Feb., 1914
T H E JOUR-TTTdL O F I , V D T S T R I A L A &IT D E iVGI L\~EE RI N G C H E M I S T R Y
107
?
divested of m a n y complicating assumptions, a n d greatly simplified. I should acknowledge m y obligations t o N r . James G r a h a m for assistance i n t h e experimental work of this paper.
ANALYSES O F P U R I F I E D COB.4LT
OXIDE
(PERCCSTAGES)
June, 1912 November, 1912 April, 1913
co . . . . . . . . . . . . . . . . . . . 7 1 . 9 9 Fe .................... 0.11 S i . . . . . . . . . . . . . . . . . . . . 0.040 s. . . . . . . . . . . . . . . . . . . . . 0.020 C a . . . . . . . . . . . . . . . . . . . 0.030 SiOz . . . . . . . . . . . . . . . . . . 0 . 1 9
ChsE SCHOOL O F APPLIDD SCIQNCE CLEVEL.4X.D. O H I O
T7.3
71.52 0.2; 0.020
0 10
Trace
Trxe
n .o j i
...
0.15 0 . i')
n. 1s
The oxides corresponding with t h e theoretical formulas would have'cobalt content a s follows: THE PREPARATION O F METALLIC COBALT BY REDUCTION OF THE OXIDE'
Formula Co2O3, . . .
71.1 CoaOi.. . . . . . . . . . . . . . . . i . 3 . 4
By H E R B E R TT. KALMUS
I n connection with t h e work on cobalt i t has been necessary t o prepare considerable quantities of t h e metal in as pure a s t a t e as possible. Nearly 1000 pounds of conimercial black cobalt oxide have been given t o this laboratory for these researches b y t h e Deloro Mining a n d Reduction Co. of Deloro, Ontario, t o whom me t a k e this opportunity of expressing our thanks. T h e writer wishes t o acknowledge t h e x o r k of Messrs. C. Harper, IT. L. Savell, C. TV. D a y a n d R . Wilcox, who, in t h e capacity of research assistants at these laboratories, h a v e done most of t h e actual experimenting. T o Professor S. F. Kirkpatrick of t h e Departm e n t of Metallurgy, Queen's University, t h a n k s are d u e for m a n y valuable suggestions. T h e process for t h e preparation of fairly pure cobalt oxide has been very completely worked out, a n d has been practised on a large scale a t several Canadian smelters. For t h i s reason t h e oxide was chosen as a r a w material from which t o prepare t h e metal. As t h e work progressed, i t became more a n d more apparent t h a t some of t h e uses for cobalt which were being demonstrated a t these laboratories a n d elsewhere, would lead t o t h e preparation of t h e metal in large quantities. Hence, i t became of increasing importance t h a t t h e metallurgy of t h e preparation of t h e metal from t h e oxide be studied, a n d this has been done with greater care t h a n was necessary merely f o r t h e production of t h e quantities required for experimental purposes. There are four i m p o r t a n t reducing agents for obtaining metal!ic cobalt in reasonably pure form from commercial cobalt oxide. T h e y are: I , C a r b o n ; 11, Hydrogen; 111, Carbon Monoxide; IT', Aluminum, T h e C o 3 0 a used2 for these experiments was made f r o m cobalt h y d r a t e , precipitated b y bleach from a cobalt chloride solution. This hydrate, i n contact with t h e atmosphere, is greenish black i n color. It was calcined a t 750' C., yielding a black oxide of approximately t h e composition Co304. This is shown by t h e following analyses, made a t widely different times, which are typical of a large number: Author's abstract of report under the above title to the Canadian Department of Mines. Published b y permission of t h e Director of Mines, Ottawa, Canada. T h e general investigation of the metal cobalt and its alloys, with reference t o finding increased commerc;al usages for them is being conducted a t the School of Mining, Queen's University, Kingston, Ontario. for t h e Mines Branch, Canada Department of Mines. F o r a consideration of t h e yarious oxides of cobalt, including the proof t h a t the black oxide used for these reductions was larselv . the - . C O J O ~see following article, page 115.
Percentage, cobalt
.......
CoaO;. . . . . . . . . . . . . . . . . 7 6 . 0 COO. . . . . . . . . . . . . . . . . . i 8 . 8
It is obvious then, when we t a k e into account t h e portion of t h e sample which is n o t cobalt oxide, t h a t t h e oxide itself is largely C0304. It is not necessary for t h e purpose of our calculations t o assume t h a t this oxide alone is present, for we shall base our computations upon t h e actual analyses as we have found t h e m . However, i n writing t h e reactions throughout this paper, we shall, for simplicity, consider t h e oxide t o be Co304. PURIFICATIOK
O F COBALT OXIDE
Cobalt oxide as we obtained it from t h e smelters, a n d as sold on t h e market, analyzed approximately as follows: Barrel 1
Percentages
Co . . . . . . . . . . . . . . . 70.36 Ni . . . . . . . . . . . . . . . 1.12 Fe . . . . . . . . . . . . . . . 0.82 ............... 0.45 As . . . . . . . . . . . . . . . 0 . 1 0 Si0 . . . . . . . . . . . . . . 0.20 Ca . . . . . . . . . . . . . . 0.50
s.
Barrels 3 a n d 4
Percentages
Co . . . . . . . . . . . . . . 6 9 . 2
Ni.. . . . . . . . . . . . . 1 . 4 Fe . . . . . . . . . . . . . . 0.50 CaO . . . . . . . . . . . . . 0 . 3 7 s . . . . . . . . . . . . . . . 0.54 Insoluble. . . . . . . . 1 . 4 6 A g . . . . . . . . . . . . . . Trace
Analyses, of course, v a r y considerably from one shipment t o a n o t h e r ; t h e above samples are high in F e , S a n d Ca, a n d would be considered b y most smelters as No. 2 grade. Metal produced from oxide analyzing as above, b y t h e method t o be described. is of sufficient p u r i t y for most purposes. This is especially t r u e if lime be added t o t h e melt t o slag off t h e sulfur. HoTverer, for other purposes metal is required in which t h e impurities, nickel, irbn, sulfur, arsenic a n d silica, are reduced t o very small percentages. I n this case it is best t o remove these impurities from t h e oxide before reduction Starting with a crude cobalt oxide, these impurities m a y be reduced as far as is desired by t h e following procedure: sILIca-Dissolve t h e crude oxide in hydrochloric acid according t o t h e reaction: CoaOl 8HC1 = 3CoC12 qHzO C12 This m a y be done best b y heating a n d agitating with steam. If silica is present, i t will not dissolve, a n d m a y be removed b y filtration or decantation. T h e same is t r u e of silicates which are not decomposed b y this t r e a t m e n t . Decomposable silicates would send a certain a m o u n t of silica into solution. which would be thrown out during t h e next step. I R O S ASD ARSESIC-TOt h e cobalt chloride solution formed b y dissolving t h e oxide i n hydrochloric acid,
+
+
+
I08
T H E JOURNAL OF I N D C S T R I 4 L A N D ENGINEERING CHEMISTRY
gradually a d d finely divided C a C 0 3 or p u r e marble, until no further precipitate is formed. T h e heavy brown mud precipitated contains t h e iron a n d arsenic content of t h e original oxide. NICKEL-For most purposes it will not be necessary t o separate t h e small a m o u n t of nickel from t h e cobalt, b u t it m a y be done as follows: T h e cobalt chloride solution, containing a certain amount,of nickel chloride, is of a n intense red or claret color. Add a solution of bleach t o t h e solution until i t has almost completely lost its color. T h e bleach solution differentially precipitates h y d r a t e s of nickel a n d cobalt, so t h a t t h e nickel is not appreciably brought down until t h e cobalt has been almost entirely precipitated. T h e bleach will precipitate a black, h y d r a t e d oxide of cobalt, a n d t h e diminishing redness of t h e solution will indicate t h e e n d point. If all of t h e steps above outlined have been applied t o t h e original oxide. this final black precipitate m a y be calcined a t a b o u t 7 5 0 " C., t o yield black Co304. SULFUR-Any sulfur present in t h e original oxide a n d carried through t o t h e final product, or introduced with t h e bleach, m a y be removed b y boiling t h e final dried oxide with sodium carbonate a n d dilute hydrochloric acid. T h e reaction is:
Vol. 6 , S o .
