AU8839598A - Process for producing cobalt compound and process for producing solution of cobalt sulfate - Google Patents

Description

Our Ref: 703222 P/00/011 Regulation 3:2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT 0 0* e 0* 0@ 0 00 0* 0000 0* *0 Applicant(s): Address for Service: Invention Title: Sumitomo Metal Mining Company Limited 11-3 Shinbashi Minato-ku Tokyo

JAPAN

DAVIES COLLISON CAVE Patent Trade Mark Attorneys Level 10, 10 Barrack Street SYDNEY NSW 2000 Process for producing cobalt compound and process for producing solution of cobalt sulfate The following statement is a full description of this invention, including the best method of performing it known to me:- 5020 PROCESS FOR PRODUCING COBALT COMPOUND AND PROCESS FOR PRODUCING SOLUTION OF COBALT SULFATE BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates to a process for producing a high-purity cobalt compound from a raw cobalt compound containing amnia and nitrate as impurities by removal of nitrogen compjnmds such as ammonia and nitrate. The present invention relates also to a process for producing a solution of high-purity cobalt sulfate economically by efficient dissolution of a high-purity cobalt compound obtained by the processimentioned above.

2. Description of the Related Art: Cobalt finds gene al use as a metal for special alloys (such as heat resistant illoy and cemented carbide) and also as a magnetic material (such as permanent magnet and magnetic tape). In general, cobalt for.magnetic materials is used in the form of cobalt sulfate.

Cobalt sulfate (in crystal form) is conventionally produced by dissolving metallic cobalt or a cobalt-containing compound (such as cobalt hydroxide and cobalt oxide) in sulfuric acid and then concentrating the solution for crystallization.

1 Cobalt ores naturally occur mostly in the form of oxide and sulfide. Cobalt is also obtained as a by-product of nickel smelting. In this case, it is essential to isolate cobalt from nickel and other impurities.

It has recently become possible to completely separate and remove impurity metals (such as nickel, copper, and zinc) in the form of ion by the aid of solvent extraction or ion exchange resin. Now, there is available a high-purity cobalt S compound containing said metal impurities in an extremely small amount.

In the meantime, iamong common processes for producing nickel and cobalt is ammonia leaching. This process consists of roasting (for reduction) of raw ores (usually in the form of oxide), leaching with ammonia, solvent extraction, and recovery of a raw cobalt compound. Solvent extraction gives rise to a raw cobalt compound in the form of cobalt carbonate or cobalt hydroxide with a small amount of metal impurities.

However, ammonia leaching inevitably contaminates the raw cobalt compound with ammonia (NH 3 at the time of recovery from the ammoniac solution. Moreover, ammonia partly oxidizes into nitric acid, thereby increasing the concentration of nitrate or nitrite (NO3, NO 2 in the raw cobalt compound.

Removal of ammoia, nitrate or nitite from the raw cobalt compound has bee i accomplished in the following manner.

A first one is repeated water washing.- (Ammonia and nitrate are readily soluble in water.) A second one is heating.

(Ammonia is volatile and nitrate is decomposed at a high temperature.) Unfortunately, removing ammonia and nitrate completely from a raw cobalt compound-by water washing needs copious water and repeated washing. In addition, water washing is not satisfactory in the case where ammonia and nitrate are present in the form of slightly soluble compound, and water washing needs close attention tofwaste water disposal. Therefore.

it is not an effective means.

Now, in the case of a raw cobalt compound containing ammonia alone, it is possible to decompose and volatilize ammonia completely by heating at about 200 C in the air.

However, decomposition and volatilization of nitrate need heating at an extremeli high temperature. For example, heating at 500" C is ne ssary to decrease the content of nitrate below 0.01 wt% i a raw cobalt compound. In other words, nitrate remains a:lmost intact at a low temperature of 200-300' C, which is high, enough for ammonia to decompose and volatilize.

On the other hand, a raw cobalt compound containing ammonia alone also poses a problem. When it is heated (or roasted) in the air (,or oxygen-containing atmosphere), ammonia is decomposed an volatilized once but oxidized into nitrate in the air. This nitrate enters the raw cobalt compound, and its complete removal needs heating at 500'C or up as mentioned above.

