AU2003246344B2 - Process for producing cobalt solution of low manganese concentration - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Process for producing cobalt solution of low manganese concentration The following statement is a full description of this invention, including the best method of performing it known to us: Freil Carter Smt edeMebun\03433 Pitd1 Spebr20 (20) pg Freehills Carter Smith Beadle Melbourne\004364363 Printed 17 September 2003 (12:09) page 2

SPECIFICATION

PROCESS FOR PRODUCING COBALT SOLUTION OF LOW MANGANESE CONCENTRATION BACK GROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a process for producing a cobalt solution of low manganese concentration, more specifically a process for producing a cobalt solution of low manganese concentration which can increase direct recovery rate of cobalt by industrially advantageously removing manganese from a cobalt solution containing manganese as an impurity by the oxidative neutralization process.

DESCRIPTION OF THE PRIOR ART Cobalt is a metal which has been widely used for industrial purposes as a material for special alloys and magnetic materials. It is normally occurring in the form of oxide or sulfide, and produced mostly as a by-product of nickel and copper smelting. It is essential, therefore, to separate impurities, nickel and copper, from a cobalt product.

In general, the first stage for producing cobalt is dissolution of a cobalt-containing starting material in a mineral acid, hydrochloric or sulfuric acid, to form the cobalt solution. A starting material for cobalt contains a variety of impurities, and the cobalt solution will contain a variety of impurities, accordingly. Cobalt is commonly recovered from the solution as the metal by electrolysis, after the solution is treated to remove impurities. Purity of the electrolysis-produced cobalt metal depends on composition of the electrolyte, and it is necessary for production of 004968817 high-purity cobalt metal to remove impurities from the cobalt solution.

c At present, solvent extraction is used as a process for efficiently separately nickel from cobalt. In solvent extraction carried out in a chloride bath, cobalt, which forms a stable chloro complex, is extracted in the organic c 5 phase to be separated from nickel, and then back-extracted from the organic phase with an aqueous solution of low chlorine ion concentration, water.

C However, manganese and copper are very similar to cobalt in behaviour in extraction and back extraction, with the result that the cobalt chloride solution as the back extract produced in the solvent extraction process contains manganese and copper.

Oxidative neutralization process is used to remove manganese and copper from the cobalt chloride solution containing manganese and copper.

For example, the applicant of the present invention has proposed to removed these impurities from a cobalt solution containing iron, manganese, zinc, calcium and copper by the treatment process involving an oxidative neutralization stage and extraction stage with phosphoric acid as the solvent as is shown in Japanese Patent Laid-open Publication no. 2000-17347.

In the above treatment process, the cobalt chloride solution is oxidized/neutralized while being controlled at an oxidation-reduction potential at 600mV or more (based on an Ag/AgC1 electrode), to remove iron, manganese and copper. However, the oxidative neutralization process involves a problem of coprecipitation with cobalt as the major component of the solution partly oxidized/neutralized into the hydroxide as the impurities, iron, manganese and copper, precipitate.

004968817 Production of a cobalt solution of low impurity concentration, in particular low manganese concentration, is accompanied by increased Cc quantity of cobalt in the precipitate. The impurity-containing precipitate is separately treated after being discharge from the system, causing another S 5 problem that the coprecipitated cobalt cannot be directly recovered.

Under these situations, there are demands for the processes which can Cc control coprecipitation with cobalt as impurities iron, manganese and Scopper) precipitate, in order to efficiently remove manganese.

SUMMARY OF THE INVENTION It is an object of the present invention, under these situations, to provide a process for producing a cobalt solution of low manganese concentration which can increase direct recovery rate of cobalt by industrially advantageously removing manganese from a cobalt solution containing manganese as an impurity by the oxidative neutralization process.

The inventors of the present invention have found, after having extensively studied precipitation behavior of manganese and cobalt in the oxidation/neutralization reactions in the process for oxidative neutralization of a cobalt chloride solution to achieve the object, that the reaction to form tetravalent manganese oxide proceeds in preference to the reaction to form trivalent cobalt hydroxide in the solution in a low pH range of 3.0 or less and high oxidative atmosphere, in a high oxidation-reduction potential range, and cobalt hydroxide can be dissolved in preference to manganese oxide, when a precipitate containing these compounds is dissolved in hydrochloric acid, and that these phenomena can be utilized to realize a high, direct recovery rate of cobalt and to produce a high-purity cobalt solution, achieving the present invention.

