Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Reduction of aqueous cobaltous sulfate by carbon monoxide Halvorson, Harold Norman 1966

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1966_A1 H25.pdf [ 7.93MB ]
Metadata
JSON: 831-1.0093636.json
JSON-LD: 831-1.0093636-ld.json
RDF/XML (Pretty): 831-1.0093636-rdf.xml
RDF/JSON: 831-1.0093636-rdf.json
Turtle: 831-1.0093636-turtle.txt
N-Triples: 831-1.0093636-rdf-ntriples.txt
Original Record: 831-1.0093636-source.json
Full Text
831-1.0093636-fulltext.txt
Citation
831-1.0093636.ris

Full Text

REDUCTION OF AQUEOUS COBALTOUS SULFATE BY CARBON MONOXIDE by HAROLD NORMAN HALVORSON B.A., University of B r i t i s h Columbia, 1955 M.Sc, University of Br i t i s h - Columbia, ,1956 A TRESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of METALLURGY We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA . March, 1966.•>-In presenting this thesis i n p a r t i a l fulfilment of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library shall make i t f r e e l y available for reference and study. I further agree that per-mission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. I t i s understood that, copying or publi-cation of this thesis for f i n a n c i a l gain sh a l l not be allowed without my written permission* Department of Metallurgy The University of B r i t i s h Columbia, Vancouver 8, Canada Date May 6. 1966 THE UNIVERSITY OF BRITISH COLUMBIA FACULTY OF GRADUATE STUDIES PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY B.A0_, The University of B r i t i s h Columbia, 1955 M.S., The University of B r i t i s h Columbia, 1956 IN ROOM 210, METALLURGY BUILDING THURSDAY, March 31, 1966, at 1:30 P.M. of HAROLD NORMAN HALVORSON COMMITTEE IN CHARGE Chairman: I. McT. Cowan W„ M. Armstrong B. R. James C. S. Samis E. Peters K. L, Pinder D. Tromans External Examiner: H. H. Kellogg Professor of Metallurgy Columbia University Research Supervisor: E. Peters REDUCTION OF ACQUEOUS COBALTOUS SULFATE BY CARBON MONOXIDE ABSTRACT This i s a study of the catalysed reduction of cobalt (IT) to metal by carbon monoxide from aqueous, amxnoniacal solutions between 180 and 230°C and from 0 to 50 atm. CO. The reaction proceeds through the intermediate for-mation of a cobalt carbonyl anion. Under the conditions of this study this intermediate i s produced homogeneously, and also heterogeneously in the presence of cobalt sul-fide. Metal formation occurs only in the presence of cobalt s u l f i d e . The stoichiometry of the production of cobalt car-bonyl anion i s consistent with the equation. 2Co(NH3) + + + 11 Co + (12-2n) NH3 + 6H20 — > 2Co(C0) 4~ + 3C0 3 = + 12NH 4 + Metal formation follows stoichiometry of-the equation 9Co(NH3) +2Co(C0)4~ + (32-9n)NH3 + 16H20 -TTT^ llCo° + 8C0 3 = + 32 NH 4 + The following equations represent a mechanism that i s consistent with the k i n e t i c observations; CoCNH^"1-1" + CO + NH3 + R2O s = £ ENH 3) n Co - C - OH] + + NH 4 + fast 0 [(NH3) Co - C - OH] CoS v fi [(NH3)nCo - C - 0H]+ d s fast ENH 3) nCo - ?C - 0H]+ d s + CoS x ((? [(NH3) Co - C - OH]° + [CoS x] + [CoS x] + + %C0 + 2NH 3 + H 20 — — - » CoS x + %C0 3~ + 2NH 4 + fast 0 Q'NHoCo - C - OH]" , + 4C0 + (3-n)NH.„ + Ho0 > ads Co(CO) 4" d + C0 3" + 3NH4 Co(C0) 4^ d g + 4,5 Co(NH 3)^ + + + (16-4.5n) NH3-.+ 8H20 — 5.5Co° + 4C0 3 = +1.6 NH 4 + A side reaction involving carbon monoxide and hydroxyl ion produces formate ion, In the presence of cobalt s u l f i d e , hydrogen rather than formate ion i s the product. The following equations represent a mechanism that i s consistent with experimental observations: CO + NH3 + H 20 HCOO" + NH 4 + rapid equilibrium HCOO" + CoSv — = ± HCOO" rapid equilibrium x ads H C 0 0 a d s + ^ 3 + H2° — • H2 + C 0 3 = + N H 4 + S l ° W A method for the separation of cobalt (II) from nickel (II) i n aqueous solution i s suggested, GRADUATE STUDIES Metallurgical Thermodynamics Metallurgical Kinetics Structure of Metal Compounds Metal. Surface Reactions H.ydrometallurgy Research Methods Theory of Alloys Chemical. Thermodynamics S t a t i s t i c a l Mechanics Kinetics Introduction, to Quantum Mechanics C. S„ Samis J, Halpern J, Halpern H. Evans E. Peters Staff P, Myers H„ M. Daggett J'„ G. Hooley W „ A, Bryc e W. Opechowski PUBLICATIONS 1. Halvorson, H.N. and Halpern, J . "Kinetics of the Re-action Between HCOOH and TL (III) i n Aqueous Solution" J.A.C.S. 78, 5562 (1956) . 2. Evans, R.S. and Halvorson, H.N. "Cause and Control of Brown Stain i n Western Hemlock", Forest Products J . j8, 11, 367 (1962). 3. Halvorson H.N., "Some Factors Affecting the Choice of a Proper Dry K i l n " B.C. Lumberman, 61_, Sept. 1962. 4. Halvorson, H.N. and Stuart,- W.M. "Improvement, of Sawmill Cutting Tool Sharp L i f e by Surface Hardening" Forest. Products J . 108, March 1963. 5. Halvorson, H.N. "Review of Wood Drying Methods", B.C. Lumberman, 42, Feb. 1963. 6. Howard, T.E., Halvorson, H.N., and Walden, CC. "Toxicity of Cu Compounds to the Snail Vector Hosts of the Agents of Schistosome Dermatitis" Amer. J . of Hygiene, 79_> 33 (1964) . Supervisor: Dr. Ernest Peters i ABSTRACT This i s a study of the catalysed reduction of cobalt (II) to metal by carbon monoxide from aqueous, ammoniacal solutions between 180 and 230°C and from 0 to 50 atm. CO. The reaction proceeds through the intermediate formation of a cobalt carbonyl anion. Under the conditions of t h i s study t h i s intermediate i s produced homogeneously, and al s o heterogeneously i n the presence of cobalt s u l f i d e . .Metal formation occurs only i n the presence of cobalt s u l f i d e . The stoichiometry of the production of cobalt carbonyl anion i s consistent with the equation 2Co(NH 3) n + + + 11C0 + (12-2n) NH3 + 6 H 20 * 2Co(C0) 4" + 3C0 3 = + 12NH 4 + Metal formation follows the stoichiometry of the equation 9Co(NH 3) n + + + 2Co(C0) 4~ + (32-9n)NH3 + l 6 H 20 > I I C 0 0 + 8C0 3 + 32 NH 4 + CoS x The following equations represent a mechanism that i s consistent with the k i n e t i c observations'. 0 ++ » + + Co(NH 3) + CO + NH 3 + H 20 - — [ (NH3) Co --C - OH'] + NH4 f a s t 9 + + [(NH 3) nCo - C - OH] + C o S x ^ = i [(NH 3) nCo - C - 0 H ] a d s f a s t n 0 i i ,? k !? [(NH 3) nCo - C - 0 H ] ^ d g + CoS x ^ [( N H 3 ) n Co - C - 0H>]° d g + [CoS x] + [CoS x] + V 2CO + 2NH3 + H 20 * CoS + 1 / 2 C 0 3 ~ + 2NH 4 + f a s t 0 [(NH 3) nCo - fi - 0 H ] ° d g + kCO + (3-n)NH3 + H 20 * C o ( C O ) 4 " a d s + C 0 3 = + JNH 4 + ++ + C o ( C O ) 4 a d s + +.5 Co(NH 3) n + (16-4.511) NH^ + 8H 20 >5.5Co° + 4C0 3 + 16 NH4 A side reaction i n v o l v i n g carbon monoxide and hydroxyl ion produces formate ion. In the presence of cobalt s u l f i d e , hydrogen rather than formate ion i s the product. The following equations represent a mechanism that i s consistent with experimental observations: CO + Ws + H 20 v ' HCOO" + NH 4 + rapid equilibrium HCOO- + CoS x s v HCOO~ds rapid equilibrium HC00~,o + NH 3 + H 20 — ^ r _ ) . H 2 + C 0 3 = + NH 4 + slow A method for the separation of cobalt (II) from n i c k e l (II) i n aqueous s o l u t i o n i s suggested. i i i ACKNOWLEDGEMENT I am grateful to Dr. E. Peters for his direction and for a stimulating and we l l conceived problem and to Mrs. A. M. Armstrong for her help i n the l a t t e r part of t h i s study, and constructive c r i t i c i s m during the preparation of the manuscript. I wish also to thank Dr. D. Tromans for the electron microscopy work and interpretation of these data. I am indebted to the people of Canada for grants i n aid of research and a Studentship through the National Research Council of Canada. To my wife I simply say thank you. i v TABLE OF CONTENTS Page I . INTRODUCTION , 1-1 General 1 1-2 Review of CO Reduction of Metal Ions i n Aqueous Solutions . 3 1-3 Structure of Carbon Monoxide and Metal Carbonyls 5 I I . EXPERIMENTAL II-1 Materials 8 II-2 Preparation of Reagents 8 II-3 A n a l y t i c a l Procedures 9 I I A p p a r a t u s 11 II-5 Experimental Procedures . . . . . 12 I I I . RESULTS I I I - l Preliminary Experiments 13 A. Chemical Species Observed 13 B. T y p i c a l Rate Curves 19 III-2 K i n e t i c Study 22 A. E f f e c t of I n i t i a l NH3 Concentration 22 B. E f f e c t of I n i t i a l (NH 4) 2S0 4 Concentration 22 C. E f f e c t of S~ Concentration 29 D. E f f e c t of Pressure of CO + + 33 E. E f f e c t of I n i t i a l Co(NH 3) n Concentration 33 F. S a l t E f f e c t 33 G. E f f e c t of Co(III) Concentration 37 H. E f f e c t of Temperature 37 I. E f f e c t of Catalysts a. Cyanide and Tart-rate -^0 b. Various Metal Ions kO III-3 Stoichiometry of the Reaction kk I l l - k Production of Magnetic M a t e r i a l . . . . 51 III-5 E f f e c t of HCOO" and H 2 51 III-6 Nature of the Cobalt Metal Product 59 IV. DISCUSSION IV-1 Summary of Results 63 IV-2 Experimental Rate Law IV-3 Calculated Rate Law Sk IV-k Evaluation of the Rate Constants 69 IV-5 Integration of the Rate Law and C a l c u l a t i o n of Reduction Curves 72 Table of Contents (cont'd) Page V. CONCLUSION 76 VI. APPLICATION OF RESULTS 78 VII. RECOMMENDATION FOR FURTHER STUDY 81 V I I I . REFERENCES 82 APPENDIX A. Tabulation of Experimental Data Qk APPENDIX B. Calculation of I n i t i a l free NH3 and OH" Concentrations 93 APPENDIX C. Kinetics and Mechanism of H 2 Formation During Reduction of Co(NH 3) n by CO 99 APPENDIX D. Microstructure of Reduction Solids 10" vi LIST OF FIGURES Page Figure 1. Infra-Red Spectra of C o ( C 0 ) 4 ~ r HCo(C0) 4 and Unknown . . 17 Figure 2. Typical Rate Curves 20 Figure 3. Effect of Initial NH3 Concentration on Rate 23 Figure k. Dependence of Max. Rate on Initial free NR3 Concentration at Constant NH4 Level 2k Figure 5. Dependence of Max. Rate on Initial 0H~Concentration at Constant NH4 Level 25 Figure 6. Effect of Initial NH4+ Concentration on Reduction Rate 26 Figure 7. Effect of Initial 0H~ Concentration on Rate at Constant NH3 Addition 26 Figure 8. Effect of Initial OH~Concentration on Rate for^Constant NH3 and NH4 Addition Series 28 Figure 9. Effect of S = Addition on Rate 30 Figure 10. Volume versus Surface Area Effect of CoSx on Rate . . . 31 Figure 11. Effect of P C Q on Rate 34 ++ Figure 12. Effect of Initial Co(NH3)n Concentrations on Rate . . 35 Figure 13. Arrheniu s Plot 39 Figure ikA. Production of Cobalt Metal and Co ( C 0 ) 4 ~ with CO . . . . k^> Figure l4B. Reduction of Co(NH 3) n + + by Co ( C 0 ) 4 " in Absence of CO 45 Figure I 5 A . Production of Co ( C 0 ) 4 ~ in Absence of CoSx 47 Figure 15B. Reduction of Co(NH3) n + + by Co ( C 0 ) 4 " in Absence of CO . . 1+7 Figure 16. Rate of Production of H2 During CO Reduction of Co(NH3)n , 56 Figure 17. Max. Rate of Reduction' of Co(NH 3) n + + and H2 Formation at Constant NH3 Addition 57 ++ Figure 18. Comparison of Rates of Reduction of Co(KH3)n by H2 and CO ! 58 Figure 19. Effect of Recycling on Rate 60 v i i L i s t of Figures (cont'd.) Page Figure 20. Effect of Co 0 on Rate 62 Figure 21. Comparison of Calculated and Experimental Rate Curves 73 Figure 22. Comparison of Calculated and Experimental Rate Curves 7I+. Figure B-I. Effect of I n i t i a l NH3 Concentrations on Vapor Pressure at 215°C 9k ++ Figure B-2 Effect of I n i t i a l Co(KH 3) n Concentration on Vapor Pressure at 215°C 95 Figure C - l Effect of I n i t i a l NH3 Concentration on H2 Production 102 Figure C-2 Effect of Addition on H2 Production 103 Figure D-l Comparison of Optical Micrographs of CoS x and Co" -CoS ' Mixtures 108 Figure D-2 Electron Micrographs of CoS x at Various Magnifications 109 Figure D-3 Electron Micrograph and Electron D i f f . Pattern of CoS x 110 Figure T)-k Thickness Extinction Fringe Patterns for CoS^ . . . . 113 Figure D-5 Electron Micrograph and Electron D i f f . Pattern of Co° l l ^ Figure D-6 Electron Micrograph and Electron D i f f . Pattern of Unidentified P a r t i c l e s 116 v i i i LIST OF TABLES Page TABLE I. Summary of Kinetic Studies of Metal Ion-CO Reactions h TABLE I I . Summary of Cobalt Carbonyl Forming Reactions 6 TABLE I I I . Indication of Cobalt Metal i n Reaction Residues . . . . 15 TABLE IV. Chemical Analysis of Cobalt Carbonyl Compound 16 TABLE V. Determination of Co(CO) 4~ i n P a r t i a l l y Reduced Solutions 18 TABLE VI. D i s t r i b u t i o n of C03~ Between Phases at 215°C 19 TABLE VII. Detection of HCOO" 19 TABLE V I I I . Salt Effect i n Reduction of Co(NH 3) n + + by CO 36 TABLE IX. Effect of Co(III) on Rate of Reduction 3 8 TABLE X. Effect of Cyanide and Tartrate on Rate of Reduction . . I n TABLE XI. Effect of Various Cations on Reduction Rate l±2 TABLE XII. Material Balance of Two Stage Run kQ TABLE X I I I . Material Balance of Single Stage Run 50 TABLE XIV. Qualitative Assessment of Presence of Co° and Co(C0) 4~ 52 ' TABLE XV. HCOO" Reduction of Co(NH 3) n T +  TABLE XVI. Production of E2, CO and HC00~ 5 5 TABLE XVII..Separation of Co(II) from Ni(II) i n Aqueous Media by CO 79 TABLE A-I. Effect of I n i t i a l NH3 Concentration 85 TABLE A-II Effect of I n i t i a l (NH 4) 2S0 4 Concentration on Rate . . . 86 TABLE A-III Effect of S~~ Concentration on Rate . . . . . 87 TABLE A-IV. Effect of P c o on Rate 89 TABLE A-V. .Effect of I n i t i a l Co(NH 3) n Concentration on Rate . . . 90 TABLE A-VI. Effect of Temperature 91 TABLE A-VII.Relative Reduction Rates of Co(NH 3) n + + by H 2 and CO . . 92 TABLE B-I. Relationship Between I n i t i a l Total and Free NH3 Concentrations at 215°C 97 i x L i s t of Tables (cont'd) Page TABLE B-II. Relationship Between I n i t i a l NH3 and OH Concentrations at 215°C 98 TABLE C-I. Effect of Various Test Parameters on H 2 Production . . . 