The conventional thod of removing ammonia and nitrate from a raw cobalt compound by heating for their decomposition and volatilization needs a high temperature above 500" C. This is economically disadvantageous from the standpoint of energy consumption.

Moreover, the abo e-mentioned process for converting a raw cobalt compound into a cobalt compound and then giving crystalline cobalt sulf e requires that the solution for concentration and crystallization should be kept at pH 1-2.

The reason for this is that the final cobalt sulfate crystallized from this solution should have pH 3.5-5.5. (With a pH lower than 3.5, the cobalt sulfate has to be neutralized with an expensive high-purity neutralizer when it is dissolved again with a pH higher than 5.5, the purity of CoSO 4 becomes lower because of Co(OH) 2 ;ontamination.) On the other hand,i trivalent cobalt compounds in the form of hydroxide and oxide are slightly soluble in sulfuric acid under normal conditions. For their rapid dissolution (to save processing time). it has been necessary to add an excess amount of sulfuric acid,:thereby greatly lowering the pH of the solution, and to raise the temperature of the solution.

The result is that the cobalt solution greatly decreases in pH and hence the resulting crystalline cobalt sulfate i decreases in pH. The p 4 ocess in this way needs acid- and heat-resistant facilities made of special materials.

OBJECT AND SUMMARY OF THE INVENTION The present invention was completed to address the above-mentioned problem.: It is an object of the present invention to provide a process for removing ammonia, nitrate and nitrite from a raw cobalt compound containing them efficiently in a simple n1 nner with less energy consumption.

thereby decreasing their concentration. It is another object of the present invention to provide a process for producing cobalt sulfate efficiently from the resulting cobalt compound by reduction and dissolution.

The present inventors carried out a series of researches on the proces- for efficient production of cobalt sulfate from a cobalt compound, which led to the finding that if a raw cobalt compoundtcontaining ammonia and nitrate is roasted at 300-500°C, preferably 350-450°C, in an inert gas stream or together with a reducing agent, it is possible to remove ammonia and nitrate from the raw cobalt compound, thereby giving a cobalt compound containing ammonia, nitrate and nitrite in an amount less than 0.01 wt% each, and that by dissolving the resulting cobalt compound together with a reducing agent in sulfuric acid, it is possible to produce cobalt sulfate efficiently. The present invention is based on this finding.

iV The above-mentioned object is achieved in the present invention by the first embodiment which covers a process for producing a cobalt compound. This process comprises roasting a raw cobalt compound at a temperature equal to or higher than 300*C and lower than 500 C in an inert gas stream, thereby removing ammonia and nitrate from the raw cobalt compound which is not yet roasted. This roasting should preferably be S. carried out at a temperature not lower than 350"C and not higher than 4500C in a nitrogen gas atmosphere.

The above-mention~8 object is achieved in the present invention by the second embodiment which covers a process for producing a cobalt compound. This process comprises roasting a raw cobalt compound together with a reducing agent at a temperature equal to or higher than 350 C and lower than 500 C, thereby removing ammonia nitrate and nitrite from the raw cobalt compound which is qot yet roasted. The reducing agent should be at least one member selected from carbon, activated carbon, hydrogen gas, and carbon monoxide. The amount of carbon or activated carbon should be no less than 0.05 wt% and no more than 5 wt% of the raw cobalt compound which is not yet roasted.

The above-mentioned object is achieved in the present invention by the third embodiment which covers a process for producing a solution of qobalt sulfate. This process comprises adding to a solution containing a cobalt compound sulfuric acid together with at least one reducing agent selected from methanol, 4 thanol. sodium sulfite, and sulfur dioxide gas, thereby dissolving said cobalt compound at a temperature not lower than 50*C. This process should be carried out by using sulfur dioxide gas as said reducing agent such that the solution containing a cobalt compound has an oxidation-reduction potential not lower than 300 mV and not higher than 700 mV.

In the third embodbent, the cobalt compound should be one which is obtained by 4oasting a raw cobalt compound at a temperature equal to or higher than 300* C and lower than 500' C, preferably not lower than 3500 C and not higher than 450° C, in an inert gas stream (such-as nitrogen) and which is free from ammonia and nitrate conta!ned in the raw cobalt compound which is not yet roasted.

