@prefix vivo: . @prefix edm: . @prefix ns0: . @prefix dcterms: . @prefix skos: . vivo:departmentOrSchool "Applied Science, Faculty of"@en, "Chemical and Biological Engineering, Department of"@en ; edm:dataProvider "DSpace"@en ; ns0:degreeCampus "UBCV"@en ; dcterms:creator "Woods, Thomas Robert"@en ; dcterms:issued "2012-02-02T00:34:42Z"@en, "1955"@en ; vivo:relatedDegree "Master of Applied Science - MASc"@en ; ns0:degreeGrantor "University of British Columbia"@en ; dcterms:description """The amount of reaction between pyrite and vapor state nitric acid-has been analytically determined at 130°, 145°, 160° and 175° C. for one hour reaction time, and for one-half, one and two hour reaction times at 160°C. The variation of pressure with time for constant-boiling (68.2 per cent) nitric acid was studied at 130° and 160°C The reaction observed between pyrite and vapor state nitric acid followed the possible chain of reactions given below: (formula omitted) with the possible reaction: Fe₂(S0₄)₃ + H₂S0₄⇄Fe₂(S0₄)₃ . H₂SO₄. At 160°C the overall reaction was found to be of an apparent zero-order as was also that for the formation of ferric sulfate and ferric oxide, over the range of almost 100 per cent decomposition of the nitric acid. The maximum amount of pyrite used was about 11 per cent. Experimental results show that reactions (3), (4),(5) and (6) must all be surface reactions. A decrease in the rates of the reactions was noted between 145° and 160°C. This was most probably caused by the change in the physical and chemical properties of sulfur in this range, and indicates that elemental sulfur has a significant retarding effect on the rate of the overall reaction"""@en ; edm:aggregatedCHO "https://circle.library.ubc.ca/rest/handle/2429/40433?expand=metadata"@en ; skos:note "STUDIES ON IRON PYRITE by THOMAS ROBERT WOODS A.THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE I n the Department of CHEMICAL ENGINEERING We accept t h i s t h e s i s as conforming to the standard r e q u i r e d from candidates f o r the degree of MASTER OF APPLIED SCIENCE Members of the Department of Chemical Engineering THE UNIVERSITY OF BRITISH COLUMBIA November, 1955 ACKNOWLEDGEMENTS I wish t o g r a t e f u l l y acknowledge the a s s i s t a n c e given by Dr. D. S. Scot t under whose guidance t h i s p r o j e c t was c a r r i e d out, and the h e l p f u l suggestions and a s s i s t a n c e i n c o n s t r u c t i n g the apparatus of ray f e l l o w classmates, espe c i a l l y Mr. Walter Hayduk; a l s o Mr. Frank Sawford, Work-shop Technician and Mr. W. Pye, Glassblower. I am indebted t o the P r e s i d e n t s * Research Fund of the U n i v e r s i t y of B r i t i s h Columbia f o r p r o v i d i n g f i n a n c i a l a s s i s t a n c e . i i ABSTRACT The amount of r e a c t i o n between p y r i t e and vapor s t a t e n i t r i c acid-has been a n a l y t i c a l l y determined at 130°, 145°> 160° and 175° Cl. f o r one hour r e a c t i o n time, and f o r one-half, one and two hour r e a c t i o n times at 160°C. The v a r i a t i o n of pressure w i t h time f o r c o n s t a n t - b o i l i n g (68.2 per cent) n i t r i c a c i d was stu d i e d at 130° and l60°C The r e a c t i o n observed between p y r i t e and vapor s t a t e n i t r i c a c i d f o l l o w e d the p o s s i b l e chain of r e a c t i o n s given below: 2 HN0 3^-=:H 20 + 2 N0 2 + £ 0 2 (1) 2 HN0 3^=:H 20 + 2 NO + 3 0 2 (2) or 2 F e S 2 + 2 °2Z=!^= F e 2 °3 * * s ^ (3) 2S„. + 2 0 9 = S - 2 S 0 o * d + °2 • u. 2 H20) + 2 S0 3=^—-2 H 2S0^ (4) Feg0 3 + 3 H 2 S 0 4 = ^ : F e 2 U 0 4 ) 3 + 3H 20 (5) Fe20 3 + 3 S0 3 - - Fe ( S O ^ (6) wi t h the p o s s i b l e r e a c t i o n : F e 2 ( S 0 4 ) 3 + H 2 S 0 4 ^ = : F e 2 ( S 0 4 ) 3 . HgSO^ At 160°C the overall reaction was found to be of an apparent zero-order as was also that for the formation of ferric sulfate and ferric oxide, over the range of slmost 100 per cent decomposition of the nitric acid. The maximum amount of pyrite used was about 11 per cent* Experimental results show that reactions (3),(4),(5) and (6) must all be surface reactions* A decrease in the rates of the reactions was noted between 145° and 160°C This was most probably caused by the change in the physical and chemical properties of sulfur in this range* and indicates that elemental sulfur has a significant retarding effect on thertfate of the overall reaction* TABLE OF CONTENTS Page Acknowledgments ^ Abs t r a c t i i i I n t r o d u c t i o n 1 Theory and Related L i t e r a t u r e D i s s o c i a t i o n of N i t r i c A c i d and Nitrogen • 2 Peroxide Absorption of Nitr o g e n Peroxide 5 D i s c u s s i o n of Some I r o n Compounds 8 Heterogeneous Reactions 9 P y r i t e s 11 V i s c o s i t y of S u l f u r 12: Experiemental Apparatus 13 Procedure Reaction of P y r i t e s 16 A n a l y t i c a l Procedure 17 Other Tests 18 Data and R e s u l t s 2:1 Sample C a l c u l a t i o n s and C a l c u l a t e d Results E s t i m a t i o n of the Amount of N i t r i c A c i d Present i n the Reactor F l a s k . 333 Oxygen A v a i l a b l e and Per Cent Used 34 Per Cent Excess S u l f a t e i n Water E x t r a c t y^j D i s c u s s i o n of R e s u l t s 3 5 Conclusions ^3 B i b l i o g r a p h y ^ v Page Appendix . Appendix A - A n a l y s i s of P y r i t e and E x t r a c t Residue Appendix B - A n a l y t i c a l Method f o r F e r r i c Ion «JQ Appendix C - A n a l y t i c a l Method f o r Eerrous Ion 5 1 Appendix D - A n a l y t i c a l Method f o r S u l f a t e Ion 5 2 Appendix E - Miscellaneous Graphs CL LIST OF TABLES Table Page I . Reaction Data 22 I I . Pressure V a r i a t i o n f o r Reaction Runs 26 I I I . Pressure Runs w i t h Constant B o i l i n g N i t r i c A c i d OQ.. v i LIST OF FIGURES Figure Page 1. Diagram of Apparatus 1^ 2. Weight Reacted vs. Temperature for One Hour Reaction Time 24 3. Weight Reacted vs. Time at 160°C. 25> 4. Pressure vs. Time for the Reaction Runs 27 $A. Pressure vs. Time for the Reaction Runs at 160°C. 28 5. Pressure vs. Time for N i t r i c Acid. Run 22-130°C. 30; 6. Pressure vs. Time for N i t r i c Acid. Run 20-l60°C. 31 7. K Values for the Association of N i t r i c Acid. 55 8. Viscosity of Liquid Sulfur. 56 v i i INTRODUCTION In the past much work has been done on the r e a c t i o n s of i r o n p y r i t e . The work, i n ge n e r a l , has been c a r r i e d out with the i d e a of commercial use of p y r i t e as a source of s u l f u r , s u l f u r d i o x i d e and i r o n oxides. Apart from the pro-d u c t i o n of s u l f u r d i o x i d e , these s t u d i e s have l e d t o a few processes such as t h a t used by Camstock-Wescott In c . of Niagara F a l l s , New York, and of Noranda Mines L t d . at Port Colborne, Ontario. However, there has been no g e n e r a l l y accepted process developed p r i m a r i l y f o r the production of s u l f u r from p y r i t e s . I n v e s t i g a t o r s i n t h i s f i e l d have worked w i t h carbon and i t s oxides (16, 24, 28, 38, 44), hydroden (12, 43), water or steam (16, 24, 27, 29, 37), s u l f u r d i o x i d e (1, 35, 49, 50), c h l o r i n e , h y d r o c h l o r i c a c i d or c h l o r i n a t i n g gases (\\2, 7, 11, 13, 18, 31, 42), and other miscellaneous chemicals (9, 23, 36). No evidence of any work was found on the use of n i t r i c a c i d as a reagent w i t h p y r i t e (except f o r the s o l u t i o n of p y r i t e samples f o r a n a l y s i s (20) ), and i t was the purpose of t h i s p r o j e c t t o i n v e s t i g a t e the mechanism of the r e a c t i o n of i r o n p y r i t e w i t h n i t r i c a c i d i n the vapor s t a t e through the temperature range of 130 - 175°C. 1 THEORY AND RELATED LITERATURE In the l i t e r a t u r e there was found considerable confusion as t o the nomenclature of the n i t r o g e n oxides. In t h i s t h e s i s the f o l l o w i n g system has been used: n i t r o u s oxide, or n i