GB2034290A - Separation of Cobalt from Nickel by Solvent Extraction - Google Patents

Abstract

A method of separating cobalt from nickel by solvent extraction in an aqueous solution containing Co and Ni salts uses an organic solvent containing, as an extractant, a compound of the general formula <IMAGE> where each of R1 and R2 is an alkyl group, e.g. an alkyl group having 8 to 10 carbon atoms. This method requires fewer stages and less organic solvent in the solvent extraction than a conventional method. This method can also enable continuous separation of Co from Ni to obtain a greater than 93% yield of Co with a purity of greater than 99% and a greater than 98% yield of nickel with a purity of greater than 95%.

Description

SPECIFICATION Separation of Cobalt from Nickel by Solvent Extraction This invention relates to the separation of cobalt from nickel in an aqueous solution containing Co and Ni salts, using solvent extraction.

Aqueous solutions containing Co and Ni salts are obtained, for example, from the hydrometallurgy of ores, the recovery of useful metals from wasted catalysts, or the recovery of useful metals from metal scraps. In many cases Ni and Co are contained together. Therefore, an effective method is necessary to separate and recover pure Co and Ni from such aqueous solutions.

Conventionally, in order to separate Co from Ni in an acidic solution a method has been employed that relies on the pH shift caused by the addition of alkali to the acidic solution to precipitate hydroxides of Co and Ni. There is another method, which is more effective than the aforementioned one, and which is capable of separating Co and Ni utilizing the difference of their solubilities when the acidic aqueous solution is extracted with an organic solvent composed of an extractant and a diluent using a solvent-solvent extraction technique.

One of the solvent extraction method extracts and separates Co selectively from the acidic aqueous solution using di-2-ethylhexyl phosphate dissolved in an organic solvent as the extractant. In this procedure, an aqueous solution containing Co and Ni is mixed with an organic solvent containing the extractant.

The aqueous solution, i.e. the aqueous phase, and the extracting solvent, i.e. the organic phase, do not dissolve in one another but are in contact with each other, such that the Co ions may be extracted across the interface into the organic phase.

The organic phase and the aqueous phase, after mixing and making contact with each other, e.g.

by stirring for a certain time, separate into an upper layer and lower layer. The Co in the aqueous solution is extracted into the organic phase and the Ni remains in the aqueous phase, i.e., the raffinate.

However, in the case where Co is extracted into the organic phase by the prior art method of contacting the aqueous solution containing Co and Ni with an organic solvent containing di-2-ethylhexyl phosphate, the separation of Co from Ni is incomplete unless the stages of extraction are many, because the Ni is also extracted to a significant extent into the organic phase under the extraction conditions which can recover Co effectively. Therefore, a multi-stage extractor is required for practical use for complete separation of Co from Ni.

As described so far, a large extraction apparatus with multiple stages is necessary if the conventional method of extraction is employed utilizing di-2-ethylhexyl phosphate as the extractant.

Di-2-ethylhexyl phosphate has insufficient ability to separate Co from Ni. Therefore, for the effective separation of Co from Ni, it is necessary to choose an extractant with an excellent ability to separate Co from Ni.

According to the present invention, there is provided a method for separating Co from Ni in an aqueous solution containing salts thereof by solvent extraction using an organic solvent containing an extractant to extract the Co, in which an alkyl phosphonic acid monoalkyl ester of the general formula

wherein each of R, and R2 is an alkyl group, is used as the extractant Preferably, each of R1 and R2, which are the same or different, is an alkyl group having 8 to 10 carbon atoms.

Preferred examples of suitable extractants are 2-ethylhexyl phosphonic acid mono-2-ethylhexyi ester (abbreviated as EHP) and/or 3,5,5-trimethylhexyl phosphonic acid mono-3,5,5-trimethylhexyl ester (abbreviated as TMHP) and/or isodecyl phosphonic acid monoisodecyl ester (abbreviated as IDP) and/or 2-ethylhexyl phosphonic acid monoisodecyl ester (abbreviated as EHIDP).