004968817 The present invention therefore provides a process for producing a cobalt solution of low manganese concentration, comprising 3 stages for producing a Cc cobalt solution of low manganese concentration by incorporating an oxidant and neutralizer in a cobalt solution containing manganese as an impurity, the 5 first stage being for oxidative neutralization of the cobalt solution controlled at c¢ an oxidation-reduction potential of 900mV or more (based on an Ag/AgCI I electrode) and pH of 3 or less to remove most of the manganese in the form of Cc¢ oxide precipitate having a Co/Mn ratio of 0.3 to 1.0 by weight, and the second stage being for the continued oxidative neutralization of the cobalt solution produced in the first stage to remove a small quantity of the residual manganese in the form of oxide precipitate containing the separated manganese oxide and cobalt hydroxide and thereby to produce the high-purity cobalt solution containing manganese at 0.05g/L or less, while keeping the same oxidation-reduction potential and pH conditions for the cobalt solution, and the third stage being for preferential dissolution of cobalt hydroxide from the precipitate using a mineral acid to form a slurry, while keeping the liquid phase of the resulting slurry at a pH of 0.05 to 2.0 and also for recycling the resulting slurry back to the first stage.

In a preferred embodiment of the invention the cobalt solution is oxidized/neutralized while being controlled at an oxidation-reduction potential of 950 to 1050mV (based on an Ag/AgC1 electrode) and pH of 2.4 to 2.8.

In another embodiment of the invention the cobalt solution containing manganese as an impurity is a cobalt chloride solution.

In another embodiment of the invention the oxidant is at least one type selected from the group consisting of chloride, hypochlorous acid and ozone.

004968817 In a preferred embodiment of the invention the neutralizer is at least one type selected from the group consisting of hydroxide and carbonate of an ic alkali and alkali-earth metal, and cobalt carbonate.

In yet another embodiment of the invention the solution is controlled at c 5 a pH of 0.1 to 1.5 in said third stage.

Cc BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph showing the relationship between Mn concentration of the final solution and pH level for the oxidation/neutrarlization reaction of the cobalt chloride solution.

Figure 2 is a graph showing the relationship between Mn concentration of the final solution and oxidation-reduction potential (ORP) level for the oxidation/neutralization reaction of the cobalt chloride solution.

Figure 3 is a graph showing the relationship between Mn concentration of the final solution and Co/Mn weight ratio of the precipitative produced by the oxidation/neutralization reaction of the cobalt chloride solution.

Figure 4 is a graph showing the effects of pH level on Co and Mn leaching rates, when the precipitate is treated with hydrochloric acid.

DETAILED DESCRIPTION OF THE PRIOR ART The process of the present invention for producing a cobalt solution of low manganese concentration is described in detail.

004968817 The present invention relates to a process for producing a cobalt solution of low manganese concentration, comprising 3 stages for producing a cobalt a solution of low manganese concentration by incorporating an oxidant and

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neutralizer in a cobalt solution containing manganese as an impurity, the first 5 stage being for oxidative neutralization to remove most of the manganese in M the form of oxide precipitate and the second stage being for the continued oxidative neutralization to remove a small quantity of the residual manganese in the form of oxide precipitate. The third stage being for separating part of 0cobalt hydroxide from the separated (removed) precipitate by preferential dissolution and recycling it back to the first stage.

First stage for removing most of manganese in the form of oxide precipitate.

This stage first sets a cobalt solution under specific conditions with respect to oxidation-reduction potential and pH level, to remove most of manganese in the form of oxide precipitate having a Co/Mn weight ratio in a specific range.

Cobalt solutions containing manganese as an impurity include a solution as a by-product of nickel or copper refining; solution resulting from a mixed sulfide of nickel and cobalt as a starting material which is leached and extracted with a solvent; cake containing iron which is removed as a byproduct of purifying the spent electrolyte discharged from electrolyte refining stage of crude nickel; and solution produced from sulfide cake as a starting material, which is recovered by treating the residual solution from preferential reduction stage of nickel in the presence of hydrogen of elevated pressure with hydrogen sulfide.