t r o g e n monoxide NO n i t r i c ©xide N2O3 N0 2 (N 20 4) N 2 0 5 n i t r o g e n pentoxide n i t r o g e n t r i o x i d e n i t r o g e n d i o x i d e or t e t r o x i d e D i s s o c i a t i o n of N i t r i c A c i d and Nitrogen Dioxide. In a study of the p r o p e r t i e s of n i t r i c a c i d , J . Dalton (15) pointed out that when a concentrated or d i l u t e s o l u t i o n was b o i l e d at atmospheric pressure the b o i l i n g p o i n t reached 120.5°C a f t e r which the d i s t i l l a t e d i d not change. H.E. Roscoe (41) found t h a t the composition of t h i s constant b o i l i n g mixture contained 68\" weight per cent n i t r i c a c i d and i t had a s p e c i f i c g r a v i t y of 1.414 at 15.5°C. However, i f the s o l u t i o n was d i s t i l l e d under incr e a s e d or decreased pressure the composition of the constant b o i l i n g mixture changed. H. J . Creighton and J . H. Githens (14) found t h a t the maximum b o i l i n g p o i n t at 760 mm. Hg was 121.70°C g i v i n g a s o l u t i o n c o n t a i n i n g 68.18\" per cent n i t r i c a c i d ; at 360 mm, 99«9^C. f o r a 67.15 per cent n i t r i c a c i d s o l u t i o n ; and at 110 mm, 74.2°c f o r a 66.8 per cent n i t r i c a c i d s o l u t i o n . When n i t r i c a c i d i s heated i t decomposes. According to P. Braham and J . W. Gatehouse (6), and H. Bottger (5) a l l the n i t r o g e n oxides as w e l l as n i t r o g e n and oxygen are formed. On the other hand, L. Carius (10) found t h a t n i t r i c a c i d decomposed according to the r e a c t i o n : 4 HN03 — — 4 N0 2 + 2 H 20 + 02 being e n t i r e l y decomposed at 256°C. Measuring the progress of the decomposition by vapor d e n s i t y methods he found: 86° 100° 130° 160° 190° 220° 250° 256° C D 2.05 2.02 1.92 1.79 1.59 1.42 1.29 1.25 a 9.53 11.77 18.78 28.96 49.34 72.07 93.03 100.0$ v 9.43 10.41 16.62 26.22 43.69 63.77 82.30 88.47 c c . where D i s the vapor d e n s i t y , a, the per cent d i s s o c i a t i o n and v, the volume of oxygen i n cc. per gram of n i t r i c a c i d . M. B e r t h e l o t (3) a l s o worked on the decomposition of n i t r i c a c i d . I n h i s experiements at 1Q0.°C he found t h a t n i t r o g e n d i o x i d e and oxygen, but no n i t r o g e n o r n i t r o u s oxide were formed. The oxide d i d not e x i s t i n the presence of f r e e oxygen. He concludes from h i s data t h a t n i t r i c a c i d i s decomposed according t o the equation: 2 HNO^ » 2 N0 2 + H 20 + 1 0 2 In t h e i r thermodynamic study of n i t r i c a c i d , Forsythe and Giauque (19) consider two r e a c t i o n s : 2 N0 2 + H20 + 1 0 2 2 NO + H 20 + 2 °2 2 2 HNO3 2 H N O 3 1 2 They give values o f the e q u i l i b r i u m constants f o r these r e a c t i o n s over a $a*ig% of 275-500°K. The values of K-^ and K 2 from 375 t© 450°K are given i n g r a p h i c a l form, i n the Appendix, f o r the r e a c t i o n s w r i t t e n above. Considering r e a c t i o n 1 w i t h a 68.2 weight per cent n i t r i c a c i d and d e f i n i n g x as the moles of n i t r i c a c i d d i s s o c i a t e d , n° as the moles of n i t r i c a c i d o r i g i n a l l y ; * present, y as the f r a c t i o n a l d i s s o c i a t i o n and c as the moles of excess water present per mole of o r i g i n a l ' - n i t r i c a c i d we have present at any time: moles of n i t r i c a c i d - n° - x moles of n i t r o g e n d i o x i d e - x moles of water - x t C n° 2 moles of oxygen - %/k By d e f i n i t i o n : ft '„ frw) (P«,o) feJ = Assuming i d e a l behavior: PA - \" A rr - J 2 ± TT At e q u i l i b r i u m : K- y 2 . 1-C/-y)z For a 6 8 . 2 per cent a c i d , c * 1 . 6 4 4 , and at 130°C;K£.=- 3 . 0 0 atm.3/2^ so t h a t at atmospheric pressure: y - 0 . 8 1 5 or t h a t the a c i d i s 81.5 per cent d i s s o c i a t e d at 130°C. S i m i l a r l y f o r r e a c t i o n 2 we f i n d t h a t : Upon s u b s t i t u t i o n of the value of c * 1.644 and K 2 = 1.038 x -7 5/2 10 atm the equation g i v e s at atmospheric pressure: y - 0.0197 or that the a c i d i s 1.97 per cent d i s s o c i a t e d at 130°C. Thus i t can be seen that we may consider t h a t r e a c t i o n 2 has l i t t l e e f f e c t on the d i s s o c i a t i o n o f n i t r i c a c i d at t h i s temperature. The d i s s o c i a t i o n of n i t r o g e n d i o x i d e has a l s o been e x t e n s i v e l y s t u d i e d . According t o A. Richardson (JpO) the vapor d e n s i t y of n i t r o g e n peroxide a t 140°C corresponds e x a c t l y t o the formula N0 2 and at higher temperatures the vapor d e n s i t y becomes s m a l l e r corresponding, at 619.5°C w i t h the completion of the change: 2 N 0 2 — - 2 NO + 0 2 Thus as soon as the change from N 20^ :=^ : 2N0 2 ^ s nearing completion the decomposition s t a r t s . M. Bodenstein and M. Katayama (4) i n t h e i r study of the decomposition obtained d i f f e r e n t values from those of Richardson. Some of t h e i r values of the per cent d i s s o c i a t i o n are l i s t e d i n the f o l l o w i n g t a b l e . Temperature 185° 222° 279° 390° 494° 619° 62h9-5° C Values of Richardson 5 - 13. - 56.5 r 100$ Values of Bodenstein and Katayama - 4-17 13.10 35.05 58.71 100 - % While there i s f a i r agreement i n t h e i r values at higher temperatures there i s complete d i f f e r e n c e i n the lower ones. However, i t can r e a d i l y be seen from the k i n e t i c data f o r the formation and decomposition of n i t r o g e n d i o x i d e given i n the I n t e r n a t i o n a l C r i t i c a l Tables that the d i s s o c i a t i o n at lower temperatures would be comparatively slow. At a temperature of 590°K (319°C) a r e a c t i o n v e l o c i t y constant f o r the decomposition i s given as 61.0 l i t r e s ^ 2 / m p l e min. w h i l e the value f o r the formation i s 670,000 l i t r e s ^ ; - / mole^ min. Since the values of the constant f o r decomposition i n c r e a s e w i t h temperature the values at lower temperatures should decrease. At 470°K ( I 9 7 0 C ) a value of 791,000 i s given f o r the r e a c t i o n v e l o c i t y constant of formation so t h a t the decomposition at t h i s temperature should be very slow. Absorption of n i t r o g e n Dioxide In the abosrption of n i t r o g e n d i o x i d e i n an aqueous s o l u t i o n the main r e a c t i o n s , according t o Burdick (8), are: 3 N0 2 + H 20^=:2 HNO^ + NO 1 2 NO + 0 2 =s=t= 2 N0 2 2 Reaction 1 i s a very r a p i d one but i t does not go t o completion, stopping a t an e q u i l i b r i u m c o n d i t i o n short of complete conversion of the n i t r o g e n d i o x i d e . The presence of n i t r i c oxide above a c e r t a i n e q u i l i b r i u m c o n c e n t r a t i o n can prevent the r e a c t i o n of abso r p t i o n and only as the n i t r i c oxide i s r e - o x i d i z e d according to r e a c t i o n 2 can the process continue. Reaction 2 i s a slow r e a c t i o n . Since the r e a c t i o n of abso r p t i o n and o x i d a t i o n progress simultaneously they are r e a l l y mutaally interdependent. The absorption of n i t r o g e n d i o x i d e i s e x t e n s i v e l y covered i n M e l l o r (34). There are given the r e a c t i o n s : 2 N 0 2 + H 20.