In general, when the carbon atom number of the alkyl group for each of substituents R and R2 is lower than 8, a loss of the extractant during extraction increases because the extractant is soluble in water, or decomposition of the extractant occurs because the hydrolyzing stability thereof is poor. On the other hand, when it exceeds 10, a viscosity of the extractant becomes high, which results in rendering the operation difficult. Thus, both cases give a number of problems during operation, e.g. a lowering in extraction ability and a reduction in solubility against diluent.

The procedure of this invention is very simple, and in addition Ni and Co can be separated and recovered in high purity and in good yield from an aqueous solution containing them. For example, a greater than 93% yield of Co with a purity of greater than 99% and a greater than 98% yield of Ni with a purity of greater than 95% can be obtained.

The excellent ability of the extractant to separate Co from Ni decreases drastically the number of extraction stages in comparison with the cases where di-2-ethylhexyl phosphate is used as the extractant Thus, the cost of the extraction equipment can be reduced as well as the amount of the organic solvent required for the extraction. This leads to the great advantages such as a drastic reduction in investment, a decrease in operation expense, and in addition simplification of operational control.

The organic solvent suitable for this invention comprises the above-mentioned extractant, and a diluent as described below, and contains 5 to 90 vol% and preferably 10 to 40 vol% of the abovementioned extractant.

The method of this invention is preferably carried out by controlling the pH at the extraction to a certain range. The method is preferably carried out by preliminary controlling the pH of the aqueous solution and/or the pH of the organic solvent such that the pH of the raffinate is 4 to 6.5. Furthermore, it may be carried out by the addition of an alkali at the mixing of the organic solvent and the aqueous solution. The pH may also be controlled by adding and mixing alkali with the organic phase. Effective alkali solutions for this purpose are those which contain an ammonium ion, alkali metal ion, or calcium ion, e.g. ammonia, caustic soda, sodium carbonate and calcium hydroxide.

An inert diluent is employed in this invention for diluting and dissolving the extractant. The diluent should be capable of dissolving the extractant and of separating from the aqueous phase at least when at rest after liquid-liquid contact of the metal-containing aqueous phase with the solvent phase. The solvent should be insoluble in water, and should not inhibit the function of the extractant in the extraction of Co from the solution containing Co and Ni. Effective diluents which can be used in this invention are aliphatic hydrocarbons, and aromatic hydrocarbons, and the mixtures of these compounds. Specific examples of aliphatic hydrocarbons are distillates of petroleum, such as kerosene; and specific examples of aromatic hydrocarbons are toluene; respectively.Furthermore, naphthenic hydrocarbons are especially preferred as the aliphatic hydrocarbons, and naphthene-rich hydrocarbons are especially preferred as the distillates of petroleum. The naphthenic hydrocarbons have an excellent property in stability when using over a long period of time. The diluent is selected taking into account solubility of the extractant, viscosity, specific gravity, flash point, and safety in use.

In the separation of the aqueous phase and the organic phase at rest, the separation of the two phases will be incomplete if emuisification occurs. It has been found that addition of 2 to 5 vol% of tributyl phosphate or isodecanol is able to prevent the formation of the emulsion whereby the extraction operation can be proceeded smoothly.

The temperature at which liquid-liquid contact and the phase separation are carried out is not a critical factor. However, the temperature is preferably maintained in the range of 20 to 800C considering the flash point of the organic solvent and the rate of phase separation.

The procedure of extraction by the contact of organic solvent and aqueous solution containing Co and Ni employed in this invention may be any one of those procedures well-known in the solvent extraction art. That is, although continuous circulation is generally preferred, batch, continuous batch, and batch circulation are also effective. Packed column, pulse column or rotating disc column, are preferably used in the countercurrent extraction with multiple stages, but any one of the well-known extraction equipment generally used for the solvent extraction is suitable for this invention. As this invention is very effective in the separation of Co from Ni, it is also advantageous to use a mixer-settler in one or more extraction stages.

The volume ratio of the organic phase to the aqueous phase which are in contact with each other may be varied over a considerably wide range but, generally, is controlled to a range of 1/4 to 4/1. The most effective ratio is selected depending on the nature and the concentration of the extractant, the diluent, and the aqueous solution containing Co and Ni, and on the method of mixing these liquids, such as the type of the equipment. In general, the ratio is selected such that substantially all the Co in solution is taken into the organic phase and a minimum amount remains in the raffinate.