2
oil-fired "Steele-Harvey" furnace of 60 pounds, metal capacity, No. 2 0 crucible, which could be controlled a t a n y t e m p e r a t u r e u p t o 1550' C., or in a modified Hoskins electric resistor furnace. This latter has a heating chamber, 8 inches cube, which can be maintained constant t o within a b o u t 1 0 - 2 0 ' C., a t a n y t e m p e r a t u r e u p t o 16 jo' C. Some of t h e small charges were r u n in porcelain crucibles heated within a n electric resistor furnace. T h e reactions for t h e reduction of cobalt oxide with carbon are:
+
++
4 c = 3c0 4 0 , (1) c0304 a n d ( 2 ) c0304 f 4 C O = 3Co 4'202; or, combining (3) zCo304 4C = 6Co 4CO2. If all t h e oxygen for t h e oxidation of t h e carbon be supplied b y t h e cobalt oxide, a n d if all t h e carbon be burned t o C o t t h e n t h e reaction goes according t o t h e last equation. I n practice, neither of these conditions is strictly obtained, b u t with proper design of furnace t h e y may be closely approximated. THE RUN-In each case t h e charge was made up b y intimately mixing a weighed a m o u n t of finely divided oxide with a weighed a m o u n t of finely ground carbon. This mixture was placed in t h e crucible, which, with its Cas04 NaZC03 = NaZS04 CaC03 charge, was placed either in t h e Steele-Harvey oil T h e soluble sodium sulfate formed is washed out with furnace or in t h e electric furnace. T h e mixture was water. A further washing is given with dilute hydro- frequently stirred with a n iron rod during t h e reduction. chloric acid, which decomposes t h e calcium carbonate THE CARBON-The form of carbon chosen for t h e i n t o soluble calcium chloride a n d COZgas. T h e CaC12 reduction, whether powdered charcoal, coke, coal, etc., is washed o u t with water. This method is, of course, depends somewhat u p o n t h e impurities f r o m which i t applicable only for t h e removal of t h e small per- is desirable t o keep t h e resulting metal free, b u t also centages of Ca a n d S found in t h e oxides in question. this choice greatly influences t h e speed of t h e reduction. A shipment of oxide from t h e smelter was analyzed T h r e e sets of experiments were made with powdered before a n d after t r e a t m e n t b y t h e above method, with anthracite coal, while further runs were made with t h e following results: lampblack or with powdered charcoal. T h e carbon was in all cases powdered t o a n extremely fine flour. Percentages Before After TEMPERATURE uEASUREMENTS-TemperatUre readC o . . . . . . . . . . . . 70.36 71.99 Ni . . . . . . . . . . . . . 1.12 0.041 ings were made a t frequent intervals with a platinum F e. . . . . . . . . . . . . 0.82 0.11 platinum-rhodium thermo-element, with a Wanner s . . . . . . . . . . . . . . 0.45 0.020 optical pyrometer, or with a FCry radiation pyrometer, C a . . . . . . . . . . . . 0.50 0.021 As . . . . . . . . . . . . . 0 . 1 0 None a n d t h e furnace adjusted t o keep t h e t e m p e r a t u r e None SiO?. . . . . . . . . . . 0 . 2 0 constant t o within a b o u t 20'. T h e charge was p u t into t h e crucible which was There are other obvious methods of purifying t h e Co304. F o r example, t h e bleach soiution may be freed within t h e furnace, b o t h crucible a n d furnace being of i t s SO4 content with BaC12, a n d t h e Ca a n d excess a t a t e m p e r a t u r e somewhat higher t h a n t h e intended Ba precipitated with N a 2 C 0 3 , t h u s yielding a fairly t e m p e r a t u r e of t h e run. Some of t h e smallest charges p u r e solution of soda bleach. T h e so4 content of t h e were inserted with containing crucible. I t was learned, CoC12 solution m a y be precipitated with BaClz a n d t h e b y experience, for t h e different sizes of charge a n d differential precipitation of cobalt a n d nickel accom- qualities of crucible, a t a b o u t what t e m p e r a t u r e t o maintain t h e furnace prior t o inserting t h e charge, plished with t h e purified solution of soda bleach. in order t h a t t h e charge might come t o t h e desired equiI-REDUCTIOK O F COBALT OXIDE WITH C A R B O N librium temperature, with proper furnace a d j u s t m e n t , METHOD O F EXPERIMENT-These experiments all in a b o u t ten minutes. There is, therefore, a period consisted in intimately mixing definite a m o u n t s of a b o u t t e n minutes, a t t h e beginning of each r u n , of finely divided carbon in various forms with C o 3 0 4 , during which t h e average temperature of t h e charge a n d heating t h e mixture t o constant t e m p e r a t u r e for is not as high as t h a t noted with t h e Wanner optical a measured time. T h e charges employed varied in pyrometer, which observes t h e surface of t h e charge. size from a few grams t o I O lbs., a n d were heated in We satisfied ourselves t h a t t h e center of t h e charge lined a n d unlined graphite crucibles, a n d in porcelain was a t t h e same t e m p e r a t u r e as t h e surface, within crucibles. 20 or 30' C., after t h e first t e n minutes, b y exploring FURNACES-The reduction took place either in a n t h e center with a thermo-element, a n d noting simul-
+
+
+
+
F e b . , 1914
T H E J O C R N A L O F I N D U S T R I A L AiVD E N G I A V E E R I N G C H E M I S T R Y
taneously i t s readings a n d those of another thermoelement near t h e surface. a n d of t h e Wanner optical pyrometer. I n t h e following runs we h a v e not a t t e m p t e d t o make a correction for t h e lag in coming t o temperature during these first t e n minutes. This lag would be considerably less t h a n t e n minutes for t h e smallest crucibles used, a b o u t t e n minutes for t h e four-pound charges. a n d possibly as long as t w e n t y m h u t e s in t h e worst cases. with t h e ten-pound charges. T h e oxides used for t h e runs reported in Tables I a n d I1 analyzed as follows: Percentages
Runs
A-H
Co . . . . . . . . . . . . . . . . . . . . . . S i ,.........
