UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Illumination and the adsorption of xanthate in the flotation of galena and marmatite Guarnaschelli, Claudio 1968-07-09

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
831-UBC_1969_A1 G83.pdf [ 7.38MB ]
Metadata
JSON: 831-1.0081187.json
JSON-LD: 831-1.0081187-ld.json
RDF/XML (Pretty): 831-1.0081187-rdf.xml
RDF/JSON: 831-1.0081187-rdf.json
Turtle: 831-1.0081187-turtle.txt
N-Triples: 831-1.0081187-rdf-ntriples.txt
Original Record: 831-1.0081187-source.json
Full Text
831-1.0081187-fulltext.txt
Citation
831-1.0081187.ris

Full Text

ILLUMINATION,AND THE ADSORPTION OF XANTHATE IN THE FLOTATION OF GALENA AND MARMATITE .by CLAUDIO GUARNASCKELLI B.Sc., University of Alberta, 1961 M.Sc, University of Alberta, 1965 A thesis submitted in partial fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY in the Department of Mineral . Engineering We accept this 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 t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h C olumbia, I a g r e e t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and Study. I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s thes.is f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . 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 Columbia Vancouver 8, Canada Date December 24, 1968 ABSTRACT The changes in the adsorption characteristics of potassium ethyl xanthate (KEtX) on galena (PbS) and marmatite [(Zn,Fe)S] due to illumination 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) is required for flotation, (3) sphalerite is a semiconductor with an energy gap of 3.6 eV whereas galena is a semiconductor with an energy gap of 0.3 7 eV. The amount of xanthate adsorbed from aqueous solu tion on galena and marmatite was found to depend on both the intensity and photon energy (0.5 to 3.5 eV) of the incident light. In the galena system, increasing the light 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 involve the tr a n s f e r of an electron from the adsorbate to the adsorbent. The e f f e c t of the presence of an oxide f i l m on the surfaces of galenas was also investigated and appeared to be l e s s s i g n i f i c a n t than the type of charge c a r r i e r o r i g i n a l l y dominant i n the mineral. When copper-activated marmatite was illuminated by l i g h t with photon energies lower than the i n t r i n s i c gap (3.6 eV), adsorption of xanthate was less than when the mineral was kept In darkness. Similar "photodesorption" e f f e c t s have been reported in the l i t e r a t u r e . These were explained by ex c i t a t i o n of electrons from traps to the conduction band and subsequent recombination with holes In the valence band. Fewer charge c a r r i e r s would then have been available to p a r t i c i p a t e i n the adsorption reactions. F l o t a t i o n experiments agreed with the adsorpti r e s u l t s above. F l o t a t i o n recovery of activated marmatite dropped ca. 10% when the mineral was illuminated with a high i n t e n s i t y of 0.6 eV photons as compared to the recovery i n daylight. A model that takes into account the surface con centration of electrons and the type and concentration of 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 of surface reactions are explained i n terms of the electrochemical p o t e n t i a l , i . e . the Fermi energy l e v e l , i v the a c t u a l p o s i t i o n and/or displacement o f which i s a f f e c t e d by the i m p u r i t i e s p r e s e n t . TABLE OF CONTENTS ABSTRACT . i i LIST OF TABLES v i i i 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 11 2.4 Illumination . 1 3 2.5 Sources of Radiant Energy 19 CHAPTER 3 - 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 (CuS04.5H20) 27 v i 3.3 Surface Area Measurements 27 3.4 Electrical Conductivity and Hall Effect 2 8 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) Analytical Procedure 52 (d) Reproducibility 55 3.8 Flotation 56 CHAPTER 4 - EXPERIMENTAL RESULTS 5 9 4.1 Surface Area Measurements. . 5 9 4.2 Effects of Illumination 63 4.3 Effect of Oxidation on Adsorption 71 4.4 Effect of Surface Characteristics on Adsorption. 76 4.5 Effect of Illumination Intensity on Adsorption . 77 4.6 Copper Activation. 81 4.7 Electrophysical Measurements 86 4.8 Correlation of Adsorption Results . 88 4.9 Flotation Experiments 92 CHAPTER 5 - DISCUSSION OF RESULTS 96 5.1 Adsorption 9 6 5.2 Photochemical Effects 99 5.3 Carrier Behaviour . 101 5.4 Impurities and Reaction Mechanism 103 v i i CHAPTER 6 - SUMMARY AND CONCLUSIONS 106 SUGGESTIONS FOR FURTHER WORK 10 9 REFERENCES 110 APPENDICES . A Hall Coefficient: Conversion of cgs Units to Practical Units 114 B Beer's Law for KEtX 115 C Reproducibility of Results 116 D Detailed Calculation of the BET Isotherm for Marmatite 120 E Oxidation of Galena Samples 12 3 F Sample Calculation ,of the Fermi Energy Level from Thermoelectric Power 12 7 G Detailed Calculation of the Hall Coefficient, Carrier Concentration and Mobility 12 8 H Calculation of Carrier Concentration in PbS Using Thermoelectric Data 130 I Calculation of the Proportionality Factor to Correlate the Number of Particles to Their Weight for Galena and Marmatite 131 J Preliminary Flotation Tests . .133 K Tabulation of Adsorption Tests 137 LIST OF TABLES Page TABLE I Electromagnetic Spectrum 19 TABLE II Analysis of Marmatite Sample 25 TABLE III Analysis of Galena Sample 2 6 TABLE IV BET Areas of Powders (100/150 mesh). . . . 62 TABLE V Calculated Surface Areas of Screened Fractions of Marmatite 62 TABLE VI 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 TABLE IX Electrophysical Characteristics of Solid Specimen 87 TABLE X Seebeck Effect of Solid and Powder Specimens 87 TABLE XI Adsorption Results in Terms of Xanthate Coverage 90 TABLE XII Summary of Flotation Results 94 TABLE XIII Oxidation Rates of Galena (Cominco) in the Presence of Water Vapour . . . . 124 TABLE XIV Oxidation Rates of Argentiferous Galena in the Presence of Water Vapour . . . . 125 ix TABLE XV Oxidation Rates of Galena in a Dry Atmosphere of Oxygen. 12 6 TABLE XVI Flotation of Galena (100/150 mesh) in Daylight Using KEtX and Dowfroth 250 134 TABLE XVII Flotation of Activated Marmatite (15 0/20 0 mesh) in 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 Distribution function and electron and hole population for impurity semi conductors 6 Figure 2 Tentative energy level diagram for the excitation and emission transitions in ZnS phosphors. 9 Figure 3 Models of luminescence according to: (a) Schon-Klasen; (b) Lambe-Klick; (c) Prener-Williams 18 Figure 4 Emission spectra of luminescence in ZnS. . . 18 Figure 5 Relative spectral energy distribution of the black body radiator normalized at ^ = 560 millimicrons 21 Figure 6 Spectral transmittances of absorption f i l t e r s 21 Figure 7 Schematic diagram of the apparatus for surface area measurements 2 9 Figure 8 Schematic diagram of the Hall effect . . . . 31 Figure 9 Ohmic connections to marmatite specimens . . 33 Figure 10 Ohmic contacts to galena specimens . . . . . 34 Figure 11 Origin of ohmic voltage drop due to misalignment when measuring the Hall coefficient 3 5 Figure 12 Schematic diagram of the Seebeck effect. . . 37 Figure 13 Origin of the Peltier effect for an n-type. 37 Figure 14 Schematic diagram of the apparatus for the measurement of the Seebeck voltage 39 x i Page Figure 15 Apparatus for the measurement of the Seebeck voltage rearranged outside the Faraday cage. 0^ Figure 16 Schematic diagram of the adsorption apparatus 4 3 Figure 17 Adsorption apparatus complete with accessories and a semi-micro flotation c e l l . 1 + 4 Figure 18 Characteristics of the Sylvania Quartz-Iodine lamps Figure 19 Measured transmittance of Corning Glass f i l t e r s 4 9 Figure 20 Adsorption on apparatus and decomposition of KEtX 5 4 Figure 21 Schematic diagram of the flotation arrangement " Figure 22 BET plot for 100/150 mesh mineral powders 61 Figure 23 Adsorption of EtX" from a solution of KEtX (9xlO-5M) on activated (Zn,Fe)S (100/150 mesh) at 20°C and natural pH ( 6.5) under controlled illumination. . 64 Figure 24 Adsorption of EtX" from a solution of KEtX (9xlO_5M) on activated (Zn,Fe)S (100/150 mesh) at 20°C and.natural pH (6.5) under controlled illumination 65 Figure 25 Adsorption of EtX" from a solution of KEtX (9xlO"5M) on PbS (100/150 mesh) at 20°C and natural pH under controlled illumination 6 9 Figure 26 Adsorption of EtX" from a solution of KEtX (5xlO"5M) on (Pb,Ag)S (100/150 mesh) at 20°C and natural pH under controlled illumination 70 Figure 2 7 Oxidation rates of galena in oxygen in the presence of water vapour 73 x i i Figure 2 8 Oxidation rates of galena in a dry atmosphere of oxygen Page . 74 Figure 2 9 Figure 30 Figure 31 Figure 32 Figure 33 Figure 34 Figure 35 Figure 36 Adsorption of EtX~ on freshly prepared surfaces of galena (100/150 mesh) from a solution of KEtX in 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 intensities of illumination at a constant wavelength (.340-.380 microns) from a 400 W7QI lamp . , 78 Variation on the amount ."of :EtX~ . adsorbed as a function of light intensity for a constant energy (3.6-3.3 eV) at 10 min . , The effect of copper activation 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 light of 3.6-3.3 eV. , The effect of washing the marmatite after copper activation, lOg of (Zn,Fe)S (65/100 mesh) with 100 ml. 79 83 4» of a 0.996xlO -3M solution of CuSO 5H20 on subsequent adsorption of EtX" at 20°C and natural pH, illuminated with light of 3.4-3.3 eV. Beer's law for potassium ethyl xanthate using a 1 cm quartz c e l l , 84 115 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. Reproducibility of testing procedure using galena. Test conditions: 400 W-QI Lamp, 20g of PbS (100/150 mesh), 20°C, 600 ml. . . 117 118 x i i i Page Figure 37 Reproducibility of testing procedures using galena. Test conditions: 500 W-QI Lamp, 20g of PbS (100/150 mesh), 20°C, 600 ml 119 Figure 38 Electronic integrator areas of volumes of nitrogen injected 122 ACKNOWLEDGEMENT I wish to express my deep gratitude and sincere appreciation to Dr. J. Leja for his guidance and useful criticism throughout the course of this investigation. My thanks are also due to a l l the members of the Department of Mineral Engineering, in particular to Dr. G.W. Poling and Dr. H. Majima and a l l the graduate students for their useful suggestions and discussions. I wish also to thank Mr. M. Clegg for spending many hours in technical discussions and meticulous proof reading 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 responsibility of bringing up a family. I am indebted to Syncrude of Canada Limited, and the National Research Council of Canada for their financial support without which this study would have not been possible. CHAPTER 1 INTRODUCTION The primary requirement for the successful flotation of a hydrophilic mineral i s the adsorption of a surfactant at the solid/liquid interface in a form that w i l l lead to a subsequent particle-bubble attachment. While the fundamental mechanism of adsorption s t i l l requires further elucidation, the role of the substrate in adsorption is becoming increasingly apparent as some investigators * ' have found that irradiation may be used successfully to increase the recoveries of the minerals floated. In general, solid-state photochemistry has not received the amount of quantitative effort dedicated to liquid and gaseous systems because of the inherent d i f f i  culties peculiar to the solid system. These include profound differences in chemical behaviour as a result of crystal defects (impurities, l a t t i c e imperfections, ion vacancies), non-homogeneous absorption of light and a change in the adsorption characteristics of the adsorbing species on illumination. These changes may result in either photodesorption or photoadsorption. Cadmium sulphide shows less a f f i n i t y for phenolphthalein when irradiated in 2 an aqueous solution of ethanol than when not exposed to illumination^', whereas the red form of mercuric sulphide shows the reverse effect. As a direct consequence, the results of studies of a given system by different investi gators are often in direct disagreement. In an attempt to correlate the energy structure of minerals with their flotation properties,Plaksin et a l ^ y considered the electrophysical properties of the solid phase as a base on which to construct a satisfactory theory of the flotation process. These authors showed that the flotation recovery of zircon is strongly affected by exposure of the solids to y-radiation. In another work Plaksin and Shafeev^) analyzed the effect of light from a 175 watt bulb on the adsorption characteristics of oleic acid on ilmenite and found that the flotation recovery increased by 12%. Since the photoelectric effect in semi conductors i s well known^4*^'^' and a l l sulphide minerals are semiconductorsv , i t i s conceivable that a photon energy of a few electron volts could cause the necessary electronic transitions that may enhance or retard the ad sorption of surfactants. The purpose of the present research was to investigate the effects of 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 level. In order to achieve these objectives, electrophysical as well as adsorption experi ments were required. The physical characteristics given by the Hall coefficient on solid samples were supplemented by measurements of the thermoelectric power on pelletized powders. Kinetic measurements of the adsorbed quantities of xanthate were obtained by circulating a xanthate solution in a closed system with the powder retained between two fr i t t e d discs. The adsorption characteristics of the xanthate on the various sulphides are presented as a function of the energy of illumination, illumination intensi ty, added impurities, oxidation and flotation. The resulting effects are further correlated in terms of the measured surface area. The adsorption characteristics of galena and marmatite depend strongly on the electronic distribution in the substrate. The n-type or p-type character dominates the adsorption behaviour more so than the effect of illumi nation. The latter is readily detectable by kinetic measurements but i s not so evident under normal flotation conditions. CHAPTER 2 LITERATURE REVIEW 2 . 1 Introduction Xanthate anions chemisorb readily on most sulphide (8 9) minerals ' but the relative amounts adsorbed vary de pending on the individual characteristics of the solid substrate. Since a l l sulphide minerals are semiconductors^ the effects of illumination on the adsorption of xanthate at a solid/liquid interface involve both an a p r i o r i know ledge of the electrophysical characteristics of the semi conductor and an understanding of the changes in the electronic distribution caused by the absorption of photons. It is this change in the electronic distribution that has been utilized in the most recent developments in flotation recovery. 2 , 2 Solid Semiconductors The crystal structure of semiconductors is cur rently described in terms of the band theory of solids. In this theory the la t t i c e ions are considered to affect the movement of electrons only by causing exclusion of bands (energy gaps, E g) from the possible e l e c t r o n i c states of motion. The density of charge c a r r i e r s (-lO^/cc) 1 2 i s lower than that for metals (^10 /cc) hence e l e c t r i c f i e l d s in the surface plane caused by surface dipoles extend for a distance of many atomic layers into the bulk material, forming a space charge region below the surface. The depth of the e f f e c t i v e space charge layer, or the Debye length, can be as great as 10,0 00 A f o r semiconductors. Usually semiconductors are c l a s s i f i e d as n-type or p-type depending on whether the charge c a r r i e r s are electrons or free quantum states (holes). F i g . 1 shows the basic structure of both n-type and p-type semiconductors with p a r t i c u l a r emphasis on the form of the Fermi d i s t r i b u t i o n function [f(E)3 as impurities are added to the e x i s t i n g structure. In Fig. l a i f an electron i s excited from a donor l e v e l into the conduction band, the semiconductor behaves as a metal. In t h i s case, the e l e c t r i c a l conducti v i t y i s due to the free movement of electrons (n-type conductance). A p-type conductance i s shown in F i g . l b when an electron i s moved into an acceptor l e v e l leaving behind a hole free to migrate. I f both donor and acceptor l e v e l s are present then the semiconductor i s of the mixed type. Pure sphalerite i s reported to be an n-type semi conductor while galena can have eith e r p or n-type j properties'^"'. The semiconducting properties of pure sphalerite Probability f Q of electron occup ation Probability l - f Q of hole occupation Density of states / gc<E> (a) N - TYPE Product f 0(E)g c(E) DONOR LEVEL Intrinsic Fermi Level Product [l- f 0 ( E ) ] g v ( E ) (b) P - TYPE Electrons Intrinsic Fermi Level ACCEPTOR LEVEL Holes Valence band Fig. 1 - Distribution function and electron and hole population for impurity semiconductors (after McKelvey4). 