004968817 0 The oxidants useful for the present invention include chlorine, hypochlorous acid and ozone, which have a sufficient oxidative power to 0 1~ oxidize the manganese ion to a valence number of Chlorine is particularly preferable, when the cobalt solution is a chloride-based one.

The neutralizer for the present invention is at least one type selected from the group consisting of hydroxide and carbonate of an alkali and alkali-earth metal, sodium hydroxide, potassium hydroxide and sodium carbonate, and cobalt carbonate. Cobalt carbonate is more preferable, when impurity accumulation in the cobalt solution causes a problem.

When chlorine and cobalt carbonate are used as the oxidant and neutralizer, the divalent manganese in the solution is oxidized by chlorine, and the reaction to precipitate the tetravalent manganese proceeds. This reaction, however, is accompanied by oxidation of cobalt as the major component of the solution into the trivalent state to form the hydroxide, which coprecipitates with manganese oxide.

The present invention involves oxidation/neutralization of a cobalt solution containing manganese as an impurity in the presence of an oxidant and neutralizer, where manganese can be mostly removed in the form of oxide precipitate, when the solution is controlled at an oxidation-reduction potential of 900mV or more (based on an Ag/AgC1 electrode) and pH of 3 or less.

The reasons for the oxidation-reduction potential and pH ranges for the cobalt solution are described by referring to Figs. 1 and 2.

A cobalt chloride solution containing Co at 80g/L and Mn at 0.45 or 0.38g/L as the starting solution was controlled at a given pH and oxidation-reduction potential (ORP) level for the oxidation/neutralization in the presence of chlorine and cobalt carbonate as the oxidant and neutralizer, to follow Mn concentration changes for 2 hours as reaction time.

The results are given in Figs. 1 and 2, where Fig.1 shows the results with the cobalt chloride solution containing Co at 80g/L and Mn at 0.45g/L as the starting solution, and Fig.2 the results with the cobalt chloride solution containing Co at 80g/L and Mn at 0.38g/L.

As shown, it is found that decreasing pH or oxidation-reduction potential level tends to hinder removal of manganese, and it is necessary to control the solution at a pH of 2.4 or more and ORP at 950mV or more, in order to keep the reaction effluent (final solution) at an Mn concentration of 0.05g/L or less, desired for production of high-purity cobalt metal by electrolysis.

Therefore, the present invention intending to remove manganese controls the first stage at a pH of 2.4 or more and ORP at 950mV or more, preferably at 2.4 to 2.8 and 950 to 1050mV, more preferably at 2.4 to and 950 to 1000mV, while continuously charging chlorine and cobalt carbonate. The first stage operating at a pH above 2.8 or ORP beyond the above range is not economical, because of increased consumption of cobalt carbonate or chlorine.

Next, the reasons for the desired oxidation/neutralization reaction to remove most of manganese in the form of the oxide precipitate having a Co/Mn ratio of 0.3 to 1.0 by weight are described by referring to Fig.3.

A cobalt chloride solution containing Co at 80g/L and Mn at 1.8g/L and kept at a pH of 0.6 as the starting solution was subjected to the oxidation/neutralization in the presence of continuously charged chlorine and cobalt carbonate while controlling the solution at a pH of 2.45, ORP of 950 to 1050mV and 50°C for 2 hours, to follow Mn concentration of the reaction effluent (final solution) and Co/Mn weight ratio of the resulting precipitate.

As a result, it is found that the precipitate has a higher Co/Mn weight ratio as Mn concentration of the final solution decreases, and, for example, the ratio of the resulting precipitate is 1.5 or more when Mn concentration of the cobalt chloride solution is decreased to a level of 0.05g/L or less, desired for production of high-purity cobalt metal by electrolysis.

It is also found that Mn concentration of the reaction effluent is around 0.15g/L and manganese removal rate is around 90%, in order to produce the precipitate of limited coprecipitated cobalt quantity, or of Co/Mn ratio of or less by weight.