100 TABLE D-I. Electron D i f f r a c t i o n Pattern of CoS x I l l - 1 -I. INTRODUCTION 1.General Recovery of metals from aqueous leach solutions has been achieved t r a d i t i o n a l l y by cementation, by electrowinning and more recently, by displace-ment with reducing gases such as hydrogen. Carbon monoxide i s also an i n t e r -esting reducing gas which has had application t r a d i t i o n a l l y i n blast furnace reductions and i n the Mond Nickel Process but has not yet been used commercially i n a hydrometallurgical application. In the laboratory i t has been tested i n a variety of aqueous reduction reactions i n much the same way as hydrogen re-duction has been studied and i n f a c t , mixtures of hydrogen and carbon monox-ide have also been studied because standard commercial processes can produce these mixtures at lower cost than the pure gas components. A review of work done with both hydrogen and carbon monoxide, as w e l l as a discussion of as-sociated c a t a l y t i c processes i s desirable i n obtaining an understanding of the carbon monoxide reduction study that i s the subject of t h i s t h e s i s . Interest i n carbon monoxide alone as a hydrometallurgical reducing agent has arisen l a r g e l y because of i t s a v a i l a b i l i t y at low cost from top gases of f e r r o - a l l o y furnaces, and from the observation that i t rapidly reduces Na2Cr04 solutions to y i e l d Cr2.03 precipitates under conditions i n which the re-action with hydrogen i s uselessly slow"1". - 2 -Because of thermodynamic l i m i t a t i o n s only those metals l y i n g below hydrogen and carbon monoxide i n the electromotive series can be reduced. Some scope i n extending t h i s l i m i t i s afforded by increasing pH, temperature and gas pressure but for both reductants cobalt (II) with an E 0 value of -0.277 has proven the l i m i t to date. Oxidation of hydrogen and carbon monoxide have been found mechanisti-c a l l y quite d i f f e r e n t . Hydrogen i s oxidized by loss of electrons; carbon monox-ide, by acquisition of an oxygen atom. With hydrogen two different mechanistic methods of destruction of the molecule have been observed: homolytic and heterolytic s p l i t t i n g . In the f i r s t the molecule s p l i t s into two atoms ( i . e . H 2'—>2E i) which then take part i n the reduction reaction. In heterolytic s p l i t -t i n g the molecule forms a proton and a hydride ion ( i . e . , H 2 — » H + + H~). The latter"then enters the reduction step. In the case of carbon monoxide the mol-ecule picks up oxygen i n the minus 2"state from hydroxyl ion or a water molecule and, simultaneously, surplus electrons resulting from t h i s acquisition are trans-ferred to the metal ion i n the reduction step. With both hydrogen and carbon monoxide i t i s obvious that t h e i r oxidations involve destruction of t h e i r mole-cular configurations as a necessary condition f o r reaction. Because of the marked s t a b i l i t y of both of these molecules t h i s step i s - u s u a l l y very d i f f i c u l t and c r u c i a l to the rate. The single bond energies "in the hydrogen and-carbon monoxide molecules are 104 and 84 k cal/mole, respectively . As the act i v a t i o n energies usually experienced i n metallic ion reductions with these gases"are i n the range 15 to 30 k cal/mole, lower energy paths than those requiring outright breaking of mol-ecular bonds must be employed. The rates of these reactions would, therefore, be very sensitive to c a t a l y t i c systems that provide such low energy paths and, i n fa c t , c a t a l y t i c action i s frequently observed. Both heterogeneous and homogen-eous catalysts have been studied. Halpern and co-workers found that Cu(II),• Ag(I), Hg(II) and Hg 2(II) are successful homogeneous catalysts for hydrogen reductions,3,^ ->5 ,6 ,7 while 8 9 metallic N i , Co, Pt, Pd and C are reported as heterogeneous catalysts ' . Halpern and Harkness"^ report that Ag(I) and Hg(II) ions are homogene-ous catalysts i n the reduction of permanganate ion by carbon monoxide. This c a t a l y t i c effect i s attributed to the favourable reaction path involving an i n t e r -mediate i n s e r t i o n complex of the type Ag - $ - 0 - Mn0 3 No mechanistic, k i n e t i c studies have yet been reported i n the l i t e r a t u r e on heterogeneous catalysis of carbon monoxide reduction of metal ions from aqueous solution. 2.Review of Carbon Monoxide Reduction of Metal Ions i n Aqueous Solutions Metal ions such as Cu(II), N i ( I I ) , Ag(I), Hg(II),>Mn0 4 " and C r 2 0 7 = have been successfully reduced i n aqueous solution by carbon monoxide. Table I summarizes the detailed, k i n e t i c studies that have been made of such reductions. A l l these studies were of homogeneous systems. Of interest i n Table I i s that the reaction of carbon monoxide with metallic ions involves formation of carbon monoxide insertion complexes as intermediates and that the less noble the metal the less tendency f o r metal formation. For certain metals the reduction product i s the carbonyl. No k i n e t i c study was found i n the l i t e r a t u r e on the reduction of cobalt (II) to metal from aqueous solution with carbon monoxide but by analogy TABLE I Summary of Kinetic Studies of Metal Ion CO Reactions Reaction Temp. °C PC0 atm Reaction Products of metallic species Reaction Intermediates of m e t a l l i c species References Mn0 4 _ + CO H g(II) + CO 25-70 25-70 1 1 Mn02 or Mn04 mercury metal (Hg-C-OH) 10 10 Ag(I) + CO i n ammine soln 25-50 1-20 s i l v e r metal 9 L-Ag-C-OH 11 A g(I)+ CO i n a c i d i c soln Cu(II) + CO 60-110 120 1-30 1-1360 s i l v e r metal Cu(C0) +, Cu20, Cu metal i? Ag-C-OAc 0 CH (Cu-C-0H) +,(Cu-C-0H) + + 12 13 Ni(II) + CO 135-220 1-100 Ni(C0) 4 [ ( N H 3 ) n Ni-C-0H] + Ik OH" •+ CO 80° C 1-30 HCOO" rH. [(>:=c = 0 ] - 15 180°C not known H 2 not known 16,17 I I with the results shown i n Table I, one would expect that the product of such a reaction would be a cobalt carbonyl and that a carbon monoxide insertion complex would be an intermediate. There i s r i c h l i t e r a t u r e on the formation of cobalt carbonyls. The work of major interest to t h i s study i s summarized i n Table I I and demonstrates the ease of formation and marked s t a b i l i t y of the cobalt carbonyls. This would support the conclusion reached from Table I that the l i k e l y product of carbon monoxide reduction of cobalt (II) would be a carbonyl and not cobalt metal. 3.Structure of Carbon Monoxide and Metal Carbonyls Carbon monoxide, which i s isoelectronic with the nitrogen molecule, has a rather stable structure. In spite of t h i s s t a b i l i t y , one of the more important properties of CO i s i t s a b i l i t y to form metallic carbonyls. A l l t r a n s i t i o n metals except zirconium and hafnium are known to form such compounds. The stoichiometry of carbonyls tends to the inert gas electron configuration for the metal atom, assuming donation of two electrons from each CO molecule. A l l are inflammable l i q u i d s or readily combustible solids at room temperature and pressure and are soluble i n non-polar solvents. With the exception of vanadium and cobalt carbonyls a l l are stable i n a i r . The vapors are highly toxic and explosive. Fe(CO) 5 and Ni(CO) 4 are p a r t i c u l a r l y dangerous because of high vapor pressures at room temperature. - 6 -TABLE I I Summary of Cobalt Carbonyl Forming Reactions Cobalt Reactant Temp. °C p CO atm Solvent Cobalt Product Ref CoI 2 ") CoCl 2 J CoBr 2 j 150 200 none Co 2(C0) 8 18 C0CO3 150 2if0(H2-tC0) none Co 2(C0) 8 19 C0I 2 ? CoS j 190 25O none Co 2(C0) 8 20 CoO 170 225 hexane Co 2(C0) 8 21 Cobalt acetate 1 Cobalt buturatesjr — — organic Co 2(C0) 8 22 Cobalt s a l t s -7208 — organic Co2(C0)8,Co° 23 Cobalt metal I85 300(H2-*€0) toluene Co 2(C0) 8 2k Co2(CO)e,S,CoS 150 85 hexane [Co 2(C0) 5S] 2 25 Cobalt cysteine") Cobalt t a r t r a t e L CoS ( Co(CN) 2 ) room temp 1 aqueous KOH Co(C0)4~ 26 Co(NH3) 6 + + 250 200-300 aqueous NH3 Co(C0) 4" 27 CoS ^ C0SO3 Co(CN)2^ 25 1 aqueous NaOH Co(C0)4" 28 CoS 60 1 aqueous NaOH Co(C0) 4" 29 K 4Co(CN) 6 room temp 1 aqueous KOH Co(C0)4" 30 The structures of carbonyls are generally accepted, to involve a metal to carbon bond with a l i n e a r M-C-0 structure. Bridging CO groups are present i n polynuclear metal carbonyls. There are two unsubstituted cobalt carbonyls: dicobalt octacarbonyl, Co2(CO)e> and tetracobalt dodecacarbonyl, Co 4(CO) 1 2. The monomolecular form only exists as the cobalt carbonyl anion, Co(CO) 4~, as i t s acid form, HCo(CO)4, as a true s a l t , e.g., Hg[Co(CO) 4] 2, and as a substituted complex, e.g., Co(CO)3NO I I . EXPERIMENTAL - 8 -1. M a t e r i a l s Only Baker and Adamson reagent grade chemicals were used. D i s t i l l e d water was employed e x c l u s i v e l y . Carbon monoxide (99-5$) w a s s u p p l i e d by the Matheson Company i n c y l i n d e r s at 1500 p s i and was used without f u r t h e r p u r i f i -c a t i o n . 2. P r e p a r a t i o n of Reagents Stock s o l u t i o n s of c o b a l t s u l f a t e were prepared i n 20 l i t e r batches by d i s s o l v i n g s u f f i c i e n t • C0SO4.1E 2 0 i n hot d i s t i l l e d water t a approach s a t u r a t i o n (about kOOg/l) c o o l i n g , f i l t e r i n g and s t o r i n g i n f l a s k s . The c o b a l t content was e s t a b l i s h e d by e t h y l e n e d i a m i n e t e t r a a c e t i c a c i d t i t r a t i o n . Ammonium s u l f i d e s o l u t i o n s were used as purchased. This was as 2 0 $ ammonium s u l f i d e " l i g h t " s o l u t i o n i n one pound l o t s . The standard s o l u t i o n s were kept immersed i n a c o l d water bath. No change i n s u l f i d e content was observed over a three week p e r i o d . Ammonium hydroxide was used at f u l l s t r e n g t h . S t a n d a r d i z a t i o n f o r each experiment was r e q u i r e d f o r accurate ammonia a d d i t i o n s . The e t h y l e n e d i a m i n e t e t r a a c e t i c a c i d s o l u t i o n was made i n 2 l i t r e batche by d i s s o l v i n g reagent grade disodium s a l t m a t e r i a l i n d i s t i l l e d water. I t was used as a primary standard. The murexide i n d i c a t o r f o r the e t h y l e n e d i a m i n e t e t r a a c e t i c a c i d t i t r a -t i o n s was mixed 1 g t o 100 g w i t h granular sodium c h l o r i d e . No d e t e r i o r a t i o n i n such mixtures was noted over three month p e r i o d s . - 9 -3. Analytical Procedures A. Divalent Cobalt The kinetics were followed by determination of Co(II) content of periodic samples. To prevent a change in solids to liquid ratio and solution loss through flashing, unfiltered slurry samples were taken through a cooling c o i l . The samples were stored in 2 oz. glass bottles, previously flushed with argon. About 50cc of material were taken per sample. A 5 or 10 cc liquid aliquot of each was obtained by settling the slurry. The aliquot was added to a solution of about lOOcc containing 2 g each of ammonium chloride and ammonium acetate. Cobalt (II) was then determined using 0.1N with murexide as indicated 3 1-' 3 2. The aliquot contained sufficient NH3 to provide the pH required for this t i t r a t i o n . The presence of varying amounts of (NH4)2S04,.Mg(II) and K(I) did not interfere but interference due to Co('III)^ Zn(II) and Cd(II) occurred. . The end point a. was sharp with a ti t r a t i o n error of 0-.05 cc of 0.1N ethylenediaminetetracetic acid. B. Ammonium Sulfide Ammonium sulfide solutions were standardized by adding a measured volume to an excess amount of standard cobalt sulfate solution in a ^00 cc volumetric flask, diluting to volume, mixing, settling and then determining the Co(II) content of the liquid phase. The reproducibility was + 1$. C. Carbonate Anion The CO3 content of the reduced end solutions was determined by t i t r a -tion with 0.5 N H 2S0 4. The C0 3 =/HC0 3" endpoint occurs about pH7 and the HC03"/ C0 2 endpoint about pH4. The difference between these gave the C0 3~ content of the solution. D. CO, H2, N2, 0 2 and C0 2 Gas analyses were performed on a Beckman GC-1 gas chromatograph using helium at 30 psi as the carrier and a filament current of 200 milliamps in a - 10 -thermal conductivity detector. -A s i l i c a gel and a molecular sieve column were used i n series. A selector valve permitted the l a t t e r column to be isolated from the gas flow. Gas samples were taken d i r e c t l y from the reaction vessel into a 3'l6 SS sampling bomb of 29-5 c c capacity containing 5 cc of 1:1 H 2S0 4. Gas was fed d i r e c t l y from the sampling bomb to the chromatograph. With both columns i n series, beginning with the s i l i c a gel column, H 2, 0 2, and N 2 peaks were observed i n that order. Immediately, after the N 2 peak, the molecular sieve column was removed from the gas t r a i n , thereby trapping CO. The C0 2 peak was then obtained from the s i l i c a gel column. Af t e r t h i s peak the molec-ular sieve column was reintroduced and the CO peak obtained. The accuracy for H 2 was + 1$ that for CO and C0 2 +5$. Carbon monoxide consumption was determined by comparing the amount of CO added at the sta r t plus that consumed during the run with the CO remain-ing a f t e r the run. The CO o r i g i n a l l y added was calculated knowing the gas volume at temperature and the t o t a l and vapor p a r t i a l pressures. Carbon monox-ide consumed during the run was measured by noting the pressure drop of CO from a small reservoir (k^O cc) that fed CO d i r e c t l y to the reaction vessel. The CO remaining a f t e r the run was calculated from the gas analysis and gas pressure of the quenched system. This technique was subject to rather large probable errors. E. Formate Ion The formate ion content of reduced solutions was determined by a c i d i f y -ing an aliquot and d i s t i l l i n g into a 10$ Na 2C0 3 s o l u t i o n ^ . Excess standard 0.1 N KMn04 was added, the solution heated and excess standard Na 2C 20 4 added, the solution was a c i d i f i e d and backtitrated with KMn04. This technique lacked pre-c i s i o n as evidenced by an error of l&jo i n a control, determination using reagent grade sodium formate. -11-F. Cobalt Carbonyl Anion 33 } 34 Hieber gives a quantitative method f o r the determination of Co(C0) 4 i n the presence of other cobalt carbonyls, cobalt metal and s a l t s . This technique was used i n t h i s study as a semi-quantitative t o o l to indicate the presence of Co(C0)4 . The reagent was made by d i s s o l v i n g 2.8 g 1,10-phenanthroline monohydrate and 1.2g NiCl 2.6H 20 i n 100 cc d i s t i l l e d water. Ten cc of t h i s was added d i r e c t l y to an ali q u o t of the unknown. The r e s u l t i n g p r e c i p i t a t e [Ni(l,10 phenanthroline) 3] [Co(C0) 4] 2, was allowed to s e t t l e , re-moved by f i l t r a t i o n , washed with NH3 - (NH 4) 2S0 4 s o l u t i o n and then with H20, then d r i e d over Si0 2 gel i n a vacuum and weighed. k. Apparatus Some preliminary runs were done i n a 120 cc capacity shaking autoclave and the r e a c t i o n followed by the pressure drop t e c h n i q u e 1 2 ' 1 4 ' 1 5 . This method, however, was not s a t i s f a c t o r y f o r t h i s system because of i t s complexity. Work done i n t h i s department by McDonald 1 5 attempting to follow the CO - Co(II) reaction using the spectrophotometric technique developed by Peters and Byerley i ; was unsuccessful. In t h i s present study the decision was therefore made to follow the r e a c t i o n by s o l u t i o n sampling and chemical a n a l y s i s . A Parr pressure reaction apparatus, ser i e s i+500, was u s e d 3 5 . I t was of 316 SS construction with a titanium l i n e r and a volume of 1993 c c at room temperature. The s t i r r e r shaft was b e l t driven at speeds between 800 and 1100 rpm. Heating was provided by a ring-type burner a c t i n g as a p i l o t l i g h t and a bunsen burner c o n t r o l l e d by a solenoid valve a c t i v a t e d by a Thermistemp temperature c o n t r o l l e r , model 71. (Yellowsprings Instrument Company). Using a thermister probe and t h i s heating system, temperature control, was maintained to within ±0.3°C. Carbon monoxide was supplied to the v e s s e l through l/l6"0. D. 316 SS tubing from a conventional - 12 -gas c y l i n d e r . Pressure i n the reactor was measured with a 1 5 0 0 p s i h e l i c o i d gauge with a scale of 1 0 p s i per subdivision. 5.Experimental Procedures To minimize Co(ILT) formation a l l charges were' f r e s h l y prepared i n 1 0 0 0 cc volumetric f l a s k s f i l l e d with argon. The charges were poured into the reaction v e s s e l previously flushed with argon. The desired volume of (NH 4) 2S so l u t i o n was added and the vessel closed. The charge was heated to temperature while s t i r r i n g and e q u i l i b r a t e d ( l / 2 hour t o t a l u s u a l l y required). Carbon monoxide to the desired p a r t i a l pressure was applied ( f i l l i n g u s u a l l y took + 5 to 6 0 seconds) and s l u r r y and gas samples taken as desired. The t o t a l pressure in the v e s s e l was maintained constant by admitting more CO. -At the end of the run the system was quenched i n cold water. - 13 -III. RESULTS 1.Preliminary Experiments Preliminary experiments established that the reduction of Co(II) to metal by CO only occurs i f solid CoSx is present. Typical conditions for convenient rate measurements were found to be: 1 liter of solution (0 .3M cobalt ion, 1 M (NH4)2S04;,3-5M NH3), 25 atm CO, 215°C and 0.06M-.;£f present as CoSx. A. Chemical Species Observed Before kinetic data are presented, the reacting chemical species as well as products observed in this study should be discussed. a. C obalt Cobalt was present in four forms: 1. cobalt (II) ion complexed with NH3, 2. cobalt (II) precipitated as CoSx, 3. cobalt metal and k. cobalt (-1) present in a cobalt carbonyl. 