-^— <-HN0 3 + HNC-2 3 HNC-2 ==::^HN03 + 2 NO + H20 f o r the ab s o r p t i o n process which when summed gives the same r e a c t i o n as number 1 above. I t i s s t a t e d t h a t the e q u i l i b r i u m of the r e a c t i o n i s a f f e c t e d by the p a r t i a l pressure of the n i t r o g e n d i o x i d e and the n i t r i c oxide which, i n t u r n , are i n f l u e n c e d by the e q u i l i b r i u m formation of n i t r o g e n t r i o x i d e from n i t r i c oxide and n i t r o g e n d i o x i d e which i s a very r a p i d r e a c t i o n . The d i s c u s s i o n continues s t a t i n g that the lower > the p a r t i a l pressure of n i t r o g e n d i o x i d e , the s m a l l e r the con c e n t r a t i o n of i t s s o l u t i o n i n water and a l s o of i t s r e a c t i o n , w i t h water. A l a r g e volume of undissolved gases passing through the s o l u t i o n causes a r a p i d evaporation of water and n i t r i c a c i d . J . L. Gay Lussac (21), P. L. Dulong (17) and F. Raschig (39) working on the abosrption of n i t r o g e n d i o x i d e i n an aqueous s o l u t i o n of a l k a l i hydroxides showed t h a t the those W i t h r e a c t i o n s were very much l i k e A w a t e r . With a concentrated a l k a l i - l y e s o l u t i o n a mixture of a l k a l i n i t r a t e s and n i t r i t e s i s formed with a s l i g h t e v o l u t i o n of n i t r i c oxide. The primary r e a c t i o n i s a 2 N0 2 + 2 KOH ^ = 5 : KNO3 + KN0 2 + HgO Di s c u s s i o n of Some I r o n Compounds In the r e a c t i o n of n i t r i c a c i d w i t h i r o n p y r i t e c e r t a i n products such as i r o n n i t r i t e s , n i t r a t e s , s u l f i t e s and s u l f a t e s might be p o s s i b l e . Some of these compounds have been i n v e s t i g a t e d as t o t h e i r p r o b a b i l i t y of forma t i o n . Ferrous n i t r i t e cannot be prepared (45) owing t o i t s immediate decomposition upon formation t o givethe f e r r i c i o n and n i t r i c oxide. Ferrous n i t r a t e (45) i s known only i n the form of two hydrates which on warming decompose t o form the f e r r i c i o n and n i t r i c oxide. F e r r i c n i t r a t e (45) i s not known.in an anhydrous s t a t e but only i n the two hydrates w i t h 6 and 9 waters. These hydrates melt at 35° and 47°C, r e s p e c t -i v e l y . No complex or double f e r r i c n i t r a t e s are known. F e r r i c n i t r i t e has never been prepared. The s u l f i t e s , i n g e n e r a l , are very r e a c t i v e being e a s i l y o x i d i z e d t o s u l f a t e s (47). Ferrous s u l f a t e (48) forms hydrates of 1, 4 and 7 waters which pass through a s e r i e s of t r a n s i t i o n p o i n t s on warming: 7 4 — - 1 — — 0 5 6 . 6 0 C . 65.0° 90° By h e a t i n g to a higher temperature the anhydrous s a l t decom-poses t o give s u l f u r d i o x i d e , b a s i c f e r r i c s u l f a t e and othe£ products. F e r r i c s u l f a t e (26) i s a very s t a b l e compound decomposing at about 700°C i n t o f e r r i c oxide and s u l f u r t r i -oxide . Heterogeneous Reactions In the study of the k i n e t i c s of r e a c t i o n s of gases t a k i n g place on the surface of s o l i d s there have been discovered r e a c t i o n s of zero or f r a c t i o n a l orders as w e l l as those of apparently simple order. I n some cases one of the r e a c t a n t s may have a r e t a r d i n g i n f l u e n c e i n s t e a d of an a c c e l e r a t i n g one w h i l e i n others the products may act as an i n h i b i t o r . (22) Langmuir ( 3 0 ) . s t a t e s , \" I n a heterogeneous chemical r e a c t i o n the a c t i v i t y of a surface depends i n general upon the nature of, the arrangement of and the spacing of the atoms forming the surface l a y e r . \" According t o t h i s theory the v e l o c i t y of r e a c t i o n s , i n g e n e r a l , i s not l i m i t e d by the rat e of d i f f u s i o n through an adsorbed f i l m , but by the r a t e at which the molecules s t r i k e the surface which i s a c t i v a t e d . There are, of course, many chemical r e a c t i o n s which are a c t u a l l y l i m i t e d by p h y s i c a l f a c t o r s , such as the r a t e of d i f f u s i o n through l a y e r s of gases or moderately t h i c k f i l m s such as the r u s t i n g of i r o n and the o x i d a t i o n of aluminum. 'AJG-coi'dingiitd-''pr.e^nft-th&ox^.the mechanism of heterogeneous r e a c t i o n s may be c o n t r o l l e d by one or more of a sequence of step s . These steps i n c l u d e p h y s i c a l processes, 1 0 , such as d i f f u s i o n of r e a c t a n t s and products t o and fvam the surface of a s o l i d from and to the f l u i d , and chemical processes, such as adsorption and desorption of re a c t a n t s an products, and the r e a c t i o n of a c t i v a t e d l y adsorbed re a c t a n t s on the surface to y i e l d products. U s e f u l r a t e equations can be deri v e d i f the s p e c i f i c sequence of steps (the mechanism of the r e a c t i o n ) i s known, and constants i n these equations evaluated from experiemental data ( 2 2 ) ( 2 5 A ) . The r e a c t i o n i n v e s t i g a t e d i n t h i s work may be considered i r r e v e r s i b l e and t h e r e f o r e r a t e s of de s o r p t i o n processes and d i f f u s i o n ofproducts need not be considered. Assuming that the only component of the f l u i d e n t e r i n g i n t o r e a c t i o n w i t h the s o l i d on adsorption i s oxygen, then the f o l l o w i n g g e n e r a l mechanisms may occur: 1 . The r a t e of adsorption of oxygen i s r a t e c o n t r o l l i n g . I n t h i s case the r e a c t i o n r a t e w i l l be a f u n c t i o n of the oxygen p a r t i a l p r essure. 2. Surface r e a c t i o n r a t e c o n t r o l s and the e q u i l i b r i u m amount of adsorbed oxygen i s not a f u n c t i o n of pressure. That i s , a l l a v a i l a b l e surface s i t e s are saturated w i t h oxygen over t h e range of experimental c o n d i t i o n s covered. I n t h i s case, a zero order may be observed. 3. The surface r e a c t i o n \" r a t e c o n t r o l s w i t h the e q u i l i b r i u m amount of adsorbed oxygen of ad-sorbed oxygen a f u n c t i o n of pressure. Reactions of t h i s type w i l l probably be of complex order 11. w i t h respect t o pressure (or t i m e ) . P y r i t e s Because of i t s h i g h s u l f u r context p y r i t e , F e S 2 > i s commonly thought of as a f e r r i c compound, but a c t u a l l y i t i s f e r r o u s being the s a l t of the anion S 2 . I t s c r y s t a l s t r u c t u r e may be thought of i n two ways. The l a t t i c e may be described as being l i k e t h a t of sodium c h l o r i d e w i t h the sodium ions being replaced by i r o n and the c h l o r i n e by p a i r s of s u l f u r atoms ( 4 5 A ) . The s t r u c t u r e can a l s o be seen as a s u l f u r atom surrounded t e t r a h e d r a l l y by three i r o n atoms and one s u l f u r atom ( 3 7 A ) . The bonding i s e s s e n t i a l l y covalent r a t h e r than i o n i c . Chemically, p y r i t e i s s c a r c e l y a t t a c k e d by anything at o r d i n a r y temperatures, but on heating i t r e a c t s w i t h many substances. I t i s known t o burn in. a i r forming f e r r i c oxide and s u l f u r d i o x i d e . Thus i t i s commonly used i n the manu-f a c t u r e of s u l f u r i c a c i d (45A). At lower temperatures p y r i t e i n the presence of moisture w i l l r e a d i l y o x i d i z e t o f e r r i c s u l f a t e . I n a n a l y t i c a l procedures p y r i t e i s o x i d i z e d by bromine f o l l o w e d by n i t r i c a c i d and evaporation t o dryness on a steam bath t o give f e r r i c s u l f a t e (20). Dr. S t r i c k l a n d (4&A) i n h i s s t u d i e s of the o x i d a t i o n i n aqueous s o l u t i o n of s u l f u r c o n t a i n i n g ores has found t h a t p y r i t e i s o x i d i z e d i n aqueous c h l o r i n e d i o x i d e s o l u t i o n t o f e r r i c s u l f a t e with no intermediate stage producing s u l f u r . 