71.36
Si02 . . . . . . . . . . . . . . .
0.20
R I- R V I I I 69.2 1.4 0.50 0.54 CaO. . . . . . . . . 0 . 3 7 Insoluble. . . . 1 . 4 6 Ag . . . . . . . . . . Trace
a t t e m p t was made t o show t h e progress of t h e reduction, b u t a t t h e close of t h e r u n t h e charge was raised as rapidly as possible t o t h e melting point a n d t h e melt poured into a n iron mould t o be weighed. Considerable reduction must t a k e place during t h e interval of melting t h e charge after t h e close of t h e run. The purpose of these particular runs was t o s t u d y t h e yields under somewhat t h e same conditions which must necessari y obtain in practice. I n t h e runs I-YIII, KO. 2 0 unlined carbon crucibles were used; no a t t e m p t was made to obtain a yield. T h e y are intended t o show t h e progress of the,reduction. It will be noticed in t h e above runs with powdered anthracite coal t h a t t h e reductions are extremely low. I t was, therefore, t h o u g h t advisable t o check these r u n s w i t h experiments on a very small scale in porcelain crucibles, in such a manner t h a t there could be n o d o u b t as t o t h e t i m e during which t h e charge was maintained a t t h e temperature in question. A number of such runs was made with a thermoelement near t h e center a n d a t t h e outside of t h e charge. I n t h e small furnace used, t h e crucible with i t s charge came t o temperature in a very few minutes, so t h a t t h e outside a n d inside thermo-element agreed t o within 20' C. A4pproximately this condition was maintained throughout t h e run. T h e results of t h e previous runs with powdered anthracite coal were confirmed b y these small scale runs, a n d a satisfactory complete reduction could n o t be obtained at temperatures much below I Z O O O C. '
T h e anthracite coal used was very finely powdered. I n t h e typical r u n s A-H, No. 1 2 unlined carbon crucibles mere used, a n d t h e charge was stirred every t e n minutes during r e d u c t i o n . . I n these runs no TABLE I-REDUCTIOX
OF Cos01 W I T H , POWDEREDANTHRACITE COAL ( 4 ) R u s s A. C, H-HARVEY-STEEL OIL FURNACE G, B, D, E, F-ELECTRICCRUCIBLEFURNACE Yield of cobalt . Charge Average Time h-0, tempera- of reducPer cent Per cent of Cor04 Coal ture tion of theo- carbon in run Lhs. 02. C. Min. 1.b. Oz. retical metal A,. ., .. 5 8.3 1200 90 3 1.5 87 98 0.18 30 2 12.5 6.9 1200 C. . . . . . 4 92 0.086 105 6 9 lh.O 1200 H . . . . . . 10 99 0.21 150 2 13 900 G, . . , . . i 6.6 99 0.29 60 2 13 1200 B... . . . 4 6.54 0.20 2 13.5 100 120 6.9 1200 D ..... 4 60 2 11.75 96 0.22 1500 ,. 4 6.9 90 2 12.7 98 0.23 1500 , . 4 6.6
--
...
REDUCTION OF
c o s 0 4 W'ITH P O W D E R E D
CHARCOAL
F u r t h e r experiments were tried on t h e reduction of CoaO4 with very finely powdered charcoal. A large number of these gave fairly concordant results, which showed a greater reduction a t all temperatures t h a n t h e corresponding powdered anthracite coal runs. Without giving t h e details of about twenty-five A-Considerable unreduced oxide slag. Carbon used is approxiruns, it m a y be said t h a t complete reduction was mately the theoretical amount according t o reaction (3). C-Melt free from unreducible oxide slag. Carbon 10 per cent in obtained with from 2 0 t o 30 per cent excess of powdered excess of theoretical requirement. charcoal, a t goo0 C. or over, in less t h a n a n hour. H-3 oz. lime added shortly before pouring. Carbon, theoretical ,4t IOOC-1100'C., t h e reduction with powdered charamount. G A t end of 2.5 hours, charge not completely reduced, b u t completed coal was very much more rapid t h a n a t 900' C.. during subsequent raising t o melting point. often completing itself in less t h a n I O minutes. Of course, t h e t i m e required depends, t o some extent. TABLE 11-REDUCTION OF Cos04 WITH POWDERED ANTHRACITE COAL (B) HARVEY-STEELE OIL FURNACE upon t h e size of t h e furnace a n d charge. Reduction R E D U C T I O N O F cos04 W I T H L A U P B L A C K Charge time t o removal Per cent No. ___7 Average Experiments on t h e reduction of C0304 with lampof sample Coin Reduction temp. of CoaOd Coal black were tried with results identical with those on Minutes sample@) complete = 100 C. run Lbs. 02. t h e reduction of Co304 with powdered charcoal. 73,6 Very slight 601 R 2 82 I.. , . 10 17.5 74.1 Very slight R3b 91 750 I1 . . . . 10 16.5 BRIQUETS-Experiments on t h e reduction of cos04 73.8 Very slight R4b 90 16.5 888 I11 . . . . IO with powdered charcoal were tried, forming t h e charge I V . . . . 10 16.5 1057 R5b 95 80.8 28 VI . . . . I O 16.5 1203 R6a 30 81.3 30 into briquets. A small' percentage of molasses was R6b 49 93 .O 74 used as a binder. These experiments were made VI1 . . . . IO 16.5 1283 R7a 31 91.1 70 under t h e same furnace a n d temperature conditions -_ R i b 47 93.9 I , as those on t h e reduction of cos04 with powdered VI11 . . . . 10 17.4 1502 1 11 76.7 12 2 16 81.8 32 charcoa in bulk. Seven such runs showed, throughout, 3 21 91 .O 66 t h a t t h e reduction was not very different in its velocity 4 26 93.9 77 5 31 9 3 . 9 Apparently some from t h e corresponding runs with powdered charcoal. 91.8 oxidation 6 36 although t h e difference was uniformly in favor of (a)These analyses are for cobalt, nickel and iron combined. of which t h e briquetted charges. A satisfactory reduction a b o u t 97 per cent was cobalt, a s may be seen from the analysis of the original oxide. Carbon analyses were of course made, a n d the percentage of cobalt given in this column takes into account the residual carbon.
1 T h e molasses would correspond t o the addition of about 1 per cent carbon.
.