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 in agreement with the fundamental absorption edge. Cheroff and K e l l e r ^ 1 3 ' attributed the photoconductivity effect at longer wavelengths to the presence of impurities in the crystal l a t t i c e . (14) Low and Weger investigated the effect of iron in sphalerite. For an iron content as low as 0.03% they recorded three strong peaks at approximately 7,000 A (1.8 eV) and a strong absorption band at 3 microns (0.4 eV). The (15) effect of manganese has been investigated by McClure who noted a number of peaks in the 3,900-5,000 A region. The absorption below these regions increased steadily cul minating in what i s commonly referred to as the fundamental absorption edge. Because of the gradual increase in ab sorption there is a discrepancy in the assignment of a particular wavelength to the fundamental frequency. Beun and Goldsmith^**' and C u r i e a s 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, for 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 level diagram for the measured electronic transitions involving absorption, excitation, emission, trapping and photocon ductivity processes. The materials studied included pure ZnS, ZnS with Cu and ZnS with Ag as added impurities, toge ther with other impurities, including Mn, Mg and Na. The author showed that there were five major trapping levels common to a l l ZnS phosphors regardless of the impurity. Fig, 2 shows the proposed energy level diagram for exci tation and emission transitions. Optical trap emptying by visible light, like thermal trap emptying, involves a process of stimulation in which trapped electrons are raised into the conduction band before returning to luminescence centers to produce emission. Natural galena is 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 attributed either to impuri- es or to non-stoichiometric proportions of Pb and S in crystals, both n-type and p-type being the object of more recent investigations. In general, the electrical pro perties of partially ionic semiconductors may be attributed to the presence of donor and acceptor levels produced either by foreign atoms or by deviations from stoichiometric proportions. The crystal 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 - Tentative energy l e v e l diagram f o r the e x c i t a t i o n and emission 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 inter s t i t i a l atoms and/or vacant la t t i c e sites. Wide variations in the absorption characteristics of various samples of galena have been observed by Paul and Jones^^' even though the impurity content was too small to be detected (21) by normal chemical procedures. Brebrick and Scaulon investigated the el e c t r i c a l properties of galena of near stoi chiometric composition prepared by controlling the tempe rature and vapour pressure of sulphur. The impurity energy gap that they calculated from their experimental results ,was 0.03 eV for an n-type crystal and 0.001 eV for a p-type crystal. The fact that galena does not show a sharp (22) absorption edge i s attributed by Gibson to the absorption of radiation with energy less than 0.37 eV resulting in an electronic transition within the conduction band. In a recent study on the photoconductivity of (23) lead sulphide films, Fleming and Alberg proposed that their films were composed of both n-type and p-type material, the p-type regions consisting of the inter- crystalline layers and the outer portions of the crystallites which had become oxidized during the preparation of the film. Plaksin and Shafeev^ 2 4' described the action of oxygen as the take-up of electrons during ionization of the adsorbed oxygen molecules. This resulted in a lowering of the height of the potential barrier at the mineral surface. The 11 chemical potential gradually f e l l off and the probability of the xanthate anions overcoming the potential barrier gradually increased. 2.3 Recent Approaches to Flotation ( 25 ) As early as 1959, Plaksin emphasized the role of oxygen and other gases in flotation. According to this author, oxygen promotes dehydration of the mineral surface and facilitates the penetration of xanthate groups thus assisting their fixation. Using an infrared multiple re- (26) flectance technique, Poling and Leja found no inter action between galena and xanthate ions solutions in 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 in 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 latest theory proposed by Plaksin and co-workers^ who invoked semiconductor principles to explain the xanthate- sulphide interactions. Since a l l sulphide minerals are semiconductors with electronic and hole conductivity, a strong chemical bond w i l l result from the transition of an anion electron to a free (anodic) vacant si t e . They proposed that the separation of sulphide minerals from non-sulphide 12 ones i s based on the following principles: a) potential energy of the surface and b) energy necessary to create an adsorption bond between a surfactant and the mineral sur face. The mosaic distribution of reagents on the surface is theoretically explained by the non-uniform potential of the surface and experimentally proven by radiographic studies of minerals treated with radioactive surfactants. According to these authors, the surface properties of mineral particles can be modified by either changing the oxidation-reduction potential of the medium or by the addition of ions that behave as donors or acceptors. Natural sphalerite does not float when short chain xanthates are used as collectors, but flotation i s f i r s t achieved with amyl xanthate and continues with higher ( 8 ) chain homologues • A short chain xanthate can be used effectively to collect sphalerite i f the mineral has been effectively activated with copper. In a recent review (28) Yonezawas ' 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 of a copper atom (10.4 A ) o and the cross sectional area of the xanthate radical (25 A ), this author showed that the ratio of copper to xanthate ions adsorbed was close to the ratio of their respective cross sectional areas when the surface coverage of copper 13 ( 2 9 ) ions i s about 100 per cent. Gaudin et a l v investigated the activation of sphalerite with Cu64 and described the activation as a rapid chemical exchange of Cu + + for Zn + + until three layers of Zn + + have been replaced. The flotation of galena with potassium ethyl xanthate i s well known, 25 mg/1 being sufficient for collection up to a c r i t i c a l pH value of 10.4 where flotation c e a s e s ^ K l a s s e n and Mokrousov^ 1^ indicate that only 20 to 40 percent coverage is required to float the mineral. Obviously these values can only indicate a trend since they are based on a hypothetical uniform distribution and vertical orientation of the collector on the surface. (2) Plaksin and Shafeev made an unusual contri bution to flotation by correlating absorption of photons and collection. Illumination of ilmenite with a common light bulb increased the mineral recovery by 12%. Using Y-irradiation Plaksin et a l ^ ^ effectively separated zircon from pyrochlore in a flotation system, thus indicat ing the improved technology resulting, from the change of the ratio of electron concentrations and electron vacancies in the mineral. 2.4 Illumination The effect of illumination i s to change the electronic distribution and thus to change the Fermi energy 14 l e v e l ^ 4 ' . Of particular importance i s the number of electrons in the conduction band because these electrons can directly participate in the formation of a chemical bond. Their distribution is given by: n = f(E) N(E) dE (2.4-1) where f(E) i s the Fermi distribution function and N(E) dE the density of energy levels in the energy range dE. The integration i s carried out over the lower part of the con duction band. The density of states, that is the number of energy states per unit volume lying between E and E+dE taking into account the states for both spins i s : dN = 4ir/h3 (2m*) 3 / 2 E 1 / 2dE = N(E) dE (2.4-2) where m* i s the effective mass of the electron. By sub- (31) stituting and integrating Many et a l N obtained the following expression: n = 2(2Trm*kT/h 2) 3 / 2 exp(E F-E c)/kT (2.4-3) or n * N c exp(E F-E c)/kT (2.4-3a) 15 where is the density of states, E Q the energy value of the conduction band and Ep the Fermi energy level. A similar equation can be derived for holes. It is this electronic density that can be modi fied by providing the reactants with the necessary quanta of electromagnetic energy. In general, wavelengths vary ing from 1,000 to 10,000 A or, in terms of energy of quanta, from about 1 eV to 10 eV (23 to 2 30 Kcal per mole), are sufficient to cause the necessary electronic 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, definite effects can be expected from the absorption of these photons. Absorption of light by an atom in the line- spectrum region results in an excited atom whereas in the continuum i t produces a dissociation (an ion plus an electron). These transitions occur in accord with the Frank-Condon principle that electronic excitations occur without affecting the positions of the nuclei. In this way, light absorption may cause the ex cited molecule to follow one of these alternatives: a) Re-emission of a quantum of the same or different frequency (luminescence). b) Collision with another molecule either trans ferring energy to cause a reaction in 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 in the case of sphalerite. Luminescent solids have been classified as pure and impurity activated. Zinc sulphide i s a typical impurity activated solid. 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 in the zinc sulphide matrix. When this material is illuminated with light of wavelength approximately 3,400 A, phosphorescence i s displayed and the solid becomes a better conductor of e l e c t r i c i t y (photo conductivity), A simple explanation consists of the ab sorption of a quantum of radiation sufficient 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 light 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 light. Electron traps, from which transitions to the ground state are forbidden, are present in 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 fa l l i n g to a lower energy,level. A transition model of luminescence was f i r s t proposed by Schon^ 3 2' and later modified by Klasens^ 3 3^. According to these authors the luminescence i s caused by an electronic transition from the conduction band to a localized level above the valence band (Fig. 3a). The Lambe and K l i c k ^ 3 4 ' model attributes the luminescence to a hole transition from the valence band to a level located below the conduction band to account for the different value of the decay constant between photo conductivity and luminescence, the latter being the smaller of the two (Fig. 3b). ( 35 ) Prener and Williams considered necessary the association of acceptors of group lb (Cu, Ag, Au) and donors of Group Vllb (CI, Br, I) or I l l b (Al, Ga, In) for the appearance of luminescence thus proposing that the transition takes place from the excited state of the donor to the ground state of the acceptor in an associated pair (Fig. 3c). In actual fact, luminescence i s far more compli cated than these simple models describe, being affected by other factors such as Impurities, defects, thermoluminescence decay and optical stimulation. Of particular interest i s the case when impurity cations are present in the crystal l a t t i c e . The emission spectra of the luminescence in sphalerite when other cations are present in the crystal lattice have been investigated M e ) by Shionoya et a l . Fig. 4, abstracted from their work, 18 CONDUCTION BAND VALENCE BAND Cc) Fig. 3 - Models of luminescence according to: (a) Schon- Klasen; (b) Lambe-Klick; (c) Prener-Williams. Fig. 4 - Emission spectra of luminescence in ZnS (after Shionoya et al ^6) 19 clearly indicates that the presence of copper alone gives a peak at 1.7 7 eV while the copper-aluminum produces a shift in the peak which now rests at 2.41 eV. 2.5. Sources of Radiant Energy The electromagnetic spectrum of interest to this study can be arbitrarily divided into three regions: ultraviolet, visible and infrared. The conventional wave length range of each of these regions is given in the following t a b l e ( 3 7 5 : TABLE I - ELECTROMAGNETIC SPECTRUM (After Strong 3 7) Spectral Region Extreme UV UV Visible Near IR Intermediate IR Far IR Wavelength Limits .050 to .200 microns .200 to .400 microns .400 to .720 microns 0.72 to 2 0 microns 20 to 40 microns 40 to 400 microns The most important natural source of continuous radiant energy i s the sun. Many spectroradiometric measure ments 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 distributions reported. In general the luminous efficiency of the sun i s equivalent to that of a lamp with an output of 80 lumens/watt. The energy distribution in the solar spectrum i s closely approximated by that of a black body at 5,U00°K. A black body, sometimes called a f u l l radiator, i s an imaginary object that, when heated, emits radiation in the form of a continuous spectrum. At room temperature radiation i s in the invisible infrared region, but at higher temperatures the radiation frequency increases and covers the visible regions. As illustrated in Fig. 5, black body colour i s precisely related to temperature in degrees K e l v i n ^ 3 8 \ The efficiency of a tungsten lamp i s approximately 11 lumens/watt and i t s spectrum i s limited by the trans mission of glass, namely from 0.31 microns to 3 microns for a thickness of 0.25 mm. Fig. 6 shows the transmittance limits of some glasses and water. If a tungsten light i s provided with a quartz bulb (50 amp tungsten at 3,400°K) the spectrum easily extends into the ultraviolet. Addition of iodine to the f i l l i n g gas of a tungsten lamp starts a regenerative iodine cycle and the new lamp i s properly called quartz iodine. The evaporated tungsten i s deposited on the walls of the lamp and con verted into a volatile iodide which, in turn, is decomposed 21 9 0 0 >-o u 2 0 0 100 4 0 0 5 0 0 6 0 0 WAVELENGTH Fig. 5 - Relative spectral energy distribution 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 (after Wyszecki 3 8). 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 is possible to increase the operating temper ature and the lamp efficiency. Mercury arcs give several strong lines in the visible, ultraviolet and infrared region but lack a good spectrum continuity. CHAPTER 3 EXPERIMENTAL METHODS 3.1 General Approach The materials used in this study were PbS, (Pb,Ag)S and copper activated (Zn,Fe)S. The original 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 for solid specimens and of the Seebeck effect for pelletized powders. The kinetics of adsorption of high purity KEtX on the individual solids under various conditions of illumina tion 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 intervals for U.V. spectroscopic analysis and immediately returned to the circulating system. The adsorption apparatus normally contained 600 ml of solution at 20+0.1°C. The solution was circulated once every 30 seconds through a 24 fluidized 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 fraction whilst a l l of the flotation ex periments were performed on a 150/200 mesh fraction. 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 original material was crushed in a mortar and pestle and screened on a carefully cleaned set of stainless steel Tyler Sieves. A l l traces of free pyrrhotite were then removed from each fraction with a hand magnet prior to a f i n a l cleaning in a Frantz Isodynamic Magnetic Separator. Each fraction 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 particles. After a final rinse with doubly d i s t i l l e d water, the sample was dried in a vacuum desiccator, thoroughly mixed, and stored under nitrogen. An analysis of the major and minor con stituents of the marmatite sample is reported in Table II. 25 TABLE II - ANALYSIS OF MARMATITE SAMPLE (by Coast Eldridge, Vancouver, B.C.) Chemical Analysis Spectrographic Analysis of major constituents-% of minor elements-% Zn: 54.05 Co: 0. 