12.. This has apparently been the experience also of other i n v e s t -i g a t o r s working i n aqueous s o l u t i o n s w i t h various o x i d i z i n g agents. V i s c o s i t y of S u l f u r The values of the v i s c o s i t y of s u l f u r are found to v a r y considerably over the range of temperatures used i n t h i s t h e s i s . The v i s c o s i t y has values (25) c l o s e t o ten c e n t i p o i s e s at the lower temperatures but at 159.5° i t s t a r t s a sharp i n c r e a s e having reached a value of 77.32 at 160.3° and 4,500 at 171.0°. These values have been p l o t t e d (see Appendix). EXPERIMENTAL APPARATUS 13. The r e a c t i o n apparatus, shown i n f i g u r e I , c o n s i s t e d of three s e c t i o n s ; the n i t r i c a c i d vapor generator; the r o t a t i n g r e a c t o r ; and the product gas absorber. A l l the connections of the apparatus were of gl a s s w i t h the exception of those t o the a u x i l a r y manometer and water j e t vacuum pump which were of rubber. The n i t r i c a c i d vapor generator c o n s i s t e d of a one-l i t r e d i s t i l l a t i o n f l a s k with a thermometer w e l l and a g l a s s cap. I n the top of the g l a s s cap was f i t t e d a two-way stop-cock. One arm of the stopcock was connected to a s i n g l e gas absorber, w h i l e the other arm was connected to the r o t a t i n g r e a c t o r . The l i n e connecting the f l a s k and the r e a c t o r had a branch i n which was f i t t e d a g l a s s check v a l v e . The r o t a t i n g r e a c t o r was made of a s p h e r i c a l s e c t i o n w i t h connectors at e i t h e r end, the whole assembly r o t a t i n g i n b a l l and socket j o i n t s between two s t a t i o n a r y end p i e c e s . The l e f t - h a n d end piece was a 20 mm. pyrex tube w i t h a male 35/20 b a l l and socket j o i n t at one end and a three-way c a p i l l a r y stopcock at the other. One branch of the stopcock was connected t o the n i t r i c a c i d vapor generator, and the other branch was connected by rubber t u b i n g t o e i t h e r the water-j e t vacuum pump or the c y l i n d e r of ni t r o g e n gas. A side tube from t h i s end piece contained a second three-way c a p i l l a r y stopcock, one arm of whichwas connected to the main mercury manometer, while the other arm was connected by rubber t u b i n g to the a u x i l a r y manometer. c J GENERA TOP ABSORBER GAS PRODUCT GAS ABSORBER TO AUXILARY MANOMETER CHECH ^ VALVE TO AiA/N MANOMETER MECANNO GEAR TO VACUUM LEFT-HAND ORNz TANK ENDP/ECE COA/MECTOR TUBE POTA T//VG PEACTOP SECT/ON RIGHT-HAND END P/ECE VAPOP GE A/EPA TOP FIGURE / - D/AGRAM OR APPARA TUS 15. The r o t a t i n g s e c t i o n was a t h r e e - l i t r e round bottomed f l a s k w i t h two concave dimples which ran across i t . The neck of the f l a s k terminated i n a female 3 5 / 2 0 b a l l and socket j o i n t . A female j | j o i n t was connected t o the other s i d e of the f l a s k . To t h i s was j o i n e d a connector tube w i t h a male ^ j o i n t at one end and a male 3 5 / 2 0 b a l l and socket j o i n t at the other. On t h i s connector tube was f i t t e d a meccano gear, held i n place by a s p r i n g taper and a paper gasket. The paper gasket was coated w i t h A r a l d i t e AN-103 r e s i n a f t e r i t was i n p o s i t i o n t o prevent any o i l from seeping under the gasket and causing s l i p p a g e . The right-hand end piece was a 20 mm. tube w i t h a female 3 5 / 2 0 b a l l and socket j o i n t at one end and a three-way c a p i l l a r y stopcock at the other. One arm of the stopcock was connected to the product gas absorber and the other arm was l e f t open. The f l a s k was r o t a t e d about o n e - t h i r d submerged i n a constant temperature both by means of the meccano gear and. a H e l l e r 6T60 motor c o n t r o l l e r and v a r i a b l e speed motor s e t . The f l a s k and connector tube were kept hot by a f i l m from the constant temperature bath. The o i l was run over the r e a c t i o n v e s s e l by means of a pump and d i s t r i b u t o r made of bent'.copper t u b i n g w i t h s m a l l h o l e s . The s t a t i o n a r y end pieces of the main s e c t i o n and t h e i r connectors t o the gas absorbers and n i t r i c a c i d vapor generator were kept hot by a wrapping of el e c t r o t h e r m a l heating t a p e l 1 6 . PROCEDURE Reaction of P y r i t e s The two gas absorbers were f i l l e d w i t h a ten per cent potassium hydroxide s o l u t i o n ( 4 0 ml. i n t he generator scrubber and 350 ml. i n the product gas scrubb e r ) . A sample of p y r i t e ( 4 0 - 8 0 mesh) was a c c u r a t e l y weighted out on an a n a l y t i c a l balance and placed i n the r e a c t i o n v e s s e l . The apparatus was assembled being sure t h a t a l l the j o i n t s were w e l l greased w i t h Dow-Corning high vacuum grease. The stop-cock (C) was opened t o both manometers but the stopcocks (D and A ) t o the product gas abosrber and n i t r i c a c i d vapor generator were c l o s e d . The system and the connections t o the generator were evacuated using the water j e t vacuum pump. The system was then c l o s e d o f f and the rubber tube was changed from the water pump to the n i t r o g e n tank. The system was f i l l e d w i t h n i t r o g e n gas, and the main manometer closed o f f . The heaters f o r the constant temperature bath were turned on and the bath brought up t o temperature. The H e l l e r motor -c o n t r o l l e r was turned on, the d i a l s et at 4 and the speed of r o t a t i o n checked t o give 6 . 7 r.p.m. (10 r e v . i n 8 9 . 6 s e c ) . The e l e c t r o t h e r m a l heating tapes were turned on. Next the stopcock (a) on the n i t r i c a c i d vapor generator was opened to the gas absorber and the f l a s k was gen t l y heated w i t h a Buns^n burner. The system and the connection to the generator were evacuated as before and the stopcock (B) c l o s e d , as was the connection t o the a u x i l i a r y manometer. The main manometer connections remained f i l l e d w i t h n i t r o g e n . 17. When a good stream of vapor was coming from the generator, the system stopcock (B) was opened t o the generator and the generator stopcock (&) was q u i c k l y switched from the gas absorber t o the main system. When the check valve opened i n d i c a t i n g that the contents of the r e a c t o r were at atmospheric pressure, the system stopcock ()B). was closed and the generator stopcock (&) q u i c k l y switched back t o the gas absorber. The main manometer was opened to the system and the i n i t i a l pressure recorded. The r e a c t i o n was c a r r i e d on f o r a s p e c i f i e d lenjih of time and pressure recorded p e r i o d i c a l l y . The heat was removed from the n i t r i c a c i d vapor generator and i t was allowed t o c o o l . To stop the r e a c t i o n , the system stopcock (B) was opened t o the n i t r o g e n tank and a pressure of a few mm. of Hg. was b u i l t up i n the system. Then stopcock (D) was opened to the product gas absorber and the i s s u i n g gas allowed to bubble through the potassium hydroxide s o l u t i o n at an approximate r a t e of 1.5 l i t r e s per minute f o r two minutes and then of one l i t r e per minute f o r f i f t y minutes. The system was then closed o f f ; the both heaters, the e l e c t r o t h e r m a l heating tapes and the motor c o n t r o l l e r were turned o f f . The v e s s e l was then l e f t t o co o l before e x t r a c t i o n . A n a l y t i c a l Procedure I n the a n a l y s i s of the r e a c t i o n products, three e x t r a c t s were made. The cooled r e a c t i o n v e s s e l was removed from the constant temperature bath and wiped f r e e of o i l . Care was taken t o remove a l l the l u b r i c a t i n g grease from the 18. b a l l and socket j o i n t s . The main p o r t i o n of t h e r e a c t i o n products was t r a n s f e r e d to a 250 ml. beaker and the v e s s e l and connection tubes were r i n s e d w i t h 100 ml. of warm d i s t i l l e d water. The r i n s e water was then mixed w i t h the main mass of the r e a c t i o n product. This mixture was f i l t e r e d through a t a r e d Gooch c r u c i b l e . The f i l t r a t e was rewarmed and passed through the r e a c t i o n v e s s e l r e p e a t i n g the process. This was done a t h i r d t i m e . The v e s s e l and beakers were then r i n s