I IO
,
T H E J O U R N A L O F I i V D C S T R I A L A N D E;t'GI,VEERING
could probably n o t be made a t temperatures below 8 o c A j o 0 C . , even briquetting t h e charges, as compared with g o o 0 C. for t h e charges i n bulk. T h e preparation of metallic cobalt b y reduction in briquets or rondelles offers distinct commercial advantages i n t h a t t h e resulting metal is i n a salable form without further melting a n d casting. T H E METAL-The metal produced b y reduction of cobalt oxide with carbon is sufficiently pure for most purposes; it need not contain more t h a n a few t e n t h s of a per cent of carbon. T h e following characteristic analyses are t a k e n a t random from a large number t o show t h e n a t u r e of t h e metal: A N A L Y S E S O F I\IETALLIC C O B A L T P R O D U C E D B Y
REDUCTIO~; O F COMMERCI.4L
COBALTOXIDE WITH CARBON(PERCESTAGES) 7-12
Co . . . . . . . . . . . . . . . . . . . . . S....................... C...................... Ca . . . . . . . . . . . . . . . . . . . . .
hln.
97.05 1.50 1.00 0.22 0.20 0.25
.......................
As.. . . . . . . . . . . . . . . . . . . . . . . . Si02 .... 0.12
8-15-12
10-10-12
10-11-12
6-11-13
98.50 0.65 0.58 0.47 . 0.22 0.60
98.84 0.61
98.62 0.50 0.15 0.22 0.13 0.27
98.30
...
...
0.14
0.11
0.11 0.12
...
... 0.13
0.56 0.21 0.24 0.24 0.06
...
Trace 1.39 0.46
... 0.58
...
with carbon n-ere those directly from t h e smelter, which had n o t been treated b y t h e method outlined above t o remove t h e impurities. T h e iron, nickel, sulfur a n d silica content could have been reduced t o mere traces b y purifying t h e oxide before reduction i n accordance with t h e method given. We have done this repeatedly, where a pure metal was required for experimental purposes. I t is, however, of importance t o note t h a t metal with very low carbon content m a y be made b y direct reduction of t h e oxide with carbon.
Yol. 6 , No.
O F M E T A L L I C COBALT B Y REDUCTION
O F THE O X I D E WITH H Y D R O G E N M E T H O D A N D APPARATUS.-These experiments consisted i n placing a n a l u n d u m b o a t , containing a weighed a m o u n t of dried cobalt oxide, in a horizontal t u b e electric resistor furnace, maintaining i t s temperature therein constant for a definite length of time, during which a stream of hydrogen gas was passed through t h e furnace. A schematic sketch of t h e a p p a r a t u s i s shown in Fig. I. After purification, t h e hydrogen entered t h e furnace , l
Y
COXCLUSIONS
I . Reduction of c0301 with powdered anthracite coal does not t a k e place rapidly enough t o make i t commercially interesting, either i n t h e oil-fired crucible t y p e of furnace or i n t h e electric crucible t y p e of furnace, until a t e m p e r a t u r e in t h e neighborhood of 1200' C. is reached. 11. I n either t h e oil-fired crucible t y p e of furnace or in t h e electric crucible t y p e of furnace, substantially complete yields of metallic cobalt m a y be obtained b y reduction of Co304 with powdered anthracite coal, i n t h e neighborhood of 1 2 0 0 ~C., for n o t more t h a n I hour, with subsequent rapid melting a n d pouring. 111. With t h e oil-fired crucible furnace, using unlined graphite crucibles, complete yields are obtained with powdered anthracite coal only when there is a n excess of approximately I O 'per cent of this latter. IV. With t h e electric crucible t y p e of furnace used b y us, complete reduction m a y be obtained, using only t h e theoretical q u a n t i t y of powdered anthracite coal. I n this furnace there is a considerable reduction due t o t h e carbon monoxide atmosphere caused b y t h e carbon resistor plates. V. Both in t h e oil-fired a n d in t h e electric crucible t y p e of furnace, greater reductions of Co304 are obtained using p o h d e r e d charcoal t h a n with powdered anthracite coal, a t corresponding temperatures.
2
V I . W i t h t h e oil-fired or electric crucible t y p e of furnace, complete reduction m a y be obtained with powdered charcoal at g o o 0 C. or higher. F o r this reduction a considerable excess of charcoal mas required: under our conditions from 20 t o 30 per cent. V I I . Powdered lampblack shows results in accordance with those for powdered charcoal. V I I I . Briquetting t h e charges with a n organic binder t e n d s t o increase t h e r a t e of reduction a t all temperatures. A minimum of a b o u t 800' C. m a y be employed for t h e reduction of Co304 with charcoal in t h e form of briquets as against * g o o o C. for t h e same charge in bulk. I X . With sufficient carbon t o get a complete yield of metal, the final product need contain only a b o u t 0 . 2 per cent of carbon. X . At this laboratory, in a n electric furnace n o t especially designed for this work, we reduce enough oxide t o make j 6 pounds of t h e metal i n a n eighthour d a y , with t h e furnace absorbing 1 2 kw. T h u s , on a commercial basis, t h e power charge for this reduction would be small. 11-PREPARATION
It is obvious t h a t t h e oxides t a k e n for reduction
CHEMISTRY
u x
w
FIG 1-ARRAKGEMENTOF APPARATUS FOR REDUCTION OF Cos04 BY HYDROGEN H = Hydrogen Tank CI and Cz = Hot Copper K = KzCrz01 Tower
0 = KOH Tower S = HzSOc Washer J = Carbon Rings
Y =Stop Cock
L = Leads t o Ammeter and Bus Bars
at F a n d t h e excess was burned at B. During t h e r u n t h e exit for t h e gas was through t h e by-pass P B , t h e end Q being sealed. T h e heating element of t h e furnace itself was a series of co-axial carbon ring plates, which could be pressed together more or less tightly b y suitable screws. T h e furnace was supplied with alternating current at 2 j volts from a transformer, a n d could be controlled at a n y temperature up t o 1350' C. T h e . d e t a i l s of t h e furnace are shown i n Fig. 2. T h e temperature measurements were made b y a
T H E J O C R S d L O F I N D L - S T R I A L A S D E S G I S E E RI S G C H E J l I S T R k’
Feb., 1914
platinum-rhodium thermo-element T h , a n d readings were t a k e n a t frequent intervals on a very sensitive millivoltmeter. I n this v:ay, t h e temperature was maintained substantially constant b y h a n d regulation of t h e screws I. All temperature measurements were made with thermo-elements calibrated a t frequent intervals, in t h e usual way, against k n o x n melting points. C O S D U C T I N G A Rus-After having heated t h e furnace t o t h e desired temperature. b y a suitable current through t h e carbon rings, runs were made as follows: ( a ) Xfter closing t h e cock X , which separates t h e purifying system from t h e furnace, t h e air was exhausted from t h e hydrogen system b y opening cock Y , a n d operating a pump. ( b ) Gas burners were lighted t o heat copper filings in tubes C1 a n d C1. (c) Solutions of potassium bichromate, potassium h y d r a t e a n d sulfuric acid were s t a r t e d flowing through t h e purifying towers K, 0 a n d S; which were partially filled with glass beads.
0 B A LT 0 X I D E R E D U C T I 0 iX
11-C
11-1T H H Y D R 0 G E S-
T h e cobalt oxide used for t h e follon-ing runs, I t o
I X , analyzed as follows in percentages: C o . . . . . . . . . . 72.3 Ca . . . . . . . . . S.... .. .. . . . h - i , . . . . . . . . . . Trace Fe , . . . . . . . . . . 0 . 10 S O ? .. . . , . , . .