01 S: 33.46 Mo: 0.003 Fe: 11.63 Ca: 0.003 Cu: 0.31 . Mg: 0.0005 Cd: 0.18 Si: 0.03 Mn: 0.14 Mn: 0.2 Insol.: 0.15 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 in a 9.97x10 M copper sulphate solution at room temperature. The weight ratio of solid to liquid was 1 to 10. Since the uptake of copper ions was almost instantaneous^ 9', the time selected to reach equi librium was more than ample. A separate investigation of the effect of varying i n i t i a l concentrations on the total amount of copper abstracted was also carried out and w i l l be described with the adsorption results. 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 available in this Department. This was re-screened prior to storage in a desiccator. A complete analysis i s presented in Table III. TABLE III - ANALYSIS OF GALENA SAMPLE Chemical Analysis Spectrographic Analysis of major constituents-% of minor constituents-% (by Cominco) (by Coast Eldridge) Pb: 84.7 S i : 0.05 S: 14.1 Ca: 0.001 Zn: 0.7 Fe: 0. 003 Fe: 0.4 Cu: 0.0005 Mg: 0.0007 99.9 Au,Ag: traces The theoretical contents of PbS are 86.6% lead and 13.4% sulphur. Another sample of galena containing 0.2 8 oz/ton of silver [hereafter referred to as argentiferous galena, (Pb,Ag)Sl was crushed in a porcelain mortar and pestle and screened for immediate use in a series of tests where ex cessive oxidation of the surface was to be avoided. (c) Potassium ethyl xanthate (KEtX). A fresh sample of potassium ethyl xanthate was prepared for this series of experiments. Redistilled ethyl alcohol was mixed with pure potassium hydroxide (Fisher Certified Reagent) to which carbon disulphide (Fisher Certified Reagent-Infrared Spectranalyzed) was added slowly at low temperature to avoid decomposition of the mixture. The product was then re- crystallized from acetone five times and stored in a vacuum desiccator. At weekly intervals, the xanthate was washed several times with ether to remove any dixanthogen formed on oxidation. (d) Water. Low conductivity doubly-distilled water was used in a l l experiments. Typical values of the specific conductance taken from the storage pyrex bottles G —6 —1 —1 ranged between 0.9xl0~ and 1.0x10 ohms cm (e) Copper Sulphate (CuSO^.5H20). Certified ACS reagent grade copper sulphate supplied by Fisher Scientific Company of Vancouver was used for a l l experiments. 3.3 Surface Area Measurements The surface areas of the 100/150 mesh size of the three powders have been measured by a continuous flow method^39'. Nitrogen was adsorbed by the sample at liquid nitrogen temperature from a gas stream of nitrogen and helium and eluted upon warming the sample. The nitrogen liberated i s measured by thermal conductivity. With this method, materials of low specific 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 level 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 initiated with the introduction of a known weight (approximately lg) of sample to a U-tube. The sample tube was then placed in the c i r c u i t as indicated in Fig. 7. When a l l the a i r was flushed out by the mixture of nitrogen and helium (5, 10 or 15% N2) the thermal conductivity detector was switched on and the bridge balanced to zero output. The sample was then cooled slowly in the liquid nitrogen and at the same time the ad sorption peak was recorded. In order to take advantage of the f u l l range of the recorder scale, the polarity switch was reversed prior to desorption of nitrogen. Desorption was achieved by rapid immersion of the U-tube in warm water. The complete sequence of adsorption was repeated three times to show consistency of results. In addition, a calibration of the volumes eluted was achieved by injecting known volumes of purified nitrogen into the system. 3.4 Electrical Conductivity and the Hall Effect The electrophysical characteristics of the solid specimens have been investigated by the Hall effect. The Hall coefficient i s given by the transverse voltage produced Nitrogen Thermometer Probes 12V Power Source Back Pressure Manometer He-N2 Mixture C ^ S E S E Thermoconductivity Cell To M i l l i v o l t Recorder Purified N2 Sample Tubes Dewar Flask Liquid N2 JCSl Oil F i l l e d Syringe Caps for Calibration QJ •M Q) 6 u O • H C O nJ > u <u w CD £ J PS w CO c <D bO 0 ... U ». • U •ri O Va p Nitrogen Thermometer Exhaust Fig. 7 - Schematic diagram of the apparatus for surface area measurements (courtesy of Mr. R. Orr). 1 to when a current i s passed through a conductor lying 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 is proportional to the current (I) in amperes, to the magnetic f i e l d (H) in oersteds and inversely pro portional to the thickness (t) in cm measured in the direction of the magnetic f i e l d . The proportionality constant (R=l/nqc) is called the Hall coefficient: V = R. IH/t = IH/nqct (3.4-1) where n i s the number of carriers, £_ their charge and c the velocity of light. A schematic diagram of the Hall effect i s presented in Fig. 8. Converting to practical units and substituting the value of c (see Appendix A): V = 10""8 IH/nqt = RH 10"8 IH/t (3.4-2) indicating that the practical Hall coefficient, R^ , i s equal to RH = + 1/nq (3.4-3) the plus or minus sign indicating hole or electron con ductivity. From a knowledge of the conductivity (a = nqu) the mobility (u) can now be readily calculated by multiply ing the Hall coefficient by the conductivity: 31 + ( p-type ) - ( n-type ) IT a - ( n-type ) + ( p-type ) Fig. 8 - Schematic diagram of the Hall effect. 32 u = a RR (3.4-4) The samples of galena and sphalerite used in the measurements of the Hall coefficients were prepared from representative samples of solid 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 plastic as shown in Fig. 9 and 10. The three-points voltage pick up is commonly used to avoid an ohmic voltage drop. When the potential contacts are not perfectly aligned and do not coincide with an equipotential line, in the absence of a static magnetic f i e l d an ohmic voltage drop proportional to the steady current w i l l be measured in addition to the Hall voltage. Fig. 11 shows the origin of this 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 of British Columbia. 3.5 Seebeck Voltage Measurements The Seebeck effect i s a simple and efficient method for determining the conductivity type of a semi conductor from the sign of the potential produced. It i s particularly useful for low mobility materials and for powder specimens where the Hall effect i s d i f f i c u l t to a) Pressure contacts 1 j / b) Indium c o n t a c t s Ohmic connections to marmatite specimens. F i g . 10 - Ohmic c o n t a c t s to galena specimens. 35 Current l e a d Voltage l e a d Misalignment X F i g . 11 - O r i g i n o f ohmic v o l t a g e drop due to misalignment when measuring the H a l l c o e f f i c i e n t . . m e a s u r e 5 ' . A schematic diagram o f the measurement o f t h i s 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 diagram i n d i c a t e s that when, there i s a temperature g r a d i e n t between the ends o f a specimen, an emf o f QAT i n m i l l i v o l t s i s produced where Q r e p r e s e n t s the t h e r m o e l e c t r i c power i n u n i t s o f m i l l i v o l t s / d e g r e e . The P e l t i e r e f f e c t which i s the i n v e r s e o f the Seebeck e f f e c t , a r i s e s when a c u r r e n t i s passed through a semiconductor: the heat absorbed at one end o f a semi conductor-metal j u n c t i o n i s l i b e r a t e d at the o t h e r . The P e l t i e r c o e f f i c i e n t TT i n u n i t s o f v o l t s i s expressed as j o u l e s o f r e v e r s i b l e heat absorbed or l i b e r a t e d p e r coulomb of charge p a s s i n g through the j u n c t i o n . The p h y s i c a l r e  p r e s e n t a t i o n o f t h i s e f f e c t i n terms o f energy l e v e l s f o r an n-type semiconductor i s shown i n F i g . 13. Under an a p p l i e d p o t e n t i a l , the energy l e v e l s slope to the r i g h t r e  s u l t i n g i n a c u r r e n t flow from r i g h t to l e f t c o rresponding to an e l e c t r o n flow from l e f t to r i g h t . E l e c t r o n s from the metal e n t e r i n g the semiconductor from the l e f t must possess an energy equal o r g r e a t e r than the energy b a r r i e r (E^-Ep) but no b a r r i e r i s p r e s e n t at the r i g h t , and semiconductor e l e c t r o n s with e x c e s s i v e thermal energy are e a s i l y added to the metal t r a n s f e r r i n g heat from l e f t to r i g h t . T h i s heat t r a n s f e r forms the b a s i s o f the P e l t i e r e f f e c t since the mobile charge c a r r i e r s d i f f u s e from the hot to the c o l d j u n c t i o n i m p a r t i n g a p o t e n t i a l o f the same s i g n as 37 - (p-type) + (n-type) Q AT ( m i l l i v o l t s ) HOT JUNCTION [Z COLD JUNCTION A + (p-type) - (n-type) AT (°K) F i g . 12 - Schematic diagram o f the Seebeck e f f e c t ( a f t e r Hannay^). F i g . 13 - O r i g i n o f the P e l t i e r e f f e c t . f o r an n-type semiconductor ( a f t e r HannayS). 38 the c a r r i e r s to the cold junction as indicated i n F i g . 12. The energy transferred therefore i s the energy required to overcome the energy barrier CCE^-Ep) for an n-type semi conductor] plus a term for the k i n e t i c energy transported by the c a r r i e r s , or: qiT = qQT = (E^-Ep) + 2kT (3.5-1) This equation indicates that the potential Q i s related to the position of the Fermi l e v e l and by substituting i n equation (2.4-3): n - p = 2(2Trm*kT/h 2) 3 / 2 exp(E p-E c)/kT (3.5-2) the number of electrons (n) or holes (p) can be calculated. A simple apparatus designed to investigate the type of semiconduction in low mobility materials i s shown in F i g . 14. A photograph of the apparatus i s shown in Fig. 15. Solid specimens as well as p e l l e t i z e d d i s c s , made by compressing powders in a standard press at 65,000 p s i , were placed between the two copper discs maintained at constant temperature. The voltage produced was measured by a Keithley Electrometer (Model 610B). F i g . 14 - Schematic diagram o f the apparatus f o r the measurement o f the Seebeck v o l t a g e . F i g . 15 - Apparatus f o r the measurements of the Seebeck voltage rearranged outside the Faraday cage. 41 3.6 Oxidation of Galena Powders The role of oxygen in xanthate adsorption on sulphide minerals is well documented. Some investigators^ 3^ propose that penetration of oxygen into the surface layer of the mineral weakens the surface bonds and increases the (25 3 0) chemical activity of the surface. Others * describe the effect of oxygen adsorption as one of surface dehydration that allows the subsequent penetration of surfactants. Other experimenters^ 4^ postulate electrophysical changes from an n-type solid to a p-type through adsorption of oxygen. In this case, the p-type solid i s described as being more susceptible to anionic adsorption. A fourth possibility is the oxidation of xanthate anions to dixanthogen^ 9'^ 6^. Since no complete agreement has been reached, i t was decided to investigate the relative oxidation rates of . the two galenas in order to differentiate between the effect of surface products, i f any, and the bulk character i s t i c s in subsequent adsorption tests. The relative rates of oxidation of the two galena .samples were analyzed with a Cahn RH Electrobalance made available by the Faculty of Forestry of The University of British Columbia. The galena powders were prepared by crushing large specimens in a porcelain mortar and pestle followed by screening the 100/150 mesh fraction in a dry box f i l l e d with purified premium nitrogen. The sealed test tubes containing the powders were then transferred to the dry box protecting the electrobalance. For the tests without water vapour, the dry box was repeatedly 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 three grams of galena were removed from the test tube, placed on the balance and equilibrated by the addition of the appropriate weight to the other pan. The recorder was then allowed to run for a few minutes to es t a b l i s h a baseline. The dry box was then evacuated and as the oxygen was admitted the chart recorder was switched on simultaneously to measure the weight increase. For the tests with water vapour the same procedure was used but the desiccants were replaced by a beaker of water. 3.7 Adsorption from Solution (a) Apparatus. The adsorption apparatus was designed to investigate the rate of adsorption of xanthate on d i f f e r e n t n-type and p-type minerals by continuously c i r c u l a t i n g the solution containing the surfactant through the solids i n a closed system. The most c r i t i c a l features to be controlled we're the energy of i l l u m i n a t i o n , the inertness of the construction material and the presence of atmospheric oxygen. The apparatus presented i n Figs. 16 and 17, i s LEGEND: a) l i g h t source b) t h e r m o s t a t i c bath c) thermometer d) sample chamber e) heat excharigers f ) flow meter 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 pump (c) (a) n (d) 0> (g) ( f ) 15 (b) (e) ( h ) F i g , 16 - Schematic diagram o f the a d s o r p t i o n apparatus. F i g . 17 - A d s o r p t i o n a p p a r a t u s c o m p l e t e w i t h a c c e s s o r i e s a nd a s e m i - m i c r o f l o t a t i o n c e l l . an improved v e r s i o n o f tha t used by the a u t h o r ^ D i n a p rev ious s tudy. The main fea tures 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 amounts o f s o l i d s and d i f f e r e n t volumes of s o l u t i o n , (3) f l u i d i z e d m i x i n g o f the s o l i d s to reduce the p roduc t ion o f f i n e s and, consequent ly , changes i n surface a rea , (4) e l i m i n a t i o n o f f i n e s removal du r ing sampl ing , (5) e l i m i n a t i o n o f s o l i d abras ion o f the pump l i n e r , (6) a b i l i t y to c a r r y out t e s t s i n i n e r t atmospheres, (7) a b i l i t y to c l e a n , wash and dry the system wi thout d i s m a n t l i n g the components, and (9) v e r s a t i l i t y , s i m p l i c i t y and r e l i a b i l i t y o f d e s i g n . Two S y l v a n i a Quar tz - Iod ine Lamps (No. 40 0 T4Q/C1/F and No. 500 T3 Q/CL/U) were used as a l i g h t source . T h e i r c h a r a c t e r i s t i c s are presented i n F i g . 