1 0  16 0  Galena 20g o f 100/150 mesh Temperature:  2 0°C  Radiant energy : Reagent :  400 W Q t z - I lamp  KEtX in- 60 0 ml  Cone. Abs.  xlO~ M  0  1.69  9.65  10  0.89  20  Time  5  Amt.Ads  Corr.  xlO~ M  •Value  5  •—  moles, 10 xl0~'  y mole g  --  5.0 9  45.6  44. 0  I . 32  7.1  0.7 9  4.51  51.4  49^4  1.48  8.0  30  0.72  4.12-  5 5.3  5 3.0  1.59  8.6  65  0.58  3. 31  63.4  59.6  1.79  9.7  100  0.49  • .. 2.80  68.5  63.5  1.90  150  0.41  2 . 34  73.1 ,  66.6  1. 98  10.7  305  0.2 7  1.54  81.1  71.1  2 .14  11.5  .  .  10.3  161  Activated  Marmatite  20g o f 100/150 Temperature:  mesh 2 0°C  Radiant energy: Reagent:  360-380  my  KEtX i n 600 ml  2 Cone.  Amt.Ads  Corr.  xlb~ M  Value  --  Time  Abs.  xlO~ M  0.  1.56  8.90  —  10  1.26  7.20  17.0  23  1.22  6.9 6  35  1.19  60  y mole  moles/cm  g  xlO  --  —  15.5 .  0.46  1.25  19.4  17.2  0.51  1.39  6.79  21.1  18.'4  0.55  1.50  1.15  6.56  23.4  19.8  0.59  1. 61  115  1.10  6.28  26.2  21.0  0.63  1.72  150  1.07  6.08  28.2  21.5  0.64  1. 74  200  1. 09 .  5 .94  29.6  21.6  0. 65  1. 77  300  0.98  5.60  33.0  22.0  0.65  1.77  505  0.92  5.25  • 36.5  22 .0  0.65  1.77  5  6  - 1 0  162  Activated  Marmatite  20g o f 100/150 mesh Temperature: Radiant  2 0°C  energy:  Reagent:  darkness  KEtX i n 600 ml  Abs.  Cone. xlO~ M  0  1.77  9.57  —  10  1.4 7  8.40  11. 7  10.2  0.31  0. 84  20  1.42  8.11  14.6  12.4  0.37  1. 01  30  1. 37  7.82  17.5  15. 0  0.45  1.22  60  1.29 .  7.3 7  22.0  18.4  0.55  1.50  130  1.20  6.85  2 7.2  21.2  0.63  1.72  200  1.16  6.62  29.5  21.5  0.64  1.74  300  1.14  6.52  30.5  22.0  0.66  1.80  470  1.08  6.17  34 .0  22.0  0.66  - 1. 80  Time  5  Amt.Ads xlO~ M 6  Co r r . Value  u mole  —  —  --  g  J  mole s/ xl0 _ 1  163  Activated.Marmatite 20g o f 100/150 mesh Temperature: Radiant  2 0°C  energy:  Reagent:  KEtX  2-2.5  u  i n 60 0 ml  Cone. xlO" M  Amt.Ads xlO" M  Corr. Value  u  mole  moles/ xlO  Time  Abs.  0  1.62  9.25  --  —  —  •— .  10  1.45  8.28  9.7  8.2  0.25  0.68  20  1.40  8.00  12.5  10.4  0. 31  0. 84  30  1.38  7.88  13.7  11.2  0. 34  0.93  60  1.31  7.49  17. 6  14. 0  0.42  1.14  130 .  1.22  6.97  22. 8  16.8  0.50 .  1.36  200  1.19  6. 80  24.5  17.0  0.51  1.39  355  1.11  6 .34  29.1  17.1  0.51  1.39  495  1.07  6.12  31.3  17.2  0.51  1.39.  5  6  g  - 1  164  Activated 20g  Marmatite  o f 100/150 mesh  Temperature:  Reagent:  " '  2 0°C  KEtX i n 60 0 ml  Time:  Abs.  