Temperature Number
Average deviation
Run
Boat
Alean
I
I
583
1 3
584
1 0
609
4.2
II(a) II@)
I I1
I11
C.
I
. T i m e of reduction Minutes 5 15 5 15 30 60 15 30 60 15 30 60
T
597
2.0
,
I1
15 70
5‘
IV(c)
598
1.7
i2i
1 5
824
4.3
965
1 0
10i3
2.1
I(d)
VI
I
I1
ELECTRIC FURNACE F O R REDUCTION OF
COaO4 WITH
HYDROGEN
VII(e)
I
( d ) Cock Y was closed a n d cock a t outlet of hydrogen
t a n k H was partially opened t o a l l o x a flow of hydrogen into t h e purifying system, until t h e pressure inside t h e system was a little greater t h a n atmospheric pressure. ( e ) Cock X was now opened t o allow hydrogen t o flow into t h e h o t furnace. (f) Flow of hydrogen was adjusted b y cock at outlet of hydrogen t a n k H , until hydrogen burned freely a t outlet e n d of furnace B. During t h e r u n t h e end Q ~ - n closed, s a n d t h e gas escaped through t h e by-pass
P-B.
u)
(9) When a d j u s t m e n t was satisfactory, assuring a n excess of hydrogen within t h e furnace, t h e weighed dried a l u n d u m b o a t , containing t h e charge of cobalt oxide, mas placed in t h e hot furnace a t t h e position A , a n d t h e time noted. ( h ) T h e r u n proper h a d now begun, durirfg which observations of time, temperature, a n d power were made, a n d t h e furnace adjusted t o keep t h e temperat u r e constant. (i) After a definite time, t h e boat, with i t s contents, was withdrawn from t h e centre of t h e furnace t o t h e overhanging cool e n d of t h e furnace core nT, in which i t was allowed t o cool, b u t through which, during t h e cooling, hydrogen was passed. ( j ) When cool, t h e boat was removed t o a desiccator a n d weighed.
0.39
TABLE111-REDUCTIONOF COBALTOXIDE WITH HYDROGEN
15
OF
0.15 0.052
I t will be noticed t h a t this oxide contained 72.4
30
2-DETAILS
C 0 0 L-
I N G I S -41- A T M O S P H E R E O F H Y D R O G E K
IV
FIG
111
I1
17111
I
I1
IX
I
I1
Loss in weight Per r e n t 25.5 25.4 25.8 26.0 26.6 26.2 26.1 26.2 26.1 16.8 22.1 22.4 25.2 25.3 25.4
..
25.4 25.2
..
Reduction 100 = complete 94.2 94.0 95.6 96.2 98.3 97.0 96.8 97 .0
96.8 62.2 81.8 a3 0 93.0 94.0 94.2
..
94.2 94.1
..
25 ..i 91.3 25.5 94.3 25.8 95.1 60 25.7 95.3 120 98.1 26.5 5 98.1 26.5 10 26.6 98.5 30 26.6 98.5 60 26.6 5 98.5 26.5 10 98.1 26.6 30 98.5 26.6 2 5 98.5 26.6 98.5 5 26.7 15 98.9 26.75 98.8 30 26.75 Y8,8 60 99.0 150 26.8 2 5 26.61 98.4 98.1 26.71 5 26,i 5 ‘18. a 15 30 26.75 98.8 99 .0 60 2 6 . 80 1 25.6 94.8 5 26.9 99.7 ‘2i.I 100.0 30 2i.l 100.0 60 99.1 1 26.8 99.4 5 26.9 99.4 26.9 30 27.0 99,1 60 2 96.8 26,?8 5 99.4 26.90 99.7 30 27.00 27.05 99.9 60 1 24.38 90.0 26.90 99.; 5 30 27.00 99.8 100.0 2 7 . 10 60 this run t h a t there was a slight oxidation 15 60
( a ) It >vas noted a t t h e close of a t one point in t h e boat. ( b ) All the reduced samples were steel-gray. (L) Boatshowed slight reoxidation a t one end whenremoved from furnace. ( d ) This final material analyzed 97.25 and 97.30 per cent cobalt o n duplicates. T h e material resulting from this r u n contained 0.75 per cent of unreducible CaSOI. CaO and SiOz, and 1.4 per cent of oxygen presumably in t h e form of c o s 0 4 (the stable oxide a t 598O C., see following article, page l l j ) , and 0.10 per cent of nickel and iron. It should, therefore, contain 100 - 2.3 = 97.i per cent of cobalt. This checks with thpvalue determined b y analyses, 97.3, t o within t h e accumulative error in the analyses. ( e ) T h e product from this run seemed t o be of a slightly lighter gray shade t h a n t h a t from t h e runs a t lower temperatures.
* T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
I12
per cent of t h e metals cobalt, nickel a n d iron, in t h e f o r m of oxides which m a y be computed without error t o be cobalt oxide. Any sample‘ contains, therefore, 0.75 per cent of unreducible calcium sulfate, calcium oxide a n d silica, 99.2 per cent of cobalt oxide r u n n i n g 72.4199.2 = 72.9 per cent in cobalt. This oxide, therefore, corresponds very closely t o Co304. T h e oxygen content of t h e substance which could be reduced b y hydrogen, is equal t o 2 7 . 1 per cent of 99.2 per cent = 2 7 . 0 per cent. This figure is accurate t o within t h e experimental error of t h e runs, a n d is used as t h e basis of t h e following computations; t h a t is t o say, in t h e column headed “ P e r c e n t a g e loss in weight,” 2 7 per cent would represent complete reduction, a n d t h e last column headed “ R e d u c t i o n where I O O per cent is complete reduction’’ is c o m p u t e d in t e r m s of 2 7 per cent actual reduction a s total. T h e boats used ranged in weight from 5 t o 6.5 g r a m s a n d t h e charges of cobalt oxide from 2 . 0 t o 2.1 grams. T h e check between t h e composition of t h e oxide used for these hydrogen reduction experiments, as determined b y analysis a n d as determined b y t h e reduction experiments. is entirely satisfactory (see following article, p. 115 ) . A n u m b e r of t h e early experiments t o reduce cos04 with hydrogen were made allowing t h e reduced product t o cool in t h e atmosphere. In every case reoxidation t o o k place. These runs were made a t various t e m peratures from 500’ C. t o 1000’ C., a n d curiously enough t h e reoxidation a t t h e higher t e m p e r a t u r e s was progressively less t h a n a t t h e lower temperatures. CONCLUSIONS
I. T h e reduction of Co304 t o metallic cobalt b y hydrogen gas takes place very rapidly a t all t e m peratures above 500’ C. 11. A t t e m p e r a t u r e s between 500’ C. a n d 700’ C., over 90 per cent of t h e reduction of C0304 t o Co takes place in a few minutes, b u t a further reduction takes place very slowly, if a t all. 111. Between 700’ C. a n d 1100’C., t h e a m o u n t of reduction of Co3O4 t o Co which takes place during t h e first few minutes increases very rapidly with rising t e m p e r a t u r e , a n d a t t h e higher temperatures i t is complete. IV. T h e hydrogen reduction method is t o be especially recommended for t h e production of moderate quantities of. very pure carbon-free cobalt for special purposes, just as i t has been used for t h e production of metallic tungsten. V. F o r t h e production of cobalt from C o 3 0 4 b y hydrogen, t h e charge must be completely cooled in a n a t m o s p h e r e of hydrogen. 111-PREPARATION
O F THE
Vol. 6, No.