18. The p a r t i c u l a r lamp used i n any one experiment was encased i n a metal box open at 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 co loured g l a s s f i l t e r s at a reasonable d i s t ance to avo id abso rp t ion o f heat . The nominal r a t ings o f the lamps were g iven as 7,500 and 10,500 lumens f o r an approximate c o l o u r temperature 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 a t 2 0°C was achieved w i t h a C o l o r a Ul t ra -Thermos ta t Ba th , Type NB, having a s p e c i f i e d accuracy o f +0 .01°C . A p r e c i s i o n thermometer with a range of -1 to +51°C in 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 fr 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 re flector (not shown in 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 circulating pump (Vanton Flex-I Liner) which was supplied by Vanton Pump and Equipment Corp., Hillside, N.J. The pump was equipped with a Kel-F liner (a polymonochlorotrifluoroethylene fluorocarbon) encased in a solid block of teflon (a polytetrafluoro ethylene fluorocarbon). A l l mechanical connections were made by squeezing a teflon gasket sheath between the tapered ends of QVF glass tubing [QVF Glass (Canada) Limited, Scarborough, Ontario], a borosilicate glass with the following typical composition: 80.60% Boric Oxide (B 20 3) 12.60% 4.15% Calcium Oxide (CaO) 0.10% 2.20% Magnesium Oxide (MgO) 0.05% 0.04% Chlorine (CI) 0.10% Sil i c a (Si0 2) Sodium Oxide (Na20) Aluminum Oxide (Al 20g) Iron Oxide (Fe 00O 48 The transmission curves f o r QVF glass in the u l t r a v i o l e t and v i s i b l e regions of the spectrum, as supplied by the manufacturer, correspond to that of Dense F l i n t Glass shown i n Fig. 6. In the present work the selection of spectral energies was achieved using colour glass f i l t e r s 5-8 3, 5-7 5 and 7-86 manufactured by Corning Glass Works of New York. The transmittance curves f o r the f i l t e r s in question were determined on a Model 4 50 Perkin-Elmer Spectrophotometer for the u l t r a v i o l e t and v i s i b l e regions and on a Model 521 Perkin-Elmer Spectrophotometer f o r the infrared region (Fig. 19). These narrow band f i l t e r s were selected so that they cover approximately the same range of photon energy in di f f e r e n t regions of the spectrum. The 5-83 f i l t e r covers the range of 0.340-0.380 microns (3.6-3.3 eV), the 5-75 f i l t e r extends from 0.44 0 to 0.4 90 microns (2.9-2.6 eV) while the 7-86 f i l t e r covers the 1.5-2.75 microns range (0.8-0.5 eV). A n c i l l a r y equipment included a Beckman Zeromatic II pH Meter and a Cenco Hyvac 7 Vacuum Pump (from Central S c i e n t i f i c Company, Chicago, 111.). (b) Typical Adsorption Procedure. The following procedure used for the adsorption of xanthate on lOg of PbS at constant illumination i s t y p i c a l f o r a l l systems. The basic differences l i e i n the type and amount of s o l i d Fig. 19 - Measured transmittance of Corning Glass F i l t e r s . material used i n the t e s t , the i n i t i a l concentration and volume of xanthate solution and the il l u m i n a t i o n conditions. To minimize the variations in surface area caused by weighing, lOg of PbS were weighed, a f t e r coning and parting, on a Mettler H15 baldnce to within +0.001 g which corresponded to an accuracy of surface area of +1.8 cm2/10g. The material was transferred to the adsorption c e l l , a l l seals were c a r e f u l l y tightened and the whole system evacuated. At the same time the appropriate glass f i l t e r was placed i n the collimator and the r e f l e c t o r positioned around the c e l l . Complete removal of i n t e r f e r i n g external i r r a d i a t i o n was achieved by darkening the adsorption assembly with a black c l o t h . The l i g h t source and the thermostatic 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 solution of KEtX were prepared and the exact concentration determined by a Perkin Elmer 450 Spectrophotometer. The solution was transferred to the evacuated apparatus while the c i r c u l a t i n g pump was operating. Thermal equilibrium was e a s i l y reached within the f i r s t two minutes, the maximum i n i t i a l deviation never exceeding +2°C. At selected time i n t e r v a l s , 4 ml of solutions were removed to record the xanthate concentration and immediately returned to the c i r c u l a t i n g system. The differences in concentration represented the amount of xanthate abstracted by the mineral sample together with losses due to decomposition. In connection with oxidation studies i t was necessary to carry out adsorption tests in an inert atmos phere. In this case oxygen contamination had to be avoided in the preparation of materials as well as during ad sorption. The powders were crushed i n a porcelain mortar and pestle and screened in a dry box containing p u r i f i e d premium nitrogen. Ten grams of material were then weighed i n the same dry box and transferred to the adsorption c e l l the ends of which were sealed o f f with removable te f l o n discs. The sealed chamber was reconnected to the main apparatus which was subsequently evacuated up to the t e f l o n seals. These seals were removed while flushing the loosened connection with helium from the previously evacuated side. The whole apparatus was then evacuated. In the meantime the xanthate solution was prepared by adding deaerated doubly d i s t i l l e d water to the proper weight of xanthate in a volumetric f l a s k , the procedure c a r r i e d out i n a portable dry box f i l l e d with helium. This solution was slowly added to the evacuated apparatus which was then pressurized with helium to atmospheric pressure. Before s t a r t i n g the c i r c u l a t i n g pump, other conditions being selected, four m i l l i l i t e r s of solution were removed for UV analysis. The test was carried to completion i n the manner previously described, except that the samples removed f o r UV analysis were not returned to the system. (c) A n a l y t i c a l Procedure. In order to r e t a i n the constancy of c i r c u l a t i n g volume, a fast and r e l i a b l e physical method of analysis was preferred to a chemical one. U l t r a v i o l e t spectroscopy o f f e r s these advantages since KEtX displays a good spectrum with a sharp absorption peak that culminates at 301 my. The absorption of radiant energy at 3 01 my follows the well known Beer-Lambert Absorption Law. This law states that the amount of energy absorbed by the excited ions i s proportional to the thickness and q u a l i t y of medium traversed, or: -dl/dx = a l (3.7-1) where I_ i s the i n t e n s i t y of l i g h t , x a distance into the medium, and a the absorption c o e f f i c i e n t . Integration at the boundary conditions (I = I Q when X = 0) gives: •I = I exp(-ax) (3.7-2) o In 1852 Beer showed that the c o e f f i c i e n t a was proportional to the concentration c of the solute, therefore, rewriting: 1 = 1 exp(-ecx) (3.7-2a) o In t h i s equation the symbol £ i s known as the molar extinction c o e f f i c i e n t , an i n t r i n s i c property that characterizes each substance. In the case of potassium ethyl xanthate, the molar extinction c o e f f i c i e n t used by Pomianowski and Leja^ ' (43) was 17,750, the value given by Majima was 17,460. As suming that these discrepancies may be caused by instrument a l c a l i b r a t i o n , an independent determination of the molar extinction c o e f f i c i e n t was car r i e d out for the p a r t i c u l a r sample of KEtX used i n these experiments (Appendix B). The extinction c o e f f i c i e n t calculated from these data i s equal to 17,500. One of the major objections to the assumption that a l l of the reagent that disappears from solution i s actually adsorbed by the mineral surface i s that no con sideration i s given to the amount of surfactant p r e c i p i t a t e d , decomposed or evaporated from solution. In order to circumvent such a d i f f i c u l t y a number of curves l a b e l l e d "Adsorption on Apparatus and Decomposition of Potassium Ethyl Xanthate" have been recorded to account, at l e a s t i n part, for these e f f e c t s . The curves are plotted i n F i g . 20 and have been used to correct a l l subsequent adsorption measurements open to atmospheric oxygen. It should also be noted that the corrections apply to the t o t a l amount of sol i d s present. For example, i n the case of 2 0g of PbS, the correction i s le s s than 4% at 10 minutes and 13% at 300 minutes. The change i n volume from 1,000 ml. to 600 ml. was introduced a f t e r the preliminary experiments to i n  crease the separation of the xanthate absorption l i n e s on the UV recorder. I t i s most i n t e r e s t i n g to observe that 20 Time - minutes F i g . 20 - A d s o r p t i o n on apparatus and decomposition o f xanthate. T e s t c o n d i  t i o n s : KEtX (10-4M), 20°C, i l l u m i n a t e d with a 400W Q/I lamp. cn when the ordinate i s changed to read in micromoles/1, the two l i n e s of Fig. 20 display almost a perfect coincidence. This suggests that the majority of the correction can be attributed to decomposition since the in t e r n a l surface area of the apparatus was a constant. (d) Reproducibility. A major concern of a l l experimenters i s to at t a i n good r e p r o d u c i b i l i t y of r e s u l t s . To e s t a b l i s h the degree of 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 selected for the tests using 1,000 ml volumes whereas galena was used f o r the te s t s using 600 ml volumes (Appendix C). The s l i g h t departure of the l i n e s displayed by the marmatite sample can be attributed to varying l i g h t conditions and/or sample devia tions from stoichiometry. A more remarkable r e p r o d u c i b i l i t y was obtained 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 choice of a 500 W/QI lamp for the l a s t experiments emerged from necessity when the burnt out 400 W/QI lamp proved to be one of the f i r s t prototypes presently out of production. In the reproducibi l i t y tests as well as most of the subsequent experiments, _4 the i n i t i a l concentration of xanthate was 10 M. In the case of marmatite, the maximum error, at the beginning of 2 10 the adsorption, was 0.08 moles/cm xlO . To a s s i s t i n the logarithmic presentation, times of l e s s than 10 minutes were omitted from the graphs. The l i n e a r i t y of adsorption i n the 1 to 10 minute region was well demonstrated in (41) previous work and i s shown for two tests from the present series i n Fig. 34. Adsorption r e s u l t s below the one minute l i m i t are not r e l i a b l e with the present apparatus since i t takes t h i r t y seconds f o r the solution to c i r c u l a t e once through the mineral bed. Adsorption below t h i s l i m i t was investigated by several authors^ 3 0'. In the case of galena, they observed that the adsorption on the active s i t e s occurred within the f i r s t s i x t y seconds, a slower ad sorption proceeding subsequently. In the present study the adsorption at times greater than one minute, was i n  vestigated by changing the surface c h a r a c t e r i s t i c s of the mineral surface with illumination. Such a range was selected because i t i s more c l o s e l y related to the actual f l o t a t i o n conditions in a plant operation. 3.8 Flotation F l o t a t i o n of the various minerals was investigated using a semi-micro f l o t a t i o n technique previously used by the author^ 4 4'. This method was preferred to the Hallimond t u b e ( 4 5 ' 4 5 ' and to the c e l l devised by P u r c e l l ( 4 7 ) f o r the ready adaptability of the design to the l i g h t attachment used i n the adsorption t e s t s . The semi-micro f l o t a t i o n c e l l , handmade from a Pyrex Glass f r i t t e d funnel of 6 0 microns porosity, i s shown i n F i g . 21. 57 LEGEND: (a) Pyrex semi-microflotation c e l l (capacity: 150 ml; porosity: 60 microns) (b) Mercury manometer (c) Needle valve bleed off Cd) Constant pressure distribution chamber (e) Gas cylinder Fig. 21 - Schematic diagram of the flotation arrangement. 58 The previously cleaned c e l l was f i l l e d with 150 ml of doubly d i s t i l l e d water while s u f f i c i e n t back pressure of nitrogen was maintained to avoid percolation through the f r i t t e d d i s c . A t y p i c a l charge of 2g of c l o s e l y sized solids [150/200 mesh in the case of (Zn,Fe)S] was weighed, af t e r coning and parting, and added to the c e l l . Potassium ethyl xanthate was then added to give a t y p i c a l concentra- t i o n of 2.5x10 M/l (0.04 mg/1) using an Agla Micrometer Syringe. Following a conditioning time of 3 0 seconds, 0.02 mg/1 of ethyl alcohol were added as a frother and the nitrogen pressure adjusted to 2 0.5 cm of Hg to produce intense but not violent a g i t a t i o n . The f r o t h product was collected for 3 minutes. Both product and t a i l i n g were dried and t h e i r respective weights used to calculate the metallurgical recoveries under conditions of normal daylight illumination. In the case where selected wavelengths were used, the procedure was e s s e n t i a l l y the same but more attention was focused on the preparation of s o l i d s . A l l sol i d s were weighed i n numbered beakers and kept in t o t a l darkness overnight. They were then added i n d i v i d u a l l y to the c e l l , the l i g h t source turned on and the sol i d s illuminated for 15 minutes p r i o r to addition of the xanthate. Subsequent steps were exactly the same as described above. CHAPTER 4 EXPERIMENTAL RESULTS The adsorption results are presented as the total amount adsorbed versus tine. Such a presentation is pre ferred to the conventional equilibrium method because flotation per se is a non-equilibrium system and more information can be obtained at selected time intervals. A detailed analysis of the rate constant, reaction order, activation energies and entropies of activation for a similar system has been presented by Guarnaschelli and Leja in a previous publication^ 4^"\ According to this, the reaction for the adsorption of xanthate i s of 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 results are discussed in terms of surface area coverages. 4.1 Surface Area Measurements The physical adsorption of nitrogen on mineral surfaces can best be represented by the Brunauer, Emmett (48) and Teller (BET) equation* : 60 P/Vad(PQ-P) = [(C-1)/Vm C] (P/Po)+l/VmC (4.1-1) where: Vad Vm C P P o p a r t i a l pressure of nitrogen saturated pressure of nitrogen at temperature of l i q u i d nitrogen used t o t a l volume of gas adsorbed monolayer volume of gas adsorbed constant This i s the equation of a straight l i n e having P/Vad(PQ-P) as ordinate and P/PQ as abscissa. Then (C-l)/VmC i s the slope of t h i s l i n e and 1/VmC the intercept. For a l i n e a r BET p l o t , the value of P/PQ should l i e between 0.05 and 0.35. In order to work within these l i m i t s , mixtures of nominally 5, 15 and 25 per cent nitrogen i n helium were used. The quantity Vm for each powder was calculated from the slope and intercept of the l i n e s of F i g . 22. In t h i s figure every point represents the arithmetic average of three independent measurements. The main parameters and surface areas of the three samples are summarized i n Table IV. A detailed c a l  culation of the surface area of marmatite i s presented in Appendix D. The large surface area of the marmatite, four times the area reported for a s i m i l a r size f r a c t i o n ^ 9 ^ , i s the consequence of the presence of porous oxidation products due to the high Iron content of the sample and the presence of inevitable f i n e s (slimes). the 100/150 mesh marmatite the areas of other screened fractions can be obtained from t h e i r average screen size. From a knowledge of the measured surface area of 10 -O (Zn,Fe)S •+ (Pb,Ag)S © -© PbS a. i o a. a. P/P Q x 10- 2 F i g . 22 - BET p l o t s f o r 100/150 mesh m i n e r a l powders, 62 TABLE IV - BET AREAS OF POWDERSQ00/150 MESH) Sample Size-g Slope Intercept Vm-ml o Area-cm /g (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 TABLE V - CALCULATED SURFACE AREAS OF SCREENED FRACTIONS OF MARMATITE Me sh Size Average Screen Size (microns) BET Area of (Zn,Fe)S cmVg Calculated Area cm^/g 65/100 177 — 2600 100/150 125 3675 — 150/200 88 — 5200 These calculated areas are shown in Table V. In addition the number of xanthate molecules and 2 the equivalent in moles/cm required to form a closely packed monolayer can be calculated in terms of the estimated 2 ( 9 ) parking area of 2 9A for the xanthate radical . The 2 16 2 2 number of xanthate radicals per cm i s 10 A /2 9 A = 13 = 34.5x10 which divided by Avogadro's Number yields -10 2 5.7x10 moles/cm . This monolayer coverage i s included in 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 in Figs. 2 3 and 24. In Fig. 2 3 the amounts of xanthate adsorbed increased as higher energy was supplied to the system. Fig. 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 in both the amount adsorbed at 10 minutes and the total 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 in darkness (Fig. 23 vs. Fig. 24). The last effect can be explained in terms of ( Monolayer coverage at 5.7 moles/cm^ x 10 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 _L _L J_ J I L 0 20 30 40 50 60 TIME - 80 minutes 100 200 300 400 500 -5 Fig. 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 illumination. (20g). ( Monolayer coverage at 5.7 moles/cm 2 x 1 0 1 0 ) Light conditions: Mercury vapour lamp Darkness 0.8 - 0.5 eV X X X LO F i g . 