1. Cobalt (II) ion Cobalt (II) was present in a l l runs as ammine complexes,. Co(NH3)n++> the most abundant form under the conditions of this work corresponding to n = 2. 2. Cobalt (II) Present as CoSx S - was added as (NH4)2 S but was present as a cobalt sulfide. X-ray and electron diffraction patterns indicated the sulfide form to be either -Co6S5 or Co 9S 8 (See section III-6-B). The chemical composition based on ~i -Co6S5 gave consistent agreement between ++ calculated and measured i n i t i a l Co ( N H 3)n concentrations and this stoichiometry - Ik -has been used, i n a l l calculations. The symbol [S ] used henceforth w i l l refer to the t o t a l s ulfide added i n moles/l but actually present as s o l i d CoS x. 3. Cobalt Metal The major product of Co(II) reduction by CO i n the presence of CoS x i s cobalt metal. I t s existence i s indicated by the results i n Table I I I i n which observed residue weights and compositions are compared with calculated values assuming cobalt metal, % -Co 6S 5 and using the difference between i n i t i a l and f i n a l Co(NH 3) n concentrations. Electron d i f f r a c t i o n studies, discussed i n section III-6B, confirm the presence of cobalt metal. To detect the presence of metal on a routine basis a permanent magnet was used. k. Cobalt (-1) A compound containing cobalt and CO was frequently observed. I t was present as white c r y s t a l l i n e flakes f l o a t i n g on the l i q u i d surface. I f a i r were excluded from such mixtures, t h i s compound was stable for months. Exposure to a i r resulted i n rapid decomposition with gas evolution as did mixing with water or acid. I t r e a d i l y dissolved i n NH4C1 - NH4O Ac solutions resulting i n some OL. ethylenediaminetetracetic acid t i t r a t a b l e Co(II). In vacuum or dry i n argon i t produced a dense white fume and slowly darkened. Sublimation occurred i n vacuum with production of orange c r y s t a l s . When heated i n an argon atmosphere, a cobalt mirror formed on the walls of the tube. The material was very sparingly soluble i n hexane, ether, carbon tetrachloride and chloroform forming a yellow solution. These results would suggest a cobalt s a l t of cobalt hydrocarbonyl. H i e b e r ^ mentions Co(NH3)6 [Co(CO) 4] 2 as a compound sparingly soluble i n organic solvents. This material i s a true s a l t and i s hydrolysed by water to HCb(CO)4 - 15 -TABLE I I I Indication of Cobalt Metal i n Reaction Residues Run Actual Reduction Residues Calculated Reduction Residue Number Weight Co S Weight Co S g i i g i j 50 15 A 93-8 3.6 16.0 96.2 3.8 15 l A 93-6 ND 1-5 90.0 10.0 150 29.I 90.0 5-6 27.0 9^ -3 5-7 155 21.0 91.9 7.2 20.7 92 A 7-6 HCo(C0) 4 i s a strong acid (dissociation .-constant about equal to that of HC1) and several of i t s sal t s have been studied. The Zn(II), Cd(II), Hg(II), S n ( I I ) , A g ( I ) , T l ( I ) , T l ( I I I ) , I n ( I I I ) , A s ( I I I ) , - Sb ( I I I ) , B i ( I I I ) , Sn(+5), K(I) and Na(I) sal t s are reported '' . HCo(C0) 4 decomposes rapidly above i t s melting point (-26°C) but i s r e l a t i v e l y stable i n the gaseous form at room temperature. I t s decomposition product i s dicobalt octocarbonyl 2HCo(C0)4 > H 2 + Co 2(C0) 8 " 1 Co 2(C0) 8 when formed t h i s way i s usually a dark brown microcrystalline s o l i d which sublimes i n vacuum forming orange crystals of Co 2(C0) 8. I t melts at 51°C and s l i g h t l y above t h i s temperature decomposes into tetracobalt dodecacarbonyl, C o 4 ( C 0 ) 1 2 . This material i s black and decomposes at 60°C. The existence of a cobalt carbonyl grouping was indicated i n the com-pound by infra-red spectrophotometry kindly performed by Mrs. A. Brewster, Department of Chemistry, The University of B r i t i s h Columbia. The results of t h i s determination on a grab sample dissolved i n CC1 4 are compared with published spectra - 1 6 -of HCo(CO)4 and Co(CO)I i n Figure I1?' ^> 1 + 1. The agreement between the spectra suggests that the unknown contains HCo(C0)4. Chemical analysis of t h i s material was d i f f i c u l t and of l i m i t e d accuracy because of i t s i n s t a b i l i t y . How-ever, a grab sample was prepared and analysed. The sample was washed rapidly with d i l u t e NH3 solution, dried i n a vacuum and stored under argon. This dried material was unstable and slowly gave off a dense white fume. About 1 2 hours elapsed between sample preparation and analysis. The result i s shown i n Table IV and compared with calculated figures for Co(NH 3) 6 [ C o ( C 0 ) 4 ] 2 . The agreement i s s u f f i c i e n t l y close to support the conclusion that the unknown i s the cobalt s a l t of cobalt hydrocarbonyl. TABLE IV Chemical Analysis of Cobalt Carbonyl Compound Element Unknown Co(NH3 ) 6 [Co(CO)4 J 2 Error molar r a t i o molar r a t i o °t> Co 3 2 . 6 3 - 0 3 5 . 2 3 9 . 9 C 1 7 . 2 7 . 6 1 9 . 1 8 7 . 4 N 1 4 . 8 5 . 7 1 6 . 7 6 1 1 . 4 0 N.D. 2 5 . 5 H N.D. 3 . 6 3 3 , 3 4 Hieber reports an a n a l y t i c a l method s p e c i f i c for Co(C0) 4 i n the presence of other cobalt carbonyls, cobalt metal, cobalt acids and organic s a l t s . to? This u t i l i z e s the p r e c i p i t a t i o n of Co(C0) 4 as Lg&(i^io-phenanthroline) 3] [ C o ( C 0 ) 4 ] 2 (see a n a l y t i c a l procedures). As shown~"in Table V, s i g n i f i c a n t amounts of precipitates were found i n reduction end solutions using t h i s reagent thus supporting the conclusion that Co(C0) 4 ~ i s present. - 1 7 -Figure 1; Comparison of Infra-red-Spectra of Co(CO) 4 HCo(CO)4 and Unknown Material. - 18 -TABLE V Determination of Co(CO) 4~ i n Random,.Partially Reduced Solutions Run [Co(CO) 4-] [Co(NH 3) n + +] moles/l moles/l 155B i n i t i a l n i l O.3I+ 151B i n i t i a l 0.0028 0.3k 151B ^5 min. 0.0037 0.33 151B 90 min. 0.0017 0.34 152A 30 min. 0.0011 0.22 152A hO min. 0.0050 0.20 15OB F i n a l O.OO56 0.09 b. Carbon Carbon was present i n three forms: 1. CO, 2 . C0 2 and 3- HCOO . 1 . Carbon Monoxide Carbon monoxide was present as free gas, and as & constituent of cobalt carbonyl (as discussed under cobalt above). 2. Carbon Dioxide Carbon dioxide was present i n both the l i q u i d as C03 = or HC03~ and i n the gaseous phase at experimental temperatures. As shown i n Table VI, no carbon dioxide remained i n the gas when the system was cooled. 3. Formate Anion The existence of formate ion i n the reduction solutions was established by KMn04 t i t r a t i o n (see a n a l y t i c a l procedures). Some t y p i c a l analyses are shown i n Table VII. c. Hydrogen Large quantities of hydrogen were i d e n t i f i e d and determined by gas chromatography during the course of the reduction reactions (see section I I I - 5 ) . - 19 -TABLE VI Dist r i b u t i o n of C03~ Between the Liquid and Gaseous Phases at 215°C — (Run 127). Gas Sample C 0 2 i n Gas C 0 2 i n Gas CO3 i n Liquid * moles moles 45 min. at 215°C 46.9 0.290 0.240 (by d i f f ) quenched sample at 45 min. 0.00 0.000 O.53O TABLE VII Detection of HCOO" Sample Temp. [ H C 0 0 - ] moles/l 155A i n i t i a l 190 0.00 f i n a l 190 0.06 155B i n i t i a l I 9 0 0.09 f i n a l 190 0.07 156A f i n a l 215 0.27 I56B f i n a l 215 0.10 B. Typical Rate Curves The rate of reduction of Co(NH 3) n was followed by determining the cobalt(II) content of l i q u i d samples. Data so obtained f i t no simple zero, f i r s t or second order rate laws. I t was observed, however, that maximum rates taken from zero order rate curves gave reproducible rates. A family of t y p i c a l rate curves i s shown i n Figure 2. The runs i n t h i s figure are part of a series showing the effect of the amount of S~ on the rate. 0.3 Expt. No. [s-] 1 Max Rate M/min • 119 0.133 0.043 0 118 .100 ,040 O 1 1 6 .070 .034 A 178 .060 • 033 A 114 .050 .030 O 112 .o4o .023 f 110 .020 .017 O i n .010 .009 0.2 0.1 10 15 20 Time (min) Figure 2: Typical Rate Curves ( I n i t i a l Conditions: 3.3M Wl3, 1.1M ( N H 4 ) 2 S 0 4 , 26 atm Co, 215°c; - 21 -The curves show an i n i t i a l period of slow rate (usually from 0 to 1.5 minutes) followed by a region of maximum rates which subsequently approach equilibrium. By examination of such curves i t was found that the curve between 2 and 5 minutes for a l l except a few runs was es s e n t i a l l y l i n e a r and the rate between these two figures represented the maximum rate. For runs i n which the sampling period was small (1 minute intervals) the maximum rate was found to be s l i g h t l y higher than the 2 to 5 minute rate, but did occur within t h i s time i n t e r v a l . To obtain a comparison with the majority of runs i n t h i s study the 2 to 5 minute rates have been used consistently throughout i n preference to these maximum rates and are included i n a l l references to maximum rates. Using t h i s technique a maximum v a r i a t i o n of +10$ i n rate was found between two or more i d e n t i c a l runs. - 22 -2.Kinetic Study A. . Effect of I n i t i a l Ammonia Concentration The effect of. the i n i t i a l concentration of N H 3 on the rate of Co(NH 3) n + + reduction was determined at three'S" l e v e l s , 0.06, 0.02 and 0.01 M. The results are shown i n Figure 3 (Table A-I, Appendix A). The rate appears to be f i r s t order i n i n i t i a l NH3 concentration up to about 3M. (or,, more correctly, f o r [NH3 ]i/[Co(NH 3^ 1 + +] i <10) after which the reac-tion i s independent of NH3. To determine i f the effect of i n i t i a l NH3 concentration was one of cdmplexing or of changing 0H~ concentration Figures k and 5 were constructed. The rate of Co(NH 3) n + + reduction i s compared with i n i t i a l free NH3 and i n i t i a l 0H-~ concentrations calculated f o r 215°C (tabulated i n Table A-I, Appendix A). These calculations are shown i n Appendix B and are based on the assumptions that the average number of molecules of NH3 complexed per Co(II) ion, n, equals 2 at 215°C and that the dependence of fi on both free NH3 and Co.(NH 3) n + + concentrations may be. neglected. These assumptions are j u s t i f i e d i n Appendix B by experimental data. B. . Effect of I n i t i a l Ammonium Sulfate Concentration Since the dependence of the rate on i n i t i a l NH3 concentration f e l l to zero order above [NH3 ] i / [ C o ( N H 3 ) n + + ] i —10, the rate i n t h i s region i s apparently independent of both complexing and i n i t i a l OH concentration. Consequently, the effect of i n i t i a l (NH 4) 2S0 4 concentration was determined at ratios below t h i s value. The results are shown i n Figures 6 and J (Table A-II, Appendix A). Figure 6 shows the relationship between rate and i n i t i a l (NH 4) 2S0 4 concentration; Figure 7 shows that between rate and i n i t i a l 0H~ concentration calculated for 215°C. • — Q [ s = ] = 0.06 O — O = °- 0 2 A A = o.oi = 0.0175/min. X T slope = 0.0054/min. • X L -D-1 r 7 Figure 5. [NH 3]i Effect of I n i t i a l NH3 Concentration on Reduction Rate at 215°C ( I n i t i a l Conditions; 1.2M. (-NH4)2S04, 0.31M Co(NH 3) n + + and 26 atm CO). • • — T J S e r i e s 1 [S ] = 0.06 O O S e r i e s 2 =0.02 O X L l 2 3 k 5 6 [ N H 3 f r e e ] i a t 215°C F i g u r e k: Dependence o f Maximum R a t e on I n i t i a l F r e e N H 3 C o n c e n t r a t i o n a t C o n s t a n t I n i t i a l N H 4 + C o n c e n t r a t i o n ( I n i t i a l C o n d i t i o n s : 1.2M ( N H 4 ) 2 S 0 4 , 0 . 3 1 M C o ( N H 3 ) n + + and 25 a t m C O ) . i 1 r • • Figure 5: Dependence of Maximum Rate I n i t i a l 0H~ Concentrantion at Constant I n i t i a l NH4 Concentration ( I n i t i a l Conditions: 1.2M (NH 4) 2S0 4, 0.31M Co(NH3) + + and 2 6 atm CO). n ro - 26 -• — D[s"] = 0.06 [m3)± = 1.6 O — O " 0 . 0 2 =2.3 1 2 [(NH 4 ) 2 S 0 4 ] i Figure 6; Effect O f I n i t i a l (NH 4) 2S0 4 Concentration on Rate ( I n i t i a l Conditions: O.JIM C o ( N H 3 ) n + + , 26 atm CO, 215°C). 1 • — D[S =] = o.o6 [NH3J = 1.6 I X -I 5 10 [0H"]i x 10 7 at 215°C Figure 7: Effect of I n i t i a l 0H~ Concentration on Rate at Constant I n i t i a l NH3 Addition ( I n i t i a l Conditions: O.JIM C o ( N H 3 ) n + + , 26 atm CO and 215°C), - 27 -Increasing (NH 4)2S0 4 concentration and, hence, decreasing 0H~ concentra-t i o n decreases the rate. I t was observed, (Table A-II,- Appendix A) that the vapour pressure of the solution (and, thus, i n i t i a l free NH3 concentration) was es s e n t i a l l y independent of the i n i t i a l ( N H 4) 2S0 4 concentration over the range investigated. The change i n rate i n Figure 7 must, therefore, be due only to changes i n 0H~ concentrations and not to NH3 complexing of cobalt ( I I ) . The curves i n Figure 7 are si m i l a r i n shape to those i n Figure 5. Such curves may be expected to follow the relationship A[OH~] A[OH"] B rate = r C T o l P T B + C [OH ] 1 + J B thus 1 = — ~ , + c rate gLOH J A Consequently, i f the data obeys such a relationship a plot of the l/rate versus l/[OH ] should be a straight l i n e . . I f the same effect i s governing the rate i n Figure 5, as i n Figure 7, a plot of l/ r a t e versus l/[OH~] should f a l l on the same l i n e f o r both series. Such a plot i s shown i n Figure 8 at two different S additions. .Sufficient agreement i s evident to conclude that the same effect i s occurring in both the NH3 and NIL* series and therefore i s due to pH rather than complexing. The rate determining reaction i s , therefore, f i r s t order i n i n i t i a l OH concentration below a [NH3],/[Co(NH3) ]. = 10 and approaches zero order i n 1 v n 1 OH" above t h i s r a t i o . 200 I 150 I CD O H.V100 - P H 50 I Constant [NH 4 +] i varying [NHa]^ series Constant [NHa]^ varying [iftLj*]^ series [S~] = 0.06 [S^] = 0.02 _L 5. 