2
oxide was supplied b y passing carbon dioxide over hot wood charcoal, which reduced it according t o t h e reaction, COz C = 2CO. Carbon dioxide, after purification, entered t h e lower e n d of t h e carbon monoxide generating furnace a t G.
+
F I G . 3--APPARATUS
FOR
REDUCTION OF coa04
WITH CARBON
MONOXIDE
This furnace was of t h e electric resistance t y p e , m a d e b y winding nichrome wire over a n a l u n d u m cylinder, t h e two being embedded in magnesite cement, a n d insulated within a cylindrical iron container. T h e wire is shown in section a t H a n d t h e iron container a t I. T h e entire core of t h e furnace was filled with wood charcoal, maintained a t a b o u t 1000’ C. b y a n appropriate current through t h e heating element. As a result, carbon monoxide gas left t h e generator a t J , with a certain a m o u n t of moisture which was absorbed b y passing t h r o u g h calcium chloride a t K. T h u s , substantially p u r e carbon monoxide entered t h e reaction furnace proper a t L, passed over t h e a l u n d u m b o a t 11, with its cobalt content, a n d t h e excess burned off a t N . THE REACTION FURNACE-The reaction furnace proper is shown in Fig. 3. It consisted of a central silica t u b e L N , 2 ft. in length, a n d I in. in internal
OF METALLIC COBALT B Y REDUCTION O X I D E IVITH C A R B O N M O K O X I D E
M E T H O D A N D APPaRATns-These experiments were performed b y placing a n a l u n d u m boat, c o n t a i n h g a weighed a m o u n t of dried cobalt oxide, in a horizontal t u b e electric resistor furnace, maintaining its t e m perature therein constant for a definite length of time, during which a s t r e a m of carbon monoxide was passed t h r o u g h t h e furnace (see Figs. 3 a n d 4 ) . C A R B O N M O N O X I D E GENERATOR-The carbon mon-
FIG.4
diameter. T h i s was wound with calorite or nichrome wire, of such resistance t h a t i t could be controlled b y a suitable rheostat R h on I I O volt direct current mains, t o m a i n t a i n a t e m p e r a t u r e constant t o within less t h a n I O ’ during a r u n , a t a n y t e m p e r a t u r e u p t o I0OO0
c.
Feb., 1914
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
TEMPERATURE MEAsvREMEKTs-The temperature measurements were made b y a platinum platinumrhodium thermo-element T h , a n d readings were t a k e n at frequent intervals on a very sensitive millivoltmeter Mv. T h e thermo-elements used for t h e temperature measurements were calibrated a t frequent intervals. C O O L I N G CHARGE I N CARBON MONOXIDE ATMOSPHERE
-The silica t u b e N L extended beyond t h e end of t h e furnace proper from 0 t o N. T h e portion 0-N was I f t . i n length a n d was kept cool b y a circulation of water, so t h a t a t t h e close of a r u n t h e boat was removed from t h e centre of t h e furnace t o 0 - N , where i t cooled t o room temperature in t h e stream of CO gas. C O N D U C T I N G A RUN-After having heated t h e reaction furnace, a n d t h e C O producer furnace, b y suitable currents, t o t h e desired temperature, runs were made as follows: ( a ) T h e cock C was opened t o allow C 0 2 gas t o pass through t h e purifying system D E F into t h e producer furnace a t G. ( b ) T h e CO gas generated in t h e producer furnace GJ passed through t h e reaction furnace L N a n d was lighted at N . (c) T h e weighed dried boat with its charge was introduced into t h e exterior O N of t h e reaction furnace. i d ) Temperature a n d time observations were begun, a n d when t h e desired temperature h a d been reached, t h e boat was moved t o M. ( e ) T h e run proper h a d now begun, during which observations of time a n d temperature were made a n d t h e rheostat R h adjusted t o keep t h e temperature constant. (f) After a definite time t h e boat, with its contents, was withdrawn from M t o O N , where i t was allowed t o cool in a current of carbon monoxide gas. (g) When t h e boat was cool, t h e current of carbon monoxide w a s gradually diminished b y closing t h e cock C, until it was finally entirely cut off. ( h ) l17hen the boat was cooled t o room temperature, i t was removed t o a desiccator a n d weighed. COBALT
OXIDE
FOR
CARBON
MOKOXIDE
REDCCTIOX
EXPERIBIESTS
The cobalt oxide for t h e CO reduction experiments was identical with t h a t used for t h e hydrogen reduction experiments so t h a t t h e column headed “Reduction where I O O per cent is complete reduction” is computed in terms of 2 7 . 0 per cent actual reduction as total. A number of t h e first runs were made, reducing c0304 with CO a n d allowing t h e reduced product t o cool in t h e atmosphere before weighing. Under these conditions, reoxidation took place rapidly, so t h a t b u t a single pair of typical runs are given. T h e boats used weighed IO.j+ a n d 13.3 grams a n d t h e charges of cobalt oxide, 2- grams. The reoxidation of cobalt oxide after reduction
1 I3
with carbon monoxide takes place with great vigor. If t h e boat be withdrawn from t h e hot furnace directly into t h e atmosphere, i t m a y be seen t o glow with great brilliancy. If t h e content of t h e boat, while still warm, be snapped out on t h e floor, i t will reoxidize with such vigor t h a t a cracking sound, as of a mild explosion, attends t h e reaction, i. e . , t h e reoxidation taking place according t o t h e reaction 6coo O2 = z C o 3 0 1is extremely exothermic. I n t h e runs of Table I V , during t h e first p a r t of t h e r u n , a n d up t o t h e time t h a t i t began t o gain in weight,
+
TABLEIV-REDUCTIONOF Cor04 Temperature Number c_*___
Run Boat I 1
I1
Mean
WITH
CO-COOLING IN
-
Time of Per cent Average reduction loss in deviation Minutes weight
602‘
9
594
12
15 30 45 60 75 82 92 107 30 45 75 9: 112 142
10.6 11.1 10.8 12.9 12.9 11.8 11.3 7.8 12.4 11.: 13.2 12.3 11.9 10.3
AIR
Reduction 100 =
complete 39.3 41.1 39.9 47.8 47.8 43.6 41.8 39.6 46.0 43.3 48.8 45.5 44.0 38.2
t h e Co304 in both boat; gradually became a gray color. This gray material is COO. -4t t h e end of t h e run i t was black again. On account of t h e irregularities of reoxidation, the furnace reaction chamber was lengthened by substituting a silica t u b e of length L N for t h e one of length LO as shown in Fig. 3. T h e overhanging t u b e O N , about I ft. in length, was cooled by water, a n d served as a cooling chamber for t h e boat while CO gas x a s still passed through it. T h e following runs, representative of a large number, shorn t h e r a t e of t h e reduction of cobalt oxide by CO gas when t h e cooling was controlled so t h a t no reoxidation could take place. The boats used weighed about 8 grams a n d t h e charges of oxide about z grams. I n R u n 111, Table T‘? t h e oxide became a greenish gray color a t t h e end of t h e first five minutes, a n d a uniform steel-gray color a t t h e end of fifteen minutes. From t h e n on it began t o gain in weight, d u e t o a deposit of carbon. A t t h e close of many runs a t this temperature, there was a n extremely heavy deposit of carbon in t h e boat. This run was typical of a number, which showed a reduction from t h e original black oxide t o the green, followed b y a change from t h e green t o the gray, and then a gain in weight, due t o a deposit of carbon. T h e only possible source of carbon was from t h e carbon monoxide gas, so t h a t t h e finely divided metallic cobalt, which mas formed during t h e first stage of t h e reduction of t h e gray oxide, probably acted catalytically t o decompose carbon monoxide gas a t this temperature. This is a n extremely interesting decomposition which might well be studied with considerab1.e care.