24 - 20 30 40 50 60 80 100 TIME - minutes 200 3000 H00 500 Adsorption of EtX from a solution of KEtX (9xlO" 5M) 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). .ummation, 66 electron-hole recombination by trapping. The traps, commonly associated with impurities and structural defects, provide l o c a l i z e d energy l e v e l s l y i n g deep within the forbidden energy gap (See Fig. 2). The addition of energy less than the energy gap value may be s u f f i c i e n t to raise the electron from a trap into the conduction band from which i t can then recombine with a hole in the valence band. Therefore the function of energy less-than-the- energy-gap value i s to promote these recombinations by supplying the required t r a n s i t i o n energies to the system. The net e f f e c t i s to annihilate an electron-hole pair and consequently to decrease chemisorption. A l i m i t i n g state <.. w i l l be reached when the energy supplied has promoted a l l the electrons from the traps to the conduction band. From the r e s u l t s of the present investigation i t may be con cluded that an energy of 0.6 eV i s s u f f i c i e n t to r a i s e an electron from the trap to the conduction band, and that 2.9 eV i s s u f f i c i e n t to rai s e electrons from the valence band into the traps. The former process r e s u l t s in a combination and removal of holes and the l a t t e r r e s u l t s in both creation of electron-hole pairs and recombination. An energy of 3.4 eV appears to be s u f f i c i e n t to promote electrons from the valence band to the conduction band thus creating electron-hole p a i r s . The existence of d i f f e r e n t equilibrium adsorption values a f t e r about two hours i s somewhat disconcerting. 67 The atomistic approach with i t s "dangling valence bonds" or active s i t e s has been quite useful i n explaining similar experimental r e s u l t s up to a monolayer value. P r e f e r e n t i a l adsorption on surfaces of d i f f e r e n t crystallographic orientation would be d i f f i c u l t to measure in the case of the mineral powders used i n the present study. Further more adsorption s l i g h t l y above the monolayer value i s d i f f i c u l t to v i s u a l i z e from the concept of dangling valence bonds. The function of illumination i s to produce more photoactive s i t e s , r e s u l t i n g in d i f f e r e n t equilibrium adsorption values. In the only case where the r e s u l t s indicated adsorption greater than the monolayer -value, that of the p-type galena, the strong a t t r a c t i o n of xanthate could be attributed to the larger number of strong (23) l y anodic s i t e s . However the rate of adsorption would be expected to decrease at the monolayer coverage. In view of the fact that the indicated surface coverage was not much greater than a monolayer, t h i s excess could, on the other hand, arise from the experimental error of the surface area measurement. If the surface area i s assumed to be correct, then the most s a t i s f a c t o r y alternative i s to describe the experimental r e s u l t s i n terms of the. p o s i t i o n of the Fermi l e v e l . When a semiconductor i s i n thermal equilibrium, the Fermi energy l e v e l assumes a certain value. Upon il l u m i n a t i o n , the quasi-Fermi l e v e l s for electron and holes 68 depend on the amount of photon energy supplied to the system. The higher the l i g h t i n t e n s i t y , the greater the, p r o b a b i l i t y of finding an electron in a surface trap and a l o c a l i z e d hole i n the depletion.: layer. This condition favours the chemisorption of xanthate anions. Since the charge density extends into the substrate, adsorption values s l i g h t l y larger than a monolayer can be accommodated. While t h i s explanation may not o f f e r an exact description of the system, these considerations, l i k e many others, are in a d i r e c t i o n to f i l l a deficiency i n the understanding of the chemisorption process. When higher-than-the-energy-gap values of radiant energy are used i n the t e s t s , less d i f f i c u l t i e s are encounter ed in. the interpretation of the r e s u l t s . In the case of galena, increasing energies always increase the amounts of xanthate adsorbed. This constant trend i s c l e a r l y i n d i  cated i n F i g . 25. Somewhat l e s s r e g u l a r i t y i s displayed by the argentiferous galena in F i g . 26. In t h i s graph, the adsorption values for the darkness and the one obtained with 0.5 eV are superimposed suggesting a minimum adsorption for the s o l i d i n question. A sudden increase i n the amount adsorbed i s displayed when 3.4 eV are used. In t h i s case two e f f e c t s must be taken into consideration: the o r i g i n a l d i s t r i b u t i o n of electrons i n the substrate and the high j energy value of i l l u m i n a t i o n . Since the (Pb,Ag)S i s pre dominantly an n-type semiconductor, less adsorption of 40 30 o o r-i X 6 o ID <D •H O e P - TYPE 20 Light conditions: 3.6 - 3.3 eV 2.9 - 2.6 eV — 0.8 - 0.5 eV Darkness o II 8 7 6 Monolayer ± J L L l 10 Fig. 25 - 20 30 40 50 60 80 100 200 300 400 500 TIME - minutes .-5. Adsorption EtX from a solution of KEtX (9xl0~ M) on PbS (100/150 mesh) at 20°C and natural pH under controlled illumination; 20g. U3 10 N - TYPE Light conditions 3.6 - 3.3 eV J 2.9 - 2.6 eV 0.8 - O.tS.eV and darkness i J L X X 10 20 30 40 50 60 80 100 TIME - minutes 200 300 400, 500 ,-5, Fig. 26 - Adsorption of EtX from a solution of KEtX (5xl0~ M) on argentiferous galena (100/150 mesh) at 20°C and natural pH under controlled i l l u m i  nation; 20g. 71 xanthate anions i s to be expected, as w i l l be discussed subsequently. The e f f e c t of 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 electron-hole d i s t r i b u t i o n r e s u l t i n g in pre- • f e r e n t i a l adsorption. A comparison between Fig. 2 5 and 2 6 shows a two f o l d difference in the amount of xanthate abstracted by the two samples of galena. This e f f e c t may be attributed to e i t h e r oxidation or to the electrophysical character^ i s t i c s of the o r i g i n a l samples and w i l l be discussed under these headings. 4.3 Ef f e c t of Oxidation on Adsorption The r e s u l t s presented in the previous section suggest that xanthate adsorption may be influenced e i t h e r by the electrophysical 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 surface or by the presence of an oxidation product on the mineral surface. Two sets of experiments were ca r r i e d out in order to d i f f e r e n t i a t e between the two alternatives. The experiments were: (1) oxidation rates of galena surfaces and (2) adsorption of xanthate on unexposed surfaces i n the absence of oxygen. In the f i r s t case the r e l a t i v e rate of oxidation of the two galena samples i s expected to indicate which sample i s the most l i k e l y to form a thicker layer of oxides and, by comparison to the previous adsorption t e s t s , the influence of t h i s layer on the f i x a t i o n of xanthate anions. The test r e s u l t s are summarized i n Tables XIII, XIV and XV (Appendix E). In these tables a column has been added to indicate the amount of oxygen uptake in terms of unit area. In the f i r s t two tables duplicate runs prove that the experimental procedure i s quite reproducible. This can be seen i n the graphical representation of Fi g . 2 7. A comparison between Fig. 27 and Fig. 28 shows the e f f e c t of water vapour on the weight increase. Regardless of the atmosphere, the weight gain of the argentiferous galena (n-type) i s approximately double that of the p-type galena at the a r b i t r a r y value of 30 minutes. As described previously i n section 3.7b adsorption of xanthate anions was studied on two samples of galena which were s p e c i a l l y prepared and tested i n an i n e r t atmosphere. These r e s u l t s are presented i n Fi g . 29. In t h i s graph the ranges of the previous adsorption r e s u l t s , when samples and solution were exposed to atmospheric oxygen, are shown as shaded areas. The e f f e c t of oxygen i s quite pronounced i n the case of the argentiferous galena. The increase in adsorption due to oxidation of the n-type galena was approximately one half of the difference in adsorption of p-type compared to n-type galena. This fact correlates quite well with the previous oxidation j experiments since the argentiferous galena i s the one that oxidized more r e a d i l y . 73 .400 360 h x 80 * 40 r 30 60 90 120 150 TIME - minutes J Fig.. 2 7 - O x i d a t i o n r a t e o f galena i n oxygen i n the presence o f water vapour. F i g . 28 - O x i d a t i o n r a t e s o f galena i n a dry atmosphere o f oxygen. o r-t O rH X e o 10 | "v. w 8 CD r-i O e 6 [ < . o 1 o° 3 f - 1 » 2 I - p - TYPE PbS -cr 5 6 F i g . 29 - 30 40 50 eu 100 200 300 40 TIME - minutes length (.340-.380 microns, 3.6-3.3 eV). ' " a t u r a l p H a n d constant wave- tn 76 4.4 Effect of Surface Characteristics on Adsorption Apart from the e f f e c t s of oxidation and i l l u m i  nation there i s s t i l l a basic difference i n the adsorption behaviour between the p-type and n-type samples. This behaviour can be analysed i n terms of the electrophysical c h a r a c t e r i s t i c s of the s o l i d s . Since the uptake of an adsorbate i s accelerated by the presence of free quantum states (holes), a p-type s o l i d i s expected to favour the chemisorption of xanthate. The reverse i s true for a s o l i d of the n-type. F i g . 2 9 shows that the order of magnitude of t h i s e f f e c t i s larger than that of eith e r illumination or oxidation. In terms of surface coverage, the amount of xanthate adsorbed in the f i r s t 10 minutes by the p-type galena reaches that of a monolayer whereas i n the case of the n-type s o l i d , the cover age i s approximately one half of the monolayer value. To summarize, the combination of the rate of oxidation and the presence of oxidation products on the adsorption of xanthate anions leads to some interesting conclusions. Since (Pb,Ag)S oxidizes more ra p i d l y than PbS, the former should have changed to a p-type semi- (24) conductor i n a r e l a t i v e l y short period . That t h i s t r a n s i t i o n did not take place i s evidenced by the Seebeck E f f e c t (n-type), discussed subsequently in section 4.7, and by the lower a f f i n i t y of (Pb,Ag)S for EtX~ than that d i s -77 played by PbS (p-type) in the adsorption experiments. Without refuting the effects of oxygen on adsorption, the present results strongly suggest that the original n-type or p-type character of the solids i s the more important factor. 4.5 Effect of Illumination Intensity on Adsorption The dependence of the adsorption on the intensity of light of a constant wavelength in the system xanthate- activated marmatite was investigated and results are shown in Fig. 30. The system is characterized by a strong photo- adsorption effect which depends on the intensity of the light. When the maximum intensity was irradiated on the sample, the amount of xanthate adsorbed in the f i r s t 10 minutes was twice the amount adsorbed by the sample kept in total darkness. These points as well as those for intermediate intensities are presented in Fig. 31. In these figures the light intensity was calculated using the mean emf of a calibrated thermopile* and the reading of a high-impedance microvoltmeter (Fluke, Model 845-AB). A l l measurements refer to the light values after f i l t e r i n g as present at the outside walls of the adsorption chamber. * Eppley Thermopile Serial No. 8 824, The Eppley Laboratory Inc., Newport, R.I. 3 ( Monolayer coverage at 5.7 moles/cm2 x 10^ ) Intensity of illumination: « 275 vi watts/cm2 •O 180 y watts/cm2 © 80 y watts/cm2 •O 0 y watts/cm2 J I I I 10 20 30 40 50 60 80 100 TIME - minutes 200 300 400 500 Fig. 30 - Adsorption of EtX" on activated (Zn,Fe)S (150/200 mesh) at 20°C and natural pH using various intensities of illumination at a constant wavelength (.340-. 380 microns) from a 400 W/QI lamp; lOg. oo 1.0 0.8 o I i : i i i i i i l 0 50 100 150 200 250 300 350 400 INTENSITY OF LIGHT - microwatts/cm 2 Fag. 31 - V a r i a t i o n on the amount o f xanthate adsorbed as a f u n c t i o n o f l i g h t ^ i n t e n s i t y f o r a c o n s t a n t energy (3.6-3.3eV) at 10 minutes. 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 ico n due tor Thermoelectric Power WV/°C Fermi Level (E C-E F) eV 0 P 34 0.97 80 P 21 0.58 180 : P 24 0.67 275 P 26 0.73 81 The electrophysical c h a r a c t e r i s t i c s of p e l l e t i z e d samples of activated marmatite a f t e r exposure to illumination and adsorption were determined as described previously. These are summarized i n Table VI. A sample c a l c u l a t i o n of the Fermi energy l e v e l from thermoelectric power measure ments i s presented in Appendix F. In a l l cases, the Fermi energy l e v e l was raised a f t e r adsorption of the donor adsorbate (EtX~). 4.6 Copper Activation Copper activation of marmatite i s normally re quired f o r f l o t a t i o n . The e f f e c t of i n i t i a l copper ion concentration on the ac t i v a t i o n of marmatite and subsequent adsorption of xanthate ions was investigated using a constant illumination. The r e s u l t s are shown in Fig . 32. Concentrations of 10" 4 and 10~3M/1 of copper sulphate had a d e f i n i t e e f f e c t on the adsorption of xanthate whereas a concentration of 10~^M/1 showed but l i t t l e improvement over the non-activated marmatite. At the higher concentra tions of copper sulphate the rate of xanthate adsorption was of the same order of magnitude as in the previous t e s t s . At the low concentration, xanthate adsorption appeared to reach equilibrium at a low surface coverage. Coverages by copper atoms were determined from the differences between the i n i t i a l and f i n a l concentration of copper i n solution 82 i n the act i v a t i o n step, assuming the parking area of the 9 ( 2 8 ) copper atom to be 10.4 kl . A l l concentrations were measured by an EEL Atomic Absorption Spectrophotometer. The r e s u l t s of Table VII together with Fig. 32 indicate that a concentration of 14% or more of the monolayer value promotes adsorption of xanthate, whereas a coverage of 2% i s i n s u f f i c i e n t . Stoichiometrically, the value of 14% i s i n excellent agreement with the calculated coverage by xanthate (13%) a f t e r the f i r s t 10 minutes, a common retention time used by f l o t a t i o n plants. The e f f e c t s of washing, non-washing and washing followed or not by drying on the adsorption of xanthate on copper activated marmatite are shown i n Fig. 33. Identical results were obtained with or without drying of the washed marmatite p r i o r to adsorption of xanthate. When the sample was not washed more xanthate was adsorbed. In t h i s case the high xanthate abstraction was due to the p r e c i p i t a t i o n of cuprous ethyl xanthate. In the absence of washing extra copper was present In the system as an aqueous f i l m around each mineral p a r t i c l e . Table VIII summarizes the electrophysical character i s t i c s of the powders p r i o r to and a f t e r xanthate adsorption. If the re s u l t s are grouped i n pairs the co r r e l a t i o n of Table VIII with F i g . 32 i s quite evident. Following a c t i  vation i n low copper concentrations the resistance stays 50 60 80 100 TIME - minutes 200 300 400 500 Fig. 32 - 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 o f KEtX (5xlO~ 5M) on (Zn,Fe)S (65/100 mesh) at 20°C and natural pH, illuminated with l i g h t of 3.6-3.3 eV;10g. oo to TIME - minutes Fig. 33 - The e f f e c t of washing the marmatite a f t e r copper activation, lOg of (Zn,Fe)S (65/100 mesh) with 100 ml of a 0. 996xlO _ 3M solution of CuS0i|.5Ho0 on the sub sequent adsorption of EtX" at 20°C and natural pH, illuminated with l i g h t of 3.6-3.3 eV. 85 TABLE VII - ADSORPTION OF COPPER ON MARMATITE (65/100 MESH) I n i t i a l Concentration of Copper xlO- 5 M/1 Fina l Concentrat ion of Copper x l 0 ~ 5 M/1 Adsorbed Copper xlO-'M/l Calculated Surface Coverage % 0 0 0 0 0.996 traces 0.9 2 9.96 3. 95 6.0 14 99.6 55. 9 43.7 105 TABLE VIII CHANGES IN THE ELECTROPHYSICAL CHARACTERISTICS OF (Zn,Fe)S ON ADDITION OF VARIOUS C u + + CONCENTRATIONS I n i t i a l Copper Concentrat ion- M/l P r i o r EtX~ Adsorption After EtX" Adsorption Type of Semic. u V/°C P. cm Type of Semic. Vi V/°C P. cm 0 P 174 2x l 0 8 P 155 2x10 8 0.996xl0" 5 . P 155 4x l 0 8 P 139 2xl0 8 0.996xl0 - 4 P 65 4xl0 6 P . 66 4xl0 7 0.996xl0 - 3 P 14 l x l O 6 P 46 2xl0 7 86 approximately the same before and a f t e r adsorption (Table VIII). This e f f e c t i s p a r a l l e l e d by low adsorption rates of xanthate i n F i g . 32. Following a c t i v a t i o n in high copper concentrations the resistance of the powders before adsorption i s less than in the previous case and increases s l i g h t l y a f t e r adsorption (Table VIII). This trend i s again c l e a r l y indicated in F i g . 32 by the higher ad sorption rate and t o t a l adsorption of t h i s p a i r . 