FI66920B - FRAMSTAELLNING AV KLORFRIA KOBOLTELEKTROLYTER - Google Patents

Description

66920

This invention relates to the electrolytic recovery of cobalt, and more particularly to its recovery from a slurry of cobalt (3) -5 oxide hydrate containing chloride ions as an impurity.

The recovery of cobalt from various process streams can be conveniently carried out by first precipitating the cobalt as a hydrogenated oxide and then dissolving it to prepare an electro-10 from which the cobalt can be separated by electricity. When, as usual, the process stream contains significant amounts of other metals, most notably nickel, a significant increase in the relative amount of cobalt present can be achieved by precipitating cobalt under oxidative conditions that ensure the formation of cobalt (3) oxide hydrate, sometimes referred to as cobalt. - (3) -hydroxide, Co (OH) Such oxidative precipitation is achieved if the process stream is treated with sodium hypochlorite or chlorine in the presence of a base.

Although, from an economic point of view, the process of forming cobalt-containing oxide hydrate with chlorine is of interest, an obstacle to its commercial application is due to the fact that the resulting filter cake is impregnated with chlorine ions. Two undesirable consequences result from the presence of chloride ions in the electrolyte from which the cobalt should be electrically recovered. First, it is necessary to use relatively expensive anodes in electrical recovery, since the lead alloys used generally corrode rapidly in the chloride-containing electrolyte. In addition, the electronic recovery of chloride-containing electrolytes involves emissions of chlorine, which is not environmentally acceptable and makes it necessary to use expensive protections, 35 in order to avoid the release of chlorine into the environment.

This invention relates to a process in which chloride-saturated filter cakes of cobalt (3) oxyhydrate can be used to prepare a solution from which electronically recovery can be performed without the above-mentioned obstacles.

In the process according to the invention, the feed cobalt material comprising the precipitate of cobalt (3) oxide hydrate is dissolved in the spent sulphate electrolyte obtained from the cobalt electroplating step, and in which at least one of the fed or consumed electrolyte contains chloride ions, and the feedstock is slurried with spent electrolyte, purifying the slurry of air for a period of time sufficient to release gaseous chlorine from substantially all chloride ions in the slurry, and substantially all of the cobalt in the dechlorinated slurry is dissolved by treating the slurry with a reducing agent selected from sulfur oxide; and organic reagents capable of reducing cobalt to its divalent state to provide a substantially chloride-free, cobalt-containing solution from which cobalt can be recovered electrically.

Particularly useful materials for preparing the cobalt feed precipitate used in the process of the invention are the mixed cobalt / nickel base precipitates formed as intermediates in various nickel recovery processes. Provided that the mixed precipitate contains nickel in an amount at least equal to its cobalt content, the base nickel material can be considered as the base required to precipitate the desired cobalt material, which can be obtained in the following manner. The mixed precipitate is divided into two fractions. The first of these fractions is dissolved in a dilute aqueous solution of mineral acid, which is then treated with chlorine while adding a second fraction of the stirred precipitate to the solution of the first fraction at a rate to maintain a pH of 3,66920 between approximately 2.5-4.5. In this way, substantially all of the cobalt in the mixed precipitate is in the form of cobalt (3) oxy dihydrate, and only a small portion of the nickel present in the mixed precipitate is present in the cobalt feedstock. This method of making the cobalt feed precipitate inevitably results in its saturation with chloride.

It has been found that a process of slurrying a cobalt-containing oxide hydrate precipitate with an acidic sulfate-containing electrolyte and introducing the slurry into air blowing is an effective means of releasing substantially all of the chloride ions present as gaseous chlorine. The chlorine removal step is necessary and is equally effective whether the impregnating chloride is present in the feed precipitate or in the electrolyte used. It is essential that the removal of chlorine from the slurry ta-15 takes place before the extraction step, i. before adding the reducing agent to the slurry. This is because the cobalt precipitate plays a role in the removal of chlorine, which is believed to occur according to the following formula: 2Co (OH) 3 + 2H2SO4 + 2H + + 2Cl "-> 2CoSO4 + Cl + 6 H2O

The above reaction can be carried out at room temperature, but for kinetic reasons, it is better to carry it out at a temperature of about 60-65 ° C. Under such conditions, a residual chloride ion concentration of less than 20 mg / L can be achieved in about 30 minutes by blowing air and applying mechanical agitation to the slurry.