e
T H E JOL'RA'AL O F I N D C S T R I A L AiVD EAITGILVEERIiITG CHEJIISTRY
1I 4 T A B L E v--REDCCTIOh-
C O B A L T OXIDE B Y C A R B O N &?OXOXIDE GAS-
OF
COOLING IN C O G a s Temperature C. Piumber r Time of w Average reduction 3Iedn deviation Minutes R u n Boat
.
I11
IV
v
VI
34;
I I
I
451 453
583
3
3 3-
5
5 15 45 60 5 15 5
I1
596
3
VIII IX
I 11
600 597
5
611
6
X
6
65 20 30 10 5 15 49 69 86 146 5 15 45 60
601
1
5
3
15 45 60 5
15
749
3
XVI
751
3
XVII
900
4
XVIII
900
4
21,4
,
81.8 49.5 79.2 48,4
60 0 97.8 98.0 99.6 100.0 98.1 98.4 ,, . 9 78.3 91 . 0 97.7 98.8 100.0 100.0 95.0 97.2 99.0 99.0 94.9 98.0 98.0 98.4 99.0 99.3 99.8 99.8 99.6 99.6 99.8 99.8 92.3 99.1 99.6 99.6 99.6 96.2 98.8 99:1 99.1 98.3 99.8 100.0 100.0 98.8
I1
XV
13.4
16.2 26.4 26.8 26.9 77.0 26.5 26.6 21 . 0 21.2 24.7 26.3 26.7 27.2 27.1 25.7 26.3 26.7
XI1
4
.... ....
,...
6
752
Deposit of carbon 22,l
13.2
594
XIV
6 i,3 93.2
Gain Gain
I
754
18.2 25.2
100 =
complete
45 60 5 15 35
XI
XI11
Reduction
I5
50
VII
Loss in weight Per cent
45 60 5 15 45 60 5 15 45 60 150 5 15 45 60 5 15 45 60 5 15 45 60
26.7 25.6 26.5 26.5 26.6 26.7 26.8 26.9 26.9 26.8 26.8 26.9 26.9 24.9 26.7 26.8 26.8 26.8 26.0 26.6 26.7 26.7 26.5 26.9 27.0 27.0 26.6 26.8 26.9 26.9
....
r -
99.7 99.8 99.8
A strong odor of hydrocyanic acid was noticed throughout r u n IT. After five minutes or so, a deposit of carbon began t o form in t h e boat, due t o t h e decomposition of carbon monoxide by finely divided cobalt, as in t h e runs a t 350' C. Throughout r u n V a strong odor of H C N was noticed. This is t r u e of all t h e reductions of cobalt oxide with carbon monoxide i n t h e neighborhood of 4 j o " C. These two runs are typical of a large number of similar ones. Our observations seem t o show t h a t the decomposition of CO b y cobalt takes place only through a temperature interval in t h e neighborhood of from 300-450' C. T h e check between composition of t h e oxide used for
5'01. 6, N O .
2
these CO reduction experiments, as determined b y analysis a n d as determined b y t h e reduction experiments themselves, is entirely satisfactory. (See following article, p. 115.) COXCLUSIONS
I. T h e reduction of Co303 t o metallic cobalt b y carbon monoxide gas takes place very rapidly a t all temperatures above 600' C. 11. Between 3 j o " C. a n d 4j o o C.: carbon monoxide a t first reduces c0304 t o cobalt, b u t after a time t h e finely divided cobalt decomposes t h e CO gas, depositing carbon. 111. At temperatures between j o o o C. a n d i jo" C., over 90 per cent of t h e reduction of C o 3 0 4t o Co takes place in a few minutes, b u t a further reduction t o completion takes place very slowly. IV. Between i j o o C. a n d 900" C . , t h e a m o u n t of reduction of Cos04 t o Co, which takes place during t h e first few minutes increases very rapidly, a n d a t t h e higher temperatures it is complete. V. Where producer gas is available i t should offer a cheap a n d efficient means of producing large quantities of pure metallic cobalt from t h e oxide. VI. For t h e production of cobalt from C o 3 0 4b y CO, t h e charge must be completely cooled in a n atmosphere of CO. IV-REDUCTIOK
O F COBALT O X I D E WITH ALUMIXUM
T h e heat of formation of a molecular weight i n kilograms of aluminum oxide (A1203) is 392,600 kilogram-calories, a n d is greater t h a n t h a t of a n y other metallic oxide. T h e molecular heat of formation of ferric oxide (FePOs) is correspondingly 19j , 6 0 0 kilogram-calories. It is therefore obvious t h a t if finely divided aluminum be intimately mixed with ferric oxide ( F e 2 0 3 ) , t h e latter, possibly in t h e form of rolling mill scale, t h a t t h e reaction Fe203 zAl = X1203 2Fe will t a k e place, provided t h e temperat u r e be raised at some point in t h e mixture sufficient t o s t a r t t h e reaction. This principle has been used b y t h e Goldschmidt Thermit C o . t o produce molten iron for welding purposes. It is obvious t h a t for every 160 kilograms of ferric oxide a n d j4 kilograms of metallic aluminum t h a t are mixed together a n d fired i n this way, there are developed 392,600 - 19j,600 = 197,000 kilogramcalories of heat. This is sufficient t o raise t h e entire mass t o a white h e a t , so t h a t t h e molten iron readily settles t o t h e bottom from where i t may be tapped. I n a similar manner: metallic cobalt m a y be prepared b y reduction of cobalt oxide with aluminum according t o t h e reaction:
+
+
3coSo4
+ 8Al
= 4&03
+ 9Co
T h e molecular heat of formation of Cos04 is 193,400 c'alories. I t is therefore obvious t h a t for every 723 kilograms Co304 a n d 216 kilograms of aluminum t h a t are mixed together a n d fired, there are developed 4 X 392,600 - 3 X 193,400 = 990,200 kilogramcalories of heat. We would, therefore, expect a reaction 1
Tables A n n u e l k s Inlcrnationales des Conslanles, 1, 428 (1910).