e d w i t h 100-150 ml. of room-temperature d i s t i l l e d water i n small p o r t i o n s and passed through the residue i n the Gooch c r u c i b l e . The above procedure was repeated w i t h warm 4 N HC1. and then w i t h hot potassium hydroxide s o l u t i o n (50 g KOH i n 100 ml. of d i s t i l l e d water)• The volumes of the three e x t r a c t s and t h e i r washes were recorded and then they were set aside f o r a n a l y s i s . The water e x t r a c t was analysed f o r i t s f e r r i c i o n , f e r r o u s i o n , and s u l f a t e i o n content. The q u a n t i t y of f e r r i c i o n and f e r r o u s i o n was determined i n the a c i d e x t r a c t and a s u l f a t e determination was c a r r i e d out on the base e x t r a c t a f t e r o x i d a t i o n w i t h hydrogen peroxide. The a n a l y t i c a l methods used were, m o d i f i c a t i o n s of those given i n S c o t t ' s Standard Methods of Chemical A n a l y s i s ( 2 0 ) . D e t a i l e d procedures are< given i n Appendices A, B, C and D. Other Tests In the f i r s t runs the complete a n a l y s i s was not made, but a s e r i e s of spot t e s t s f o r various ions were performed on 1 9 . the e x t r a c t s . The water e x t r a c t was subjected t o the f o l l o w i n g t e s t s : the potassium thiocyanate t e s t f o r f e r r i c i o n ; the potassium f e r r i c y a n i d e t e s t f o r f e r r o u s \"Ion; the permanganate t e s t f o r n i t r i t e and s u l f i t e i o n s ; and the barium c h l o r i d e t e s t f o r s u l f a t e i o n . The potassium thiocyanate and potassium f e r r i c y a n i d e t e s t s were run on the a c i d e x t r a c t , a l s o . A f t e r o x i d a t i o n w i t h hydrogen peroxide the b a s i c e x t r a c t was a c i d i f i e d and then t e s t e d w i t h a barium c h l o r i d e s o l u t i o n . At v a r i o u s times c e r t a i n other checks were performed on the e x t r a c t s . The complete e x t r a c t i o n and t e s t procedure was c a r r i e d out on an unreacted sample of p y r i t e t o be sure that the p y r i t e i t s e l f d i d not i n t e r f e r e i n the a n a l y t i c a l procedures. A s u l f a t e i o n t e s t was run on the a c i d e x t r a c t . A check of the scrubber s o l u t i o n was made by t i t r a t i n g the o r i g i n a l and r e s u l t a n t s o l u i t o n s a g a i n s t a standardized s u l f u r i c a c i d s o l u t i o n . With the a i d of t h i s check and the l o s s i n weight of the n i t r i c a c i d vapor generator a balance f o r the n i t r i c a c i d was made. The temperature of the vapor from the vapor generator t o the r e a c t o r f l a s k was measured w i t h the e l e c t r o t h e r m a l h eating tape turned on. A p l a s t i c coated thermocouple was i n s e r t e d i n t o the l i n e through the g l a s s j o i n t of the r e a c t o r f l a s k and placed c l o s e t o the c a p i l l a r y s e c t i o n of the f l a s k stopcock ( B ) . The s u l f u r t o i r o n r a t i o of the p y r i t e sample and of the residue of run number 1 1 was determined by the method o u t l i n e d i n Appendix A. The two r a t i o s were compared. 2 0 , The volume of the apparatus was found by completely f i l l i n g the assembled apparatus w i t h water andmeasuring the volume of water i n a graduated c y l i n d e r . A study of the v a r i a t i o n of pressure over a time i n t e r v a l was made f o r n i t r i c a c i d at 1 3 0 ° and 160°C. The measurements were made by c a r r y i n g out the r e a c t i o n procedure without the use of p y r i t e . The manometer was read at ten minute i n t e r v a l s u n t i l a constant pressure was obtained. DATA AND RESULTS 21. I n the experimental work a s e r i e s of runs were done at a r e a c t i o n time of one hour w i t h v a r y i n g temperature. There were d u p l i c a t e runs made at 130°C. and s i n g l e runs at 145°, 160° and 175°C. Another s e r i e s of runs were made at 160° f o r r e a c t i o n times of 30, 60 and 120 minutes. Data on these two' s e r i e s of runs are presented i n Table I and the v a r i a t i o n s i n the t o t a l pressure w i t h time i n each run are given i n Table I I and shown i n F i g u r e s 4 and 4A. The amounts of each product formed are shown on F i g u r e 2 f o r the runs at v a r y i n g temperatures and i n Figure 3 f o r the runs at 160° and v a r y i n g r e a c t i o n s time. Data on the runs using n i t r i c a c i d only are gigen i n Table I I I and shown g r a p h i c a l l y i n F i g u r e s 5 and 6. TABLE I - Reaction Data 22. Run No. 1 4 8 9 10 11 Teraperature°C 140 185 130 130 130 130 Evacuated to: mm. Hg 732 740 742 739 739 732 Gas used: N 0 2 N 0 2 HNO3 HNO3 1 .00 HN0. HN0 3 1 .00 Length of run Hr. 9 .834 5.25 1.00 1.00 Wt. of p y r i t e used g. 19.93 9 .49 9 .38 7.63 6 . 2 9 6 6 8.4313 Wt. of residue s- - _ 3.14 7.03 5.7443 7.8742 Amt. reacted 1 Fe F e — H o 0 - 1.24 0 . 6 0 0.5523 0.5571 V.F. N. V.F. N. 0.314 0.0126 0.117 T. 0.2536 T. 0.2349 T. ^.Permanga-nate test so 4 ~ s Fe\"\"\" 4NHC1 Ext. Fe~~ KOH S Ext. Amt. reacted by analysis 2 % error 1-2 x 100 1 N. V.F. F. N. F. N. V.F. E. N. F. 0.969 0.643 0.7734 0.7504 0.324 0.215 0.2580 0.2504 0.0186 0.0165 0.00671 0.02259 T. T. T. T. 0.00305 0.007211 0.009126 0.3516 0.5255 0.5170 41.4 4.85 7.20 Note: Runs No. 2 and 3 had to be shut down due to fluctuations i n temperature. Runs No. 5, 6, 7, 12, and 13 had to be shut down due to condensation i n the reactor f l a s k . N = no t e s t ; F = f a i n t t e s t ; V.F. • very f a i n t t e s t ; T - traces TABLE I Reaction Data (continued) 2 3 . Run No. 1 4 15 1 6 1 7 1 8 1 9 Temperature°C 1 3 0 1 4 5 1 6 0 1 7 5 1 6 0 1 6 0 Evacuated t o : 726 7 3 6 732 7 2 6 7 4 5 7 3 9 mm.Hg Gas used: HNO^ HNO^ HN03 HNO3 HN03 0 . 5 0 HNO^ Length of run hr . 1 . 0 0 1 . 0 0 1 . 0 0 1 . 0 0 2 . 0 0 Wt. of p y r i t e used g. 8.1797 8.1440 8 . 1 2 6 3 8 . 1 0 0 0 8 . 0 5 6 1 8 . 0 8 7 6 Wt. of residue g« 7 . 7 1 0 4 7 . 6 4 1 7 7 . 7 9 4 6 7 . 7 7 3 4 7 . 8 9 4 8 7 . 4 4 5 1 Amt. reacted 0 . 4 6 9 3 0 . 5 0 2 3 0 . 3 3 1 7 0 . 3 2 6 6 0 . 1 6 1 3 0 . 6 4 2 5 Fe 0 . 2 0 9 3 0 . 1 9 8 8 0 . 1 3 7 4 0 . 1 3 2 8 0 . 0 6 4 0 6 0 . 2 5 1 9 H 2 0 F e - \" Ext Permanga-nate t e s t - - - - -_ — — . T — — s o 4 - 0 . 6 0 2 9 0 . 6 0 4 4 0 . 3 7 5 5 0 . 3 7 5 5 0 * 1 7 9 0 0 . 8 5 9 4 s 0 . 2 0 1 2 0 . 2 0 1 7 0 . 1 3 5 3 0 . 1 2 5 3 0 . 0 5 9 7 3 .0 .2867 4NHC1 Ext. Fe F e — KOH S Ext. Amt. reacted by a n a l y s i s 2 % e r r o r 1-2 x 100 1 0.027160.040540.029740.02869 0.01492 0.05036 0.008043 O.OO7698 0.007J23 0.004462 0.0049 52 0.006174 0.4457 O . 4 4 8 7 0.2996 0.2913 0.1437 0.5913 2.90 10.67 9.68 10.84 10.91 7.97 Note: Runs No. 2 and 3 had to be shut down due to f l u c t u a t i o n s i n temperature. Runs No. 5, 6 , 7 , 1 2 , and 13 had t o be shut down due t o condensation i n the r e a c t o r f l a s k . K •= no t e s t ; F - f a i n t t e s t ; V.F. = very f a i n t t e s t ; T s t r a c e s 2 4 . 0.6 C5 Q O Q: k 0.5 0.4 0.3 — 0.2 — a/ /30 /40 /so /eo /70 TEMPERA TOF>E, °C FIGURE 2 - WE/GHT REACTED VS. TEMPERATURE FOR OA/E HOUR REACT/ON T/ME nsv WTD/FF\\ W T O BY AA/ALVS/SJ A /ROM AS FERR/C SULFATE X /ROM AS FERR/C OXIDE T/MEt HOURS FIGURE 3 - WT: REACTED KS. T/ME AT /GO\" TABLE I I - Pressure V a r i a t i o n f o r I n d i c a t e d Runs Run No. 10 11 14 Temperature 130 130 130 Pressure at s t a r t 776 770 783 10 min. 776 772 783 20 min. 773 772 785 30 » 777 7^5 781 40 » 777 785 .-783 50 » 777 771 785 60 •» 775 777 785 70 \" — 8o n _ _ 90 \" 100 \" 110 » 120 » 15 16 17 18 19 145 160 175 160 160 777 820 747 664 660 777 822 759 712 712 807 820 778 808 719 823 820 797 828;. 