In the third embodi4ent, the cobalt compound should be one which is obtained by roasting a raw cobalt compound together with a reducing agent at a temperature equal to or higher than 350" C and lower than 500 C and which is free from ammonia and nitrate contained in the raw cobalt compound which is not yet roasted, with ,said reducing agent being at least one member selected from carbon, activated carbon, hydrogen gas, and carbon monoxide.t The amount of carbon or activated carbon should be no less than 0.05 wt% and no more than 5 wt% of the raw cobalt compound which is not yet roasted.

DESCRIPTION OF 1HE PREFERRED EMBODIMENTS According to the resent invention, the process for producing a solution of cobalt sulfate comprises adding to a solution containing a cobalt compound (obtained by removing ammonia and nitrate from,-i raw cobalt compound as mentioned below) sulfuric acid together with at least one reducing agent selected from methanol, a hanol, sodium sulfite, and sulfur dioxide gas. thereby disgolving said cobalt compound at a temperature not lower tn 50' C. This process should be carried out by using sulf~* dioxide gas as said reducing agent such that the solution cintaining a cobalt compound has an oxidation-reduction potential not lower than 300 mV and not higher than 700 mV.

Although ammonia is readily volatile at about 200" C as mentioned above, it is cqnsidered that nitrate and nitrite decompose and volatiliz to be removed according to the equation below respectively. The reaction involved needs a high temperature above 500 C.

2HNO 3 2NQ 30 H 2 0 (1) 2 2NO 0 H 2 0 (2) In view of this, the present invention employs the following two methods to temove nitrate and nitrite instead of the conventional method mentioned above.

That is, the first method for removing nitrate and nitrite, which is used in the first embodiment, utilizes the 8 characteristic of a raw cobalt compound which contains both ammonia, nitrate and nit ~te. It consists of roasting a raw cobalt compound in an inert gas stream, thereby causing ammonia and nitrate to react with each other. Thus ammonia and nitrate radical are removed at a temperature lower than 5006 C.

In other words, this method employs ammonia in the raw cobalt compound as a reducing agent for removal of nitrate.

:09This method does not nee~ high temperatures for removal of nitrate unlike the conventional one. Ordinary roasting 9 carried out in the air capses nitrate to be removed from the raw cobalt compound by de domposition and volatilization. In f act, ammonia contained in the raw cobalt compound can be used as a reducing agent to remove nitrate at a low temperature.

This is true only when there exists ammonia sufficient for reaction with nitrafe. Fortunately, the raw cobalt compound obtained from .ihe ammonia leaching method only contains ammonia in prin6 iple, although it contains nitrate and nitrite formed secondarily by oxidation of ammonia.

Therefore, ammonia exists usually in large excess relative to nitrate and nitrite. it follows that both amxnonial, nitrate and nitrite are removed by r-oasting in an inert gas atmosphere.

The amount of ammnonia neqpssary for reduction of nitrate is 0.3 wt% or above.

According to the present invention, the temperature for roasting in an inert gas stream is not the one necessary for decomposition of nitrate but the one necessary for reaction between nitrate and ammonia. Therefore, it is much lower than the temperature (above 500*C) necessary for roasting in the air. The reaction proceeds at a temperature down to 300 C to remove both ammonia and nitrate almost completely.

Removal of nitrate approaches perfection as the roasting temperature increases. However, roasting at 500C S or above is not desirable because it needs as much energy as the conventional technology. Moreover, roasting at an excessively high temperature tends to prevent cobalt from being leached out in t4 e subsequent leaching step. A preferred temperature range is 350-450*C, although removal of ammonia and nitrate is> not substantially affected by temperatures exceeding 450°C.

Examples of the inert gas are nitrogen, argon, and helium which are in general use. They are not specifically restricted but nitrogen is;preferable because of its low price and its easy handling. Pure nitrogen is essential because removal of nitrate and nitrite is susceptible to oxygen however small its amount may be. Incidentally, the inert gas is not specifically restricted in flow rate and other factors because it is not involved directly with reaction.

S Incidentally, the process of the present invention is designed to perform roasting in an inert gas atmosphere at a temperature equal to or higher than 3000C, so that excess ammonia which does not react with nitrate volatilizes to be removed efficiently withqut oxidation. Besides, the process of the present invention ican be applied directly to the raw cobalt compound obtained by the ammonia leaching method which is in the form of fine powder. In the case where the raw cobalt compound is in the form of large granules, it is desirable to S. crush it into particles of adequate size prior to treatment.