Feb., 1914
T H E J 0 L- R S A L 0 F I S D
r.52' RI .4 L
quite a s vigorous, if not more vigorous, t h a n t h e corresponding one with ferric oxide. Experiments n-ere t.ried, October, 191 2 , using a s t a n d a r d Goldschmidt T h e r m i t conical welding furnace. I n t o t h i s was charged j-IO lbs. of finely divided C o s 0 4 with t h e theoretical a m o u n t of aluminum, 8A1 = 4.k1203 according t o t h e equation 3 C 0 3 0 1 9Co. T h e reaction was s t a r t e d b y lighting a fuse of finely divided aluminum a n d potassium chlorate, rolled in a piece of tissue paper. T h e furnace fired with extreme violence, in every case becoming a n intense white h e a t . T h e vigor of t h e reaction was so great t h a t t h e lining of t h e furnace, although t h e best alundum-magnesite-cement mixture, n-ould s t a n d u p for only t v o or three charges. T H E METAL-The metal produced in this manner n-as readily t a p p e d from t h e b o t t o m of t h e furnace i n t o iron or sand moulds. I t frequently contained less t h a n 0.1 per cent of aluminum. and, of course, was carbon-free. T h e various metals, chromium, molybdenum. etc., made b y t h e Goldschmidt Co. b y this method. as t h e y h a r e come t o us, r u n a b o u t 0 . j per cent i n aluminum a n d are carbon-free. c 0 sc L U S I Oss This aluminum reduction method c a n obriously be used with considerable satisfaction where a b soltitely carbon-free metal is required, a n d where a somewhat increased cost is n o t prohibitive. XIoreover, i t affords a method of preparing cobalt-aluminum alloys a t once b y adding a n excess of metallic aluminum. T h e price of crude aluminum, such as might be used for t h i s purpose, is i n t h e neighborhood of I ; cts. per lb. One pound of a l u m i n u m \%-ill reduce a n d melt . i n this way a little over t w o pounds of metallic cobalt. Therefore, there is a charge of 1 7 cts. in t h e form of I 11). of metallic aluminum, for t h e power for reducing a n d melting t w o pounds of metallic cobalt. There might, of course, be some r e t u r n for t h e fused a l u m i n u m oside which resulted from t h e process, b u t even allowing liberally for this, t h e costs are high a s .compared with t h e carbon a n d carbon monoxide methods of reduction described elsewhere in this paper. I t is obvious t h a t t h e heating costs must be high b y t h e aluminum method, for h e a t is being supplied a t a t e m p e r a t u r e greater t h a n 2100' C., t h a t is, a t a t e m perature far in excess of w h a t is required for t h e reduction of t h e oxide a n d t h e melting of t h e metal, a n d with consequent a t t e n d a n t increased losses, d u e t o conduction a n d radiation.
+
ELECTROCHEMICAL AND >fETALLURGICAL S C H O O L OB M I N l i Y G , KISGSTON,
+
RESEARCH LABORATORIES
QUEEN'S U N I X 7 E R S I T Y
ONTARIO
-
OXIDES OF COBALT' By HERBERT T. KALMUS
T h e following oxides of cobalt h a v e been described in various places throughout t h e literature: C o 2 0 , COO, COSO,, C O 6 0 7 , C O 4 0 5 , CO304, c O , o ~ o , c0203,
'
Published by permission of the Director of Mines, Ottawa, Canada. See footnote t o previous article, page 107.
-1 S D E S G I S E E RI AJ-G C H E M I ST R Y
11;
C O ~ ~ OC, o ~ 3, 0 5 ,C o o 2 , a n d considerable disagreement is t o b e found among t h e statements concerning t h e m . T h e existence of m a n y of these compounds is doubtful, a n d there are b u t three of t h e m which particularly concern t h e commercial manufacturer of cobalt oxide: Co304, CoeO; a n d COO. These concern us in t h e production of metallic cobalt. TTe shall. therefore, describe these three oxides as m-e have observed t h e m in t h e course of t h e experiments reported in our previous article, p. 1 0 7 of this issue of THISJ O U R S A L . C 0 B .4L T 0 - C 0 B A L T I C 0 X I D E ,
c 030 .I
T h e ordinary black commercial cobalt oxidc which has been prepared from t h e h y d r a t e , b y calcining in the neighborhood of ; j o o C.?is a mixture of C o 3 0 4 a n d C o 6 0 7 ,b u t largely t h e former. There is a n abundance of proof throughout t h e previous paper t h a t this black oxide is lai-gely C o 3 0 4 , of which t h e following m a y be particularly noted: ( a ) T h e purified cobalt oxide used for hydrogen reduction experiments. making allowance for t h e impurities according t o t h e analyses, w a s computed t o contain 7 2 . 9 per cent c o b i l t . T h e hydrogen reduction experiments, using this same oside. showed, n-herever t h e reduction xyas complete, a loss of oxygen amounting t o 2 7 . 0 per cent. A s was s h o w n on p . I I I , this checks m-ith t h e 7 2 . 9 per cent of cobalt, with allowance m a d e for t h e slight impurities. Hencc, this black oxide m u s t be largely Co301>a s m a y bc seen from t h c following theoretical percentages: Per ccrit cobalt Co?Oa..
.
CoaOl.. . , . Co,07., , , . . , .
. ,.. .. ..., .
, . coo . . . . . . . . . . . . , ,
. 71 1 . 73.4 , , , . . i5.9 ,, . , , 7 8 . 8 , ,
,
( b ) T h e purified cobalt oxide used for t h c carbon monoxide experiments, making allowance for t h e impurities according t o t h e analysis, was computet1 t o contain 72.9 per cent cobalt. T h e C O reduction experiments, using this same oxide, whererc'r reduction was complete, showed a loss of oxygen a m o u n t ing t o 2 7 . 0 per cent. As was shown on pp. I I O and 111, this checks with 7 2 . 9 per cent cobalt, with allow-:ince made for t h e slight impurities. Hence, this black oxide must be largely Co304 according t o t h e table under ( a ) . -1s a further proof t h a t t h e black oside calcined (c) a t a good red heat is C0~0.3,t h e following experiment was tried: A pure black h y d r a t e of cobalt was made from electrolytic cobalt b y t h e potassium-cobalti-nitrite method. This was calcined t o constant v e i g h t a t I O j O C., yielding a chocolate-brown powder, which was uniform under t h e microscope. Several samples of this brown powder were calcined t o constant \\-eight a t 640' C., a n d in each instance showed a loss of water between I I . 5 per cent a n d I I .8per cent. Therefore, t h e brown powder corresponds very closely t o C0203.HaO. T h e material resulting from these calcinations n-as a black powder identical in appearance under t h e microscope with t h e black cobalt oxide of commerce.
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