Therefore, the optimum conditions for the first stage for the present invention are determined from the relationship between manganese precipitation rate (removal rate) and coprecipitated cobalt quantity, and it is preferable to keep Co/Mn ratio of the resulting precipitate of limited coprecipitated cobalt quantity at 1.0 or less by weight. Moreover, the Co/Mn ratio of 0.3 or more by weight, which corresponds to a manganese removal rate of 70% or more, is preferable in consideration of all of the stages involving manganese removal. Therefore, the Co/Mn ratio of the resulting precipitate is set at 0.3 to 1.0 by weight, preferably 0.3 to 0.8.

Stage for producing a high-purity cobalt solution The second stage for the present invention continues the oxidation/neutralization reaction while controlling the cobalt solution, produced in the first stage, at a given oxidation-reduction potential and pH level to remove a small quantity of the residual manganese in the form of oxide precipitate and thereby to produce the high-purity cobalt solution containing manganese at a specific level or less, as described above.

The second stage is controlled at a pH of 2.4 or more and ORP at 950mV or more, preferably at 2.4 to 2.8 and 950 to 1050mV, more preferably at 2.4 to 2.5 and 950 to 1000mV, as is the case with the first stage. The second stage operating at a pH above 2.8 or ORP above 1050mV is not economical, because of increased consumption of cobalt carbonate or chlorine.

The second stage conditions are set to decrease manganese concentration of the solution to 0.05g/L or less, preferably 0.03g/L or less, in order to give a high-purity cobalt product, as described above. In the second stage, quantity of manganese to be removed is small, because it has been mostly removed in the first stage, and quantity of coprecipitated cobalt decreases. In other words, coprecipitation of cobalt in the precipitate can be controlled, when manganese is removed in 2 stages.

Stage for recycling cobalt in the form of slurry The third stage for the present invention is for separating part of cobalt hydroxide from the precipitate by preferential dissolution and recycling it back to the first stage directly in the form of slurry.

The cobalt hydroxide is preferentially dissolved out of the precipitate separated in the second stage at a specific pH level. How the pH level is determined is explained by referring to Fig.4.

The precipitate (Co concentration: 37.0%, Mn concentration: 17.0%), prepared in the second stage under the conditions of pH: 2.4 and ORP: 950 to 1050mV, was incorporated with hydrochloric acid to change its pH level, to follow Co and Mn leaching rates.

As a result, it is found that manganese is little leached out of the precipitate, while cobalt is preferentially leached out, until the pH level is decreased to 0.1 or so, and that at least 50% of cobalt can be leached out at a pH of around Therefore, cobalt is dissolved out of the precipitate preferably at a pH of 0.05 to 2.0 in the third stage, particularly preferably 0.1 to 1.5. Most of cobalt present in the precipitate is dissolved in the solution in the third stage, and the resulting slurry containing undissolved manganese is recycled back to the first stage. This allows cobalt to be effectively utilized, thereby directly contributing to improved yield of cobalt.

Cobalt hydroxide is leached out less at a higher pH level of the solution.

In this case, the recycled cobalt hydroxide precipitate works as a neutralizer for the first stage for the present invention, decreasing cobalt carbonate consumption. As a result, part of the precipitate formed in the second stage can be directly utilized as a neutralizer for the first stage.

Several methods, precipitation with a sulfide and cementation with cobalt metal, have been proposed to remove copper, when it is present in the cobalt chloride solution. It can be removed efficiently by these conventional techniques.

Moreover, electrolysis of the high-purity cobalt solution produced by the above methods gives cobalt metal of high quality.

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004968817 cEXAMPLES The present invention is described by EXAMPLES, which by no means limit the present invention. Weight of the precipitate prepared in each of EXAMPLES is on a wet basis.

Cobalt chloride solution containing manganese: SThe back-extract solution (Co concentration: 80.0g/L, Mn concentration: C 1.85g/L, pH; 0.6) from the solvent extraction process was used as the cobalt chloride solution.

EXAMPLE 1 The first two stages of the present invention, removing manganese in 2 stages, was verified using a reactor tank holding about 100L of the reaction solution.