The second method ;for removing nitrate and nitrite, which is used in the second embodiment, is characterized by the reduction of nitrate (which is less volatile than ammonia) into ammonia (which is: readily volatile), followed by 0oo* efficient removal of the volatilized ammonia without oxidation. As mentioned above, ammonia is readily volatile and it decompose and volatilize at about 2000 C, whereas nitrate and nitrite decomposes and volatilizes through the conceivable reaction represented by the equation and (2) given above, and this reaction needs a high temperature.

However, the fact that ammonia can be removed more easily than nitrate and nitrite suggest that nitrate would be volatilized and removed easily if it 'is reduced into ammonia by the aid of an appropriate reducing agent. In other words, the second method in the present invention is designed to roast a raw 11 cobalt compound containing nitrate in the presence of a reducing agent which is #eliberately added. Therefore, it reduces hard-to-remove nitrate into ammonia, and at the same time, it efficiently decomposes and volatilizes reduced ammonia as well as originally contained ammonia. In this way it is possible to remove both nitrate and ammonia at a temperature equal to or higher than 3500 C and lower than 500' C.

The reducing agent: used in the process of the present •'i..nvention includes carbo, activated carbon, hydrogen gas, S carbon monoxide gas, and julfur dioxide, which are in general use. Of these, solid oneslsuch as carbon and activated carbon S* are easy to handle because they can be simply mixed with the *0 raw cobalt compound prior to rbasting. Excess carbon will undesirably remain unreacted in the resulting cobalt compound. The amount of :carbon or activated carbon varies depending on the concent tion of nitrate in the raw cobalt compound; it is usually t*o equivalents for nitrate. In the case where the raw cobal, compound is one which is obtained by the ammonia leaching method, the amount of carbon or activate carbon should preferably be 0.05-5 wt% of it. in view of the fact that it contains a very small amount of nitrate which originates secondarily from ammonia by oxidation. The reducing agent less than .05 wt% is not enough for reduction into ammonia, and the reducing agent in excess of 5 wt% will partly remain unreacted in the resulting cobalt compound.

12 The advantage of r~ducing hard-to-remove nitrate into readily volatile ammonia J-s that the removal of ammonia and nitrate can be accomplish~d at a low temperature equal to or higher than 350e C and lo*.er than 5000 C as mentioned above.

This advantage leads to energy saving and cost reduction.

Moreover, roasting! in a reducing atmosphere permits volatile ammnonia to be re4ved efficiently without oxidation into nitrate.

The ao-v-etoemtospertaining to the first and second embodiments of tJpresent invention give rise'to a coal copondwt nitniate removed. This cobalt compound is a mixture of divalent and trivalent cobalt hydroxide (as major components) and cob4 .t oxide (as minor components) which result from cobalt hydrokiLde by roasting.

*According to the. present invention, a solution containing the cobalt c~on'(with ammonia and nitrate removed by roasting) is kfficiently dissolved in sulfuric acid. -This object is achlieved by reducing trivalent cobalt in the cobalt compound. 4Dissolution in this manner saves sulfuric acid and prevent# the cobalt sulfate solution from decreasing in pH (keeping .Lt pH This permits the cobalt compound to be dissolved eef iciently at 500 C and above f or the production of cobalt sulftte.

I I It is considered that the following reaction (equation 3) takes place for dissol tion when sulfuric acid is added to cobalt oxyhyroxide (CoOOH) as one of the cobalt compounds.

CoOOH H2SO 4 Cd' S 3 2

H

2 0 1 0 (3) On the other hand, it is also considered that the following reaction (equation 4) takes place for dissolution when sulfuric acid is added together with sulfur dioxide gas as the reducing agent.

CoOOH 1/2 H 2

SO

4 1 SO2 Co 2

SO

4 2

H

2 0 (4) The reaction is slower than the reaction and the former needs a high temprature.