10 15 20- 25 10-5/tOH-Ji (moles- 1 1) 30 Figure 8; Effect of I n i t i a l OH- Concentration on Maximum Rate for Both Constant I n i t i a l NH3 and NH 4 + Concentration Series; 0 0 - 29 -C. Effect of Sulfide Ion Addition The effect of S addition on the rate was investigated at 190 and 215°C At 215°C experiments were conducted at two levels of i n i t i a l NH3 concentration to determine the effect of S concentration^regions of zero and,first order depen-dence on i n i t i a l NH3 concentration. The two temperatures were used to indicate i f the apparent activation energy was dependent on the amount of S and hence i f the rate-controlling step changed as S~ l e v e l changed. The results are shown i n Figure 9 (Table A - I I I , Appendix A). At both temperatures there i s a measurable rate of Co(NR"3) n + + removal from solution i n the absence of CoS-x . . This i s due to carbonyl formation, and i s small enough compared to t o t a l rates, when Co^ i s present, to be ignored. With the addition of increasing amounts of S~ the rate increases. This dependency i s not l i n e a r , and, i n f a c t , a plot of log rate versus log [S~] shown i n Figure 10 indicates the order i n S concentration to be about 0.6 to 0.7. This dependency?:is consistent with a l i n e a r dependency i n surface area i f the CoS x p a r t i c l e numbers and shapes are unchanged with increasing S~ concentration but the sizes of the precipitate p a r t i c l e s are larger. .In such cases, the area increases as the two-thirds power of the volume of material precipitated, which i s within the observed range of S concentration dependency. Because the reaction i s heterogeneous, several experiments were conducted at s t i r r i n g speeds both above and below the normal speed of 1005 rpm (+20$ change employed) to eliminate poor agitation as the cause of the non-linear dependency ~* To be discussed l a t e r . -1.0 _ 1.5 2.0 - log [S -] Figure 1 0 : Volume versus Surface Area Effect of CoSx- P a r t i c l e s on the Rate ( I n i t i a l Conditions: O.JIM Co(NH 3) n + + J ) l.LM (NH^SO.!, 2 6 atm CO). i I—1 I - 32 -of the rate on S~ concentration. The rates f o r these experiments are plotted i n Figure 9 and the change i n rate due to a change i n s t i r r i n g speed i s withinr experimental error. From Figure 9 "the slopes of "the curves at 215 a n d 190°C give an apparent act i v a t i o n energy for the CoS K supported reaction of approximately 11 k cal/mole. The apparent ac t i v a t i o n energy at zero addition of S~ i s approximately 18 k c a l / i mole. - 33 -D. Effect of Carbon Monoxide Pressure The effect of carbon Monoxide pressure on the rate of reduction of Co(NH3) n + + i s shown i n Figure 11 (Table A-IV, Appendix A). Four series at various S and i n i t i a l NH3 concentration were done to check for possible interdependence of the variables. Over the range of variables used, the effect of increasing carbon mono-xide pressure i s i n i t i a l l y to increase the rate. At higher values the rate be-comes independent of carbon monoxide pressure. The i n i t i a l dependence i s appar-ently f i r s t order. The l e v e l at which the rate becomes independent of carbon mono-xide pressure varies according to the NH3 andS~ concentrations present but at the pressure usually used i n determining the effect of the other variables, 26 atm, the rate i s independent of carbon monoxide pressure. E. Effect of I n i t i a l Cobalt (II) Concentration The effect of i n i t i a l cobalt (II) concentration was determined at [NH 3]i/ r + + n = LCo(NH 3) n >10 and at three levels of S additions. Each series was done at constant i n i t i a l NH3 concentration. The results are shown i n Figure 12 (Table A-V Appendix A). The reaction appears f i r s t order i n i n i t i a l Co(NH 3) n- + concentration at low levels t a i l i n g off to an apparent zero order~ at high l e v e l s . The largest ++ Co(NH 3) n concentration shown i n Figure 12 i s the maximum concentration obtain-able with the stock reagent"solutions used. F. Salt Effect Table VIII shows the effect of adding Mg + + and K + on the rate of Co(NH 3) n reduction by CO. Any difference i n rate experienced by these additions i s within experimental error. - 35 -Figure 1 2 : Effect of I n i t i a l Co(NH 3) n Concentration on Rate ( I n i t i a l Conditions: L I M (NH4) 2 S0 4 , 26 atm CO, 215°C). - 36 -TABLE VIII Salt- Effect i n Reduction of Co(NH 3) n + + by CO ( I n i t i a l Concentrations: 0.31MCo(NH3)n++, 1.1M (NH4)2S04, 26 atm CO, 215°C) Experiment Number [Mg + +] Series 1 [NH3] >4.2 207 176 175 180 89 91 93 0.045 n i l n i l n i l Series 2 [NH3] =4.0 0.29 0.29 n i l Series 3 [NH3] =2.3 [K+] [S ] = 0.060 n i l n i l n i l n i l [S =] = 0.035 n i l n i l n i l [S =] = 0.020 Max. Rate M/min 0.0347 0.0351 0.0335 0.0377 0.0260 0.0277 0.0233 102 107 n i l n i l 0.79 n i l 0.0120 0.0123 1 - 3 7 -G. Effect of Cobalt (III) Concentration As noted previously, precautions were taken to exclude 0 2 from the reaction solutions to prevent formation of Co(III). To determine the effect of Co(II I ) , runs i n which i t was present are compared to Co(III) free runs i n Table LX. The Co(III) concentration was determined by noting the difference be-++ tween the Co(NH 3) n concentration added and that obtained" by extrapolation of the reduction curves back to zero time. The data i n t h i s table indicate^ that Co'(III) does not enter the reac-++ t i o n other than that i t s formation lowers the i n i t i a l Co(NH 3) n concentration and thus retards the rate. H. Effect of Temperature The temperature dependence of the reaction was determined over the range 180 - 230°C at high S~ additions and at three different i n i t i a l NH3 l e v e l s . Two series were done i n the range of f i r s t order and the t h i r d i n zero order de-pendence on i n i t i a l NH3 concentration. The corresponding Arrhenius plots are shown i n Figure 13 (Table A-VI, Appendix A). The three series give apparent activation energies of 12.5, 10.6 and 12.2 k cal/mole. In section III-2-C an act i v a t i o n energy of 11 k cal/mole was obtained f o r the S addition series at 190 and 215°C. These ac t i v a t i o n energies are within experimental error of the same value and indicate that the same mech-anism i s rate-controlling over the range of conditions used i n t h i s work having an apparent ac t i v a t i o n energy of 11 + 1 k cal/mole. I - 38 -TABLE IX Effect of Co(III) on Rate of Co(NH 3) n + + Reduction by CO. ( I n i t i a l Conditions: IM NH3, 1.1M (NH 4) 2S0 4, 0.02M S =, 29 atm CO, 215°C) Experiment [Co(NH3) n + + +] i [Co(WH 3) n + +] i 0-20 min rate ; Number M/min 106 n i l 0.325 0.0051 50 n i l 0.285 o.oo4o 52 0.033 0.292 o.oo46 53 0.034 0.290 0.0059 54 O.O53 0.270 o.oo46 58 o.o4i 0.288 0.0034 & In these runs, i n i t i a l sampling was infrequent and maximum rates could not be calculated. For comparison purposes, therefore, the rate based on the f i r s t 20 minutes i s used. - 3 9 -2.00 2.05 2.10 2.15 2.20 l / T x 105 ++ Figure 13: Arrhenius Plot . ( I n i t i a l Rate: 0.31M Co(NH3.)n , 0.06'MS~, 26 atm CO, 1.2M ( N H 4 ) 2 S 0 4 ) . - ho -I. Effect of Catalysts a. Effect of Cyanide and Tartrate Anions 26 Blanchard reports better yields of Co(CO) 4 using cobalt cyanides and tartrates than with s u l f i d e s . The effects of these reagents on the reaction rates i n t h i s study were also examined and-are summarized i n Table X. Tartrate at 190°C increases the rate of reduction i n the absence of S by about while cyanide yields a. 235$ rate increase. At 215°C the rate increases by 70$ with the addition of 0 . 0 5 M C N - i n the absence of S~. When S~ i s present, scattered results obscured'any possible effect of CN". In no case was a s o l i d cobalt s a l t of cyanide or tartr a t e observed. The results i n Table'X indicate a lower ac t i v a t i o n energy f o r the reaction i n the presence of O.O5M cyanide and, therefore, suggest that cyanide becomes involved i n the mechanism. b. C a t a l y t i c A c t i v i t y of Various Metal Ions In previous studies of H2" and CO reductions of metal ions from aqueous solution homogeneous cataly s i s by such ions as Hg(II), Cu(II), and Ag(I) was ob-served. Experiments were conducted to determine i f these ions would be active i n th i s system. This work was conducted i n a shaking autoclave at O .8MNH3, 1.1M (NH4 ) 2 S 0 4 , 0.32M Co(NH 3) n + +, 58 atm. CO and 2l6°C. Metal "catalysts" were added at a concentration of 0.016 M. .Two runs were done with each catalyst: one with the metal ions- only and the other with metal ion and'S~ addition. I t was hoped "that i f the metal ion added as a homogeneous catalyst were i t s e l f reduced to metal, ++ t h i s fresh - surface would act as a heterogeneous catalyst for Co(NH"3)n reduction by CO. The results are tabulated i n Table XI. Only a quali t a t i v e assessment i s available based on whether or not cobalt metal was produced. TABLE X + Effect of Cyanide and Tartrate Anions on Reduction of Co(NH3) n ( I n i t i a l Conditions*-> 3 . 7 M N H 3 , 0.31M C o ( N H 3 ) n + + 1.2M(NH4)2S04 and 2 6 atm CO) Expt. - [Cyanide J 1 [ tartrate] 2 Tempt,: ns~]: Max. $> Change No. °C .Rate in Rate , M/min 1^ 9 n i l n i l 190 n i l 0.0021 +5 154A n i l n i l 190 n i l 0.0017 -15 155A n i l n i l 190 n i l 0.0020 n i l 1 5 1 A n i l 0.05 190 n i l 0.0029 +45 152A 0.05 n i l 190 n i l 0.0067 +235 156 n i l n i l 215 n i l 0.0060 n i l 162 0.05 n i l 215 n i l 0.0103 +72 F i g . 9 n i l n i l 215 0.01 0.0103 n i l 111 n i l n i l 215 0.01 0.0090 -13 159 0.05 n i l 215 0.01 0.0103 n i l F i g . 9 n i l n i l 215 0.05 0.0270 n i l 138 n i l n i l 215 0.05 0.0283 +5 137 n i l n i l 215 0.05 O .O277- +3 136 n i l n i l 215 0.05 0.0247 +8 I58 0.05 n i l 215 0.05 0.0350 - +30 F i g . 9 n i l n i l 215 0.07 0.0370 n i l 116 n i l n i l 215 0.07 0.0337 -9 160 0.05 n i l 215 0.07 0.0363 - 2 1 added as KCN 2added as H 2 C 4 H 40 6 - 4 2 -TABLE XI Effect of Various Metal Cations on the Reduction of C o ( N H 3 ) n + + by CO Run Metal Ion Amount Number Added S = Added Result moles/l 24 Ag(I) n i l No cobalt metal produced. Presence of Ag° indicated. 2 5 Ag(I) 0 . 0 0 7 Cobalt metal produced. Presence of Ag° indicated. 2 6 Cu(II) n i l No cobalt metal but fine metallic copper powder produced. 27 Cu(II) 0 . 0 0 7 Cobalt metal formed but Cu° not v i s i b l e . 2 8 Fe(II) n i l No cobalt metal formed. 2 9 Fe(II) 0 . 0 0 7 Cobalt metal formed. 3 0 -Hg(II) 0 . 0 0 7 Cobalt and mercury metals formed. - 43 -None of the metal ions added are active as homogeneous catalysts. Mercury, s i l v e r and copper metals are not heterogeneous catalysts f o r cobalt metal production. The only active heterogeneous catalysts are s o l i d metallic s u l f i d e s . In'fact i t would appear l i k e l y that i n these cases (with the exception of CuS) the active ingredient i s actually CoS x, as the alternate-metal ion i s reduced to e/o metal (mercury and s i l v e r ) a s d i t s sulfide i s more soluble than CoS x (FeS). In other miscellaneous tests carried out through t h i s study i t was found that titanium metal (the autoclave l i n e r ) , n i c k e l metal, cadmium sulfide and cadmium ( I I ) , n i c k e l (II) and zinc (II) ions are inactive as catalysts f o r the reduction of Co(NH3) to metal by CO. These experiments do not lead to any conclusions regarding the a c t i v i t y of any of the above species to the formation of Co(CO) 4 . - kk -3.Stoichiometry of the Reaction I t would be expected that Co(NH 3) n + + and CO would.react, i f metal form-ation occurred, according to the stoichiometric equation C o(NH 3) n + + + CO '+ (4-n)NH3 + 2H 20—»Co° + C 0 3 = + km** k - + Cobalt metal, C0 3 and NH4 should be the only products. However, three important observations were made when this- reaction was attempted: 1. A s o l i d cobalt carbonyl compound i s evident i n the end solutions of a l l experiments to which no S = i s -added and i n some to which i t i s added. 2. A catalyst, CoS x, i s required before any Co° metal i s produced. 3 . HCOO" and H 2 are present as products. To determine the importance of the cobalt carbonyl to the mechanism, the following two part experiment was done under conditions with which - experience had shown cobalt metal and substantial amounts of carbonyl were formed. At the end of the run the autoclave was quenched, CO gas was released and a l l residual CO was flushed from the vessel with N 2. The bomb was opened, fresh C6S04-7H20 was added to replenish the i n i t i a l Co(NH 3) n concentration, the bomb was closed and the charge taken to temperature where i t was held without CO addition. Liquid samples were taken to see i f reduction of Co(NH 3) n + + occurred. The result i s shown i n Figures i k A and ikB. ++ I t i s evident that Co(NH 3) n i s reduced, by C"o(C0)4-. . I t i s not possible from these data to state whether or not CoS x i s essential to t h i s reduction. To answer t h i s point two additional experiments were conducted. The f i r s t of these (experiment 151) was i d e n t i c a l to the one above except that no-S~ was added to io 15 Time (minutes Figure ika.: Production of Cobalt Metal and-Cobalt Carbonyl with CO. ( I n i t i a l Conditions: 0 . 0 4 6 M S = , 0 . 3 0 8 M Co(NH3) n + +, + . 9 M N H 3 , 1 . 1 M (NH 4 ) 2 S 0 4 , 2 7 . 2 atm CO). 0.03 0 . 0 2 0 . 0 1 1 1 1 — -Reached' \ ^ — Tempe rat ure\ s Q Quenched sample contains no s o l i d ^ s carbonyl. 1 1 1 15 30 45 ) Figure lVb: Reduction of C o ( N H 3 ) n + + by Cobalt Carbonyl i n Absence of CO. - ( I n i t i a l Conditions: 0.0U6MS=,O.318M Co(NH 3) n UM NH 3 J ). 1.6M (NH4-) 2S0 4 , a l l reduction products from.l^a present). ( - p -VJl 1 - ke -either part A or Bj the second (experiment 155) had CoSx- present only i n part B. The rate of reduction of Co(NH 3) n + + i s shown i n Figures I5A and 15B. Without the addition of S to part A,only Co(C0) 4~ but no metal i s pro-duced. Only when S~ i s added to part B does the reduction of Co(NH3) + + by 00(00)7 occur. In Figures I5A and I5B three other experiments are shown. These were s i m i l i a r two-part runs but show the effect of ta r t r a t e and cyanide catalysts and temperature. These were discussed i n section III-2-Ia but are included here as further indication that C o ( C 0 ) 4 ~ does reduce Co(NH 3) n + +. I t i s interesting to note that both t a r t r a t e and cyanide catalyse the production of C o ( C 0 ) 4 ~ with cyanide being very effective and the 0 0 ( 1 ^ 3 ) n / C o ( C 0 ) 4 ~ reaction i s much more temperature dependent than i s C o ( C 0 ) 4 ~ production. On the oasis that Co(C0) 4 i s a necessary intermediate i n the reduction of C o ( N H 3) n + + by CO to metal a material balance was done for run I55. The calcula-tions are summarized i n Table XII. Run I5IB supports the hypothesis reached e a r l i e r that the s o l i d cobalt car-bonyl i s a cobalt (II) s a l t of HCo(C0) 4. In t h i s run i t i s seen that holding the charge at temperature increased the C o(NH 3) n + + concentration s l i g h t l y . Gas analysis showed that 0.1 moles of CO gas formed over the same period. -Assuming that t h i s CO resulted from destruction of Cb(NH 3) 6 [C8(C0) 4] 2, 0.013 moles of Co(NH3) + + should have been formed as compared to the observed increase of 0.018. The marked s t a b i l i t y of Co(C0) 4~ i s also demonstrated. From the fact that s o l i d cobalt carbonyl was not observed i n the cooled samples u n t i l the 6 minute one i n run I 5 I B the s o l u b i l i t y of Co(NH 3) 6 [Co(C0) 4] 2 i s calculated to be 0.02M Co(C0) 4~ at room temperature i n these solutions. X T Expt. [s~] Temp 151B n i l 190 155B O.O5 190 152B 0.05 190 I56B 0.05 215 o metal formed metal formed ; t a l formed metal formed 80 Figure 1*5A ++ 10 20 30 20 Time (minutes) : -Production of Cobalt Carbonyl i n Figure P 5 B : Reduction of Co(NH 3) n Absence of CoSx. ('Initial Conditions: i n Absence of C 0 ( I n i t i a l Conditions: >1.1M 1.1M (NH 4)2S0 4, 26 atm CO, 5M NH 3). (NH 4) 2S0 4, >5M NH3, products of Part A). by Cobalt Carbonyl - 48 -TABLE X I I Material' Balance of Two Stage Run Part' A + + Co(CO) 4" formation from Co(NH 3) n and CO Moles/mole Co(NH3) Co(NH 3) n reduced 0.061 moles LO Co(CO) 4 _ produced 0.06l 1.0 CO consumed O.5O 8.2 N H 3 neutralized O.38 6.2 H 2 produced n i l 0 C 0 3 = produced 0.10 1.6 HCOO" produced 0.06 1.0 Part B Cobalt Metal Formation from Co(NH 3) n + + and C o ( C 0 ) 4 _ Moles/mole C o ( C 0 ) 4 " Co(NH 3) n reduced 0.206 moles 3.6 C o ( C 0 ) 4 " consumed i n reduction O .O58 1 CO produced 0.008 0.l4 NH3 neutralized O.9I I5.7 - '• H 2 produced 0.04l 0.7 C 0 3 = produced O.31 5.3 HCOO- consumed 0.025 0.43 Co° produced 0.264 4.6 - k9 -The l a s t column i n Table XII i s indicative of the observed stoichiometry for Co(C0)4~ formation, the the o r e t i c a l equation being Co(NH3) n + + + 5.5CO + 6NH3 + 3H 2 0 — » 0 0 ( 0 0)4* + 1 . 