4.7 Electrophysical Measurements In the previous two sections some pertinent electrophysical measurements were introduced. In t h i s section, some basic electrophysical c h a r a c t e r i s t i c s of as-received s o l i d and powder specimens are presented. These include a study of c a r r i e r type and concentration, from both the Hall 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 on s o l i d specimens by measuring the Hall voltage. A detailed c a l c u l a t i o n of one of the measurements i s shown in Appendix G. In the case of galena r e l i a b l e r e s u l t s were obtained with pressure contacts, solder contacts y i e l d i n g similar r e s u l t s . Since no measurement could be made on the ground marmatite from Broken H i l l , a s o l i d sample of B r i t i s h Columbia sphalerite was prepared as a possible a l t e r n a t i v e . Because of i t s high resistance, measurements with e i t h e r 87 TABLE IX - ELECTROPHYSICAL CHARACTERISTICS OF SOLID SPECIMENS Sample Semic. Type R e s i s t i v i t y J2 cm' Hal l Coeff. cm 3/coul Carriers Concen|r*n cm" Mobility cm2/ /v o l t cm PbS P 0.4 280 2.2xl0 1 6 700 (Pb,Ag)S n 1.3xl0""7 0. 013 6x10 1 7 10 5 TABLE X - SEEBECK EFFECT ON SOLID AND POWDER SPECIMENS Sample Semiconductor Type Q Mil l i v o l t s / d e g r e e R e s i s t i v i t y ft cm PbS powder s o l i d (Zn,Fe)S act .powd non act.powd (Pb,Ag)S powder s o l i d P P er p er p n n 0.0018 0.0012 0.0028 0.0012 0.0031 0.0026 56 2 0 1x101 2x10° 5xl0 " c 2x10 8 8 pressure or indium solder contacts were not successful. No further work was warranted on 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 obtained on both s o l i d and powder specimens. A sample c a l c u l a t i o n of the c a r r i e r concentration i s presented in Appendix H. The 18 3 value obtained, 5.1x10 holes/cm , i s not in agreement with the value previously calculated from the Hall voltage, 2.2x10-'-^ , as i s commonly found when using thermoelectric power data. Similar discrepancy has been attributed to an i n t e r a c t i o n between the anisotropic l a t t i c e vibrations, due to the thermal gradient, and the mobile charge c a r r i e r s ^ 5 0 The c a r r i e r s are p r e f e r e n t i a l l y scattered toward the cold end of the sample by the non-equilibrium 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 . Furthermore, i n Appendix H the e f f e c t i v e mass of the electron has not been measured i n the galena specimens and has been assumed to be 0.3 the mass of the electron, a value previously used by S l a t e r ^ 5 l \ Because of these uncertainties, the a p p l i c a t i o n of the Seebeck e f f e c t has been confined to the d i f f e r e n t i a t i o n of n-type and p-type specimens. 4.8 Correlation of Adsorption Results The i n d i v i d u a l behaviour of galena and marmatite has been characterized by adsorption and electrophysical measurements under various conditions of i l l u m i n a t i o n . To 89 be able to compare the adsorption effects with each other, a common base had to be selected. The most l o g i c a l choice was that of percentage surface area coverage. Then the surface covered by the surfactant could be used to represent the tendency for the adsorption to take place. This ten dency has been expressed as percent of monolayer coverage. Table XI i s a compendium of surface coverages for the various systems investigated. The main trends are quite apparent. Namely, the p-type galena adsorbs a mono layer of xanthate i n the f i r s t 10 minutes whilst the n-type galena adsorbs only one half of i t s monolayer value. More over, the amount of xanthate adsorbed by the two galenas d i f f e r s l a r g e l y from the amount of xanthate abstracted by the marmatite. The l a t t e r shows an adsorption that never exceeds an equivalent coverage of 23% under the most favour able conditions. These trends strongly indicate that the e l e c t r o  physical c h a r a c t e r i s t i c s of the substrate are of paramount importance i n adsorption. Since the adsorption of xanthate i s a p-type reaction i t i s accelerated by free quantum states and the p-type galena i s expected to adsorb a mono layer of xanthate in 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  ference i n the adsorption c h a r a c t e r i s t i c s can be attributed to the difference i n the energy gaps. If the tests with 0.6 are chosen i n each case, the r a t i o between the t h e o r e t i c a l 90 TABLE XI - ADSORPTION RESULTS IN TERMS OF XANTHATE COVERAGE Monolayer Coverage-% conditions tor Material Adsorption at 10 miri. at equilibrium (Zn,Fe)S Hg lamp 23 31 u Darkness 14 30 ti 3 . 6 - 3 . 3 eV 22 30 ti 2 . 9 - 2 . 6 eV 17 26 it 0 . 8 - 0 . 5 eV 12 24 it 7000 lumens 15 26 II 56 00 lumens 14 22 II 2450 lumens 11 21 II Darkness 7 20 ti Cu + + - 1 0- 5M / 1 19 37 ti Cu + + - 1 0- 4M / 1 13 35 n Cu + +-10- 3M /1 11 18 ti Cu - 0 M/1 12 13 PbS 400 W-QI 115 180 tt 5 00 W-QI 115 200 tt 3 . 6 - 3 . 3 eV 115 190 tt 2 . 9 - 2 . 6 eV 105 175 ti 0 . 8 - 0 . 5 eV 95 165 II Darkness 90 150 PbS Unox-3.4 eV 88 110 (Pb,Ag)S Unox -3 .4 eV 35 50 (Pb,Ag)S 3 . 6 - 3 . 3 eV 62 120 n 2 . 9 - 2 . 6 eV 53 72 II 0 . 8 - 0 . 5 eV 44 63 ti Darkness 44 63 91 values of the energy gaps i s in good agreement with the r a t i o of t h e i r surface coverages at the ten minute value and at equilibrium. Namely, the t h e o r e t i c a l energy gap r a t i o of 10 compares favourably with the r a t i o s of 8 and 7 for the experimental coverages. The test with 0.6 eV has been chosen because with t h i s energy the traps are emptied and the marmatite more c l o s e l y resembles the i n t r i n s i c semiconductor. Under these conditions i t was acceptable to use as the t h e o r e t i c a l energy gap value the published figure for sphalerite. The same trend towards Increased adsorption i s observed when the unoxidized forms of galena are compared with the oxidized. The unoxidized p-type galena adsorbs 88% of a monolayer in the f i r s t 10 minutes instead of a f u l l monolayer. The unoxidized n-type galena adsorbs approxi mately 1/4 of a monolayer rather than one half of a mono layer during the same period of time. Thus a 5 0% difference between the adsorption behaviour of the two forms of galena i s s t i l l apparent whether or not they are oxidized. When the i n d i v i d u a l marmatite systems are taken into consideration, i t i s noted that i n the f i r s t ten minutes the amount of xanthate adsorption increases as the illumination energy, l i g h t i n t e n s i t y or copper concentration increases. At the equilibrium conditions, a s i m i l a r i n  crease i s observed but to a le s s e r extent in the case of photoexcitation. In the case of copper a c t i v a t i o n at 92 equilibrium conditions a greater adsorption of xanthate was observed. The effect of illumination on each variety of galena was to increase adsorption. However during the f i r s t 10 minutes, the amount of xanthate adsorbed by PbS was enhanced by 25% whilst the increase i n adsorption displayed by the (Pb,Ag)S was only 18%. Thus the o r i g i n a l electrophysical character i s t i c s of the substrate are more s i g n i f i c a n t than the effects of illumination on the adsorption of xanthate. 4.9 Flotation Experiments The differences in the adsorption rates of xanthate anions on galena and marmatite suggest the p o s s i b i l i t y of u t i l i z i n g controlled i l l u m i n a t i o n in the p r a c t i c a l separa t i o n of the two minerals. The actual application has been investigated using a semi-micro f l o t a t i o n technique describ ed i n section 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 of p a r t i c l e to bubble attachment to both minerals by using the same number of p a r t i c l e s i n a l l tests (Appendix I ) . As soon as the f i r s t series of te s t s had been completed (Appendix J ) , i t became apparent that i t was extremely d i f f i c u l t to detect s i g n i f i c a n t differences between tests of varying l i g h t energies since comparable high- recoveries were obtained i n a l l t e s t s . To circumvent thi s d i f f i c u l t y , starvation quantities of surfactant were calculated as follows. Since only 10% of the surface of marmatite i s covered by xanthate (present work) i t i s not necessary to have more than t h i s equivalent amount in solution. In the case of galena 20 to 40% coverage i s required f o r f l o t a t i o n ^ 3 0 ' . Using 150 ml of solution and 2g of 150/200 mesh marmatite (5,200 cm 2/g), 0.04 mg/1 are required for a surface coverage of 9%. In the case of PbS, again using 150 ml of solution and 2g of 100/150 mesh 2 fr a c t i o n (1,850 cm /g), 0.08 mg/1 are required f o r a surface coverage of 32%. The fact that two di f f e r e n t reagent con centrations were required, necessitated an i n d i v i d u a l treatment of the minerals. A summary of the f l o t a t i o n r e s u l t s i s presented i n Table XII. The data indicate that the f l o t a t i o n of galena 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 daylight or l i g h t of 2.5 microns wavelength was used in the experi ments. A d e f i n i t e trend towards lower recoveries was present when marmatite was investigated under equivalent test conditions. The recovery of marmatite decreased by 11% when i r r a d i a t e d with l i g h t of 2.5 microns wavelength compared with that in daylight. The trend of the previous adsorption experiments was thus confirmed even though a p r a c t i c a l separation of the mixed minerals would be extre mely d i f f i c u l t to achieve since 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 DISTRIBUTION (A r i t h . Ave. of 5 tests) Standard Deviation Confidence Limit (68.27% l e v e l ) % Sample Light KEtX mg/1 Ethanol mg/1 Float T a i l s 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 tions of xanthate were required. Furthermore, inconclusive res u l t s were obtained with marmatite when tests conducted in daylight were compared with tests where a 150 watt l i g h t bulb was used. Similar recoveries suggest that the o p t i c a l excitation was of the same order of magnitude in both cases. CHAPTER 5 DISCUSSION OF RESULTS 5.1 Adsorption In the present study two d i s t i n c t adsorption stages can be i d e n t i f i e d : (a) a rate dependent stage that extends from 1 to approximately 100 minutes and, (b) a stage above the 100 minutes where the rate i s greatly d i  minished. Another region where adsorption takes place i n less than 1 minute has been previously described by other i n v e s t i g a t o r s ^ 3 ^ . No investigation of the k i n e t i c s below one minute could be made because of the inherent l i m i t a t i o n s of the equipment used nevertheless, a short discussion must be included since the mode of adsorption i n thi s region constitutes the basis for subsequent adsorption. The k i n e t i c s of adsorption below the one minute l e v e l vary depending on monolayer or multilayer coverages^ 3^' The supporting data indicate that the rate of c o l l e c t o r ad sorption depends on the concentration of reagent i n solution. These results 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 with multilayer adsorption. Presumably these coverages r e f e r to the hypothetical orderly arrangement of the sur factant on the mineral surface. This i s of paramount importance because the main i n d i c a t i o n of multilayer ad sorption comes from the c a l c u l a t i o n of the amount adsorbed on the unit area of the mineral surface. Calculations of multilayer coverages are not correct because of the non uniform d i s t r i b u t i o n of reagents on the mineral surface, the difference between the uniform and non-uniform d i s t r i  bution accounting for the multilayer coverage. Thus ad sorption at low concentrations and within the f i r s t sixty seconds may 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 at the active s i t e s with random orientation of non-polar r a d i c a l s . In the present experi ments multilayer adsorption should not have occurred with the low concentration of xanthate used f o r the adsorption (=15 mg/1). These predictions were confirmed by the experi ments where the calculated monolayer values appeared only around the two hour l i m i t . In the l-to-100-minute region the rate of ad sorption was found to vary according to the s p e c i f i c experi mental conditions. A study of these variations was the main objective of t h i s investigation since enhanced or reduced adsorption resulted on changing the electron-hole d i s t r i b u t i o n of the substrate with i l l u m i n a t i o n . When more active s i t e s were induced i n the substrate more xanthate could be adsorbed by the increased e l e c t r o s t a t i c a t t r a c t i o n 98 At t h i s stage the molecules have a strong tendency to orient themselves on the mineral surface forming the equivalent of a two dimensional " l i q u i d f i l m " . Two e f f e c t s are apparent: (1) increased adsorption due to an increase i n the number of surface s i t e s and/or an increase 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 holes l o c a l i z e d at the active s i t e s , and (2) adsorption f a c i l i t a t e d by the association between hydrocarbon chains. Furthermore, multilayer formation i n t h i s region may be accompanied by a physical adsorption of metal xanthate molecules and dixanthogen molecules previously formed i n the e l e c t r i c a l double layer surround ing the mineral p a r t i c l e s . In t h i s case extensive ad sorption of neutral molecules would occur through i n t e r a c t i o n of hydrocarbon chains but without e l e c t r o s t a t i c repulsion since the polar heads are uncharged. In the region above 100 minutes the r e s u l t s indicate that the adsorption rate i s n e g l i g i b l e . Because chemisorption i s responsible for the main adsorption of xanthate on galena, only physical adsorption may be operative i n t h i s region. When chemisorption occurs, i t i s usual f o r the surfactant to react completely unless the s o l i d surface becomes saturated. It i s d i f f i c u l t to understand why t h i s does not occur i n the xanthate-galena system. It could be postulated that the reaction i s very slow at a p a r t i c u l a r concentration of xanthate but speeds up at higher concentration 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 roduc t s . A l t e r n a t i v e l y the r e a c t i o n cou ld be due to the presence o f a very low con c e n t r a t i o n o f another r eac tan t which becomes exhausted o r d i f f u s e s s lowly through a cont inuous f i l m o f adsorbed xanthate ( i . e . oxygen i n s o l u t i o n ) . In 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 extremely low a d s o r p t i o n , an e f f e c t which was observed e x p e r i m e n t a l l y . 5.2 Photochemical E f f e c t s The concen t r a t ions o f e l e c t r o n s and holes fo r an i l l u m i n a t e d c r y s t a l vary from those o f a c r y s t a l kept 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 to i n f l uence 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 . Photo- adso rp t ion o r pho todesorp t ion , t h e r e f o r e , may be observed depending on the p o s i t i o n o f the Fermi l e v e l , presence o f i m p u r i t i e s e t c . T h e o r e t i c a l l y , the presence o f an acceptor i m p u r i t y tha t lowers the Fermi l e v e l , o the r c o n d i t i o n s being e q u a l , should r e s u l t i n pho toadsorp t ion . In the case o f ga lena , an e a s i l y o x i d i z e d m i n e r a l , the chemisorbed oxygen present a t the surface may take pa 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 thus r educ ing the va lue 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 the a d s o r p t i o n o f xan tha te . The r e s u l t s o f F i g . 25, 26, 29: con f i rm these p r e d i c t i o n s . Furthermore, o x i d a t i o n o f the n- type galena inc reased the adsorp t ion o f xanthate by 50% ( F i g . 29) i n contrast with the lower adsorption of the p-type galena which was less r e a d i l y oxidized. In the case of marmatite a photon energy of 0.6 eV i s capable of causing a captured electron 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 create an electron-hole p a i r . A depletion of electrons and holes results i n a lowering of the amount of reagent adsorbed, an e f f e c t which i s readily observed i n Fig. 24. Furthermore the energy capable of causing these recombina tions i s of the same order of magnitude as the Lambe and 17 Klick stimulation band [quoted as 2.6 microns (0.5 eV) ] as previously indicated i n Fig. 3b. An al t e r n a t i v e ex planation of 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 pro- posed by Bubes and presented i n F i g . 