Cone. xlO" M  0  1.58  9.03  '  Amt.Ads xlO" M  5  6  Corr. Value  u mole g  moles/cm' xlO" 1 0  10  .1.27  7.26  17.7  16.2  0.49  1.33  22  1.23  7. 03  20. 0  1.7. 8  0. 53  1.44  33  1.20  6.86  21.7  19.1  0.57  60  1.16  6.63  110  1.09  6.24  27.9  22.9  0.68  160  1.04  5.95  30.8  22.4  0.67  200  1.01  5.77  32.6  22.8  0.68  1.85  0.96  5.49  35.4  22.9  0.68  1.85  0.87  4.97  40.6  23.0  0.68  1.85  300 500  ,  .  24.0  ;  20.5  1.55  0.61  1.66 1.85 '  1.83-  165  Activated  Marmatite •  20g o f 100/150 mesh Temperature:  2 0°C  Radiant energy: Reagent:  KEtX  42 0-4 70 my i n 600 ml  Cone. Time  Amt.a ds  Corr.  xlO~ M  Value  —  —  y mole  moles/  Abs.  xlO~ M  0  1.62  9.25  —  10  1.38  7.88  13.7  12.2  0.35  0. 98  20  1.35  7.74  15.1  13.0  0.39  1.06  ' 30  1.33  7.60  16.5  14. 0  0.42  1.14  60  1.28  7.31  19.4  15.8  0.47  1.28  100  1.23  7.05  22. 0  17.0  0.51  1.39  150  1.18  6.67  25.8  18.4  0.55  1.50  200  1.15  6.57  26.8  18.8  0.56  1.53  295  1.09  6.25  30. 0  19. 0  0.56  1.5 3  495  1.02  5.83  34.2  18.5  0.56  1.53  5  6  g  xlO  - 1  —  166  Activated lOg  Marmatite  o f 65/100 mesh  Temperature:  2 0°C  Radiant energy: Reagent:  Time  KEtX  Abs.  (pH  =  6.5)  daylight i n 100 0 ml  Cone. xlO" M  Amt.Ads xlO" M  5  6  1. 64  9.37  —  10  1.56  8.-91  4.5  18  1.55  8.86  30  , 1.53  8.78  60  1.51  8.63  100  1.50  150  Corr. Value  — .  u mole g  moles/ xlO - 1  —  —  3.5  0. 35  1. 35  5.1  3.9  0. 39  1.5 0  5. 9  4.5  0.4 5  1.73  7.4  5.3  0.53  2. 04  8.56  8.1  5.2  0.52  2.00  1.48  8.46  9.1  5.3  0.53  2.04  200  1.46  8. 34  10. 3  5.3  0.53  2. 04  300  1.44  8.23  • 11.4  5.3  0.53  2.04  1.40  8.00  13.7  5.3  0. 53  2.04  0  500  .  .  (  167  Activated lOg  Marmatite  o f 65/100 mesh  Temperature: Radiant  2 0°C (pH .=  energy:  Reagent:  6.5)  daylight  KEtX i n 1000  ml  Abs.  Cone. xlO~ M  Amt.Ads xlO" M  0  1.64  9. 37  --  10  1.56  8.94  18  1.55  30  Corr. Value  u mole g  —  —  4.3  3.3  0.33  1.27  8.88  4.9  3.8  0.38  1.46  1.54  8. 82  5.5  4.2  0.42  1. 62  60  1.51  8.65 '  7.2  5.1  0. 51  1. 96'  170  1.48  8.46  9.1  5.1  0.51  1.96  205  1.46  8.54  10.3  5.3  0.53  2.04  300  1.44  8.23.  11.4  5.3  0.53  2. 04  500  1.40  8.00  13.7-  5.4  0.54  2.05  Time  5  5  .  moles/cm xl0~ 1 0  

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