After the eictraction of Co into the organic solvent and the separation of the aqueous phase from the organic phase, the organic phase is transferred to a stripping circuit where contact is made with an inorganic acid to remove the cobalt in a conventional manner. The stripping circuit may be carried out using conventional equipment for liquid-liquid contact. For example, a mixer-settler having 1 to 2 stages of equipment enables a recovery of substantially all of the amount of the Co from the organic phase.

The volume ratio of the organic phase to the inorganic acid in stripping depends on the concentration of Co and on the inorganic acid and may be varied over a considerably wide range based on the desirable concentration of Co salt in the aqueous phase which has been removed and recovered.

Generally, the volume ratio of the organic phase to the inorganic acid in stripping is controlled to 5/1 to 1/5.

As for the inorganic acid, sulfuric acid, nitric acid or hydrochloric acid of 0.5 to 5 N is advantageous. The choice of the acid is dependent upon the kind of Co salt desired. The organic phase from which Co has been removed may be fed back to the extracting circuit.

The pqsitioning of a scrubbing circuit between the extraction circuit and the stripping circuit is also effective for improving the purity of the Co by removing small amounts of Ni present in the organic phase. The organic phase is effectively scrubbed using an aqueous solution containing a diluted inorganic acid or Co salt, or with a part of the aqueous phase obtained from the stripping circuit, in the solvent extraction equipment of a well-known design. Co and Ni remaining in the aqueous phase after scrubbing is recovered by feeding back to the extraction circuit.

It is desirable to minimize the concentration of impurities such as iron, zinc, copper, arsenic, etc., in the aqueous solution of Co and Ni, prior to the extraction. The impurities may be eliminated from the aqueous solution by an established technique such as precipitation by pH adjustment, etc.

In the accompanying drawings: Figures 1(A), (B), (C), (D) and (E) are graphs in which the extraction coefficients of Co and Ni extracted into the organic phase from an aqueous solution containing Co and Ni salts are plotted against the pH of the raffinate where conventionally di-2-ethylhexyl phosphate, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, 3,5,5-trimethylhexyl phosphonic acid mono-3,5,5trimethylhexyl ester, isodecyl phosphonic acid monoisodecyl ester, and 2-ethylhexyl phosphonic acid monoisodecyl ester, respectively, are used as the extractant.

Figures 2(A) and (B) show graphs in which the concentrations of Co and Ni, respectively, extracted using an extraction solvent according to the method of the present invention are plotted against the pH raffinate.

Figures 3(A), (B) and (C) are graphs in which the concentrations of Co and Ni extracted from sulfate, nitrate and chloride salt solutions with an extraction solvent according to the method of the present invention are plotted against the pH of the raffinate.

Figure 4 shows a graph in which the extraction of Co and Ni at 200C is plotted against pH.

Figure 5 is a block diagram illustrating a continuous separation of Ni from Co in which Figures (A), (B) and (C) relate to the cases where an aqueous sulfate solution has a concentration of Co and Ni of 1 5 g/l, 14 g/l and 13 g/l, respectively.

The invention will now be described in more detail in the following examples.

Example 1 This experiment was carried out to compare the Co and Ni separation ability of the extractant used in this invention, i.e., EHP, TMHP, IDP and EHIDP, with that of di-2-ethylhexyl phosphate used conventionally under the same conditions.

Each extractant was dissolved in kerosene to give a concentration of 20 vol% and then, a predetermined amount of ammonia water was added thereto. The solvent thus-prepared was brought in contact with an aqueous solution containing cobalt sulfate and nickel sulfate so that the extraction might be performed.

The contact was carried out by shaking for 10 minutes in an Erlenmeyer flask in a water-bath thermostaticaily set at 500C.

The ratio of volume of the aqueous phase to that of the organic phase was 1 :1, and the initial concentration of Co and Ni in the aqueous solution was 10 9/l each.