In short, the present invention is designed to produce cobalt sulfate by the efficient dissolution of a cobalt compound at 50 C or above, which is achieved by adding sulfuric acid together with a reducing agent to a solution containing a cobalt compound. The milar ratio of sulfuric acid (H 2

SO

4 to cobalt (Co) should preferably be 0.5-0.7. The reducing agent may be a water-soluble one selected from methanol, ethanol, sodium sulfite, And sulfur dioxide gas, which are in general use. Of these reducing agents, sulfur dioxide gas is suitable for the production of a solution of high-purity cobalt sulfate, because it is free from carbon and sodium.

However, excess splfur dioxide should be avoided because it remains in th4 cobalt solution, giving rise to sulfate ions, which enter the cobalt sulfate (as the product) to lower its pH. In this case it is necessary to decompose sulfate ions with an oidizing agent (such as hydrogen peroxide) for post treatent.

Consequently, the ;amount of sulfur dioxide gas for reduction and dissolution should be such that the solution containing a cobalt compound has an oxidation-reduction potential of 300 mV or above. If sulfur dioxide gas is used in an excess amount (with an oxidation-reduction potential lower than 300 mV), post treatment with an oxidizing agent S would be necessary for decomposition. To attain a practical rate of dissolution, it is necessary to add sulfur dioxide in an amount sufficient to produce an oxidation-reduction potential lower than 700 mV. Therefore, an adequate amount of sulfur dioxide gas is such that the resulting solution has an oxidation-reduction pQtential ranging from 300 mV to 700 mV.

My.

Dissolution should. be carried out at 50'C or above because the saturated concentration of cobalt sulfate is low at temperatures lower than 50 C. On the other hand, dissolution at temperatures in excess of 1000C is not economical due to energy loss. Hence, the upper limit is about 1000 C.

The invention will be described in more detail with reference to the following examples and comparative examples.

Example 1

V.

(Removal of impurities bt' heating in an inert gas stream) This example uses cobalt hydroxide containing 63.6 wt% cobalt as a raw cobalt compound. This cobalt hydroxide (10.0 g) was roasted at 300-5000,C (as shown in Table 1 below) in an nitrogen gas stream. For comparison, roasting was carried out at the same temperature inthe air. Incidentally, this cobalt hydroxide contains 0. 84 wt". ammonia (NH 3 and 0.42 wt* nitrate

(NO

3 :Af ter roasting f or J. hour at the specifiled temperature, the samples were analyzed Ior NH 3 and NO 3 The results are shown in Tale1 inTable 1.

9* Roasting Roasted inthe air Roasted in nitrogen gas ternperature (OC) NH 3 (Wt% O NH 3 w% NO(w) Before roasting 0.84 0.42 0.84 0.42 300 <0.005 0.008 0.012 350 <0.005 1~0.63 0.033 0.008 400 <0.005 0.27 <0.005 0.008 450 <0.005 0.077- <0.005 0.008 500 <0.005 0.008 <0.005 <0.005 It is noted from Table 1 that in the case of roasting in nitrogen gas, the content of ammonia and nitrate is reduced below about 0.01 wt* at a temperature as low as 300 0 C. By contrast, in the case of. roasting in the air, ammonia is removed almost completely at 300* C but nitrate as much as 0. 077

-I

wt% remains even at 450 Roasting at a temperature higher than 500'C is necessary or its complete removal.

Examele 2 (Removal of impurities by heating in an inert gas stream) The same raw cobalt compound as used in Example 1 was roasted at 4000 C for 1 hour in a nitrogen gas stream containing oxygen in varied amounts 'as shown in Table 2 below. After roasting, the samples are analyzed for NH 3 and NO3. The results are shown in Table 2.

Table 2 O NH3 (wt%l NOs (wt%) Before roasting 0.84 0.42 0 <0.005 0.008 7 <0.005 0.19 10 <0.005 0.30 13 <0.005 0.27 <0.005 0.27 It is noted from Table 2 that pure nitrogen is desirable as the roasting atmosphere. The more the amount of oxygen.

the more it is difficult "to remove nitrate (NO 3 Example 3 (Removal of impurities by heating in the presence of a reducing agent) This example uses cobalt hydroxide containing 63.6 wt% cobalt as a raw cobalt compound. After thorough mixing with carbon (0.1 this cobalt hydroxide (30.0 g) was roasted at 300-5000 C (as -shown in *;;able 3 below) in the air. Likewise, after thorough mixing wi h activated carbon (0.5 this cobalt hydroxide (150.0 g~was roasted at 300-5000 C (as shown in Table 3).