5 C 0 3 = + 6.NH4+ + nNH3 5 After subtracting the CO and NH3 consumptions leading to formate v i a the reaction, WH3 + CO + H 2 0 >HCOO" -+ NH4+ 6 the experimental discrepancies with equation 5 are 8 $ , 7 $ 31$> respectively, = x for NHs, C0 3 and CO . A s i m i l i a r treatment of the cobalt metal forming reac-t i o n indicates that the discrepancies from the expected stoichiometry as pre-dicted from the equation 4 . 5 C o(NH 3) n + + + CO(CO)4" +16NH3 + 8 H 2 0 * 5 * 5 C o ° + kC03~ +l6NH 4 + +4.5nNH3 7 ++ = are 1 8 $ , 3 $ , 1 5 $ and 1 8 $ f o r Co(NH 3) n , NH3, Co° and C0 3 , respectively, after subtracting the effects of equation 6 and subsequent hydrogen forming reaction HCOO~ + H 2 0 + NH3 > H 2 + C 0 3 = + NH 4 + 8 C b ^ The agreement between these experimental and theoretical" stoichiometries supports the hypothesis that Co(C0) 4 i s an intermediate i n the reduction of Co(NH 3) n + + to metal by CO. Table XIII compares an experimental and the o r e t i c a l material balance for a normal run i n which Co(NH 3) n + + was reduced i n the presence of CoS x to metal i n As outlined i n section II - 3> a large error i n CO analysis i s expected and the agreement i s considered satisfactory. - 5 0 -TABLE XIII Material Balance of a Normal, .Single-Step Run Measured Theoretical Error ++ Co(NH3) reduced n 0 . 2 9 7 0 . 2 9 7 n i l CO consumed 0 . 6 3 9 O . 5 8 I 9 NH3 neutralized 2 . 0 4 0 1 . 7 5 6 14 H2 produced 0.28k 0 . 2 8 4 n i l CO3 produced 0 . 5 3 0 O . 5 8 I 10 I n i t i a l Conditions: 4 . 9 M NH3, 0.048MS , 1 . 1 M (NH4)2S04, 2 6 . 5 atm CO, 0 . 3 0 6 M Co(NH 3) n* 215°C, volume of charge = I O 8 3 cc. a single step. This run was done under conditions i n which no Co(C0)4~ was evident at the end of the run. .The th e o r e t i c a l material balance was done — + + assuming that Co(C0)4 i s an intermediate and i t reduces Co(NH3)n producing metal. The agreement i s s u f f i c i e n t l y close to support the hypothesis ++ that the ov e r a l l reduction of Co(NH 3) n to metal by CO follows the stoichiometry given by summation of the two half reactions (equations 5 and 7 ) . - 51 -Production of Magnetic Material As an aid i n distinguishing between the production of Co(CO) 4~ and the production of cobalt metal as the rate-determining process, the times of i n i t i a l appearance of magnetic cobalt metal and of s o l i d Co(CO) 4 compound were estimated and are tabulated i n Table XIV. These data suggest that the Co°-forming process i s slow at 190°C and at low S - additions ( i n fact i t i s absent at zero S~ addition). Under these conditions i t i s much slower than the Co(CO) 4 production process and hence the rate measurements apply to th i s l a t t e r process. At higher S levels and at 215°C the metal forming process i s faster than the Co(CO) 4 process and the oxidation of carbon monoxide therefore, i s rate determining. Again the rate measurements apply to Co(CO) 4 formation (the temperature effect already noted i n section I I I - 3 shows that the metal forming process i s much more temperature dependent than was the Co(CO) 4~ forming process. Consequently, over the whole ++ range the k i n e t i c studies apply to the reaction of CO and Co(NH3)n to form Co(CO) 4". 5. Effect of Formate Anion and Hydrogen I t has already been seen-(Table VII) that HCOO- i s a by-product of ++ the reduction of Co(NH3) N' by CO. The material balance studies reported i n section I I I - 3 s i m i l i a r l y show that considerable H 2 also forms during the reaction. Both H 2 and HCOO are strong reducing agents (H 2 i s used commercially to reduce cobalt ( I I ) 4 2 ' 4 3 ) . Before an evaluation of the k i n e t i c data of the Co(NH 3) n + + -CO reaction was attempted the possible effects of both HCOO- and H 2 were examined; A. .Effect of Formate Anion From Table VII the HCOO" concentration expected i n a normal run would be about O.JM. A test was therefore done to which 0.32M HCOO- but no CO was added. TABLE XIV - 52 -Qualitative Assessment of the Presence of Cobalt Metal and S o l i d Carbonyl Material' Variable Series Cobalt Metal C o ( N H 3 ) 6 [ C o ( C 0 ) 4 ] 2 S = n i l to .ikU 215°C: cobalt metal made at a l l levels of [S =] but rate increased with increasing [ S = ] . No Co° made at [S=],= 0 190°C: no cobalt metal formed at low S = levels 215°C: no s o l i d carbonyl made except at high S~ or at no S = where trace appeared about 5 minutes and then was consumed 190°C: l o t s of C o ( C 0 ) 4 " formed at a l l S -levels NH3 0.6 8M 215°C, 0.06 MS =:cobalt metal at a l l NH3 levels i n 1 minute samples 215°C, O.OIMS":cobalt formed by 5 minute sample at 5MNH3 215°C, 0.06 MS =:no C o ( C 0 ) 4 " made except trace at 6MNH3 which was consumed as run continued' 215°C, 0.01MS =:lots of s o l i d C o ( C 0 ) 4 " formed at 5 M N H 3 (NH 4 ) 2S0 4 0.5 -*3M 215°C, 0.06MS", 1.6MNH 3: Co° formed by 1 min sample 215°C, 0.06MS = 1.6M NH3: no C o ( C 0 ) 4 formed P c o 215°C, 0.06MS=, 1.6M NH3: CO° formed at a l l levels but appeared l a t e r as pressure decreased 215°C, 0.01MS =, 3 . 5 M NH3, 30 atmos: Co° formed by k min 8 atmos: Co° formed by 8 min 215°C, 0.06MS, 1.6M NH3: no C o ( C 0 ) 4 ~ up to i+5 atmos. At atmos. trace formed •215°C, 0.01MS =, 3 -5MNH 3 : 30 atmos: l o t s ' C o ( C 0 ) 4 _ formed 8 atmos: no C o ( C 0 ) 4 " formed ^Determined by the presence or absence of magnetic solids (cobalt metal) and s o l i d Co(NH 3) 6 [ C o ( C 0 ) 4 ] 2 i n each sample a f t e r i t had cooled. - 53 --The results are compared i n Table XV with a normal experiment. HCOO" does not reduce Co(NH3)n + + at an appreciable rate under the test conditions i n use in t h i s study. B. .Effect of Hydrogen Table XVI compares H 2, CO and HCOO- productions for several two-part experiments. H 2 production i s only s i g n i f i c a n t i n the B parts, i . e . when CoS x i s present. HCOO" forms i n the absence of CoS x and i s p a r t i a l l y consumed i n i t s presence. . CN" catalyses H 2 formation. This effect of CoS x on the production rate of H 2 i s better i l l u s t r a t e d i n Figure 16. No attempt was made to evaluate rigorously the k i n e t i c s of H 2 f o r -mation. However from gas analyses taken of various experiments i t i s possible to obtain a semi-quantitative assessment of these k i n e t i c s . This data i s summarized i n Appendix C. -A mechanism i s also postulated i n t h i s appendix for H 2 formation. Because of the large amount of H 2 present i n a t y p i c a l CO reduction of C o ( N H 3 ) n + + , a knowledge of the r e l a t i v e rates of reduction of Co(NH 3) n + + by H 2 and CO i s essential. Figure 17 (based on data tabulated i n Table C - l , .-Appendix C) compares the rate of Co(NH 3) n + + reduction by CO with that of H 2 production i n a series studying the effect of [NH 3]^ on the rate. A l i n e a r relationship i s observed between increasing i n i t i a l NH3 concentration and the amount of H 2 produced (Figure C - l , Appendix C) but i n Figure 17 the rate of Co(NH3) n + + reduction appears to be independent of H 2 concentration i n a region i n which the l a t t e r i s s t i l l increasing. This would indicate l i t t l e Co(NH 3) n + reduction by H 2. To compare the actual reduction rates of H 2 and CO runs 85 and 87 were done i n which only H 2 and no CO was added. These runs are compared i n TABLE XV HCOO" Reduction of Co(NH 3) n ( I n i t i a l Conditions: 0 .32MCo(NH 3)- n + +, 5 M N H 3 , 1 . 2 M(RH 4) 2 S 0 4 0.06 MS= ,215°C Experiment Number [ H C O O - ] . ^ PC O Max.. Rate Moles H 2 Formed atm M/min after min 196 115 0.32 n i l n i l 0.0003 26.5 O.O383 0.0012 0.2220 TABLE XVI Production of H 2, CO and HCOO" i n Two Stage Experiments ( I n i t i a l Conditions: 1.1M(NH4)2S04, 5MNH3, 1.1M(NH4)2S04,.0.J5M Co(NH 3) n ) Experiment [Catalyst] Temp. Gas Sample Gas Analysis Moles Produced Number of Run Time temp. (i bv vol) °C (min) H 2 N 2 C02 CO HCOO" H 2 CO Part A Co(CO) 4~ Production 155A n i l n i l 190 ho 27 n i l i I 6 . 1 . L ' n i l L 9h< p . 0 6 l :. n i l ; _151A n i l 0.05M tartrate 190 39 190 .1 5 .1 1-5 96 - 0.001 -152A n i l 0.05MCN" 190 39 190 • 9 4-5 5 . 0 90 - 0.005 -I56A n i l n i l 215 ho - 27 i.h + .3 h.6 9h 0.200 0.013 -Part B Metal Production 155B 0.0k6 n i l 190 90 27 +5-7 h$.h n i l 9 0.025* o . c 4 i 0 .008 151B n i l 0.05M tartrate 190 85 190 3-0 2 3 . 2 29.3 53 - 0.006 0.099 152B 0.C46-- 0.05MCN" 190 85 190 31 .0 8 . 2 51.3 l 0.135 0.004 I56B 0.0k6 n i l 215 85 215 2 3 . 1 7-9 58.4 n i l 0.095 0.105 n i l HCOO" consumed - 56 -0 . 1 2 Expr. No. X 82 O 83 [ C o ( N H 3 ) n + + ] 1 [S~] n i l • 314 .326 0.03 0.03 n i l [Zn(II)] CoSx Co° Brcduced .33 yes no -1 n i l yes yes n i l no no 0 . 1 0 0.08 0 . 0 6 o.o4 0.02 20 30 Time (minutes) 50 Figure 16: ++ Rate of Production of H 2 During CO Reduction of Co(NH 3) n ( I n i t i a l Conditions: 26 atm CO. 2.2 M-NH3, 1.1M (NH 4 ) 2 S 0 4 , 215°C). Max. Rate Co(NH 3) n Reduction at Various [m3]± (M/min x 100) ; - 58 -Expt No. Pe'C- P H 2 • 85 n i l 13.6 2.3 A 96 11.9 n i l 2.3 • 87 n i l 21.8 4.6 O 88 27.5 n i l 4.0 •A 10 20 30 Time(mins) Figure 18: 50 ++ Comparison of Rates of Reduction of Co(NH 3) n '_by H 2 and CO. ( I n i t i a l Conditions: 1 . 1 M (NELjJsSO^ 0.033M S = v 215°c; - 59 -H 2 reduction of Co(NH 3)n occurs under the conditions of t h i s study but at a much lower rate. With the same gas pressure the rate of reduction with CO i s four times larger than with H 2. The experiment i n which the most H2 was produced had Pg at 4-5 minutes equal to 11 atm. Consequently, the rate towards the end of a run can, at the maximum, be increased by only 20$. Since maximum rates are used and as they occur within the f i r s t 5 minutes, error i n the rate of less than 2$ i s expected from H 2 reduction. 6 . Nature of the Cobalt Metal The k i n e t i c data provide , l i t t l e insight into the reaction producing cobalt metal. To obtain some information on t h i s both the effect of recycling of reduced material and the micro-structure of reduced product were investigated. A. Effect of Recycling Experimentally, recycling was d i f f i c u l t because of plugging of tubing by ammonium carbonate. Of fi v e attempts only one was successful. The procedure consisted of using the reduced solution and solids from a f i r s t run as p a r t i a l feed to a second ( i n addition C0SO4 6H 20^ NH3 and water were added to regain the o r i g i n a l concentrations). The second reduction was, therefore, i d e n t i c a l to the f i r s t except that CoS x, although present i n the same quantity, was not fresh, and that cobalt metal was present from the s t a r t . The result of t h i s recycling i s shown i n Figure 19. The two runs have rates i d e n t i c a l within experimental error. Consequently, the rate i s apparently independent of the amount of cobalt metal present and CoSx. i s as active on recycling as i t i s when fresh. The active s i t e s on CoSx are apparently not destroyed by coating with cobalt metal. - 60 -10 Time (minutes) Figure 19: Effect of Recycling on Rate ( I n i t i a l Conditions: 0.046M S , > 5 M NH3, 1.2M (NH 4) 2S0 4, 26.5 atm CO, 215°C). - 61 -The result i n Figure 19 also indicates that the other products of the reaction, primarily G O 3 - , have no measurable effect on the maximum rate of reduction. An additional run was done to confirm the independence of the rate on cobalt metal. To t h i s experiment 50g of cobalt metal powder was added. Because of plugging no samples at temperature were taken. The run was quenched and the ++ Co(NH3)n- concentration compared with that at the same time for an i d e n t i c a l run to which no metal was added. The results are shown-in Figure 20. Apparently cobalt powder has l i t t l e effect on the rate of 00(1^3^ + + reduction supporting the conclusion reached above. B. Microstructure of Reduced Solids The structures of the soli d s obtained by reduction of Co(NH 3) n + + i n the presence of CoS x were examined by election microscopy by Dr. D. Tromans of t h i s department. This work i s presented i n Appendix D. The data obtained has been interpreted as showing that CoS x i s present as spherical p a r t i c l e s with cobalt metal apparently present as p l a t e l e t s . A cobalt p a r t i c l e completely free of CoS:x was found. These results substantiated the conclusion of part A of t h i s section that the deposition of cobalt metal does not cover the CoS x surface and hence lower i t s c a t a l y t i c a c t i v i t y . However, nucleation of cobalt metal on CoS x and growth outward from the surface has not been eliminated. - 63 -. I V . . D I S C U S S I O N 1. Summary o f R e s u l t s The p r o d u c t i o n o f c o b a l t m e t a l by , t h e r e d u c t i o n o f C o ( N H 3 ) + + b y CO was shown t o p r o c e e d i n two s t a g e s : (1) t h e p r o d u c t i o n o f C o ( C O ) 4 a n d (2) t h e r e d u c t i o n o f C o ( N H 3 ) n b y C o ( C O ) 4 ~ . - S t a g e 1 p r o c e e d s h o m o g e n e o u s l y b u t i s a c c e l e r a t e d b y CoSx i n a s e p a r a t e h e t e r o g e n e o u s r e a c t i o n p a t h . S t a g e 2 o n l y o c c u r s i n t h e p r e s e n c e o f CoSx: c a t a l y s t . -Thea/OxldationuOfhCO. i n , . S t a g e 1 i s c o n c l u d e d 1 t o . be ' r a t e - d e t ' e ' ^ M h i r i g . ldv'e't ^tlie' r a n g e 'o f c o n d i t i o n s d e s c r i b e d i n t h i s t h e s i s - . U n d e r l o w i n i t i a l r e a c t i o n c o n c e n t r a t i o n s (PQQ «= 26 a t m . y [ C o ( N H 3 ) n - + + ]^ a n d [ . N H 3 ] i / [ C o ( N H 3 ) n + + ] ; [ i <10) t h e r a t e o f r e a c t i o n . i s f i r s t o r d e r i n O H " , ++ = C d ( N H 3 ) n . a n d i n CO p r e s s u r e a n d 0.6 o r d e r i n S c o n c e n t r a t i o n . U n d e r h i g h i n i t i a l r e a c t a n t c o n c e n t r a t i o n s t h e r a t e i s 0.6 o r d e r i n t h e amount o f S - a d d e d b u t becomes z e r o o r d e r i n o t h e r r e a c t a n t s . U n d e r a l l c o n d i t i o n s u s e d i n t h i s w o r k t h e r e a c t i o n c a n be t a k e n a s i n d e p e n d e n t o f N H 3 c o m p l e x i n g o f C o ( l l ) a s n was f o u n d n e a r l y c o n s t a n t o v e r t h i s r a n g e o f c o n d i t i o n s . . No s a l t e f f e c t i s i n d i c a t e d . - The r e a c t i o n r a t e a p p e a r s i n d e p e n d e n t o f C o ( l l l ) a n d C0 3 c o n c e n t r a t i o n s and. t h e p r e s e n c e o f c o b a l t m e t a l . I n t h e a b s e n c e o f CoSx a s i d e r e a c t i o n b e t w e e n CO a n d OH~ r e s u l t s i n t h e f o r m a t i o n o f HCOO". .When CoSx i s p r e s e n t , , H 2 i s p r o d u c e d , p r e s u m a b l y f r o m d e c o m p o s i t i o n o f HCOO". - 6k -2.. Experimental Rate Lav f o r Co(II)Reduction The k i n e t i c data lead to the following experimental rate laws ^ • ^ d T ^ 1 = k l ^'h^]°'6[co(m3)n++]± P C O . ++. v a l i d for 0 <: [WH3 ] i/[Co(NH 3) n ]£ < 10 0 < [S =] 0 PC0 •"='26 atmos 0 ^[Co(NH;3)£++]i. < 0.6 v a l i d for [NH 3]^/[Co(NH 3)n ]± > 10 0 [S =] PQ Q 26 atmos. [Co(WH 3) n + +] i > 0.6 In these rate law expressions the contribution of the homogeneous formation of Co(C0) 4 to the o v e r a l l rate i s omitted because i t i s small i n comparison to the heterogeneous contribution at a f i n i t e S - addition. 