After removal of chloride ions from the slurry, a reducing agent is used to dissolve the cobalt in the precipitate.

The reducing agent may be sulfur dioxide, in which case the extraction is likely to involve the following reaction: 2Co (OH) 3 + H2SO4 + SO2 -> 2CoSO4 + 4H2O 35 Since dissolution in this way increases the sulphate ion concentration, it becomes necessary to control its formation. This can be done by removing a portion of the cobalt sulfate solution, preferably before purification, and treating it with sodium carbonate to precipitate cobalt carbonate, a portion of which can be used to treat the impure electrolyte to remove iron while the residue can be redissolved in the purified electrolyte to adjust its pH.

Alternatively, the cobalt (3) precipitate can be dissolved without sulfate formation if a reducing agent other than sulfur dioxide is used. Hydrogen peroxide can be used as a reducing agent for this purpose, although its price makes it less interesting than other reagents.

It is known that many organic reagents are oxidized with cobalt hydroxide, and such reagents are suitable for reducing cobalt to its divalent state.

The use of alcohols, aldehydes and ketones for this purpose is suggested in publications such as S. Ludwik: "Oxidation of Some Organic Compounds by Cobaltic Hydroxide", Roczniki Chemii, 1973, 47, p. 43, and C.E.H. Bawn and A.G.

20 Whittle; “Reactions of the Cobaltic Ion, Part III: The

Kinetics of the Reaction of the Cobaltic Ion with Aldehydes and Alcohols ", J. Chem. Soc., 1951, p. 343. Particularly preferred is the use of methanol as a reducing agent for cobalt, in which case the reaction is believed to be as follows: 6Co (OH) 3 + 6 H 2 SO 4 + CH 3 OH -> 6CoSO 4 + CO 2 + 17H 2 O This reaction proceeds rapidly in the early stages of dissolution, 30 However, it has been found that after cobalt dissolution has progressed to 85-90% of full, extraction becomes slower and it is better to resort to The final treatment can be suitably carried out with sulfur dioxide or hydrogen peroxide, in which case a total dissolution of 98-99% of cobalt can be achieved, the total extraction time being 6 6920 in the same order as when using sulfur dioxide as the sole reducing agent.

When SC> 2 is used for all or part of the extraction, it is desirable to use a short air blow after extraction 5 to eliminate all SO 2 from the solution.

While the dechlorination step performed in accordance with the invention removes chloride ions from the slurry that were present as such in either the feed precipitate or the recycled spent electrolyte, problems may arise if the electrolyte contains chlorate ions. The latter may be due to the chloride saturation of the supporting electrolyte to be treated due to the impurity of the added reagents, e.g. when adjusting the pH. Anodic conditions during electrical recovery of the lead-15 support can result in the formation of chlorate ions from any chloride in solution. The air treatment does not remove chlorate ions, and the subsequent reduction of cobalt would involve the reduction of chlorate so that the "dechlorinated" slurry again contains chloride ions as an impurity. Similarly, when chlorate ions are present in the recycled spent electrolyte, the problem described above is avoided by reducing the chlorate ions to chloride ions before slurrying this electrolyte with the cobalt (3) feedstock. This can be achieved in many known ways, e.g. by short blowing of sulfur dioxide. The sequence of steps in such a case is: i) treating the spent electrolyte with sulfur dioxide to reduce ClO 3 to Cl; Ii) slurrying the treated electrolyte with a cobalt-containing feed precipitate; iii) applying an air jet to the slurry to release the present Cl as gaseous chlorine, and iv) adding a reducing agent to effect dissolution.

6 66920

When some of the residue remains insoluble at the end of the extraction step, it may not be economical to separate it at this stage. Thus, the residue can be left in solution until the latter has been treated to remove lead and iron therefrom, and the combined residue and precipitated impurities can then be separated from the solution.

Separation of lead and iron from the cobalt solution can be performed in any conventional manner. It is preferred to treat the solution with barium carbonate 10 to remove lead and then with cobalt carbonate to remove iron. When copper is present as an impurity, some of the copper may be precipitated during the iron removal step.

It is preferred to remove the zinc, copper and nickel impurity purities by means of ion exchange resins. Such a purification method is made economically acceptable by using it in the context of an electrical recovery step in which a substantial part of the cobalt is removed, i. reducing the cobalt content in the electrolyte by at least about 35 g / l. When supplied with such a high amount, concentrated electrolytes can be used, so that purification of a given amount of cobalt involves the treatment of a relatively small amount of electrolyte which can be treated in a relatively small layer of resin.