2. The p r a c t i c a l r e s u l t was an 11% reduction i n the f l o t a t i o n recovery (Table XII), a r e s u l t which was p a r a l l e l e d by P l a k s i n ^ in the f l o t a t i o n of zircon and pyrochlore; on i r r a d i a t i o n , the f l o t a t i o n of pyrochlore was reduced by 4 0%. In terms of photochemical e f f e c t s , the r e s u l t s of the present study indicate that: (1) photoadsorption i s the result of illuminating a semiconductor with energy higher-than-the-energy-gap whilst (2) photodesorption i s the r e s u l t of i l l u m i n a t i n g the semiconductor with energy lower-than-the-energy-gap. 101 5.3 Carrier Behaviour Measurements of the Hall c o e f f i c i e n t could only be carried out on galena specimens, the high resistance of the marmatite being outside the working l i m i t s of the available equipment. These measurements and l i m i t a t i o n s (5 2) (53) are i n accord with the r e s u l t s of Putley and Saito . The work of t h i s l a s t investigator i s of p a r t i c u l a r interest because his r e s u l t s indicate that the t r a n s i t i o n from n-type to p-type may be followed through a change i n resistance, a r e l a t i v e l y simple measurement to carry out. (6) Increased resistance has been emphasized also by Mark The tendency f o r the resistance of activated marmatite to increase af t e r adsorption i s evident from Table VIII. The Seebeck e f f e c t has been used successfully i n measuring the n-type or p-type character of the pressed powders. The most important application i s presented i n F i g . 29 where the amount of xanthate anion adsorbed i s d r a s t i c a l l y reduced i n the case of the n-type semi conductors. Without the p o s s i b i l i t y of measuring the electronic character of the powders, i t would have been impossible to interpret the experimental r e s u l t s . The p o s i t i o n of the Fermi l e v e l within a c r y s t a l and the degree of curvature of the energy bands e s t a b l i s h the e l e c t r i c a l conductivity of a semiconductor. The closer the Fermi l e v e l i s to the conduction band, the larger i s the value of the electron density and the more pronounced are the n-type c h a r a c t e r i s t i c s of the semiconductor. Thus semiconductors are c l a s s i f i e d as n-type or p-type when the hole component or elec t r o n i c component respectively i s ne g l i g i b l e . The concentration of free charge c a r r i e r s that take part i n the reaction must be responsible f o r the reaction rate. A p-type reaction (donor) i s one which i s accelerated by free quantum states and an n-type reaction (acceptor) i s one which i s accelerated by electrons. Since the measurements of the Hall c o e f f i c i e n t and the Seebeck ef f e c t indicate that the galena i s a p-type semiconductor, the increase i n e l e c t r i c a l conductivity when the s o l i d i s illuminated and a p a r a l l e l increase in adsorption rate suggest that the reaction i s of the p-type. This i s in agreement with the structure of the negative xanthate anion that requires a free quantum state or hole, and with the mechanism of photoconductivity o r i g i n a l l y described by S l a t e r ^ ^ . This author recognizes n and p-type regions in the galena structure and the ex c i t a t i o n of an electron to the conduction band when l i g h t i s absorbed anywhere i n the c r y s t a l , leaving a hole i n the valence band. The electron so introduced into the conduction band w i l l now tend to f a l l to the lowest possible energy, or into an n-type region, and a hole w i l l in a sim i l a r way f i n d i t s way into a p-type region. The presence of extra electrons in the n-type region, extra holes i n the p-type region, w i l l 103 neutralize some of the potential barriers. Thus the barriers will be lowered and, in agreement with Plaksin (7) et al , the xanthate adsorption w i l l be enhanced. This fact has been demonstrated repeatedly in the present work with the effect of illumination on adsorption, an effect that provides a good correlation between photoconductivity and adsorption. 5.4 Impurities and Reaction Mechanism In this section emphasis i s placed on the a c t i  vation of marmatite, namely the role of copper in 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 substitutional foreign atoms), depending on the type and concentration, displaces the Fermi level causing either an acceleration or a retardation of the adsorption reaction. Impurities, therefore, can be of two types: acceptors or donors. Acceptor impurities always lower the Fermi level, while donor impurities raise i t . In terms of n-type and p-type reactions, an acceptor reaction then will 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. Thus a given impurity may act as a promoter f o r one reaction and as a poison for another. It has been shown in the present study that marmatite a c t i v a t i o n by copper ions r e s u l t s i n enhanced adsorption, that i s , the adsorption reaction i s promoted by copper. This may be caused by an increase in concentration of free quantum states (or holes), a fact which indicates that t h i s p a r t i c u l a r type of impurity imparts acceptor properties to the mineral surface. This conclusion i s i n agreement with the proposed energy l e v e l diagram of Bube (Fig. 2) and with P l a k s i n ^ ' who o f f e r s an additional explanation for the a c t i v a t i n g e f f e c t of copper ions by describing a removal of electrons from the surface layer as the copper ions d i f f u s e into the l a t t i c e . Impurity concentration i s another important parameter that regulates the position of the Fermi l e v e l . For an n-type semiconductor as the acceptor impurity concentration increases, the n character i s diminished u n t i l i t i s changed to a p-type, increasing thereafter. For a donor reaction (p-type) the net r e s u l t i s a continuous increase i n the reaction rate. Thus, again, the p o s i t i o n of the Fermi l e v e l uniquely describes the poisoning or promoting c h a r a c t e r i s t i c s of a semiconductor on an ad sorption reaction, the type of impurity being the cause of the s h i f t of the Fermi l e v e l . Fig. 32 and Table VIII show how the adsorption of xanthate i s affected by d i f f e r e n t l e v e l s o f copper a c t i v a t i o n , as w e l l as the minimum copper c o n c e n t r a t i o n f o r a c t i v a t i o n o f xanthate a d s o r p t i o n . T h i s i m p l i e s that i n a f l o t a t i o n system i t i s p o s s i b l e t o . r e g u  l a t e not o n l y the r e a c t i o n r a t e ( a c t i v i t y ) but a l s o the s e l e c t i v i t y o f the f l o a t by c o n t r o l l i n g the c o n c e n t r a t i o n o f e f f e c t i v e i m p u r i t i e s . CHAPTER 6 S U M M A R Y AND CONCLUSIONS The basic purpose of this investigation was to study the effect of illumination on the adsorption of xanthate on galena and marmatite and to present experi mental evidence on the role of the electronic character of solids in flotation. The experimental results indicate that: 1. Absorption of 0.6 eV photons by copper- activated marmatite causes a decrease in the amount of xanthate adsorbed as well as a de crease in the adsorption rate. These effects can be explained by the excitation of electrons from traps to the conduction band and sub sequent 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 illumination, the 107 l i g h t i n t e n s i t y from darkness to 275 microwatts per cm i s to double the adsorption of xanthate on the activated marmatite. 4. Under conditions of constant energy of 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 galena i s three times the amount adsorbed on the n-type, suggesting that the adsorption reaction may depend on the tr a n s f e r of an electron from the xanthate anion to the substrate. The re s u l t s of t r e a t i n g the p a r t i c u l a r marmatite with various copper solutions of concentrations incremented by a fac t o r of 10 indicate that solutions of 10~4M produce a pronounced Increase i n both adsorption rate and amount of xanthate adsorbed as compared TO the. act i v a t i o n with a 10""°M copper s o l u t i o n . F l o t a t i o n tests using starvation quantities of xanthate indicate that lower recoveries may be expected when marmatite i s i r r a d i a t e d with l i g h t of 0.6 eV compared with those i n daylight. On the basis of the res u l t s discussed above i t i s suggested that the e l e c t r o n i c d i s t r i b u t i o n in the substrate plays a v i t a l role i n surface reactions. I t i s postulated that the p o s i t i o n of the Fermi l e v e l may control the adsorption rate and that t h i s could be modified 108 by a j u d i c i o u s c o n t r o l o f the i m p u r i t y c o n c e n t r a t i o n . The a p p l i c a t i o n o f photo-induced a d s o r p t i o n to a f l o t a t i o n system may be warranted when h i g h r e c o v e r i e s are r e  q u i r e d o r when s e l e c t i v i t y i s the main o b j e c t i v e o f the o p e r a t i o n . 109 SUGGESTIONS FOR FURTHER WORK An investigation of the surface charge and the function of donor and acceptor p a r t i c l e s would be of i n t e r e s t . Experimentally, two e f f e c t s could be ob served: (1) a change i n the work function; (2) a change in the e l e c t r i c a l conductivity. Another aspect that could be further i n v e s t i g a t  ed i s the e f f e c t of q u a l i t y and quantity of added impuri t i e s on the a c t i v i t y and s e l e c t i v i t y of a f l o t a t i o n process. Depending on the type of semiconductor, the concentration of an impurity can control the reaction either by adding or removing excess quantities of electrons ( s e l e c t i v i t y ) . REFERENCES 1. Plaksin, I.M., Shafeev, R.S., Chanturia, V.A., S3, VIII Int. Min. Proc. Cong., Leningrad (1968). 2. Plaksin, I.M. and Shafeev, R.S., "Flo t a t i o n Properties of Rare Metal Minerals", Primary Sources (1967). 3. Calvert, J.G., P i t t s , J.N., "Photochemistry", John Wiley S Sons, Inc. (1967). 4. McKelvey, J.P., "Solid-State and Semiconductor Physics", Harper and Row (1966). 5. Hannay, N.B., "Semiconductors", Reinhold Publishing Corporation (1960). 6. Mark, P., "Surfaces and Interfaces I", Syracuse University Press, Burke J . et a l Editors (1967). 7. Plaksin, I.N., Shafeev, R.S. Celostatni Konf. Rudn. Hornictvi Upravnictvi, Prague 1962, 7-23. 8. Sutherland, K.L. and Wark, I.W., "P r i n c i p l e s of Flotation", Aust. I r . s t . of Min. and Met., Melbourne (1955). 9. Gaudin, A.M., "F l o t a t i o n " , McGraw-Hill Book Co. Inc., New York (1957). 10. Dekker, A.J., "Solid-State Physics", Prentice H a l l , 1962. 11. Kingery, W.D., "Introduction to Ceramics", John Wiley g Sons, Inc., New York (1963). 12. ' Gudden, B. and Pohl, R., Physik Z., 23, p. 417 (1922). 13. Cheroff, G. and K e l l e r , S.P., Phys. Rev., I l l , p. 98 (1958). 14. Low, W., and Weger, M., Phys. Rev., 118, p. 1130 (1960). I l l 15. KcClure, D.S., J. Chem. Phys., 39, p. 2850 (1963). 16. Eeun, J.A., and Goldsmith, G.J., Helv. Phys. Acta., 33, p. 508 (1961). 17. Curie, D., "Luminescence i n Crystals", Methuerr and Co. Ltd., London (1963). 18. Bube, R.K., Phys. Rev., 90, 70 (1953). 19. Gibson, A.F., Proc. Phys. S o c , B 65, p. 378 (1952). 20. Paul, W. and Jones, R.V., Proc. Phys. S o c , B 66, p. 194 (1953). 21. Brebrick, R.F., and Scaulon, W.W., Phys. Rev., 96, p. 598 (1954). 22. Gibson, A.F., Proc. Phys. S o c , B 63, p. 756 (1950). 23. Fleming, P.J., Alberg, M..J. , J. Appl. Phys., 35, 12, p. 3522 (1964). 24. Plaksin, I.N., Shafeev, R.S., I.M.M., p. 715 (1963). 25. Plaksin, I., Trans. AIME, 319 (1959). 26. Poling, G.W., Leja, J . , J. of Phys. Chem., 67, 2121, (1963). 27. Tolun, R., Kitchener, J.A., I.M.M., p. 313 (1964). 28. Yonezawa, T., Trans. Inst. Min. Met., 70, Part 6, p. 329 (1961). 29. Gaudin, A.M., Fuerstenau D.W., Mao, G.W., Min. Eng., p.430, (1959). 30. Klassen, V.I. and Mokrousov, V.A., "An introduction to the Theory of Fl o t a t i o n " , Butterworths, London (1963). 31. Many, A., Goldstein, Y., Grover, N.B., "Semiconductor Surfaces", North-Holland Pub. Co., Amsterdam, 1965. 32. Schon, M., Z. Physik, 119, p. 463 (1942). 33. Klasens, H.A., J. Electrochem. Soc., 100, p. 72 (1953). 34. Lambe, J . J . , Klick, C C , Phys. Rev. 98, p. 909 (1955). 112 35. Prener, J.S., 'Williams, F.E., J. Electrochem. Soc. 103, p. 342 (1956). 36. Shionoya et a l , J. Phys. Soc. Japan, 19, p. 1157 (1964). 37. Strong, J., "Procedures in Experimental Physics", Prentice Hall (1966). 38. Wyszecki, G., S t i l e s , W.S., "Color Science", John Wiley S Sons Inc., New York (19 67). 39. Nelsen, F.M., Eggertsen, F.T., Anal. Chem. 30, No. 8, 1387 (1958). 40. Stone, J.E., Nickerson, L.F., Pulp and Paper Magazine of Canada, T155 (1963). 41. Guarnaschelli, C. and Leja, J . , Separation Science, 1(4), p. 413 (1966). 42. Pomianowski, A. and Leja, J ., Can. J. of Chem., 41, p. 2219 (1963). 43. Majima, H., S c i . Rep. Res. Inst., Tohoku Univ., Ser. A 13, p. 183 (1961). 44. Morrow, J.G., Cleary, M.H., Guarnaschelli, C., C.I.M.M. Trans. 66, 374 (1963). 45. Hallimond, A.F., Mining Magazine, 70, 87 (1944). 46. Fuerstenau, D.W., Metzger, P.G., Seele, G.D., Eng. S Min. J . , 58, No. 3, 93 (1957). 47. P u r c e l l , G., Min. Eng., Vol. 17, No. 11, 68, (1965). 48. Brunauer, S., Emmett, P.H., T e l l e r , E., J. Am. Chem. S o c , 60, 309 (1938 ). 49. Bushell, C.H.G., Krauss, C.J., Brown, G., C.I.M.M. Trans. 64, 177 (1960). 50. Geballe, T.M.,Hull, G.W., Phys. Rev., Vol. 94, No. 5, . 1134 (1954). 51. Slater, J.C., Phys. Rev., Vol. 103, No. 6, p. 1631 (1956). 52. Putley, E.H., "The Hall E f f e c t and Related Phenomena", Butterworths (1960). S a i t o , K.j Gauseki Kobutsu Kosho G a k k a i s h i , 4 6 , p. 148 ( 1 S 6 1 ) . 114 APPENDIX A H a l l C o e f f i c i e n t : Conversion of cgs u n i t s to P r a c t i c a l  U n i t s . The f o l l o w i n g equat ion i s expressed i n cgs u n i t s : v - — nqc t S ince : 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 (1x3x10 ) H 300 n (qx3xlQ9) ( 3 x l 0 1 0 ) 1 -8 IH V = _ i io — nq t 115 APPENDIX B 1.4 0 2 4 6 8 10 12 C o n c e n t r a t i o n - xlO~^M F i g . 34 - Beer's Law f o r potassium e t h y l xanthate u s i n g a 1 cm q u a r t z c e l l . 116 A P P E N D I X C 10 9 o° 2 Monolayer _L 10 20 30 40 50 60 70 80 100 200 300 400 500 TIME - minutes F i g . 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 d a y l i g h t , lOg o f a c t i v a t e d 1000 ml of 10~ 4M KEtX. procedure u s i n g marmatite. Test (Zn,Fe)S (65/100 mesh), 20°C, pH c o n d i t i o n s : = 6.5, 30 - 20 — Monolayer 5 - 4 I I I I ! I I I I I | I I 10 20 30 40 50 60 80 100 200 300 400 500 TIME - minutes F i g . 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 procedure u s i n g galena. Test c o n d i t i o n s : 400 V/ Q I lamp, 20g o f PbS (100/150 mesh), 20°C, 600 ml of 10~ 4M KEtX. 30 - 20 - Monolayer 5 — 41 l ! I l I l I i I 1 | 1 10 20 30 40 50 60 80 100 200 300 400 500 TIME - minutes H F i g . 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 procedure u s i n g galena. Test c o n d i t i o n s : 500 W/QI *° lamp, 20g of PbS (100/150 mesh) 20°C, 600 ml o f 10 _ 4M KEtX. 120 APPENDIX D D e t a i l e d c a l c u l a t i o n o f the BET isotherm f o r marmatite A p l o t o f the e l e c t r o n i c i n t e g r a t i o n areas vs. volumes i n j e c t e d i s shown i n F i g . 38. Using the d e s o r p t i o n areas obtained i n each run, the e q u i v a l e n t volumes adsorbed can be read d i r e c t l y from the graph. For a 5.05 8 5% n i t r o g e n mixture: V l P l T o 31x757.4x273  v = = — o o r , n r n = 2 9ul at STP o T p 295 .1x750 P/P = (0 . 050585x757.4)/(757. 4+198) = 4.01xl0~ 2 o P/V™ (P -P) = 38.3/0.029 ml (955.4-38.3) = 1.44 m 0 For a 15.5 9 8% n i t r o g e n mixture: P P T 43x757.4x273 V = 1 1 0 = = 40 ul a t STP ° T,P 295.2x760 1 o -2 P/P = (0.15598x757.4) (757.4+215) = 12.15x10 o P/V (P -P) = 118/0.040(972.4-118) = 3.45 m o 121 For a 25.3807% n i t r o g e n mixture: V ^ T 43x754 . 8x273 V = L°L = . _ = 44 u l at STP ° T,P 296.5x750 1 o P/P = (0 . 253807x754 . 8)/(754 . 3 + 215) = 19. 7 5 x l 0 ~ 2 o P/V (P -P) = 191/0.044(969.8-191) = 5.57 m o From F i g . 22, the slope i s 25.4 and the i n t e r c e p t i s equal to 0.4 or: 1 C - l 0.4 = and 25.4 = s o l v i n g f o r V^: V m = 0.03 9 ml T o t a l s u r f a c e area o f 0.039mlx6.023.10 " molec/molexl6.2A /molec 0.4600 g 1 0 1 5 A 2/cni 2x22414 .6 ml/mole 2 = 169 0 cm 2 Surface area = 3675 cm /g 122 0 100 200 300 400 500 600 AREA F i g . 