For comparison, roasting was carried out in the same manner as above except .that neither carbon nor activated carbon was used.

Incidentally. thi cobalt hydroxide contains 0.84 wt* ammonia (NH 3 and 0 .42 W nitrate (NO,) Af ter roasting for. hour'at the specified temperature, the samples were analyzed ior NH, and NO,. The results are shown in Table 3.

Table 3

I

I 999 *9 9 9 9 9999*9 Roasting None CabnActivated carbon temperature (OC) NH., N03 NH3 NO% NH, NO3 (wt%) Before roasting 0.84 0.42A -0.84 0.42 0.84 04 300 <0.01 <0.01 0.37 350 <0.01 0.63.. -0.01 0.08 <0.01 0.06 400 <0.01 02.1 <0.01 0.03 <0.01 C0.011 450 <0.01 0.08 <0.01 C0.01 <0.01 <0.01 500 <0.01 0.01.. <0.01 <0.01 <0.01 <0.01 It Is noted from Table 3 that roasting at 400* C without carbon removes ammonia almost completely (wiLth the concentration of residual amnmdhia being less than 0.01 wt4) but removes nitrate incompletely (with the concentration of residual nitrate being 0.27 By contrast, it is also 18 noted that roasting withi 0. 1 wt% carbon under the same conditions removes ammonla as well as nitrate down to 0. 01 wt* or less. This demonstrates the effect of the reducing agent.

Likewise, roasting with Pi.5 wt% activated carbon under the same conditions removes axdonia as well as nitrate down to 0. 01 wt% or less.

The same raw cobalt compound as used in Example 3 was :roasted at 4500C for 1 hour in. t-he air, with the amount of carbon changed as shown Table 4. The roasted samples were a. analyzed for NH 3 and NO,. The results are shown in Table 4.

Table 4 a..

a a a. a Carbon

NH

3 I'l NO 3 (Wt%) 0 <0.01 0.08 0.05 <0.01 .0.01 0.1 <0.01 <0.01 1<00 0.2 <0.01 <0.01 2.3 <0.01 40.01 It is noted from Iahble 4 that roasting with 0.05 wt* carbon removes ammonia well as nitrate down to 0.01 wt%.

This demonstrates the eff ect of the reducing agent.

Example 6 (Dissolution with a reducing agent) This example uses,' the cobalt hydroxide containing <0.005 wt% ammnonia, 0.008. wt.% nitrate, and 63.6 wt% cobalt, which was obtained in Example 1 by roasting at 400"C in nitrogen. This cobalt hydroxide was made into a slurry having a concentration of 100 g/L. Cone. sulfuric acid was added to the slurry in such an amount that the molar ratio of sulfuric acid to cobalt is 0.6. Further, sulfur dioxide gas (as a reducing agent) was added to effect dissolution at 70 C such that the oxidation-reduction potential (ORP) was maintained at 300-700 mVt The results are shown in Table below.

Table S. Molar ratio of Reaction Final pH Final ORP Solubility of HSO/Co tie (min) (mV) Co Cobalt hydroxide 0.6 ,360 1.5 440 99.7 It is noted from Table 5 that the reducing agent helps increase the solubility of cobalt (up to 99.7%) despite the less amount of sulfuric acid. Incidentally, the final pH was 1.5 and the final oxidation-reduction potential was 440 mV.

Example 7 This example is intended to confirm that roasting in Examples 1 to 5 permits efficient dissolution even though the cobalt hydroxide (CoOOH) undergoes partial oxidation to give cobalt oxide (Co30 4 Cobalt oxide (Co 3 0 4 containing 72 wt% cobalt was dissolved at 70 C in sulfuric acid (to which sulfur dioxide gas as a reducing agent had been added) in the same manner as in Example 6. The results are shown in Table 6.

i Table 6 Molar ratio of Rpaction Final pH Final ORP Solubility of

H

2 SO4Co ei (min) (My) CO N% Cobalt oxide 0.6 1 .360 2.0 480 97.0 It is noted from T~ble 6 that the reducing agent helps Increase the solubility of cobalt (up to 97.0t) despite the less amount of sulfuric a~bd. Incidentally, the final pH was and the final oxidatl-on-reduction potential was 480 mW.