3..Calculated Rate Law for Go(H)Reduction by CO The mechanism has been shown to consist of two distinguishable stages: the formation of Co(C0) 4~ and the formation Qf Gobalt metal. - -From the l i t e r a t u r e the k i n e t i c s of the reduction of metallic ions by CO are seen to involve a rate-determining step consisting of the formation - 65 -of a CO insertion complex. 0 li i . e . -(M - C - OH) In the case of C u ( l l ) , Ag(l) and Hg(ll) t h i s insertion complex then reacts with another metallic ion resulting i n metal or ions i n a reduced valence state. In the case of N i ( l l ) the insertion complex reacts with further CO to form stable Ni(C0)4 and no metal resulted. The present work indicates that C o ( l l ) behaviour with CO i s more comparable to the N i ( l l ) reaction than with those of the others since a stable carbonyl, Co(C0)4 , also forms. This i s the product of the reaction unless a catalyst i s present which permits t h i s carbonyl to react with additional C o ( l l ) ions forming metal, not unlike the reaction of the insertion complexes of A g ( l ) , Hg(ll) and C u ( l l ) . The formation of Co(C0)4~ i s more complicated than that of Ni(C0)4 i n that the cobalt product has an awkward electronic charge not obtainable through simple capture of CO molecules and normal decomposition of the C o ( l l ) insertion complex. Rather the cobalt CO insertion complex must be further reduced. Since CoSx i s a l i k e l y vehicle for t h i s reduction either of the following three steps may be rate-determining: 0 0 ft 2[(NH 3) n. Co-C-OH]+ + 2 CoS^—> 2[ )NH3)n-Co-C-0H]°+2(CoSx-)+ 11 2(CoSx) + + CO + km3 + 2 HsO-^tCoSxO+COa + 4NH4+ ' 12 2[(NH 3) n -CoiLoH]0 + 8 C 0 + 6NH3 + 3H20 > 2Co(C0) 4~ + 6NH 4 + + 2C0 3 = 13 (CoS x) denotes the removal of an electron from a CoSx c r y s t a l . This process may i n fact involve a more complicated process such as exchange of ions with the solution to permit the Co inCoS^.. to have variable valence without loss of e l e c t r i c a l n e u t r a l i t y . - 66 -Of these only equation 11 can be rate-determining and at the same time consistent with the experimental rate low. From t h i s reasoning i t i s now possible to calculate a rate law based-on the following assumed mechanism: ++ Ki PI + + Co(NH 3) n + CO + NH3+H20 s = [ (NH3 )n> Co-C-OH] + NH4 ik 0 K 2 0 [(NH 3^-Co-C-0H] + + Cg ^ ^ [(NHa^-Co-C-OH]^ 15 0 kr- 0 [(NH 3) n Co-C-0H] a d s + CoS x- i I-*[(M 3) r iCo-C-OH]° d s +(CoSx)+ 16 (CoS x) + + VsCO + 2NH3 + HsO^g-^ CoS x + VsCOs" + 2NH 4 + 17 0 [(NH3)n€o-C-0H]°ds +4C0+(3-n)WH3+H201^Co(C0)r a d . + C0 3 = +3NH 4 + 18 Co(CO) 4" • - + 4 . 5 C o(NH 3) n + + + (l6-^5n)NH3+ 8H20 f a s t>5 . 5Co° + kC03~ + 16NH4 19 Where C s i s the number of free s i t e s on CoS x available for adsorption. Such a mechanism supposes that the CO insertion complex i s adsorbed on a c a t a l y t i c surface before electron transfer occurs. CoSx i s assumed to be the electron source and the electron transfer i s assumed rate-determining. The reaction shown i n equation 18 may follow a desorption step. For such a mechanism the rate of reduction i s : ++ 0 + -d[Co(NH3) ] = k [(NHa)-Tflo-C-OH] a d s 20 dt r n Because of the complexity of the system and the great d i f f i c u l t y that would be experienced mathematically i n treating the effect of concentrations of a l l the possible adsorbed species (H2>HC00~, CO, C0 3 -,•Co(WH 3^ + + , [(NH3 ^Cco-C-OH ] , - 67 -o [(NH 3) n Co-C-OH]"), the simplifying assumption has been made that the number of sit e s occupied by other species i s small compared to the t o t a l number of s i t e s , C 0, and can be ignored. Therefore, the number of si t e s available i n i t i a l l y 0 for [(NH 3) n Co-6-OH] adsorption i s assumed equal to the t o t a l number of i n i t i a l s i t e s . Since C G i s proportional to the amount of surface area of CoS x present. Co <* [S-]°*6 21 r = A 6 = 0 [S ] 22 from equation 15. [(NH 3) n C6-$-0H]^ds = K 2C s[(NH 3)--Co-?-0H] + 2J = 0 [S]°-6 - C 2k s C s = Q [S=] 0' 6 ff 25 1+K2 [ (NH3 ) h -C o -C -OH ] [(HHa ^ C o X c f l ] " 1 " . = Kg[(NH3b-Co-C*0H] + 0 [S =]°' 6 \ ^ / n ads 1 — ^ n ^ 1 + K2[(NH3)n„-Co-C-0H]+ 26 from equation Ik n [(NH3)n-Co-C-0H]+ = ^ [ 0 0 ( ^ 3 ) n + + ] [NH 3]P C 0 27 [NH4 ] - 68 -= Kj ++ [Co(NH3)n_ ] [OH ] P c o 28 where [NH 4 +] = K 3[NH 3 3 [OH-] Equation 20 can now be written -d[Co(NH 3) n +^ =  - 0 6 k rK 2K 1Q[Co(NH 3)^ + + ] ' E 0 H " ] P C Q [ S " 3 d t 1 + ^ [Co(NH3) n + +][0H"]P C 0 K . 3 29 30 In equation 30 the concentrations represent those at t i m e t . Since., experimentally, i n i t i a l rates are being considered, the concentration terms can be considered to be i n i t i a l ones. Consider, now, the condition of a high value for the product [ C o ( N H 3 ) n + + ] i [0H~]i P C Q then ^ [ c o ( r a 3 ) n + + ] . [on"]. P c o ^ i Equation 30 then reduces to -d[Co(NH 3) n" +] = Q k r [ s ^ j 0 ' 6 , 5 1 dt - 69 -Equation 31 i s i d e n t i c a l to equation 10, the experimental rate law v a l i d f o r these conditions i f 9 k r = K2. At a s u f f i c i e n t l y low value f o r the product [ C o ( W H 3 ) n + + ] i [0H~]j_ PCQ and equation 30 reduces to Kga [ C o ( N H 3 ) / + ] . [OH"]. P C Q <^ 1 -d[Co(NH 3) n + +] = Qk^gKx [ C o ( N H 3 ) i 1 + + ] i [OH -]. P C Q [ S - ] 0 " 6 ' ^ dt K 3 Equation 32 i s i d e n t i c a l to experimental rate law, equation 9> i f K 3 k. Evaluation of the Rate Constants ++ From Figure 12 showing the e f f e c t of i n i t i a l Co(NH 3)n concentration the rate appears independent of t h i s v a r i a b l e at about O.O65 and 0.040M/min f o r 0.06 and 0 . 0 3 5 M S - , r e s p e c t i v e l y . These values should apply to equation 31> hence Q k 2 = -d[Co(NH 3)n + +] dt '/[s=] = 1 0.6 53 = 0.42 and 0.36/min for these two conditions consequently, Q k 2 = 0.39 * .03/min 34 - 70 -From equation 32, a p l o t o f maximum rate versus i n i t i a l Co(NH"3) n and 0 H ~ concentrations or PQQ at constant S - a d d i t i o n , where these m a t e r i a l s are present i n low co n c e n t r a t i o n , w i l l have a slope of i^. 3KjK2 . In Figure 11 K 3 showing the e f f e c t of PQQ on the maximum r a t e there are two curves t h a t obey these c o n d i t i o n s . They have slopes of 0.00123 and 0.00052M/min/atms f o r s e r i e s c o n t a i n i n g Is&M NH 3(^> 8xl0" 7 MOH"), 0.311MGo(WH3)nL++ and 0.06MS and 2 . 2M NH 3 (=0= l4xl0" 7 MOH"), 0.319M C o ( N H 3 ) n + + and 0 . 0 2 M S = , r e s p e c t i v e l y . Consequently, slope = [ C o ( N H 3 ) n + + ] i [OH"]. [ S = ] 0 ' 6 5 5 = 3«3xl04 and 1.5xl0 4 f o r the two c o n d i t i o n s The value of 3-3 x10 4 w i l l be used as i t i s based on b e t t e r data, t h e r e f o r e K QKiKg = 3.3XIO4 I 2 moles" 2 36 K 3 From the l i t e r a t u r e K 3 = 2 x l 0 _ 6 m o l e s / l at 215°C 4 5 and from equation 3^ 0k r = 0.39 * 0.03/min t h e r e f o r e K3K2 = 0.17 1 m o l e s - 1 a t m - 1 37 The assumption used t o s i m p l i f y the denominator i n the r a t e law expression, equation 30, can now be checked. The statement was made t h a t a t low PQQ and ++ i n i t i a l C o ( N H 3 ) n and OH concentrations 71 K 2 K 1 Ka ++ [Co(NH 3) n ] ± [OH"]i P C Q ^  1 38 f o r K 2K X = 0.17 K 3 = 2x10"6 [ C o ( N H 3 ) n + + ] . = 0.1 [0H"] i = 7x10"7 PQQ = 10 atm Equation 38 becomes 1 + 0.005 — 1 and the assumption i s v a l i d . At high P ^ and , ++ i n i t i a l OH and Co(NH 3) n concentrations the.assumption was made that 1 + Z£i [ C o ( N H 3 ) n + + ] . [OH"]! P C 0 5€> 1 39 for K 2 K i = 0.17 K 3 = 2x10-s [ C o ( K H 3 ) n + + ] . = IM [OH -]. = 24x10~T ([NH 3]. = 3.5) PQQ = 30 atm Equation 39 becomes 1 + 6.1 1. The erro r i n making t h i s assumption was, therefore, 14$. From the data a v a i l a b l e the values of K x and K 2 cannot "be evaluated separately. \ - 7 2 -5. Integration of the Rate Lavs and Calculation of Reduction Curves Equation 31 on integration gives [Co(NH 3) n + +] •= -Qk r[S =]°' 6 t'+ [Co(NH 3) n + +J 1 . . . . . kO and equation 32 log[Co(NH 3) n + +] •= -Ok-JCiKa [OH-] P c 0 (S=]°"6t 2.3K 3 ++ + log[Co(NH 3) n ] i . . . . . kl Using the values derived for Q k^ and KXK2 i t i s possible v i t h equations kO and kl to calculate reduction rate curves and compare them with experimental rate curves, thereby checking the v a l i d i t y of the mechanism. This has been done i n Figures.21 and 22 which represent experimental conditions to which equations ko and kl} respectively, should apply. The agreement between calculated and experimental curves i s considered s u f f i c i e n t l y good i n both cases to support the mechanism i n view of the magnitude of the error i n evaluating the constants 0k r and KiK 2. The mechanism of reduction of cobalt (11) by CO to carbonyl (Co(CO)4~) i s distinguishable from .the reduction of other metals studied i n that a heterogeneous mechanism involving a cobalt sulfide surface i s involved. As i n several previous cases, the proposed insertion complex i s i n equilibrium with reactants and i t s f ormatio'ri""is not rate-determining. This heterogeneous reaction path involves an activation energy of only 11 kcal/mole compared,with a simultaneously observed homogeneous path of 17 kcal/mole. - 73 -4 6 8 Time (Minutes) Expt. No. (NH 3]^ [S ] P c o Error i n Rate • 167 7.25 0.01 27.9 35$ A 200 5.20 0.06 27.2 20$ B 201 5.20 0.06 27.2 5$ Fig. 21. Comparison of Calculated and Experimental Rate Curves. (Rate should obey [Co(NH 3) n + +] = -Qkr[S=]°-6t+ [Co(NH 3) n ].) —I I I L_ 10 15 , 20 25 Time (Minutes) Expt. Wo. [ 0 H ~ ] x l 0 7 pco [s~] Error i n Rates • 96 lk.0 11.9 0.03 • 193 8.7 5.3 0.06 A 19k 8.7 15.6 0.03 Fi g . 22 Comparison of Calculated and experimental Rate Curves. (Rate should obey log [Co(WH 3) n + +] = kj-.QK3.K~2 [ 0 H - ] [ S = ] 0 ' 6 P C Q t + log [Co(NH3)+ +] .) . . . _ . . 2 . 3 K 3 - 75 -The role of the CoSx surface could be that of a catalyst, but direct reaction of this precipitate with CO may also occur, as reported by Behrens29, who mentions the reaction _ \ SCoS + 11C0 + 120H »2[Co(C0) 4 ] + 3C03 +2S +6H 20 42 This reaction proceeds readily at 1 atm CO and 60°C in NaOH solutions, provided S~ is first removed from solution. Under conditions of cobalt reduction described in this thesis, the S = would be removed by subsequent precipitation as fresh CoSx through reaction with Co(NH 3) n + +. - 76 -V. ,CONCLUSIONS In ammorriacal solutions in,the temperature range 180 to 230°C and CO pressures from 0 to 50 atmospheres the reduction of C o ( l l ) to metal by CO i n aqueous solution i s found to proceed through the formation of Co(C0)4 as an intermediate step. The production of metal results from the reduction of ++ 00(1^3^ by Co(C0) 4 . CoS x catalyses both steps of the ove r a l l reaction. Co(C0) 4 can be produced by a homogeneous step but at a much slower rate than when CoS x i s present. -The rate determining step i s postulated to be the ++ reduction of a CO insertion complex of Co(NH 3) n adsorbed on a CoSx surface. The ki n e t i c s are found to be consistent with the following mechanism Co(NH 3) n + CO +NH3 + H20 >[(NH3) Co-C-0H]+ + NH 4 + fast equilibrium S 0 [(NH3)nCo-C-0H] + CoS x »[(JIH3) Co-C-OHj^ fast equilibrium [(NH3)n3o-C-0H]ads + CoS x -gxo^ C (NH3)nCo-C -OHl a d s + (CoS x) + (CoS x) + + i CO + 2NH3 + H20 r a s t > CoS x + £ C 0 3 = + 2 NH 4 + [(NH3)nCo-C-OH]ads + ^ CO + (3-n) NH3 + H20 Co(C0)I a d s + C0 3" + 3 NH4 + C o ( C 0 ) 4 a d s + 4 . 5 C o(NH 3^ f + + (l6-4.5n)NH3+8H20 f a s t > 5 - 5 0 o o +k2Q3= + l6NH 4 + - 77 -The steps a f t e r the rate-determining step are required f o r consistency with the stoichiometry. This mechanism .neglects a contribution to the ov e r a l l rate by a homogeneous step for the production of Co(CO) 4". The mechanism suggested here i s seen to be electrochemical i n nature i f step 3 and step k are proceeding at the same rate. CO reacts with OH" to form HCOO" which i n the presence of CoS x reacts to form H2. A mechanism i s suggested for the heterogeneous reaction. Under the conditions used.in t h i s work CO i s a more effective reductant, f o r C o ( I I ) than i s H 2. \ - 7 8 -VI. APPLICATION OF THE RESULTS Among possible applications of the results of t h i s study, besides the obvious one of production of cobalt metal,,are the following: (a) a method of separation of Co(II) from Ni(II) i n aqueous media and (b) a method for reacting CO to produce H 2. (a) Separation of Co(II) from Ni(II) H i r s c h 1 4 showed that reduction of Ni(II) from aqueous solution with CO resulted i n Ni(CO) 4. This study has shown that without Co3 x present Co(II) . reduction by CO results i n Co(CO) 4 which precipitates as a true s a l t , Co(NH3)6 [Co(CO) 4] 2. Since Ni(CO) 4 b o i l s at kyc a separation should be possible. The experiments reported i n Table XVII were designed to determine the f e a s i b i l i t y of t h i s separation. From the data a possible separation i s indicated. In the absence of S -, reduced n i c k e l i s present as Ni(CO) 4 which was e a s i l y boiled away. When S was present, reduced n i c k e l was present as the metal at 215°C but s t i l l as Ni(CO) 4 at 1 9 0°C. These preliminary data indicate that almost complete separation of Ni(II) and Co(II) i n aqueous media might be possible by CO reduction by removing Ni(CO) 4 i n a homogeneous system or n i c k e l metal i n a heterogeneous system. A problem i n the l a t t e r case would be the separation of Ni° from the CoS x catalyst. - I f , as the results indicate the metal does not coat CoS x, separation by f l o t a t i o n might be feasible. Of interest i n these results i s the marked a c t i v i t y of CoS v during n i c k e l metal production. I f the mechanism for n i c k e l metal production i s analogous ++ to that of cobalt metal, then CoS x must catalyse the reduction of Ni(NH 3) n by Ni(CO)4-. TABLE X V I I Separation of C o ( l l ) from N i ( l l ) i n Aqueous Media by CO Reduction End Analyses N l Run No. [C o ( H H 3 ) ^ + ] i [NitNHajJ+Ji. [NH 3 l i [s~] NI° Added g Temp Length L i q u i d °C of Run Volume min cc So l u t i o n [Co(NH3)n +][Ni(NH 3 ) 5 + Residue ] $ Nirp Reduced Based on l i g samples Form of Reduced Ni 20 0.16 0.19 0.9 n i l n i l 216 30 83 0.15 0.100 ND 46 Ni(C0) 4 19 0.13 0.19 0.9 0.009 n i l 216 9^ 83 0.11 0.002 77 99 metal 21 n i l 0.18 0.4 0.009 n i l 216 256 83 n i l 0.008 95 96 metal 209 0.20 0.24 1.1 n i l 4 215 30 1000 0.18 0.02 96 92 Ni(C0) 4 210 0.16 0.24 1.1 0.021 n i l 190 60 1000 0.14 0.01 26 96 Ni(C0) 4 &Due to the low [NH 3], p r e c i p i t a t i o n of cobalt hydroxide occurred, and the decrease i n C o ( l l ) content of the s o l u t i o n during the run i s att r i b u t e d to s a l t formation and not t o reduction to metal or carbonyl. 