The relation between the pH of the raffinate obtainable from extraction with each organic solvent and the extraction coefficients (%) of Co and Ni into the organic phase from the aqueous solution containing Co and Ni, is shown in Figures 1(A), (B), (C), (D), and (E). Figures 1(A), (B), (C), (D), and (E) show the cases where the conventional di-2-ethylhexyl phosphate EHP, TMHP, IDP and EHIDP were used, respectively, as the extractant. The curves (1), (3), (5), (7) and (9) and curves (2), (4), (6), (8) and (10) are the extraction curves with respect to pH for Co and Ni, respectively.

As shown in Figure 1(A), not only was Co but also Ni extracted in a large amount when the conventional di-2-ethylhexyl phosphate was used as the extractant. On the other hand, when the extractants of this invention were used, the amount of Ni extracted together with the Co was remarkably small. It is, therefore, evident that the agents used in this invention, i.e., EHP, TMHP, IDP and EHIDP are remarkably superior to the conventionally used di-2-ethylhexyl phosphate.

Example 2 Determination of the Extraction Ability for the Extraction of Co or Ni The same procedure as that of Example 1 was used. Namely, to a kerosene solution containing 20 vol% of EHP was added a predetermined amount of ammonia water, and then the resultant solution was brought into contact with an aqueous solution containing Co or Ni so that the ratio of the aqueous phase and the organic phase might be 1:1.

The temperature at extraction was 500C, and the initial concentrations of the metal in the aqueous solution containing of cobalt sulfate or nickel sulfate were 30 g/l each.

The relation between the concentration of Co or Ni extracted into the organic phase and the pH of the raffinate after extraction is shown in Figures 2(A) and (B). Figures 2(A) and (B) are curves of concentration of the metal in the organic phase (g/l) in relation to the pH of raffinate when Co or Ni alone were present, respectively. In both cases, phase separation was insufficient when the pH was around 7.

The relation between the amount of Co extracted and the concentration of EHP in the extracting solvent in the range of 5 to 70 vol%, was studied. The experiment was carried out in such a manner that the temperature of extraction was 300C and the pH of the raffinate was 5+0.5 to evaluate the extraction ability of the extractant varied proportionally with the concentration of EHP in the solvent.

The Co amounts thus extracted are given in the following table. The viscosity of the phase was found to increase with the concentration of EHP-Co complex in the organic phase.

Table 1 Co Concentration in EHP in the the Organic Phase Solvent pH of the (after extraction) lvoP/o) Raffinate (g/l) 5 5.5 3.8 10 5.5 7.3 20 5.5 15.5 40 5.0 27.8 70 4.5 45.8 Example 3 Influence of the Nature of Salts of Co and Ni in the Aqueous Solution Containing Co and Ni on the Extraction Result The experiment was carried out on sulfate, nitrate, and chloride aqueous solutions, using a kerosene solution containing 20 vol% of EHP. The procedure was the same as that of Example 1, except that the initial Co and Ni concentrations were 1 5 g/l each. The extraction results in relation to the nature of salts are shown in Figures 3(A), (B) and (C).Figures 3(A), (B) and (C) show the relation of the metal concentratión in the organic phase (g/l) and the pH of the raffinate in the extraction of the sulfate, the nitrate, and the chloride, respectively. Curves (13), (15) and (17) are for Co, and those of (14),(16) and (18) are for Ni.

As is evident from the results shown in Figures 3(A), (B) and (C), the nature of salt was found not to have much affect on the efficiency of extraction of Co and Ni.

Example 4 Influence of the Extraction Temperature on the Extraction of Co and Ni The extraction experiments were carried out at 200 C.

The procedure was the same as that of Example 3, except that the temperature was varied.

Figure 4 is the result of an extraction at 200C of the kerosene solution containing 20 vol% of EHP from an equivalent volume of an aqueous solution of sulfates of both Ni and Co containing 1 5 g/l each of Co and Ni. Curve (19) is the extraction curve of Co and Curve (20) is that of Ni. Comparing Figure 4 and Figure 3(A), no difference of the efficiency of separation of Ni and Co with temperature is substantially observed.

Example 5 Continuous Extraction Experiment to Recover Ni and Co from Their Aqueous Solution by Practical Operation For continuous extraction, a mixer-settler with 2 stages was employed because it is most commonly used and to show that this invention can practically be applied with a countercurrent liquidliquid extraction with only a few stages.