The solution was treated in the first stage for 2 hours, while it was controlled at a pH of 2.45 and ORP of 950mV in the presence of continuously charged chlorine gas and powered cobalt carbonate. The resulting precipitate was filtered to obtain 1.2kg of a precipitate having a Co/Mn ratio of 0.40 by weight and 99L of a crude solution containing Mn at 0.45g/L. The first stage performed an Mn removal rate of 75.7% and Co yield of 99.3% (precipitate lost from the system: 0.7%) The crude solution produced in the first stage was passed to the second stage, where it was treated under the same conditions as in the first stage in the presence of continuously charged chlorine gas and powdered cobalt carbonate. The precipitate produced in the second stage was filtered to obtain 98L of a high-purity cobalt chloride solution containing Mn at 0.Olg/L and 0.7kg of a precipitate having a Co/Mn ratio of 1.7 by weight. The Mn and Co distribution rates in the precipitate produced in the second stage were 23.8 and respectively, based on the Mn and Co amounts charged to the manganese removal process of the first stage.

004968817 *Mn removal rate of 99.5% and direct Co yield of 98.4% were recorded by the process.

Cc EXAMPLE 2 In this Example manganese is removed in 2 stages in a similar manner 5 to Example 1 followed by a third slurry recycling stage. In the first stage, 100L Cc of the solution was treated in the first stage for 2 hours, while it was controlled at a pH of 2.45 and ORP of 950mV in the presence of continuously Cc charged chlorine gas and powdered cobalt carbonate, after it was incorporated Swith 1.3L of the slurry produced in the second stage, and treated with the dissolved in hydrochloric acid to be adjusted at a pH of 0.1.

The resulting precipitate was filtered to obtain 1.8kg of a precipitate having a Co/Mn ratio of 0.40 by weight and 100L of a crude solution containing Mn at 0.45g/L. The first stage performed an Mn removal rate of 75.7% and Co yield of 99.2% (Precipitate lost from the system: The crude solution produced in the first stage was passed to the second stage, where it was treated under the same conditions as in the first stage in the presence of continuously charged chlorine gas and powdered cobalt carbonate. The precipitate produced in the second stage was filtered to obtain 99L of a high-purity cobalt chloride solution containing Mn at 0.01g/L and 1.1kg of a precipitate having a Co/Mn ratio of 1.7 by weight. The Mn and Co distribution rates in the precipitate produced in the second stage were 23.8 and respectively, based on the Mn and Co amounts charged to the manganese removal process of the first stage.

Then, the precipitate produced in the second stage was passed to a leaching tank, where it was treated with hydrochloric acid for 1 hour at a pH of 0.1 to prepare the slurry to be recycled back to the first stage.

Mn removal rate of 99.3% and direct Co yield of 99.2% were recorded by the process.

COMPARATIVE EXAMPLE 1 Manganese was removed by a conventional process, where 100L of the solution was treated for 4 hours, while it was controlled at a pH of 3.00 and ORP of 900mV in the presence of continuously charged chlorine gas and powdered cobalt carbonate. The resulting precipitate was filtered to obtain 98L of a high-purity cobalt chloride solution containing Mn at 0.01lg/L and 6.1kg of a precipitate having a Co/Mn ratio of This process performed an Mn removal rate of 99.5% and direct Co yield of 95.4% (precipitate lost from the system: It is apparent, when the results of EXAMPLES are compared with those of COMPARATIVE EXAMPLE, that the present invention can have a greatly higher direct recovery rate of cobalt than the conventional process.

The present invention can remove manganese almost completely from a cobalt chloride solution containing manganese as an impurity while increasing a direct recovery rate of cobalt, and hence is of very high industrial value.

Claims (4)

1. 2. A process according to Claim 1 wherein said cobalt solution is oxidized/neutralized while being controlled at an oxidation reduction potential of 950 to 1050mV (based on an Ag/AgC1 electrode) and pH of 2.4 to 2.8.
2. 3. The process according to Claim 1 wherein said cobalt solution containing manganese as an impurity is a cobalt chloride solution.
3. 4. The process according to any of the preceding Claims wherein said oxidant is at least one member selected from the group consisting of chlorine, hypochlorous acid and ozone. 004968817 The process according to any of the preceding Claims wherein said neutralizer is at least one member selected from the group consisting of hydroxide and carbonate of an alkali and alkali-earth metal, and cobalt carbonate.
4. 6. The process according to any of the preceding claims wherein said solution is controlled at a pH of 0.1 to 1.5 in said third stage.