1 —j vo - 8 0 -(b) Hydrogen Production from Carbon Monoxide The observation that CO reacted with basic solutions i n the presence of CoS to give H 2 might be of interest where gas containing CO i s wasted but H 2 would be a desirable material. VII RECOMMENDATION FOR FURTHER STUDY - 81 -This study has indicated several areas of research that could possibly be pursued. The reduction of C o ( l l ) by CO to cobalt metal was shown to go through the formation of C o ( C 0 ) 4 ~ intermediate. This was found to be produced by both homogeneous and heterogeneous reactions. The l a t t e r pre-dominates and i t alone was studied. A detailed study of the homogeneous reaction may be warranted. S i m i l a r l y , since the production of Co(CO) 4 _ was rate-determining, l i t t l e mechanistic insight into the production of metal by Co(CO) 4 _ reaction with C o ( l l ) was obtained under the conditions of t h i s study. I t might be possible to study t h i s reaction by finding a suitable catalyst for C o ( C 0 ) 4 - production to make metal formation rate-determining and hence amenable to k i n e t i c investigation. A l t e r n a t i v e l y , Co(CO) 4 - can be manufac-tured i n the absence of CoS x and then metal formation studied i n the presence of CoS x but without CO. The fact that the reduction of N i ( l l ) by CO i n the presence of CoS x results i n metal while i n i t s absence Ni(CO) 4 i s the product presents an interesting k i n e t i c study. A general survey of t r a n s i t i o n metal carbonyls and t h e i r possible production i n aqueous solution should be considered. Based on an analogy with the results of t h i s present work, such a survey might indicate other metals that could be produced by CO reduction of t h e i r ions from aqueous solution i n the presence of suitable catalysts. The study of the c a t a l y t i c behaviour of CoS x might show why and how CoS x appears to be so sp e c i f i c f o r metal formation from Ni(CO) 4 and Co(CO) 4". An equally s p e c i f i c catalyst might result from such a study which would not contaminate the metallic product as does CoS x. - 82 -V I I I REFERENCES 1 . P e t e r s , E . , P r i v a t e C o m m u n i c a t i o n 2 . C o t t o n , F - . A . , a n d W i l k i n s o n , G . , " A d v a n c e d I n o r g a n i c C h e m i s t r y " I n t e r s c i e n c e P u b l i s h e r s , New Y o r k ( 1 9 6 2 ) . 3 . H a l p e r n , J . , . Q u a r t . R e v s . , 1 0 , 463 ( 1 9 5 6 ) . 4 . B a s o l o , F . a n d P e a r s o n , R . " M e c h a n i s m o f I n o r g a n i c R e a c t i o n s " , J o h n W i l e y a n d S o n s , New Y o r k , 1 9 5 8 , , C h a p . 8 . 5 . W e b s t e r , A . H . , a n d H a l p e r n , J . , J . P h y s . C h e m . , 6_0, 2 8 0 ( 1 9 5 6 ) . 6 . P e t e r s , E . , a n d H a l p e r n , J . , J . P h y s . Chem. 5_£, 793 ( 1 9 5 5 ) . 7 . K o r i n e k , , O . G . , a n d H a l p e r n , , J . , J . P h y s . Chem. 6 0 , 285 ( I 9 5 6 ) . 8 . K a n e k o , T . M . a n d W a d s w o r t h , M . E . , J . P h y s . Chem. 6 0 , 457 ( I 9 5 6 ) . 9 . M a c k i w , V . N . , e t a l . , J . M e t a l s , £ , 786 ( 1 9 5 7 ) . 1 0 . H a r k n e s s , A . C . , " K i n e t i c s o f Some O x i d a t i o n - R e d u c t i o n R e a c t i o n s i n Aqueous S o l u t i o n s " , P h . D . T h e s i s , D e p t . o f C h e m i s t r y , U n i v e r s i t y o f B . C . , 1 9 6 3 . 1 1 . N a k a m u r a , S . " R e d u c t i o n o f S i l v e r Ammine C o m p l e x e s b y C O ' V M . S c . T h e s i s D e p t . o f C h e m i s t r y , , U . B . C . I962. 1 2 . M c A n d r e w , R . T . , a n d P e t e r s , E . , , C a n . M e t . Q u a r t , 3 , 153 ( 1 9 6 4 ) . 1 3 . B y e r l e y , J . J . , a n d P e t e r s , E . , i n A . I . M . E . - S o c . C o n f e r e n c e s , V o l . 2 4 , " U n i t P r o c e s s e s i n H y d r o m e t " E d . W a d s w o r t h , M . E . , G o r d o n a n d B r e a c h S c i . P u b l i s h e r s New Y o r k ( I 9 6 3 ) . 1 4 . H i r s c h , E . , a n d P e t e r s , E . , , C a n . . M e t . Q u a r t . , 3 , 137 ( 1 9 6 4 ) . 1 5 . - M c D o n a l d , R . D . , "The K i n e t i c s o f CO A d s o r p t i o n i n B a s i c S o l u t i o n s a t E l e v a t e d T e m p e r a t u r e s " , M . S c . T h e s i s , . D e p t . o f M e t a l l u r g y , U . B . C . I 9 6 3 . 1 6 . R o y e n , , P . , , E r d o l u . K o h l e , 9_ 19 ( I 9 5 6 ) . 1 7 . H i r s c h , E . , P r i v a t e C o m m u n i c a t i o n . 1 8 . H i e b e r , . W . , Z . A n o r g . C h e m i e , 2 4 3 , 145 ( 1 9 3 9 ) ; ( C A 3 4 : 5 3 6 7 s ) . 1 9 . W e n d e r , I . e t a l , B u l l 6 0 0 , U-.S. B u r e a u o f M i n e s 1 9 6 2 . 2 0 . H i e b e r , . W . , Z . A n o r g . C h e m i e , 240, 2 6 l ( 1 9 3 9 ) ; (CA33 : 3 2 8 5 5 ) . 21 E d g e l l , , W . J . , e t a l . J . A . C . S . , 7 8 , 4185 ( 1 9 5 6 ) . 2 2 . R u d k o v s k i i , D - . M . , a n d G a n k i n , V . C A 6 0:7502H. 2 3 . M a r k o , , L . a n d B u d a v a r i , 0 . , C A 5 5 : 2 0 6 g . - 83 -2k. K r i n k i n , D.P., and Rudkovskii,, DM., Khim. Prom. 9 , 655 (I963); CA60 :5058e 25. -Marko, L., et al..CA59:213b. 26. Blanchard, A.A.,, J.A.C-.S., 5_8, 2160 (1936). 27. Reppe,,W. Experientia, 5_, 93 (19I4.9). 2 8 . "Organic-Metallic Chemistry",, Ed.. Zeiss,. H., A.C.S. Monograph No.ll+7, Reinhold i 9 6 0 , Chap. 10. 29. Behrens, H., and Eisenmann, E., Z.-Anorg. Chemie, 278, I55 (1955). 3 0 . Blanchard,. A.A., J.A.C.S., 62, 1192 (19^0). 3 1 . -West, T.S., "Analytical Applications of E.D.T.A.", B r i t . Drug House, 2nd Ed., I960. 3 2 . Vogel,, A.I., "Textbook of Quantitative Inorganic Chemistry", Longmans, Green and Co., Toronto, 2nd Ed., 1951. 3 3 . Hieber, W., and Fraenkel H.,, Chem.-Ber. 86, 710 (1953). 3 4 . Wender, I.,,Anal. Chem. 2k, rjk (1952). 35- Hahn, E.A., "Kinetics of Copper Reduction by Hydrogen from Aqueous Solutions", .Ph.D. Thesis,,Dept. of Metallurgy, U.B.C., I963. 3 6 . Emeleus,,H.J., and Anderson, J.S., "Modern Aspects of Inorganic Chemistry", 3 r d Ed., Van Nostrand,, Toronto, i 9 6 0 . 37- Zeiss, H., "Organic-metallic Chemistry" A-.C .S Monograph No. 147, Reinhold, Chap. 10 ( I 9 6 0 ) . 3 8 . Hieber, W.,,Z. Anorg. Chemie, 2k9, 43 (1942). 39- - Wender,. S., et a l , J-.A.C.S., 75_, 2717 (1953). h0. Orchin, M., J-.A.C.S., 8 l , 3598 (1959). kl. Bellamy, L.J., "Infra-red,Spectra of Complex Molecules", John Wiley and Son, J New York, 1958. k2. Kunda, W. et a l , Can. Mining and Met. Bu l l . , , LXV, 21 (1962). 4 3 . Schaufelberger,, F.A., U.S. Patent 2 ,734,821 (1956) . kk. A.S.T.M. X-Ray D i f f r a c t i o n Patterns 4 5 . Landolt-Bernstein, "Physikalische-chemische Tabellen", 5 t h Ed., Springer Verlag, B e r l i n , p.1164 and 1122 (1923). - 8k -APPENDIX A Tabulation of Experimental Data. The tables that follow contain data displayed i n figures i n the body of the text. These tables are i n the same sequence as that i n which the data are discussed. - 85 -T A B L E A . - I Test Effect of [NH 3] 1 on Rate of Reduction at 215°C at Constant [NH 4 +] i [NHg ] i [NH3 free at 215°C [0H~] 10"5 at 215°C LOH-; x 107 [NH 3]j [ C o (NH3) ] Max Rate M/min Max Rate 1.mins/mole series 1 [Co(NH3 ) + + ] 'n J i = 0.31, [(NHOaSOJi = 1.2 [s - ] = °-o6> p C 0 i = 26 atm 175 6.85 5.90 52.5 1.9 22 0.0355 29.9 176 6.09 5.15 46.2 2.3 20 O.0351 28.5 177 5-5+ 4.34 40.0 2.5 18 0.0313 31.9 Fig. 9 5.00 4.10 37-0 2.7 16 0.0335 29.9 180 4.22 3.40 30.6 3-3 14 0.0377 26.5 178 5.09 2.32 21.1 ^•7 10 0.0525 30.8 182 2.56 1.62 15.1 6.6 8 0.0267 37-5 Fig. 9 2.50 -1-59 14.8 6.8 8 0.0278 36.0 179 1.62 0.95 9-0 l l . l 5 0.0227 44.0 Fig.11 I.58 0.94 8.8 11.4 5 0.0210 47.6 181 O.87 0.25 2.9 34.5 3 0.0113 88.5 1See Appendix B for calculation of these values series 2 [Co ( N H 3 ) N + + ] ± = 0.31, [(NH 4) 2S0 4] i =1.2, [s - ] = 0.02 , p C O i = 26 atm. 104 8.0 7-0 62 1.6 25 0.0167 59-8 109 6-5 5-5 50 2.0 20 0.0183 54.6 105 5.1 4.2 38 2.6 16 0.0173 57-9 Fig. 9 5.0 4.1 37 2.7 16 0.0150 66.6 110 4.4 5.6 32 3-1 14 0.0165 60.6 108 3-7 2.9 26 3-9 11 0.0167 59-8 102 2.3 1.6 15 6.7 7 0.0120 83.4 100 2.3 1.6 15 6.7 7 0.0117 85.5 68 2.3 1.6 15 6.7 7 0.0120 83.4 Fig. 9 2.3 1.6 15 6.7 7 0.0120 83.4 Fig.11 2.2 1.6 14 7.1 7 0.0135 74.1 106 1.2 0.6 5 20.0 4 0.0062 161.0 series 3 [Co ( N H 3 ) n + + ] i = 0.31,. [(NH 4) 2S0 4 3i = 1.2, [s=] = °-01> P C 0 i = 26 atm 170 5.1 4.2 38 16 0.0081 Fig.11 5.0 4.1 37 16 0.0090 Fig.9 5.1 •4.2 38 16 0.0103 111 4.9 4.0 56 15 0.0090 159 4.9 4.0 56 15 0.0103 70 2.3 1.6 15 7 0.0110 Fig. 9 2.3 1.6 15 7 0.0080 - 8 6 -TABLE A-II Effect of I n i t i a l ( N H 4 ) 2 S 0 4 Concentration on Rate of Reduction of Co(NH3) n + + at 2 1 5°C and Constant lmh1± Experiment [(M^)zSoTii tOH-] 1 0 " ^ Vapor Max. Rate 1 Number at 2 1 5°C [O H ~ 1 Pressure M/min Max. Rate x 1 0 T at 2 1 5°C 1 min/mole atms. series 1 [Co(NH3) n -J i . 3 1 , im3]± = 1 . 6 [ S = ] = 0 . 0 6 P C 0 = 2 6 1 8 4 3 - 0 3 3 . 2 7 3 0 . 6 _ 0 . 0 1 2 0 8 3 . 2 1 8 5 2 . 2 9 4 . 4 2 " 2 2 . 7 2 1 . 4 0 . 0 1 4 0 7 1 - 5 1 9 1 1 . 9 2 5 . 1 5 1 9 . 2 2 2 . 1 0 . 0 1 7 3 5 7 - 8 1 8 6 1 - 5 * ' 6 . 4 2 1 5 - 6 2 1 . 7 O.OI87 5 3 - 5 F i g . 3 1 . 2 0 8 . 2 5 1 2 . 1 2 1 - 5 0 . 0 1 9 5 5 1 - 3 F i g . 1 1 1 . 2 0 8 . 2 5 1 2 . 1 2 1 . 7 0 . 0 2 1 0 4 7 . 6 1 8 7 0 . 8 0 12.40 8 . 1 2 1 . 4 O.OI83 5 4 . 6 series 2 [CoCNHs)^ l i = 0 . 3 . 1 , [NH 3 i] = 2 . 3 [S=] = 0 . 0 2 P C 0 = 2 6 9 8 2 . 2 2 7 - 1 3 1 4 . 1 2 5 . 8 0 . 0 0 9 7 1 0 3 . 0 1 0 3 1 . 6 7 9.48 1 0 . 5 2 6 . 2 0 . 0 0 9 7 1 0 3 . 0 1 0 7 1 . 1 0 1 4 . 4 6 . 9 24 . 8 0 . 0 1 2 3 8 1 . 3 1 0 2 1 . 1 1 1 4 . 3 7 - 0 2 5 . 5 0 . 0 1 2 0 8 3 . 4 1 0 0 1 . 1 1 1 4 . 3 7 . 0 2 5 . 5 0 . 0 1 2 3 81 .3 64 1 . 1 0 1 4 . 4 6 - 9 2 5 . 1 0 . 0 1 2 3 81 .3 6 8 1 . 1 0 1 4 . 4 6 . 9 2 5 . 1 0 . 0 1 3 0 7 7 - 0 6 5 1 . 1 0 1 4 . 4 6 . 9 2 5 . 6 0 . 0 1 5 3 6 5 . 4 TABLE A-III Effect of S = Concentration on Eate - 8 7 -Experiment Number [J3=J] log [JS-J Max. Rate M/min log Max. Rate series 1 0 .31 M C o ( N H 3 ) n + + , 1.1 M ( N H 4 ) 2 S 0 4 , 3-TMNH3, 26 atm. C O , 215°C 119 0.133 -O.876 0.0430 -I.367 118 0.100 -1.000 0.0470 -1.328 116 0.070 -1.155 0.0337 '-1.472 178 0.060 -1.222 0.0325 -1.488 175 0.060 -1.222 0.0335 -1-475 176 0.060 -1.222 0.0351 -1.455 Figure 3 0.060 -1.222 0.0333 -1.478 114 0.050 -1.301 0.0297 -1.527 138 0.046 -1-337 0.0283 -1.548 137 0.046 -1.337 0.0277 -1.558 136 0.046 -1-337 0.0247 -1.607 113 0.040 -1.398 0.0237 -1.625 112 0.030 -1.523 0.0233 -1-633 Figure 3 0.020 -1.699 0.0170 -1.770 109 0.020 -1.699 O.OI83 -1.738 108 0.020 •1.699 O.OI67 ' -1-777 110 0.020 -I.699 O.OI65 -1.783 104 0.020 -1.699 O.OI67 -1-777 105 0.020 -1.699 0.0173 -1.762 111 0.010 -2.000 0.0090 -2.046 161 0.005 -2.301 0.0077 -2.114 156A n i l 0.0060 -2.222 series 2 0.31 M Co ( N r ~ 3 ) n + + , 1.1 M(NH4)2S04, 2-3 M NH3, 26 atm C O , 215°C 77 O.O76 -1.119 0.0320 -L495 182 0.060 -1.222 0.0267 -1.574 F i g . 6 0.060 -1.222 0.0178 -1.750 71 0.055 -1.260 0.0253 -1-597 80 0.053 -1.276 0.0253 -1-597 69 0.042 -1-377 0.0250 -1.602 66 0.024 -1.620 0.0117 -1.932 107 0.020 -1.699 0.0123 7I.910 102 0.020 -1.699 0.0120 -1.921 68 0.020 -1.699 0.0120 -1.921 Fig .11 0.020 -1.699 0.0138 -1.860 F i g . 3 0.020 -1.699 0.0120 -I.921 70 0.012 -1.921 0.0110 -1.959 I 6 9 0.010 -2.000 0.0130 -1.886 TABLE A-III (cont'd.) - 88 -Experiment [S J log [S .] Max. Rate log Max. Rate Number series 3 0 . 2 8 M Co(NH3)n , 1 .1M (NH^sSOii , 4.6M N H 3 , 2 6 atm CO, 1 9 0 ° C 1 2 1 0 . 1 4 6 - O . 8 3 6 0 . 0 2 2 5 -1.648 1 2 0 0 . 1 3 4 - 0 . 8 7 3 0 . 0 2 0 5 -1.688 1 2 2 0 . 0 9 0 -1.046 0 . 0 1 6 6 - 1 . 7 8 0 1 2 3 0 . 0 6 0 - 1 . 2 2 2 0 . 0 1 0 0 - 2 . 0 0 0 series 4 0 . 3 1 M C o(NH3) n + +, 1.1M ( N H 4) 2S0 4, 5M N H 3 , 2 6 atm CO, 1 9 0 ° C 1 6 6 0 . 0 3 9 - 1 . 4 0 9 0 . 0 1 2 0 - 1 . 9 2 1 • I 6 5 0 . 0 2 0 - I . 6 9 9 0 . 0 1 0 3 - I . 9 8 7 1 6 4 0 . 0 1 0 - 2 . 0 0 0 O . O O 6 7 - 2 . 1 7 4 1 4 9 n i l 0 . 0 0 2 1 - 2 . 6 7 8 - 89 TABLE A-IV Effect of Pco on Rate ++ ( I n i t i a l Conditions: 0-31M Co(RH3) N , 1.2M(NH 4)^S0 4, 215°C) Experiment Number PCO (atm) Max. Rate Series 1 0.0U6 M S =; >4-9M NH3 129 39-5 0.0327 131 31-3 0.0290 i4o 26.5 0.0310 138 26.5 0.0283 F i g . 9 25-7 0.0270 l42 25-5 0.0230 137 25.1 0.0277 132 15-5 0.0270 134 13-9 0.0182 133 4.4 0.0043 Series 2 0.060 M S =; I.6M NH3 195 46.2 0.0213 192 31.6 0.0220 •179 26.5 0.0227 F i g . 3 25-7: 0.0195 194 15,6 0.0193 193 5-3 0.0120 Series 3 0.020 M S =; 2.2 M Rife 97 40.8 0.0157 F i g . 3 26.3 0.0119 96 11.9 O.OO67 Series 4 0.010 M S =; 5 M RH3 170 27.5 0.0071 111 26.5 0.0090 159 25.9 0.0103 F i g . 9 25.7 0.0102 168 7-8 0.0073 TABLE A-V Effect of I n i t i a l Co(NH3)n++ Concentration on Rate ( I n i t i a l Conditions: 1.1M(NH4)2S04, 26 atm CO, 215°C) Experiment Number [Co(NH 3) n + + ]± [m3]± , . [Mg^] Max.' Rate Series 1 [S ] = 0.060 [Co(NH 3) n ) ± (M/min) 201 O.586 8.9 0.0573 200 0.425 12.2 0.0457 Fig.3 0.505 20.0 0.0333 180 0.305 13.8 0.0377 176 0.305 20".0 0.0351 175 0.305 22.6 0.0335 Figure 9 0.317 >10 0.0335 207 0.305 17.1 0.0347 202 O . I 8 7 27.8 0.0263 206 0.157 33-1 0.0223 205 0.118 44.0 0.0177 203 O .O89 58.4 0.0093 204 0.042 123.8 0.0037 Series 2 [S =] = O.O35 88 0.576 7.0 n i l 0.0300 94 0A52 8.9 0.12 0.0297 Figure 9 - 0.317 14.0 n i l 0.0220 89 0.286 14.0 0.29 0.0260 93 0.286 14.0 n i l 0.0233 91 0.286 i4.o 0.29 0.0277 95 0.143 28.0 0.43 0.0130 Series 3 [S =] = 0.010 171 0.452 0.0140 167 0.452 0.0147 159 0.327 0.0112 111 0.327 0.0090 Figure 11 0.320 15.6 0.0090 Figure 3 0.322 15.9 0.0097 Figure 9 0.317 0.0103 172 0.133 0.0045 TABLE A-VI 91 -Effect of Temperature ( I n i t i a l Conditions:.0 .3LM Co(NH 3) n + +,. 0.06 MS , 26 atm. CO, 1.2M (NH 4 ) 2 S0 4 ) Experiment Number Temp, °C 10' Max. Rate M/min log Max Rate Series 1. [NH3 ]J_ = 2.3 71 215 2.050 0.0220 -I.658 80 215 2.050 0.0209 -1.680 73 200 2.115 0.0138 -1.860 7^ 180 2.210 0.0080 -2.097 75 190 2.165 0.0160 -2.000 Series 2; [NHa > 3-7 -198 229 1.992 0.0470 -1.328 Figure 3 215 2.050 0.0333 -IA78 Figure 9 215 2.050 0,0335 -1A75 Figure 12 215 2.050 0.0355 -I.4-5O 199 202 2.105 0.0237 -1.625 Series 3. [NH3 ]^  = 1.6 188 230 1.985 0.0297 -1.527 Figure 6 215 2.050 0.0190 -1.721 Figure 3 215 2.050 0.0195 -1.710 Figure l l 215 2.050 0.0210 -I.678 190 202 2.105 '0.0157 -1.804 Series 4. [NH 3] ± = 4.9 [CN-] =0.05 162 215 2.050 0.0103 -1.987 152A 190 2.165 O.OO67 -2.174 TABLE A-VII Relative Reduction Rates of Co(NH 3) n + + by H 2 and CO ( I n i t i a l Conditions: 0.31 MS=, , 1.1M-(NH4)2S04, 215°C) Experiment P C Q Pg Max. Rate mm Number atm atm " M / J Series 1. O.31 M Co(NH 3) n + +, 2.3M NH3 85 n i l 13.6 0.0017 96 11.9 n i l O.OO67 Figure 9 26 n i l O . OI7 5 Series 2. O .58M C o ( N H 3 ) n + + , 4.3 M Mfe 87 n i l 21.8 0.0066 88 27.5 n i l 0.0236 - 93 -APPENDIX B Calculation of Free Ammonia and Hydroxyl Ion Concentration at 215°C Free NH3 and OH concentration are related by the expression KB = [NH4 + ] [OH"] B - l [NH3 free] Freee NH3-- i s the total--NH3 f^lessa i t rhat i n the gas phase and that bound as Co(NH3) n . To determine free NH3 concentration, therefore, the value of n and the p a r t i a l pressure of NH3 are required. The l a t t e r i s readily available using Figure B-I, which i s an experimental curve r e l a t i n g the t o t a l amount of NH3 added to the resulting pressure. I f i d e a l gas behaviour i s assumed, the t o t a l vapor pressure minus the steam, pressure of pure water at the temperature (20.8 atm for 215°C) equals the NH3 p a r t i a l pressure. To evaluate n the data shown i n Figure B-2 was obtained. This figure correlates i n i t i a l C o(NH 3) n + + concentration and vapor pressure at constant i n i t i a l NH3 concentration. The l i n e a r i t y in' Figure B-.2 indicates — ++ that n i s l i t t l e affected by i n i t i a l Co(NH 3) n concentration and i s just a function of i n i t i a l free NH3 concentration. From the data i t i s seen that ra i s i n g i n i t i a l C o ( N H 3 ) N + + concentration from 0.31 M to 0.6l M at 5.1 M NH3 lowers the vapor pressure by 37 p s i . From,Figure B - l such a reduction i n pressure i s the equivalent of decreasing the amount of NH3 added from 5.1 to h.kM. Consequently,. 