The countercurrent liquid-liquid contact was conducted as follows. Extracting solvent introduced into the mixer of the first stage (F) was brought in contact with the aqueous phase sent from the settler of the second stage (S) by stirring. The suspension of the organic phase and the aqueous phase was then sent into the settler of the first stage and kept still until the organic phase and the aqueous phase separated into upper (AV-1) and lower layers AW-1), respectively. The organic phase (F) containing Co overflow from the settler, was transferred into the second mixer, and was similarly brought in contact with the original aqueous solution containing Co and Ni, by stirring, and thus separated into phases AV-2 and AW-2.

The original aqueous solution containing Co and Ni was introduced into the second mixer followed by contact with the organic phase from the first settler and the phase separation in the second settler, while the aqueous phase was sent to the first mixer, countercurrent to the organic phase. That is, the organic phase was introduced into the first mixer and removed from the second settler, while the aqueous phase was introduced into the second mixer and removed from the first settler.

During this process, the kerosene solution containing 20 vol% of EHP and 3.6 volume of ammonia water per 100 volume was introduced into the mixer of 100 ml at a rate of 1.041/her.

The aqueous solution of the sulfates of Co and of Ni was introduced at a rate of 1.0 I/hr.

The extraction was carried out at 500+30C and the result is outlined in Figure 5, in which (A), (B) and (C) indicate the cases where the concentration of Co and Ni in the sulfate solution were 1 5 g/l, 14 g/l, and 13 g/l each, respectively.

In Figure 5(A), AV-1 stands for the organic phase in the first stage (F), and AW-1 for the aqueous phase of raffinate of the same stage. AV-2 stands for the organic phase of the second stage (S), and AW-2 for the aqueous phase of raffinate of the same stage. Similarly, BV-1 stands for the organic phase in the first stage, BW-1 for the aqueous phase of the raffinate of the stage, BV-2 in (B) for the organic phase in the second stage (S), BW-2 for the aqueous phase of the raffinate, CV-1 in (C) for the organic phase of the first stage (F), CW-1 for the raffinate, CV-2 in (C) for the organic phase in the second stage (S), and CW-2 for the aqueous phase of the raffinate.

The concentrations of Co and Ni and pH value of each phase are shown in Table 2.

Table 2 Co Ni Phase (gel) Kg/lJ pH AW-1 0.74 14.8 5.8 AV-2 14.0 0.003 - BW-1 0.12 13.7 5.8 BV-2 13.4 0.005 - CW-1 0.08 12.8 5.9 CV-2 12.7 0.005 - In the experiment of countercurrent extraction with two stages by the mixer-settler outlined in Figure 5, Co was separated in the purity of more than 99% and in the recovery of 93 to 98%, while Ni was recovered in the raffinate in the purity more than 95% and in the recovery of more than 98%.

Example 6 The Influence of the Addition of Tributyl Phosphate (TBP) and Isodecanol to the Extracting Solvent as an Emulsion Inhibitor on the Extraction Efficiency In this experiment, after converting the extracting solvent into its ammonium salt by the addition of 3.6 parts of concentrated ammonia water per 100 parts (volume unit) of the extracting solvent, the solvent was brought in contact with 100 parts of an aqueous solution containing Co and Ni. The extraction temperature was 500C and the contact time was 10 minutes.

The result is shown in Table 3, in which Solvent A refers to the kerosene solution containing 20 vol% of EHP, and Solvents B and C are the kerosene solutions containing 20 vol% of EHP and 5 vol% of TBP or isodecanol, respectively.

The material aqueous solution (a) is a solution of sulfates containing 14 g/l of Co and Ni each, and (b) is the solution containing 12 g/l of Co and 16 g/l of Ni.

Table 3 Organic Material Phase Raffinate Experiment Extracting Aqueous (g/lJ (g/l) pHof No. Solvent Solution Co Ni Co Ni Raffinate 1 A (a) 13.6 0.66 0.21 13.4 5.6 2 B (a) 13.0 0.40 0.90 13.6 5.6 3 C (b) 11.6 1.6 0.55 13.9 5.6 The addition of an emulsion inhibitor, TBP or isodecanol, does not result in the formation of emulsion, thus, the extraction was proceeded effectively.