38 - E l e c t r o n i c i n t e g r a t o r areas o f volumes o f N2 i n j e c t e d . 12 3 APPENDIX E 124 TABLE XIII OXIDATION RATES OF GALENA (COMINCO) IN THE PRESENCE OF WATER VAPOUR Run No. 1 Run No. 2 TIME min. Wt increase - u g =3.007535g) Amt. Ads. g/cm2x-10l0 Wt increase-ug (WQ=2.999612g) Amt. Ads. g/cm 2xl0 1 0 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 60 115 206 115 209 150 112 201 125 TABLE XIV OXIDATION RATES OF ARGENTIFEROUS GALENA IN THE PRESENCE OF WATER VAPOUR Run No. 1 Run No. 2 TIME min. Wt o increase-ug =2.999466g) Amt. Ads. g/cm2 x10l° Wt (WQ increase-yg = 2 .999148g) Amt. Ads. g/cm2 x10 1 0 0 2 69 181 80 210 9 2 241 93 244 6 100 262 97 255 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 Ag-PbS PbS TIME min. Wt increase-yg (WQ=2.983964g) Amt. Ads. g/cm 2xl0 1 0 Wt increase-ug (W =3.001441g) Amt. Ads. g/ cm2 x10 1 0 0 — — — . — 2 10 25 5 9 4 14 37 9 16 6 16 42 11 20 8 18 47 13 23 10 19 50 15 27 12 . 21 55 16 29 IH 24 63 18 32 16 26 69 20 36 18 27 71 22 40 20 28 74 2 3 . 41 30 35 92 29 52 60 44 116 29 52 90 50 132 28 51 100 52 137 250 64 169 • • ,i 300 65 171' 500 74 195 127 APPENDIX F Sample C a l c u l a t i o n of the Fermi Energy L e v e l from Thermo e l e c t r i c Power • , q QT = ( E C - E F ) + 2kT (co u l ) ( m i l l i v o l t s / d e g r e e ) (degrees))=(E c-Ep)+2kT Changing to e l e c t r o n v o l t s : (Q) ( 1 . 6 x l 0 ~ 1 9 ) ( 1 0 3 ) ( 3 0 0 ) ( 1 0 7 ) 2 ( 1 . 3 8 x l 0 ~ 1 6 ) ( 3 0 0 ) = (E«-E P)+ 1 . 6 x l 0 " 1 2 C F 1 . 6 x l 0 ~ 1 2 c o u l v o l t s degree erg ev _ ^ _ E ^ + ergs degree ev degree c o u l v o l t e rg " C F degree ergs Q 30 = ( E c - E p ) + 0.0517 ev ( E C - E F ) = (Q millivolts/°C) 30-0.052 f o r Q = 0.0 34 m i l l i v o l t s / 0 C ( E C - E F ) = 1.02 - 0.05 (E c-Ep) = 0.97 ev APPENDIX G D e t a i l e d C a l c u l a t i o n o f the H a l l C o e f f i c i e n t , C a r r i e r Dimensions o f the galena specimen: 1 = 1.30 cm a - 0.2 5 cm — t = 0.10 cm Re s i s t a n c e o f the sample measured a t 10 mA: R = 19.54 + 0.01 ohms Rat 19.54x0.25x0.10 R e s i s t i v i t y = p = —^~ = —— = 0.4 o: H a l l R e s i s t a n c e = — = 0.280 + 0.005 ohms Semiconductor type: P (hole c o n d u c t i v i t y ) The H a l l coefficient.R„ i s : . C o n c e n t r a t i o n and M o b i l i t y V = 10 -8 0.28x0.10x10 8 cm 3 R. 8 = 280 H coulomb The number o f p o s i t i v e c a r r i e r s i s : 129 1 1 ]_s h o l e s n = RHq- = '280x1.6x10-19 = 2 * 2 x l ° Therefore the m o b i l i t y y i s : - 1 1 H nq nqp 1 cm ( 2 . 2 x l 0 1 6 ) ( 1 . 6 x l 0 - 1 9 ) (0.4) co.ul ohms cm cm 2 130 . APPENDIX H C a l c u l a t i o n o f C a r r i e r C o n c e n t r a t i o n i n PbS U s i n g Thermo  e l e c t r i c Data From Appendix B: , (E -E v) = ( m i l l i v o l t s / d e g r e e ) 30-0.052 = 0.0030x30-0.052 = 0.038 eV 2TTm*kT 3/2 p = 2 ( . 0 ) exp (E P-E,.)/kT ,'h2 . J: V s i n c e m* = 0.3 m f o r galena: P = % — 2 8 -16 - i 3/ 2 6.28x2.74xl0~ gxl.38x10 erg/degreex300 degree ( 6 . 6 2 x l 0 " 2 7 ) 2 e r g 2 s e c 2 x exp (0.038/0.026) n , n * / 2,3/2 1.H6 p = 2 (0.6x10 g/erg sec ) e 12 2 2 2 3/2 p = 2 (0.6x10 g sec /g cm sec ) ,x 4.3 18 , .3 p =5.1 x 10 holes/cm APPENDIX I C a l c u l a t i o n o f the P r o p o r t i o n a l i t y F a c t o r Required to  C o r r e l a t e the Number o f P a r t i c l e s to t h e i r Weight f o r  Galena and Marmatite I (a) I f screened m a t e r i a l s o f the same mesh s i z e are a v a i l a b l e , t h e i r weight i s : Wt = Vp where V i s the volume and p the d e n s i t y . Using the s u b s c r i p t s g f o r galena and s_ f o r s p h a l e r i t e W t g = V g P g W W s ' but V = V = same volume = same number o f p a r t i c l e s s g wt = wt ££ = wt 111 g 3 Ps S 4.0 Wt = 1.9 Wt g s (b) I f screened m a t e r i a l s with the f o l l o w i n g mesh s i z are a v a i l a b l e : ' PbS: 100/150*mesh (average diameter = 0.125 mm) ZnS: 150/200 mesh (average diameter = 0.088 mm) 132 Assuming c u b i c p a r t i c l e s : Vt = Wt V p /V p g s g H g s K s Wt (0.125) 3x7.5/(0.088) 3x4.0 = 5.3 Wt s 133 APPENDIX J j 134 TABLE XVI - F l o t a t i o n o f Galena (100/150 mesh) i n ' D a y l i g h t Using KEtX and Dowfroth 250. (a) KEtX = 30 mg/1 • Dowfroth 250 = 130 mg/1 Tes t 1 Tes t 2 Recovery Recovery Wt-g % Wt-g % F l o a t 7.49 99.9 7.42 99.3 T a i l s .01 .1 .05 .7 T o t a l 7.50 100 .0 7.47 100 .0 •(b) KEtX = 15 mg/1 Dowfroth 250 = 130 mg/1 Test 1 Test 2 Recovery Recovery Wt-g % Wt-g 0. '0 F l o a t 7.48 99. 8 7.45 99.5 T a i l s .02 .2 .04 .5 T o t a l 7.50 100.0 7.49 100,0 135 TABLE XVII - F l o t a t i o n o f A c t i v a t e d Marmatite (150/200 mesh) i n D a y l i g h t Using KEtX and Dowfroth 25 0 (a) KEtX =30 mg/1 Dowfroth 2 50 = 130 mg/1 Test 1 Test 2 Recovery Recovery Wt-g % Wt-g % F l o a t 3.95 99.1 3. 95 99.2 T a i l s .04 .9 .03 .8 T o t a l 4.00 100.0 3.98 100.0 (b) KEtX = 15 mg/1 Dowfroth 250 = 13 0 mg/1 Test 1 Test 2 Recovery Recovery Wt-g % Wt-g % F l o a t 3. 91 98.2 3.89 98. 7 T a i l s .07 1.8 .05 1.3 T o t a l 3.98 100.0 3. 94 100.0 136 TABLE XVIII - F l o t a t i o n o f A c t i v a t e d Marmatite (150/200 mesh) Using KEtX, Dowfroth 250 and L i g h t of 2.5 Microns (a) KEtX = 15 mg/1 Dowfroth 250 = 130 mg/1 Recovery Wt-g % .Float 3.88 98.1 T a i l s .07 1.9 T o t a l 3.95 100 .0 (b) KEtX = 5 mg/1' Dowfroth 250 = 130 mg/1 Recovery Wt-g % F l o a t 3.89 9 8.2 T a i l s .07 1.8 T o t a l 3.96 100.0 J 137 APPENDIX K} 138 Galena 20g o f 100/150 mesh Temperature: 2 0°C Radiant energy: 360-380 my (500 W) Reagent: KEtX i n 60 0 ml Cone Amt.Ads Corr. u mole moles/cm Time Abs. x l 0 ~ b M x l 0 ~ 6 M Value g x l O " 0 1.54 8.80 -- — — -- 10 0.55 . 3.14 . 56.6 55.1 . 1.65 8.9 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 1 U 7 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 12.1 139 Galena 20g of 100/150 mesh Temperature: 2 0°C Radiant energy: 360- 380 mu (5 00 W) Reagent : KEtX i n 600 ml Time Cone. Abs. x l 0 - 5 M Amt.Ads X10-&M Corr. Value y mole . g moles/ i xlO-1 0. 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 m o A r g e n t i f e r o u s galena lOg o f 100/150 mesh Temperature: 2 0°C Radiant energy: 2-2.5y (50 0 W) Reagent:' KEtX i n 600 ml Cone. Amt.Ads. Corr. y mole moles/cm' Time Abs xlO~ 5M xlO~ 6M Value g x l 0 - 1 Q 0 0. 95 5 .42 -- — __ • __ 10 0. 8 3 4. 74 6 .8 5. 3 0 .32 2.5 20 0.81 4.62 8.0 5.9 0.35 2.8 30 0. 79 . 4. 51 •"• 9.1 . 6. 6 0. 39 3.1 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 3.4 141 A r g e n t i f e r o u s galena lOg o f 100/150 mesh Temperature: 2 0°C Radiant energy : 420-480 my (500 W) Reagent : KEtX i n 600 ml Time Abs. Cone. x l O _ 5 M Amt.Ads. x l 0 _ 6 M Corr. Value y mole g moles, x l 0 ~ 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 4.0 142 A r g e n t i f e r o u s galena lOg o f 100/150 mesh Temperature: 2 0°C Radiant energy: 350-380 my (500 W) Reagent: KEtX i n 60 0 ml Time Abs Cone. x l O - 5 M Amt. Ads. x l O - 5 M Corr. Value u.:.mble g moles/( x l O " 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 14.2 10.6 0. 64 ' 5.1 110 0.65 3.71 . 17.1 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 2 14 3 A r g e n t i f e r o u s galena lOg o f 100/150 mesh Temperature: 20°C Radiant.energy: darkness Reagent: KEtX i n 60 0 ml Time Abs Cone. x l 0 " 5 M Amt.Ads x l O - 6 M Corr. Value u mole g moles/• . x l 0 - i 0 0.93 5.32 — — — . 10 0.81 4.63 6.9 ' 5.4 0. 32 2.5 20 0. 78 4.46 8.6 6.5 0.39 3.1 30 0.77 4.40 9.2 . 6.7 0.40- 3.2 75 0.73 4.18 11.4 7.4 0.44 3.5 145 0. 69 3.95 13.7 7.6 0.45 3.5 300 0.63 3.60 17.2 7.3 0.44 3.5 144 Galena 20g o f 100/150 mesh Temperature: 2 0°C Radiant energy: 360-380 my Reagent: KEtX i n 6 00 ml I n e r t atmosphere: • helium 2 Cone. Amt.Ads y moles moles/cm Volume Time Abs. xlO" 5M xlO~ 5M g x l 0 ~ i O 600 0. 0 1.57 8.95 596 1 1.15 6.57 592 3 1.03 : 5.89 5 88 • • 10 0.97 5.54 584 20 0.91 5.20 580 40 0.87 4. 96 576 60. : 0.84 4.80 572 100 0. 80 .4.57 564 200 0. 74 4.23 560 300 0.72 4.12 2 3.8 0.71 3. 8 30.6 0.90 • 4.9 34.1 1. 00 5.4 37.5 1.10 5.9 39.9 1.15 6.2 41.5 1.19 6.4 43.8 1.24 6.7 47.2 1.32 7.1 48.3 1.35 7.3 145 A r g e n t i f e r o u s Galena. lOg o f 100/150 mesh Temperature: 2 0°C Radiant energy: 360-380 my Reagent: KEtX i n 600 ml In e r t atmosphere: helium 'olume Time Abs. Cone. x l O - 5 M Amt.Ads xlO' 6M u mole g moles/( x l O " 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 lOg o f 65/100 mesh Temperature: 2 0°C Radiant energy: 360.-38 0 my Reagent: KEtX i n 6 00 ml Time Abs. Cone. xlO" 5M Amt .Ads xlO" 6M Corr. Value y mole . g moles/1 x l O - 1 0 0.95 5.42 -- -- — • 10 ' ' 0. 87 4.97 4.5.' 3. 0 0.18 0.69 20 0.86 4.91 5.1 3.0 0.18 0.69 30 .0. 85 4.86. ' 5.6 3.1 0.19 0.73 60 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 ( 0 . 9 96xlO~ aM Cu ) lOg o f 65/100 mesh Temperature: 2 0°C ' Radiant energy: 360-380 mu Reagent: KEtX i n 6 00 ml Time Abs. Cone. xlO" bM Amt. Ads xlO~ bM Corr. Value . u mole g moles/f x l O - 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 Activated Marmatite (0.996x10"4M Cu ) 10 g of 65/100 mesh Temperature: 20°G Radiant energy: 360-3 80 my Reagent: KEtX i n 600 ml Time Abs. Cone. xlO _ i 5M Amt.A ds xlO- 6M Corr. Value y mole . g moles/< xlO- 1 -o 1.14 6.51 — . -- -- — • 10 . 1.05 6.04 4.7 3.2 0.19 . 0.73 20 . 1.03 5.88 6.3 4.2 . 0.25 0.96 30 1.01 5.76 7.5 5.0 0.30 1.15 60 0.96 . 5.48 10.3 6.7 0.40 1.54 100 0.91 5.20 13.1 8.4 0.50 ' .1.92 165 , 0.88 5.0 3 14.8 8.5 . 0.51 1.96 300 0.80 4.57 19.4 8.4 0.50 1.92 149 A c t i v a t e d Marmatite ( 0 . 996xlO""dM Cu ) F i l t e r e d but n e i t h e r d r i e d nor washed lOg o f 65/100 mesh Temperature: 2 0°C Radiant energy: 360-380 my Reagent: KEtX i n 60 0.ml Time Abs. Cone. xlO~ 5M Amt.Ads x l O - 6 M Corr. Value y mole g moles/ x l 0 _ 1 0 0.96 5.52 -- — — — 12 0.78 4.46 10.6 . .9.1 0.55 2.02 20 0.76 "4.34 • 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 . 3.04 150 A c t i v a t e d Marmatite (0 .996xlO~ dM Cu) lOg o f 65/100 mesh Temperature: 20°C Radiant energy: 360-380 mu Reagent: KEtX i n 600 ml Time Abs. Cone. x l 0 - 5 M Amt. Ads x l 0 - 6 M Corr. Value u mole g moles/( x l O - 1 , 0 •0.8 9 5.08 — — — — 10 0.78 4.46 6.2 4.7 0.28 1.08 20 0.75 4. 34 7.4 5.3 0.32 1.23 30 0.73 "4.17 ' 9.1 6.4 0.38 • 1.46 60 . 0.69. 3.94 11.4 7.8 0.47 1.81 100 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 2 151 A c t i v a t e d Marmatite (0.996xlO"°M) lOg o f 65/100 mesh Temperature: 2 0°C Radiant energy: 360-380 my Reagent: KEtX i n 6 00 ml Cone. Amt.Ads Corr. y mole moles/cm Time Abs. x l 0 - 5 M • xlO~ 6M Value g ' x l O - 1 0 2 0 1.18 6.75 — — — -- . i o 1. 08 6.17 5. 3 4.3 0.26 1.00 20 1.05 6.00 7.5 5.4 0. 32 1.2 3 30 1.03 •" 5.88 . 8.7 6.2 ' 0.37 1.42 70 0.98 5.60 11. 5 7.7 0.46 1.77 150 0. 92 5.25 15.0 9. 0 0.54 .2.08 235 0.88 5.03 17.2 9.1 0.54 2.08 300 0. 85 4;. 86 18.9 9.0 0. 54 2.08 152 A c t i v a t e d Marmatite lOg of 150/200 mesh Temperature: 20°C Radiant energy: 360-380 mu I n t e n s i t y o f l i g h t : 0 watts/cm Time Abs . Cone. x l O - 5 M Amt.Ads x l 0 ~ 6 M Corr. Value u mole g moles/< x l O " 0 1.03 5.72 — — — — 10 0.92 5.26 4.6 3.6 0.22 0.42 20 0. 89 5.09 6 . 3 5.0 0.30 0.58 30 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 A c t i v a t e d Marmatite lOg o f 150/200 mesh Temperature: 20°C Radiant energy: 360-380 mu 2 I n t e n s i t y o f l i g h t : 80 u watts/cm Time Abs. Conc.- xlO'^M Amt.Ads xl0"°M Corr. Value U mole g moles/< x l O - 1 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 1.15 154 A c t i v a t e d Marmatite lOg o f 150/200 mesh Temperature: 20°C Radiant energy: 360-380 my I n t e n s i t y o f l i g h t : 180 y watts/cm 2 C o n e Amt.Ads Corr. y mole moles/cm Time Abs. xlO" 5M x l O _ 6 M Value g x l O - 1 0 0 0.91 5.20 — -- — 10 0.77 . 4.40 8. 0 7.0 0.42 0. 81 2 0 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 155 A c t i v a t e d Marmatite lOg o f 150/200 mesh Temperature: 2 0°C Radiant energy: 360-380 mV Reagent: KEtX i n 6 00 ml I n t e n s i t y o f L i g h t : 2 75 U watts/cm Time Abs. Cone. xlO" 5M Amt.Ads xlO" 6M Corr. Value u mole g moles, xlO " 0 0.90 5.14 — — 10 0.75 4.28 8.6 7.6 0.46 0.88 20 0. 71' 4.11 10. 3 9.0 0.54 1.04 30 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 mesh Temperature: 2 0°C Radiant energy: 360-3 80 my Reagent: KEtX i n '600 ml Time Abs. Cone. xlO~ 5M Amt.Ads x l O - 6 M Co r r . Value y mole g moles/ x l O ' 1 ' 0 1.68 9.60 -- — — — 10 0.86 4. 91 46.9 45. 5 1. 37 7.4 20 0.74 4.23 53.7 51.5 1.55 8.4 30 0.67 3.83- 57.7 55.2 1.66 9.0 100 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 mesh Temperature: 2 0°C Radiant energy: 435-480 mjj Reagent: KEtX i n 6 0 0. ml Time Abs. Cone. xlO~ 5M Amt.Ads xl 0 ~ 6 M Corr. Value u mole g moles, x l 0 ~ 0 1.80 10.28 — — — — 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 22.91 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 ' 71.0 2.13 11.5 ( s m 2 J 158 Galena 20g o f 100/150 mesh Temperature: 2 0°C Radiant energy: 2-2.5 .u Reagent: KEtX i n 6 00 ml' Time Abs. Cone. xlO~ 5M Amt.Ads x l O _ 6 M Corr. Value y mole . g moles, x l 0 ~ 0 1.63 9. 30 — — — 11 0. 95 5.43 38 .3 37.7 1.13 6.1 20 0.82 ' 4.74 45.6 43.5 1.27 6.9 32 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 H Q 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 • 1.26 80.4 65.0 1.95 10.6 , 2 159 Galena 20g o f 100/150 mesh Temperature: 2 0°C Radiant energy: darkness Reagent: KEtX i n 500 ml Cone. Amt.Ads Corr. y mole moles/cm' Time Abs. xlO~ 5M xlO" 6M Value g x l O - 1 0 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 16 0 Galena 20g o f 100/150 mesh Temperature: 2 0°C Radiant energy : 400 W Qtz-I lamp Reagent : KEtX in- 60 0 ml Time Abs. Cone. xlO~ 5M Amt.Ads xlO~ 5M Corr. •Value y mole g moles, xl0~' 0 1.69 9.65 • — -- 10 0.89 . 5.0 9 45.6 44. 0 I. 32 7.1 20 0.7 9 4.51 51.4 49^4 1.48 8.0 3 0 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 . 10.3 150 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 10 161 A c t i v a t e d Marmatite 20g o f 100/150 mesh Temperature: 2 0°C Radiant energy: 360-380 my Reagent: KEtX i n 600 ml 2 Cone. Amt.Ads Corr. y mole moles/cm Time Abs. xlO~ 5M x l b ~ 6 M Value g x l O - 1 0 0. 1.56 8.90 — -- -- — 10 1.26 7.20 17.0 15.5 . 0.46 1.25 23 1.22 6.9 6 19.4 17.2 0.51 1.39 35 1.19 6.79 21.1 18.'4 0.55 1.50 60 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 1.77 162 A c t i v a t e d Marmatite 20g o f 100/150 mesh Temperature: 2 0°C Radiant energy: darkness Reagent: KEtX i n 600 ml Time Abs. Cone. xlO~ 5M Amt.Ads xlO~ 6M Co r r . Value u mole g mole s/ x l 0 _ 1 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 J 163 Activ a t e d . M a r m a t i t e 20g o f 100/150 mesh Temperature: 2 0°C Radiant energy: 2-2.5 u Reagent: KEtX i n 60 0 ml Time Abs. Cone. xlO" 5M Amt.Ads xlO" 6M Corr. Value u mole g moles/ x l O - 1 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. 164 A c t i v a t e d Marmatite 20g of 100/150 mesh " ' Temperature: 2 0°C Reagent: KEtX i n 60 0 ml Cone. Amt.Ads Corr. u mole moles/cm' Time: Abs. xlO" 5M xlO" 6M Value g x l O " 1 0 0 ' 1.58 9.03 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 1.55 60 1.16 6.63 . 24.0 ; 20.5 0.61 1.66 110 1.09 6.24 27.9 22.9 0.68 1.85 160 1.04 5.95 30.8 22.4 0.67 ' 1.83- 200 1.01 5.77 32.6 22.8 0.68 1.85 300 , 0.96 5.49 35.4 22.9 0.68 1.85 500 0.87 4.97 40.6 23.0 0.68 1.85 165 A c t i v a t e d Marmatite • 20g o f 100/150 mesh Temperature: 2 0°C Radiant energy: 42 0-4 70 my Reagent: KEtX i n 600 ml Time Abs. Cone. xlO~ 5M Amt.a ds xlO~ 6M Corr. Value y mole g moles/ x l O - 1 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 1.53 166 A c t i v a t e d Marmatite lOg o f 65/100 mesh Temperature: 2 0°C (pH = 6.5) Radiant energy: d a y l i g h t Reagent: KEtX i n 100 0 ml Time Abs. Cone. xlO" 5M Amt.Ads xlO" 6M Corr. Value u mole g moles/ x l O - 1 0 1. 64 9.37 — — . — — 10 1.56 8.-91 4.5 3.5 0. 35 1. 35 18 1.55 8.86 5.1 3.9 0. 39 1.5 0 30 , 1.53 8.78 5. 9 4.5 0.4 5 1.73 60 1.51 8.63 . 7.4 5.3 0.53 2. 04 100 1.50 8.56 8.1 5.2 0.52 2.00 150 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 2.04 500 . 1.40 8.00 13.7 5.3 0. 53 2.04 ( 167 A c t i v a t e d Marmatite lOg of 65/100 mesh Temperature: 2 0°C (pH .= 6.5) Radiant energy: d a y l i g h t Reagent: KEtX i n 1000 ml Cone. Amt.Ads Time Abs. xlO~ 5M xlO" 5M 0 1.64 9. 37 -- — — 10 1.56 8.94 4.3 3.3 0.33 1.27 18 1.55 8.88 4.9 3.8 0.38 1.46 30 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 Corr. u mole moles/cm Value g x l 0 ~ 1 0 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0081187/manifest

Comment

Related Items