0.3 moles cobalt (II) ion addition complexed 0.7 moles of'NH3 or n = 2.3. The data for 4.1M NH3 gives n = 2.0. - 9+ Figure B-L: Effect of I n i t i a l Ammonia Concentration on Vapor Pressure at 215°C•(Initial Conditions: O.JIM Co(NH 3)' 0.01-0.06M.S", 0.4-J.'0M (WH4)2S04) .' - 96 -The value of n equal to 2 w i l l be used i n calculations that follow. Consequently, the t a c i t assumption i s made that n i s e f f e c t i v e l y independent of NH3 concentration at 215°C over the range covered i n t h i s study. Using n = 2 and obtainable from Figure B-I, the i n i t i a l free NH3 concentration at 215° can be calculated knowing the amount of NH3 added at room temperature. Once the i n i t i a l NH3 concentration i s known the i n i t i a l OH" concentration can be calculated using equation B-I and the l i t e r a t u r e value for Kg at 215°C (I.98 x 1 0 " 6 ) 4 5 . The calculation of free NH3 i s given i n Table B - l and that of 0 H ~ i n Table B-II. In Table B-IIa calculated pH at 215°C i s compared with the measured pH at room temperature. NHatotal moles 97 TABLE B-I Relationship Between Total and-Free Ammonia. Concentrations at 215°C ( 2 . 2 M NH 4 +; 0 . .31M Co(NH3 ) n + + ) Total Vapor Pressure ( P K + PT. •NH3 *R20> atm 1)2 P W H 3 atm N H / ' 3 ^gas moles N H 3 f r e e + N H 3 b 0 u n d N H 3 f r e e 4 moles moles 0.4 0.8 1.0 .1.5 2.0 2- 5 3- 0 3.5 4.0 ^•5 5.0 6.0 7.0 8,0 21.5 21.8 22.1 23.1 24.1 25.1 26.5 28.0 29.6 31.4 33.3 37.1 41.5 46.2 0.7 1.0 1.3 2.3 3-3 4.3 5-7~ 7-2 8.8 9.6 12.5 16.3 20.7 25.4 0.01 .0.02 0.03 0.05 0.07 0.08 0.11 0.1k 0.17 0.19 0.25 0.32 o.4o 0.50 0.61 0.7 1.0 1.5 3.4 3.8 ^ 5 4.8 5-7 6.6 7-5 n i l 01 0.4 •0.8 1.3 1.8 2.3 2.7 3.2 3-7 4.1 5-1 6,0 6.9 1 » PH 20 a t 2 1 5 ° c = 2 0 - 8 a t m 2Assume perfect gas 3Gas volume = 788cc at-215°C 4 n assumed, to be constant and equal to 2.1. .one 1. .of solution charged at room temperature TABLE B-II Relationship Between Ammonia and Hydroxyl Ion Concentrations at 215°C (2.2M NH 4 +; 0.31 M Co (NH3) + + ) t o t a l ] i [NH3 f r e e ] i [OH"]. pH 1 pH 2 x 107 at 2150 room 0.6 n i l n i l 8.4 0.8 0.1 1 4.3 8.7 1.0 0.4 4 4.9 8.9 1-5 0.8 7 5.1 9-3 2.0 1-3 12 5-4 9-6 2.5 1.8 16 5.5 9.8 3-0 2.3 21 5.6 9-9 3-5 2.7 24 5-7 10.0 4.0 3-2 29 5-8 10.1 ^•5 3-7 33 5-8 10.17 5-0 4.1 37 5-9 10.22 6.0 5-1 4 6 6.0 10.35 7-0 6.0 54 6.0 10.45 8.0 6.9 62 6.1 IO.56 "''Calculated using K H 2 Q at 215°C = 461 x 1 0 - i 4 («) 2Measured, value - 99 -•APPENDIX- C Kinetics and Mechanism, of H 2 Formation During: Reduction of Co.(NH3)n"f"t" by CO The effects of various test parameters on-H2 formation are tabulated i n Table C-l.and Figures C - l and C-2. The rate-determining step appears to be f i r s t , order i n NH3,. or more s p e c i f i c a l l y , i n OH- concentration, and i n S addition. The effects of the other, variables are not as w e l l established However, from Table C - l increasing P , temperature and (NH4.)2S04. increase the rate while the rate i s apparently, independent-• of Co(NH 3) n concentration when CoS x i s present. .The effect of P^ , i s larger the lower the i n i t i a l . NH3 concentration. From these data,the rate-controlling step for H 2 formation i s f i r s t order i n N H 3 and S~ concentrations,, some1 positive order i n P Q Q and i n i t i a l ( N H 4) 2S04 concentrations, zero order i n i n i t i a l C o ( N H 3 ) N + + concentration and i s catalysed by C6S X. The stoichiometric studies (section I I I - 3 ) suggest that H 2 production obeys the equations: ; CO + NH3 +: H20 > HCOO- ' •+ • NH4 1 HCOO" + NH3 + H 20 -Ha + C0 3 + NH4 . 2 C6S X Based on these equations and assuming adsorption- of HCOO" ardCoS , the following mechanism.can be .postulated: K l + ; CO + NH3.+ H20 r ^ HCOO" + NH4 „ 3 HCOO" + (CoS ;) free K g vHCOO" , ..... k v x' •< -ads HCOO" • += NH3 . + H20 k l > H 2 + C 0 3 = + NH 4 4 . ........ 5 ads i"~T - 100 -• TABLE C -l The Effect of Various Test Parameters on Production of H 2 Run No. [NH 3J i [(NH 4) 2S0 4 ] ± [ s = ] Pco atms Temp. °C CoS x Present H 2 formed moles Sampling Time min. Max. Rate M/min Effect of [NH3 ] i at 0.3M Co(NH 3) n +•+ 10k 8.0 ' 1.1 .0197 26.5 215 yes • 1735 45 .0167 109 6.5 11 " 11 " .1423 4 5 .0183 105 5.1 11 " 11 .1172 56 ,0173 110 4.4 11 11 11 " .0790 45 .0165 108 3-7 11 " , 11 " " .0706 45 .0167 107 2.3 11 11 " -.0325 45 .0123 106 1.2 11 ,0159 45 .0062 Effect of S at 0.27 to 0.39 M Co(NH 3) n 121 4.6 0.9 0.146 26.5 190 Yes .2310 26 120 IT It 0.134 It 190 11 • 1575 26 122 II II 0.090 IT 190 i t .0635 26 148 4-9 1.2 • 0.046 t t 190 11 .0087 17 151A 11 1.1 n i l 28.3 190 no .0010 39 155A t l t l n i l 27.2 190 no n i l 39 116 t l 11 0.070 26.5 215 yes .1980 45 115 11 It 0.060 i t 215 " .2220 45 127 ! ! 11 0.048 II 215 " .2680 45 113 II II 0.040 11 215 " .1210 45 112 II 11 0.030 11 215 " .1128 45 111 11 It 0.010 i t 215 " .0278 45 I56A 4.9 1.2 n i l 27.2 215 no .0130 41 Effect of [NH 4S0 4] i at 0.3M ,Co(NH 3) n + + 102 2.3 1.11 .020 26.5 215 yes .0874 60 101 It O.56 11 t i i t I t .0184 60 100 II 1.11 11 i t t i t l .0875 89 Effect o f PC0 at 0.3M Co(NH 3) n + + 136 4.9 1.2 .046 25.5 215 yes .0420 17 134 t l 11 11 14.0 11 yes .0298 17 82 2.3 1.1 .031 26.5 11 11 .1245 70 96 2.2 1.1 .030 11.9 i t 11 .0382 72 - 101 -TABLE C-l (Cont'd) Run [Co(NH 3) n ] ± [NH3 ]j_ [S ] P c o Temp. CoS x H 2 formed Sampling Wo atm °C present moles Time min. Effect of [Co(NH 3) n ] ± at 1.2 M,(NH 4) 2S0 4 197 n i l 5.2 0.060 27.5 215 no n i l 37 115 .386 4.9 0,060 26.5 11 yes .2220 45 81 n i l 2.2 0.031 27.9 11 yes .0825 50 82 .314 2.2 0.031 11 yes .0890 50 Effect of Temperature at 1.2 M (NH 4) 2S0 4 148 .308 4.9 0.046 26.5 190 yes .0087 17 136 25.5 215 yes .0492 17 155A .318 n i l 27.3 190 yes n i l 41 156A • 373 26.5 215 yes .0130 4l - 102 -Fig. C - l . Effect of I n i t i a l NH3 Concentration on H 2 Production ( I n i t i a l Conditions: 0.02 MS-, 0.32 M Co ( N H 3 ) n + + 1.1M (NH 4) 2 S0 4, 26.5 atm. CO, 215°C) 0 .2CJ-0.15L o ^ o U P H 01 W o.iq 0.05I • 19P°C; O 215°C; — i , — 0.31-.39M Co(NH 3) n 0.27-.32M Co(NH 3) n + + o L 0.02 0.04 o.o6 _ 0.08 [s~] 0.10" 0.12 Figure C-2's Effect of S Concentration on H 2 Formation ( I n i t i a l Conditions: 26.5 atm CO and 1 . 1 M (NELaJaSO^. 0.14 4 . 9 M N H 3 , c The rate of H 2 formation i s - 10k -ISyjkl = kj. [HCOO~] . [NH3] - kg P^ [C0 3 ] [ffii 4] ..... 6 dt a a s " "2 Assume k 2 « k]_ then equation 6 becomes • t l iSal ~ kj. [ H C o o " ] a d s [NH3] From 4 [ H C© 0 " ] a d s = K 2 [HCOO] [CoSx ] f r e e 8 Consider that the Rideal mechanism i s operative and that reaction i s taking place between an adsorbed species (HCOO-) and a non-adsorbed species (<NH3). Let [CoS x] free = number of vacant s i t e s = C g C^  = number of t o t a l s i t e s o< [S =] ft C x = sites not available to H 2 •'• [ H C°°" ]ads = C b-C 8-C k but from equation k [HCOO"] a d s =K2[HCOO"]Cs = C^-Cs-Cx ..... 9 K2[HCOO"]Cs + C s = C0-Cx ..... 10 Assuming C x i s n e g l i g i b l e , c s = C b 1"+ K2[HCOO"] . 11 ft Recall that some CoS:x s i t e s must be occupied by Co(CO) 4~ and/or Co(WH 3) n , and possibly by H 2, C0 3" and CO . [HCOO"] a d s = K2[HCOO"] / , C 0 \ V 1 + K 2 [HCOO-]/ the rate, equation 7, can now be written. +d[HgJ = kjKatHSOO"] C Q [NH 3]  d t 1 + K2[HCOO~] From equation 3 equation 13 becomes +d[H g] = kxKgKj, P C Q [ N H 3 ] 2 C Q + J K 2 K i P C 0 [ N H 3 ] [NH4+] Since both P Q Q A N D - [ N H 3 ] > > [ N H ^ ] , assume that K 2 K i P C O [ N H 3 3 V N [NH4+] consequently equation 15 reduces to - 1 0 5 12 [HCOO-] = K!P C Q[NH 3] l l + [NH4 +] 15 +d[H 2] = dt ki[NHa] 16 - 106 -i . e . C 0 = Qi [S -] 17 equation 16 becomes dt l5al = k i 0X [NH3] [S-] 18 Equation 18 i s only v a l i d at high i n i t i a l NH3 concentration and P Q Q and at l o w - i n i t i a l N H 4 + concentration and where a l i n e a r relationship exists between the number of s i t e s available for H 2 adsorption and S = concentration. The k i n e t i c results showed that the rate of H 2 formation did i n fact obey an experimental rate law i d e n t i c a l to equation 18 j u s t i f y i n g the mechanism proposed above.* This statement i s v a l i d i f the experimental data for the effect of (NH 4) 2S0 4 are ignored. This i s probably v a l i d because of the small number of runs performed. - 107 -APPENDIX D Microstructure of Reduction Solids ++ The structures of the solids obtained by reduction of Co(NH 3) n by CO were examined by electron microscopy. This work and interpretation of data was kindly performed by Dr.. D.Tromans of t h i s Department. An Hitachi HV 1 1 A instrument operating at 100 K.V. was used. • Specimens were held on a carbon f i l m supported by a copper g r i d . .The specimens were supported on a carbon support held perpendicular to the electron beam. Two different types of specimens were observed (1) pure" CoS x ; made under actual run conditions except no CO was added (run 128) and (2) CoSx-C0 metal mixtures which were products of actual runs (runs ikk and 150). Figure D-l gives an indication of the general appearance of these two types as observed by o p t i c a l microscopy. .Both materials display.relatively.uniformly sized p a r t i c l e s with the CoS x being somewhat f i n e r and. lacking the metallic l u s t r e of the mixture. The la c e - l i k e structure displayed.by CoS v i n t h i s figure i s observed also with the electron microscope as shown i n Figure D-2 at magnifications from 7;000 to 67,000. Figure D-3 shows a t y p i c a l d i f f r a c t i o n pattern obtained for CoS x and the actual p a r t i c l e s that produced the pattern. Table D-l l i s t s the interplanar spacings obtained for various CoS x particles, and compares them with published data for Co 6S 5 and CogS 8. -A s u f f i c i e n t l y . close agreement between ft -Co 6S 5 and Co 9S 8.and.the unknown,, CoS , i s obtained to indicate that CoS is"probably one of x x these materials. The difference between ft -Co 6S 5 and CogSg.d spacings i s so s l i g h t as not to permit a.conclusion as to which of the two represents CoS x. F i g . D-l Comparison of Optical Micrographs of CoSx and Co°-CoSx Mixture. - 109 F i g . D-2D Run 128 mag=46,500 F i g . D-2E Run ikk mag=67,000 F i g . D-2 Electron Micrographs of CoS^. at Various Magnifications Fig. DH3B Cobalt Sulfide P a r t i c l e s from Run No.lW* mag. = 28,000 Fig. D-J. Electron D i f f r a c t i o n Pattern and Electron Micrographs Of Cobalt Sulfide P a r t i c l e . - I l l -TABLE D-l Ele c t r o n D i f f r a c t i o n Patterns of CoSx p a r t i c l e s Compared with Published Patterns of ^-Co^S^ ; Co^Sg and «< Co 0 44 kk kk Published Published Published Pattern for Pattern f o r Pattern f o r <*Co IfCogS^ Coo,S8 Run Run Run Run Run Run Run Run Run 1281 l 4 4 2 1502 150 144 150 150 Ikk 128 6.02 5 . 0 6 4.98 4 . 9 9 4 . 5 5 3 . 9 0 3 . 7 7 3.52 3.hQ 3.51 3.^6 ; . ' ' " 3.22 3-l4 3.00* 2.97*^ 3.01 2 .97* 2 .97 2 .99 2 .97 2 .87 2.85* 2 .88 2 .75 2.1+8 2.47 2 .49 2 .59 2.40 2.kk* 2.46 2.28* 2.27* 2 .26 2 .27 2 .26 2 .31 2 .16 2.22 2.22 2 .15 2 .19 2.02*- 2.02 2.01 2 .08 1.95 2 .08 2.02 1.91* 1.91*" 1.91* I . 8 9 I . 9 I I . 8 9 I . 8 3 I . 8 5 . . ' I . 7 6 * 1.78 1'.81*1.78* I . 7 8 * 1 .75* 1.73 1-73 1-74 1.74 1 . 6 8 . 1 .68 I . 6 7 I . 6 5 I . 6 5 I . 6 3 I . 5 2 * 1.52 1.54 I . 5 2 * 1-53 1.48 1 .50* 1 .51* 1-48 1 .50 1.48 1 .49* I . 4 3 1 .43 1.44 1 .44 1 .37 1-37 1.37 I . 2 9 * 1 .29* 1 .27*1 .30 1 .28 I . 3 0 1.25* 1.24* 1.24* 1.24 1 .26 1.25 1.21* 1.21 1 .23 1.21 1.17 1.17 1.15* 1.15* 1 .13 1 .13 1.15 1.14* 1 .14* 1.11 1 .08 I . 0 9 * 1 .07* 1 .06 I . 0 5 * 1.04* 1.04* 1.04 1.04 1.02 1.01* 0 .99 1.00 1.00 1.02 O . 9 6 O .95 O .96 0.95 0 .86 0 .89* 0 .87* 0 .78* 0 .78 0 .79 0.75 0.76 0.74* 1. Run No. 128 residue should be pure CoS^:. 2~. Residue i s CoSx-Co° mixture ~ 3 . The st a r i s used to ind i c a t e a strong l i n e ~>50) - 112 -In Table D-l the samples from runs ikk and 150 are actually from the product of a reduction run and hence are from a mixture of cobalt metal and CoS x. From the patterns i n the table i t i s possible to say that CoS x was present i n every sample but i t i s impossible to say whether or not the patterns unequivocally indicate the presence or absence of cobalt metal. The patterns of y-Co 6S 5 and Co 9S 8 mask the Co° l i n e s e f f e c t i v e l y . From thickness extinction fringe patterns for CoS - p a r t i c l e s , as shown i n Figure B-k, i t i s obvious that the CoS x p a r t i c l e s are not f l a t but have a rounded shape. Figure D-5A i s an electron micrograph of a .particle from a Co-CoS^. mixture and Figure D-5B i s i t s electron d i f f r a c t i o n pattern. Measurements of o the spot spacings gave values of interplanar spacings which were within +O.O5A of those for cobalt metal. Therefore the p a r t i c l e i s only Co and contains no CoS x. Figure D-5A shows the p a r t i c l e to be plate-shaped with i t s width o o approximately 10,000A and i t s thickness considerably less than 1000A (estimated by the ease of electron transmission and the lack of contrast). 'Further analysis shows the f l a t surface p a r a l l e l to the micrograph to be p a r a l l e l to the (0001) plane hence major growth i s occurring i n the close packed directions, [1010], which would be expected for cobalt and i t s hexagonal c r y s t a l structure. i n3 F i g . L - h Thickness Extinction Fringe Patterns f o r CoSx P a r t i c l e taken from Run 150 mag = 168,000 - Ilk F i g . D - 5 A . Particle of Co 0 composed of two grains (grain boundary indicated) mag.= 1 + 5 , 5 0 0 F i g . D-5B. Diffract ion Pattern of Particle i n f i g . £=3*. F i g . D-5. Electron Micrograph and Electron Diffract ion Pattern of Co° Par t i c le . Run 150. - 115 -The above results indicate that CoS x i s present as spherical shapes, cobalt i s present as f l a t plates and that cobalt p a r t i c l e s can be found completely'free of CoS x. Throughout t h i s examination, p a r t i c l e s were observed whose d i f -f r a c t i o n patterns could not be matched with that of published data for any cobalt species'that might possibly be present. Such a p a r t i c l e i s shown i n Figure D-2A i n the lower l e f t corner. Another s i m i l a r p a r t i c l e and i t s d i f f r a c t i o n pattern are shown i n Figure D-6. The pattern displays hexagonal symmetry and the p a r t i c l e s are seen to be f l a t plates. I t s interplanar spacings are 4.62, 2.65 (strong), 2.31, 1.73, 1.52 (strong), 1.32 (strong), 1.27, 1.13, 1.06 (strong), 1.00, O.9O, O.87, 0.82, O.73 and O . 7 O . Whether or not t h i s i s a species s i g n i f i c a n t to the cobalt deposition or i s simply an oxidation product of CoS x created during sample preparation, cannot be said. However, the agreement between i t s f l a t plate shape and possible hexagonal c r y s t a l structure and those of cobalt metal might be s i g n i f i c a n t . I t should be noted that the number of specimens examined i n t h i s study was small and the conclusions reached are open to some degree of question. - 116 F i g . D-6A Electron Micrograph of Unidentified P a r t i c l e s . mag= 3 3 , 0 0 0 F i g . D -6B . Electron D i f f r a c t i o n Pattern of P a r t i c l e i n fig.D - 6 A F i g . D-6 Electron Micrograph and Electron D i f f r a c t i o n Pattern of Unidentified P a r t i c l e s Observed i n both CoS x and CoSx-Co° Mixtures. 

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.831.1-0093636/manifest

Comment

Related Items