Example 7 Experiment of Stripping of Co from the Organic Phase into which Co was Extracted The experiment was carried out with the Co-containing organic phase obtained in Example 6, using 1 N or 0.5N sulfuric acid, or 0.5N nitric acid as the solution for stripping.

The ratio of the volume of the organic phase to that of the aqueous phase was 1:0.5 in all cases, the contact time being 5 minutes.

The result is shown in Table 4.

Table 4 Aqueous Phase Organic Phase after the after the Treated Solution Times Experiment Experiment Experiment Organic for of (g/l) (gfl) No. Phase Stripping Stripping Co Ni Co Ni 1 Example 6 1 NH2SO4 1 25.2 0.78 Experiment 2 No.2 2 0.16 0.01 3 3 0.00 0.00 < 0.00 < 0.00 4 Example 6 0.5NH2SO4 1 13.0 0.78 Experiment 5 No.2 2 11.8 0.02 6 3 0.09 0.00 < 0.00 < 0.00 7 Example 6 0.5N-HNO3 1 11.13 2.94 Experiment 8 No.3 2 11.63 0.13 9 3 0.12 0.00 < 0.00 < 0.00 Table 4 shows the cases where H2SO4 or HNO3 was used for stripping, but when hydrochloric acid is used as the solution for stripping, Co may also be easily removed from the organic phase similarly.

Example 8 A scrubbing test was performed in order to eliminate a small amount of Ni that has been extracted together with Co into the organic phase.

The organic phase containing 11.9 g/l of Co and 1.5 g/l of Ni was subjected to this experiment, using the aqueous phase after the stripping test of Experiment No. 4 in Example 7 and the aqueous sulfate solution containing 1 3 g/l of Co, as the scrubbing solution.

The contact for scrubbing was done for 10 minutes at the ratio of the volume of organic phase to that of aqueous phase of 1:0.5 in all cases.

Table 5 Organic Phase Aqueous Phase pH of Volume (g/l) (g/l) Aqueous Ratio Co Ni Co Ni Phase Organic phase 2 11.9 1.5 before scrubbing Recovered solution 1 13.0 0.82 3.2 for stripping After scrubbing 13.5 0.09 11.8 4.1 4.7 CoSO4 solution 1 13.0 0.00 4.5 for scrubbing After scrubbing 13.7 0.11 11.5 3.2 4.8 As is shown in Table 5, Ni in the organic phase was eliminated to become less than 1/10 of the original concentration, while the organic phase could extract a small amount of Co with this contact so that the concentration of Co increased.

Co and Ni lost into the raffinate on scrubbing was recovered by feeding back to the extraction circuit.

By an appropriate combination of extraction circuit, scrubbing circuit, and stripping circuit, as is done in Example 6 to Example 8, separation of Co and Ni in sufficiently high purity and in high yield was found to be attained conveniently with a solvent extraction equipment with comparatively few stages.

In Examples 2 to 8, EHP was used as the extractant but similar results may be obtained even if the other extractants in this invention, TMHP, IDP and EHIDP are used.

Claims (6)

Claims

1. A method for separating Co from Ni in an aqueous solution containing salts thereof by solvent extraction using an organic solvent containing an extractant to extract the Co in which an alkyl phosphonic acid monoalkyl ester of the general formula

wherein each of R and R2 is an alkyl group, is used as the extractant.

2. A method as claimed in claim 1, wherein each of R1 and R2 which are the same or different, is an alkyl group having 8 to 10 carbon atoms.

3. A method as claimed in claim 1 or 2, wherein said organic solvent comprises, as a diluent, an aliphatic hydrocarbon, an aromatic hydrocarbon, or a mixture thereof.

4. A method as claimed in claim 3, wherein said diluent consists mainly of naphthenic hydrocarbons.

5. A method as claimed in any preceding claim, wherein said organic solvent contains, as an emulsion inhibitor, tributyl phosphate or isodecanol.

6. A method as claimed in any preceding claim, wherein the pH of said aqueous solution from which the Co has been extracted is 4 to 6.5.