735 831 820 814 — 765 781 820 828 _ 781 777 820 836 — 781 •-- — - 761 — — - — 777 •- - _ — 786 - - - — 797 — — — .797 - - - - 785 860 840 740 720 OA zs T/ME, MINUTES SO FIGURE 4 - PRESSURE VS T/ME FOR THE REACT/ON RUNS -Q RUN /Ot //, Y4 - /JO ° _0L RUN /S ~/-4S° -G RUN /6 ~/60° -0 RUN 17 -/7S° 840 800\\— 640V-600 25 SQ 7S T/A4£~, M/A/UT£S /OO /25 E/GURE 4A - PRESSURE VS T/ME FOR THE REACT/OA/ RUNS AT /60° — e — - e — -e RUNJ6 RUN /8 RUN/? TABLE I I I -2 9 . Pressure Runs w i t h Constant B o i l i n g N i t r i c A c i d Run No. 20 21 22 Wt. of P y r i t e none none none Temperature 1 6 0 ° 1 3 0 ° 1 3 0 ° Evacuated t o 739 740 720 (mm Hg.) Pressure at s t a r t 638 698 760 10 min. 655 686 734 2 0 . \" 653 662 713 30 \" 654 631 704 40 » 647 623 692 50 \" 639 621 680 $0 \" 631 611 663 70 \" - 603 656 80 \" 631 589 649 90 » 629 580 647 100 « 631 572 649 110 » 629 56$ 649 120 \" 631 567 649 30. rrcuRr s - PRESSURE I/S T/ME FOR HNO3. RUN NUMBER £2.- /3Q°C 31 FIGURE 6 - PRESSURE: VS T/ME ROR HN03. RUN NUMBER -/6O0C 32. A d d i t i o n a l Tests The e x t r a c t s of the unreaeted p y r i t e gave no r e s u l t s f o r the a n a l y t i c a l spot t e s t s . No s u l f a t e i o n was found i n the a c i d e x t r a c t s . In the product gas scrubber s o l u t i o n there was no or l i t t l e s u l f a t e i o n ( no p r e c i p i t a t e , but o c c a s i o n a l l y a s l i g h t l y m i l ky t e s t ) . The balance attempted on the n i t r i c a c i d s o l u t i o n d i d not give s a t i s f a c t o r y r e s u l t s . The temperature of t h e vapor i s s u i n g i n t o the f l a s k a f t e r passing through the heated connector tube was found t o be 139.5°C. The average s u l f u r t o i r o n weight r a t i o of a f r e s h p y r i t e sample was found t o be 1.1634 which agreed w e l l w i t h the value of 1.1633 femnd f o r the r e s i d u e . The volume of the apparatus was found to be 3.135 l i t r e s . 33. SAMPLE CALCULATIONS AND CALCULATED RESULTS Es t i m a t i o n of the Amount of N i t r i c A c i d Present i n the Reactor F l a s k . I f i t i s assumed t h a t the r e a c t i o n t a k i n g place i n the runs using n i t r i c a c i d alone i s : 2 HNO3 H2O + 2 N0 2 + 1 0 2 Then the e q u i l i b r i u m constant can be used as before: At 130° the value of K i s 3.00 atm | and the value of C i s 1.644 f o r a 68.2 per cent n i t r i c a c i d . I f i t i s assumed th a t when the n i t r i c a c i d a t t a i n e d constant pressure the r e a c t i o n has reached e q u i l i b r i u m then the e q u i l i b r i u m pressure from Fi g u r e 5 i s 0.&53 atm. S u b s t i t u t i o n of these values i n the equation f o r g i v e s : y = 0.831 Assuming an i d e a l gas then: n. = itV - 0.853 (3.135) = 0.0809 moles z RT 0.082 (403) A l s o y = x o nHN03 and n t - n° HNO3 3/4 x n HNO, 0 34. S o l v i n g these equations f o r n 0 HNO-j we o b t a i n : n° = 0.0247 moles HN03 Oxygen A v a i l a b l e and Per Cent Used Since i n the runs u s i n g both n i t r i c a c i d and p y r i t e the oxygen i s being removed the e q u i l i b r i u m of the r e a c t i o n : 2 HNO3 = = : 2 NO + H 20 + 2 00 2 * w i l l be s h i f t e d considerably to the r i g h t . Thus, i t may be considered that the t o t a l amount of oxygen a v a i l a b l e f o r the o x i d a t i o n of the p y r i t e i s given by t h i s r e a c t i o n . Consider-i n g run number 11 at 130°C the amount of a v a i l a b l e oxygen i s : 0.0247 (2) 32.0 = 0.593 g. 4 Oxygen found by a n a l y s i s : S O 4 \" : 0.7504 64.0 - 0.500 96.06 F e 2 0 3 : 0.0226 48|0 a 0.00973 0.50973 or 0.510g 0 2 Therefore per cent a v a i l a b l e oxygen used: 0.510(100) s 86.0$ 0.593 Run No. 11 16 18 19 A v a i l a b l e 0 2,g. 0.593 0:521 0.521 0.521 0 2 by A n a l y s i s , g. 0.510 0.263 0.125 0.594 Per cent 0 2 used: 86.0$ 50.4$ 24.0$ 114$ Per Cent Excess Sulfate i n Water Extract 35 I f i n the analysis of the water extract we take the f e r r i c i r o n analysis as correct and the i r o n present as f e r r i c sulfate we can calculate the amount of su l f a t e ion which should be present. Considering run number 11 we f i n d the amount of sulfate which should be present i s : 0.2349 3(96.06) - 0.607 g. SOr 2(55.84) The amount of sulfate found by analysis: 0.7504 g S0^~ Per cent excess s u l f a t e : 0.7504- - 0.607 (100) - 19.1$ 0.7504 Run No. 11 15 16 17 18 19 Theoretical SO,\"\"g. 0.609 0.515 0.356 0.344 0.166 0.652 SO/,- by Analysis, g. 0.7504 0.6044 0.3755 0.3755 0.1790 0.8594 Per cent Excess 19.1$ 14.8$ 5.19$ 8.40$ 7.25$ 24.1$ DISCUSSION OF RESULTS 36. In the p r e l i m i n a r y runs the e x t r a c t s of the r e a c t i o n products were given t e s t s f o r v a r i o u s i o n s . The water e x t r a c t was found t o con t a i n f e r r i c i o n , t r a c e s of f e r r o u s i o n and s u l f a t e i o n , but n i t r i t e , n i t r a t e or s u l f i t e t e s t s were negative. The f e r r i c i o n and t r a c e s of f e r r o u s i o n , but no s u l f a t e i o n were found i n the a c i d e x t r a c t . The b a s i c e x t r a c t contained s u l f u r which was detected as s u l f a t e a f t e r o x i d a t i o n of the e x t r a c t w i t h hydrogen peroxide. These t e s t s i n d i c a t e d that the water contained f e r r i c s u l f a t e ; the a c i d e x t r a c t , f e r r i c oxide; and the b a s i c e x t r a c t , elemental s u l f u r . A search of the l i t e r a t u r e e l i m i n a t e d the p o s s i b i l i t y of the formation of f e r r o u s or f e r r i c n i t r i t e s add n i t r a t e s and made the formation of f e r r o u s or f e r r i c s u l f i t e and fe r r o u s s u l f a t e d o u b t f u l . F e r r i c s u l f a t e was found t o be a very s t a b l e compound. In the i n v e s t i g a t i o n of the decomposition of n i t r i c a c i d two r e a c t i o n s were found: 2 HN0 3==rH 2 0 + 2 N0 2 + \\ 0 2 (1) 2 H N 0 3 = ^ H 2 0 + 2 NO + 2 0 2 (2) The e q u i l i b r i u m constants of these two equations show a d i s s o c i a t i o n of #1.5 per cent and 1.97 per cent o r e s p e c t i v e l y at 130 and atmospheric pressure. Since the oxygen w i l l be removed by the r e a c t i o n w i t h the p y r i t e the . . . .. 3 7 . e q u i l i b r i u m w i l l be s h i f t e d c o n s i d e r a b l y t o the r i g h t . Thus both equations must be considered as the source f o r the oxygen consumed i n the r e a c t i o n . Considering these f a c t s i t was p o s s i b l e to p o s t u l a t e the mechanism as f o l l o w s : 2 HNO3 ==• H 2 0 + 2 N 0 2 + h 0 2 (1) 2 HNO3 ~T~ H 2 0 + 2 NO * 2 ° 2 (2) • . 2 2 F e S 2 + 2 ° 2 ~-r\"~\" F e 2 ° 3 + * S 2 (3) >2S2 f 2 O2 =&=*=• 2 S 0 2 + 0 2 2 H 2 0 + 2 S 0 3 = ^ = r 2 H2SO^ (4) F e 2 0 3 «• 3 H 2 S 0 4 = s r F e 2 ( S 0 4 ) 3 * 3 H 20 (5) I t may be considered that r e a c t i o n (4) w i l l stop at the formation o f s u l f u r t r i o x i d e and t h a t r e a c t i o n (5) should be w r i t t e n F e 2 0 3 + 3 S0 3 =*=2=-Fe 2 ( S 0 4 ) 3 (6) However, i t has been noted t h a t there was no s u l f a t e or mere t r a c e s of s u l f a t e i o n i n the product gas scrubber s o l u t i o n s . T h i s i n d i c a t e d that t h e r e were p r a c t i c a l l y no s u l f u r oxides i n the product gases. I t was a l s o found t h a t there was always an excess of s u l f a t e i o n ( 5 - 2 4 per cent) compared to the i d e a that eithej? f r e e s u l f u r i c a c i d was present or a molecule of s u l f u r i c a c i d or s u l f u r t r i o x i d e had been absorbed i n t o the f e r r i c s u l f a t e molecule or was s t r o n g l y adsorbed by . . . 