ComparatIve Example The same procedure. as In Example 6 was repeated except that sulfur dioxide gas *as not added and dissolution was carried out at 85-950C. ,,The results are shown in Table 7.

Table 7

C

p. C Molar ratio of Reaction time Final pH Solubility of Co Final ORP (mV)

H

2 SOJ/Co (min) N 0.8 360 0.6 87.0 900 360 0.4 98.6 700 1.8 360 0.6 97.0 600 2.4 180 <0 100 400 It is noted from Table 7 that excess sulfuric acid is necessary to increase the solubility of cobalt. As the results, the resulting solIution decreases in pH (lower than pH 1).

[Effect of the invention] P:IWPDOCS\PAIRCOMPISE 9/10/98 -22- As shown above, the present invention provides a process for freeing a raw cobalt compound of ammonia and nitrate down to low concentrations in an easy, efficient manner with less energy consumption, and also provides a process for efficient production of cobalt sulfate from the thus obtained cobalt compound by reduction and dissolution.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims (13)

1. A process forkproducing a cobalt compound which comprises roasting a raw cobalt compound at a temperature equal to or higher than 30' C and lower than 500' C in an inert gas stream, thereby remoting ammonia and nitrate from the raw cobalt compound which is not yet roasted.

2. A process for poducing a cobalt compound as defined in Claim 1, wherein the roasting is carried out at a temperature not lower tha 350 C and not higher than 450' C in a nitrogen gas atmosphere.

3. A process for producing a cobalt compound which comprises roasting a raw cobalt compound together with a reducing agent at a temperature equal to or higher than 350' C and lower than 500"C. thereby removing ammonia and nitrate from the raw cobalt compound which is not yet roasted.

4. A process for poducing a cobalt compound as defined in Claim 3, wherein the reducing agent is at least one member selected from carbon, activated carbon, hydrogen gas, and carbon monoxide.

A process for producing a cobalt compound as defined in Claim 4, wherein roasting is carried out by using carbon or activated carbon as the reducing agent in an amount not less than 0.05 wt% and not more than 5 wt% of the raw cobalt compound containing ammonia and nitrate which is not yet roasted.

6. A process for poducing a solution of cobalt sulfate which comprises adding to a solution containing a cobalt compound sulfuric acid together with at least one reducing agent selected from methanol, ethanol, sodium sulfite, and sulfur dioxide gas. thereby effecting dissolution at a temperature not lower than

7. A process for producing a solution of cobalt sulfate as defined in Clam 6, wherein sulfur dioxide gas is used as the reducing agent suchf'that the solution containing the cobalt compound has an xidation-reduction potential not lower than 300 mV and not higher than 700 mV.

8. A process for producing a solution of cobalt sulfate as defined in Clam 7, wherein the cobalt compound is one which has undergone roasting at a temperature equal to or higher than 300" C and lower than 500' qiin an inert gas stream, for removal of ammonia and nitrate from the raw cobalt compound which is not yet roasted.

9. A process for producing a solution of cobalt sulfate as defined in Clam 8, wherein the roasting is carried out at a temperature not lower than 3500C and not higher than 4500C in a nitrogen gas atmosphere.

A process for producing a solution of cobalt sulfate as defined in Clam 7, wherein the cobalt compound is one which has undergone roasting together with a reducing agent at a temperature equal to or higher than 300 C and lower -9/10/98 than 500 0 C, for removal of ammonia and nitrate from the raw cobalt compound which is not yet roasted.

11. A process for producing a solution of cobalt sulfate as define din Claim 10, wherein the reducing agent is at least one member selected from carbon, activated carbon, hydrogen gas, and carbon monoxide.

12. A process for producing a solution of cobalt sulfate as defined in Claim 11, wherein roasting is carried out by using carbon or activated carbon as the reducing agent in an amount not less than 0.05 wt% and not more than 5 wt% of the raw cobalt compound containing ammonia and nitrate which is not yet roasted.

13. A process for the production of cobalt compounds, and compounds so produced substantially as hereinbefore described with reference to the Examples/ DATED this 9th day of October 1998 SUMITOMO METAL MINING COMPANY LIMITED By Its Patent Attorneys DAVIES COLLISON CAVE