38. the s o l i d s u r f a c e . Thus i t seemed most probable t h a t r e a c t i o n s . ( 4 ) and (5) proceeded as given , or by r e a c t i o n (6) proceeding e x c l u s i v e l y on the s o l i d s u r f a c e , w i t h an a d d i t i o n a l p o s s i b l e r e a c t i o n : F e 2 ( S 0 4 ) 3 + H 2 S 0 4 = r F e 2 ( S 0 4 ) 3 . H 2 S 0 4 I f n i t r i c a c i d was taken as the l i m i t i n g r e a ctant such t h a t i t could be considered t h a t r e a c t i o n (2) went t o completion the equations were found t o t o t a l as f o l l o w s : 4 Fe S 2 + 16 HN03 ==: 8 H 20 + 16 NO + ZS? + 2 F e 2 ( S O ^ Since i n the r e a c t i o n products there was found f e r r i c oxide and excess s u l f a t e i o n i t can be seen that the o v e r a l l mechanism d i d not f o l l o w a s t o i c h i o m e t r i c r e a c t i o n , but acted as a sequence of r e a c t i o n s of v a r y i n g r a t e s . The r e s u l t s of the runs could best be seen from the p l o t s of the data. I n the p l o t of weight reacted versus time at 160°C, Figu r e 3, the data p o i n t s were found t o l i e on s t r a i g h t l i n e s which passed through the o r i g i n . This showed t h a t the ra t e of r e a c t i o n was a constant; i . e . , dx z constant dt Therefore the r e a c t i o n was of apparent zero-order w i t h respect to n i t r i c a c i d (or oxygen) at 160° not only on an o v e r a l l b a s i s but f o r the formation of f e r r i d s u l f a t e and f e r r i c oxide as w e l l . Thus the r e a c t i o n was completely independent of the 39. pressure and the surface of the p a r t i c l e s , and according-to Langmui^s theory^was almost completely covered at a l l times with reacting molecules. The maximum amount of p y r i t e s reacted i n any run was about 11 per cent.Therefore,the p y r i t e s were present i n large excess, and the n i t r i c acid was the l i m i t i n g reactant. The curves given i n the plot of weight reacted veisis temperature f o r one hour, Figure 2, showed a marked decrease i n the amount of reaction between 145° and 160° f o r the t o t a l weight curve and the curve representing the amount of i r o n as f e r r i c s u l f a t e . The curve f o r the i r o n as f e r r i c oxide stayed approximately constant. Since the reaction a t 160° was of zero order a surface reaction was indicated. This marked decrease could be caused by a change i n the propertiescf the surface and i t s consequent deactivation. As the amount of f e r r i c oxide remained e s s e n t i a l l y constant and as the amount of f e r r i c sulfate decreased the rate of reaction (3) of the mechanism must have been disturbed by the increase i n temperature. In surface reactions the reaction rate can be i n h i b i t e d by a reactant or product, or by a general change i n surface a c t i v i t y . I t waw noted that at about 159.5° c the v i s c o s i t y of s u l f u r started a sharp increase from about 10 cp. at the lower temperatures to 4,500 cp. at 171°C. This marked change i n the v i s c o s i t y , and consequently other physical properties, of s u l f u r could change the surface l a y e r properties giving a deactivation as shown by the curves of Figure 2. 40. In the runs using n i t r i c acid alone the pressure of the gases was measured at i n t e r v a l s . From the plots of the data f o r runs 20 and 2 2 , Figures 6 and 5 respectively, i t can be seen that i n general the pressure decreases from the i n i t i a l pressure to some equilibrium value. The p l o t f o r 1 6 0 ° shows an i n i t i a l increase i n pressure then the descent to the equilibrium tfalue. Since the n i t r i c a c i d vapor was found to enter the f l a s k at a temperature of 1 3 9 .5°C. the. increase would be due to the Harming of the gases to l 6 0°C. The decrease i n pressure to an equilibrium value can be r e a d i l y understood by examination of the equilibrium At 130°C. i t has been found by t h i s equation that 6 8 . 2 per cent n i t r i c acid was 81.5 per cent dissociated at one atmosphere, and 83.I per cent dissociated at 0.853 atmospheres. In other words as the pressure decreased the per cent d i s s o c i a t i o n increased. As the reactor f l a s k was evacuated to within 2 0 - 4 0 mm, Hg. i n order to f i l l the f l a s k with n i t r i c a c i d vapor, i t can be seen that the i n i t i a l vapors were entering i n t o a very low pressure and that t h i s pressure would b u i l d up as the f l a s k was f i l l e d . Since the f l a s k f i l l e d slowly (about one minute) the vapors i n i t i a l l y were more dissociated than they should have been f o r equilibrium. As the d i s s o c i a t i o n comes back to i t s equilibrium value the pressure w i l l decrease due to the s h i f t i n g to the l e s s e r number of moles. constant. 41. The pressure curves f o r the reaction r uns, shown i n Figures 4 and 4A, were found generally to increase. There were some deviations from t h i s but they did not seem to be serious ones. At 160° f o r runs l£ and 19 there were found d e f i n i t e increases i n pressure. Since the n i t r i c acid vapor entered the f l a s k at a lower temperature, part of t h i s increase would be due to the warming up of the gases. Also as the oxygen was being removed by the reaction with p y r i t e then the gases would become more dissociated thus causing a greater increase i n pressure. I t should be noted that i n run 16 the pressure appeared to remain constant. This e n t i r e l y disagreed with runs 18 and 19 and showed that i t may be i n error. Since the pressure was so very constant i t was most probably due to a clogged manometer stopcock. Run 17 can be explained i n the same manner as runs 13 and 19. At the lower tempeaatures there was found a somewhat d i f f e r e n t behaviour. In run 11 at 130°C the pressure was found to remain f a i r l y constant r i s i n g s l i g h t l y i n the middle and f a l l i n g again. Since the acid vapor entered the f l a s k at a temperature above that of the f l a s k the cooling of the vapors would compensate f o r the changes made by the s h i f t i n g of the equilibrium keeping the pressure r e l a t i v e l y constant. For run 17 at 145°C. the pressure was found to r i s e considerably then to f a l l back to the o r i g i n a l pressure. The r i s e must be due to the increase i n temperature and the s h i f t i n g of the equilibrium which must eventually have caused the pressure to f a l l to i t s o r i g i n a l value. 42.. I t was noted that i n the c a l c u l a t i o n of the percentage oxygen f o r run 19 (l60°C f o r 2 hours) that 114 per cent of the a v a i l a b l e oxygen was used up. The amount of a v a i l a b l e oxygen was c a l c u l a t e d from the amount of n i t r i c a c i d o r i g i n a l l y placed i n the r e a c t o r f l a s k . This value f o r the n i t r i c a c i d was only an approximation having been c a l c u -l a t e d from e q u i l i b r i u m data which, i n t u r n , was based on thermodynamic data. I n the c a l c u l a t i o n of t h i s value there were made such assumptions as i d e a l behaviour of the gases. Thus, i f the gases a c t u a l l y deviated t o some measurable degree from i d e a l i t y and i f the e q u i l i b r i u m data was accurate t o w i t h i n say only ten per cent, then there would be considerable e r r o r i n the amount of o r i g i n a l n i t r i c a c i d and, consequently, of the a v a i l a b l e oxygen. The n i t r i c a c i d v a l ue was only an approximation and was intended t o show the r e l a t i v e amount of r e a c t i o n t h a t had taken place w i t h respect t o the n i t r i c o a c i d . A l s o the values would show i f the l i m i t of the r e a c t i n , due t o the l a c k of f u r t h e r oxygen, had been reached. Since the amount used i n run 19 gave a value g r e a t e r than the c a l c u l a t e d amount i t could be assumed that the r e a c t i o n a t t h i s p o i n t approached the l i m i t . o CONCLUSIONS 43. A suggested mechanism f o r the r e a c t i o n of p y r i t e w i t h vapor s t a t e n i t r i c a c i d may be w r i t t e n as f o l l o w s : 2 HN0 3==r H 20 + 2 N0 2 + & 0 2 (1) 2 HNO3 =3=s= H 20 + 2 NO t 2 02 (2) 2 FeS 2 + 2 ° 2 : : 5 ± - = : F e 2 0 3 * * ( 3 ) ^So + 2 0 2 52= 2 S 0 2 + °2 U 2 H 20 + 2 S0„ = T 2 H oS0, (4) * 3 2 4 F e 2 0 3 + 3 H 2 S 0 4 = = F e 2 ( S 0 4 ) 3 - 3 H 20 (5) or Fe2°3 * 3 SO3 F e 2 ( S 0 4 ) 3 (6) wi t h t he p o s s i b l e r e a c t i o n : F e 2 ( S 0 4 ) 3 + H 2 S 0 4 = 5 = F e 2 ( S 0 4 ) 3 , H 2S0 4 o The weight reacted versus time curve f o r 160 showed that the r e a c t i o n was of zero-order at t h i s temperature. Since the aero order would i n d i c a t e strong oxygen ad s o r p t i o n and no s u l f u r oxides appeared i n the gases the r e a c t i o n s (3)> (4)> (5) and (6) must a l l be surface r e a c t i o n s . 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Chem. Soc. l^., 164 (1861); L i e b i g ' s Ann. 116, 203 (i860) (See M e l l o r , l o c . c i t . 574). 42. Rowe, R.C. Can. Mining. J . j>9_, 181-3 (1938). 43. Schwab, G.M. and J . P h i l i n i s , 3. Am. Chem. Soc. 69, 2588-96 (1947). 44. S c o r t e c c i , A. and M. S c o r t e c c i . M e t a l Prog. 60, 72-5 (1951). Chem. Eng. j>8, 350-1 (1951)1 45. Sidgwick, N. V. The Chemical Elements and T h e i r Compounds. Oxford U n i v e r s i t y Press, London, 2, 1333 (1950). 45A. I b i d . 1330. 46. I b i d . 1357. 47. I b i d . 909. 48. I b i d . 1334. 48A. S t r i c k l a n d , X D , H . B r i t i s h Columbia Research C o u n c i l . . P r i v a t e correspondence. 49. S u z u k i , H. B u l l . I n s t . Phys. Chem. Research (Tokyo) 22, 293-7 (1943). 50. Wahler, M a r t i n and Schmidt. Z e i t . f u r Anorg. A l g . Chemie. 127, 273-94 (1923). 48. APPENDIX A Analysis of Pyr i t e and Extract Residue. The sample was ground to pass an 80-mesh screen and dried f o r one hour at 1 0 0°C. Approximately 1 . 3 7 3 g. of the sample was weighed out accurately and placed i n a 400-ml beaker. Ten ml. of bromine-carbon tetrachloride reagent (carbon t e t r a c h l o r i d e saturated with bromine) was added, the beaker covered with a watch glass and the mixture l e f t to stand f o r 15 minutes i n a cold bath with occasional shaking. Next, 15 ml. of concentrated n i t r i c acid was added and the mixture was allowed to stand f o r 15 minutes at room-temperature. The mixture was then warmed on an asbestos board on a steam . bath with the watch glass cover raised, by glass r i d e r s . When the reaction had ceased and a l l the bromine had been vaporised the mixture was evaporated to dryness on a steam bath. Once the residue was dry ten ml. of concentrated hydrochloric acid was added and the mixture again evaporated to dryness. Then there was added 1+ ml. of concentrated hydrochloric acid and the mixture l e f t to stand f o r 5 minutes. Next 1 0 0 ml. of hot d i s t i l l e d water was added and the mixture boiled f o r 5 minutes. At t h i s point a l l of the sample except f o r the s i l i c i o u s materials was i n s o l u t i o n . Twenty ml. of concen-trated ammonium hydroxide was added and the p r e c i p i t a t e f i l t e r e d to dryness using suction. The p r e c i p i t a t e was redissolved i n 20 ml. of 4 N HG1 and re p r e c i p i t a t e d with concentrated ammonium hydroxide. The p r e c i p i t a t e was again 49. f i l t e r e d o f f , washed w i t h d i s t i l l e d water and sucked t o dryness. The ammoniacal f i l t r a t e s were combined f o r a s u l f a t e a n a l y s i s (Appendix D). The i r o n p r e c i p i t a t e was d i s s o l v e d w i t h 20 ml. of 4 N h y d r o c h l o r i c a c i d and the f i l t e r paper r i n s e d w i t h d i s t i l l e d water. A f e r r i c a n a l y s i s (Appen-d i x B) was run on the s o l u t i o n . 50. APPENDIX B A n a l y t i c a l Method f o r F e r r i c Ion In the a n a l y s i s f o r f e r r i c i o n a sample of the e x t r a c t (20 ml.) was p i p e t t e d i n t o a 250-ml. Erlenmeyer f l a s k and 4 ml. of 4 N HC1 was added. Next 2 g. of K l was weighed out and d i s s o l v e d i n 10 ml. of d i s t i l l e d water. The potassium i o d i d e s o l u t i o n was added to the a c i d i f i e d sample and l e t stand f o r three minuttes. The mixture was t i t r a t e d w ith a standardised 0.1 N t h i o s u l f a t e s o l u t i o n . F i v e ml. of s t a r c h s o l u t i o n was added near the end point and the t i t r a t i o n completed t o the disappearance of the deep iodo-blue c o l o r . The sample was then t i t r a t e d t o a deep blue end-point w i t h a 0.1 N i o d i n e s o l u t i o n which had been compared to the t h i o -s u l f a t e s o l u t i o n . The necessary c a l c u l a t i o n s were then made to determine the f e r r i c i o n content using a m u l t i p l i c a t i o n f a c t o r t o f i n d the t o t a l f e r r i c i o n i n the e x t r a c t . 51. APPENDIX C A n a l y t i c a l Method f o r Ferrous Ion For the f e r r o u s i o n determinations a sample of the e x t r a c t (20 ml.) was taken and 15 ml. of s u l f u r i c -phosphoric a c i d mixture (150 ml. H-^ PO^ - 150 ml h^SO^ d i l u t e d t o 1 l i t r e . ) were added. The sample was then d i l u t e d t o 100 ml. w i t h d i s t i l l e d water and three drops of diphenylamine i n d i c a t o r added. The mixture was t i t r a t e d w i t h a standardised 0.1 N dichromate s o l u t i o n to a very deep v i o l e t - b l u e end point adding the l a s t few ml. drop by drop. APPENDIX D 52. A n a l y t i c a l Method f o r Sulfate Ion Since for the sulfate analysis f e r r i c ion i n t e r -fered i t had to be removed. Also any s u l f u r , i n a lower oxidation state than the sulfate ion, had to be oxidized to the sulfate state with hydrogen peroxide. In the following analysis there has been given steps to remove the f e r r i c i on and to oxidize the s u l f u r to the sulf a t e state, but these steps have been l e f t out i n any amalysis i n which they did not apply. A sample of the extract (50-150 ml. depending on the strength of the extract) was taken and the i r o n precip-i t a t e d out with an excess (5-10 ml.) of concentrated ammonium hydroxide. The p r e c i p i t a t e was f i l t e r e d to dryness using suction. The residue was then d i s s o l v e d with hydrochloric acid and the iro n r e p r e c i p i t a t e d with an excess of ammonium hydroxide. The p r e c i p i t a t e was again f i l t e r e d off and washed with d i s t i l l e d water. The f i l t e r a t e s were then combined. Next the lower forms of sulfur were oxidized to sulf a t e ion by adding hydrogen peroxide and leaving to stand i n a covered beaker. The solution was then brought to a b o i l to expel any excess oxygen. The solution was cooled and then neutralized with 4 N HC1 using a methyl orange i n d i c a t o r . Two hundred ml. of 10% Ba C l 2 solution was made up, a c i d i f i e d with 8 ml. of 3 N HC1 and heated to b o i l i n g . The neutralized sample was added to the hot Ba C l 2 solution drop by drop with 53. continuous s t i r r i n g . The mixture was digested ab or near the b o i l i n g p o i n t f o r one hour. The mixture was allowed to stand i n order t o c o o l and to s e t t l e out the p r e c i p i t a t e . The mixture was f i l t e r e d through a t a r e d Gooch c r u c i b l e washing the p r e c i p i t a t e by decantation w i t h water. The p r e c i p i t a t e was then heated i n a F i s h e r burner f o r one hour and subsequent f i f t e e n minute periods t o constant weight. APPENDIX E cellaneous Graphs 55. 375 400 425 TEMPERATURE, °K F/GURE 7- AC VALUES FOR THE ASSOC/AT/O/V OF /V/TR/C AC/D FORSYTHE,¥.R.. AND W.F..GIA.UQUE. J'.AM.CHEM..S0C.6^ ,60 (1942) 56. FIGURE & - V/SCOSITY OF L/QU/D SULFUR HANDBOOK OF CHEMISTRY AND PHYSICS. CHEMICAL RUBBER PUBLISHING CO. 1735 (194$) "@en ; edm:hasType "Thesis/Dissertation"@en ; edm:isShownAt "10.14288/1.0059120"@en ; dcterms:language "eng"@en ; ns0:degreeDiscipline "Chemical and Biological Engineering"@en ; edm:provider "Vancouver : University of British Columbia Library"@en ; dcterms:publisher "University of British Columbia"@en ; dcterms:rights "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en ; ns0:scholarLevel "Graduate"@en ; dcterms:title "Studies on iron pyrite"@en ; dcterms:type "Text"@en ; ns0:identifierURI "http://hdl.handle.net/2429/40433"@en .