Zinc is preferably removed using a resin containing di (2-ethylhexyl) phosphoric acid (hereinafter abbreviated as D2UHPA). Such a resin, commercially available under the trade name Bayer AG, is known as: Lewatit 0C1026 (trademark) and is a macroporous copolymer of styrene-divinylbenzene containing about 150 g of D2EHPA per liter of resin layer.

The use of this resin to remove zinc from sulphate solutions containing 40 g / l cobalt is known per se and has now been found to be effective in treating more concentrated solutions which are preferred in the process of the present invention in the order of 100 g / l cobalt. or greater.

7 66920

The removal of nickel is preferably performed using a resin having functional bis- (2-picolyl) amine groups, such as the resin available from Dow Chemicals under the designation XF4195. Although the reported selectivity of this resin 5 between cobalt and nickel is less interesting than the reported selectivity values for many other resins, XF4195 resin was surprisingly found to be much more effective than any other such resin in removing nickel from low 10 levels of concentrated cobalt solutions. 50 g / l cobalt).

The methods currently used for electronically recovering cobalt invariably involve bagless cells and working with a relatively low cobalt-15 droplet concentration (i.e., less than 15 g / L) to achieve acceptable current efficiency. Although the use of cathode boxes to achieve higher concentrations is well known in the electrical recovery of nickel, cobalt producers have not been able to use such methods due to their tendency to precipitate cobalt oxide sludge and also gypsum, which causes diaphragm clogging. It has now surprisingly been found that if the concentration applied is not slightly but substantially higher, i.e. approximately between 35 and 60 g / l, e.g. 45 g / l, then, provided that diaphragm cells are used, the electrical recovery can proceed satisfactorily with high current power and without problems of sludge formation. We prefer to use cells in which the diaphragm is in the form of a bag surrounding each anode, the anodes being a conventional lead-based material because chloride ions are absent from the electrolyte.

The method of the invention will now be described in more detail with reference to the following examples.

Example 1 A wet Co (OH) ^ "cake containing 23% 35 Co and 0.1% Cl" was used. (Unless otherwise indicated, all percentages given herein are by weight.) Initial experiments 8,66920 showed that if such a cake is merely dissolved in an acidic sulfate solution to produce an electrolyte of the order of 50 g / l Co, the resulting electrolyte contains at least 0.2 g / l Cl .5 which is very much more than can be allowed. The dechlorination process according to the invention was carried out as follows: 3.45 g of cake were slurried with 14.5 l of consumed cobalt sulphate electrolyte containing 42 g / l Co, 0.23 g / l Ni, 3.3 mg / l Pb and 85 g / l The H 2 SO 4 slurry 10 was stirred mechanically maintaining the temperature at 65 ° C while blowing air for 30 minutes. After this time, experiments showed that about 93% of the chloride ions had been eliminated, while only about 4% of the cobalt in the cake had dissolved. The filtrate contained 20 mg / l Cl, 41 g / l Co and 1 g / l Ni at the end of the dichloro-15.

To further test the efficiency of the dechlorination process, the above process was repeated with a solution containing Cl added so that the initial concentration in the slurry was 1 g / l Cl. The resulting slurry 20 was blown with air at 60 ° C and sampled at various intervals to determine the chloride content of the solution, which was found to be in accordance with Table 1.

Table 1 25 Blowing time (min) _Cl test (mg / ml) 0 1000 5 20 30 20 60 20 30 150 13

It is clear that the dechlorination proceeds rapidly at this temperature and that an acceptable level of Cl can be achieved with a blowing time of 30 minutes or less, even if the solution and the feed cake contain a large amount of Cl ”ions as an impurity. Of course, as described above, if solution 9,66920 contains more ClO 2 ions than Cl ions, blowing air alone will not remove ClO 2 ions, and it is necessary to reduce ClO 2 ions relative to Cl ions before forming a slurry. .

The dechlorinated slurry obtained as described above was then subjected to reductive extraction by introducing sulfur dioxide at a blow rate of 0.21 mol per liter. The progress of the extraction was monitored by monitoring the redox potential (relative to the saturated Kalo-10 melielectrode). The initial redox potential of + 900mV had dropped to + 200mV after 130 min of extraction, which corresponds to a consumption of sulfur dioxide of 0.5 moles per mole of cobalt in the feed cake. At this point, the experiment showed that the solution contained: 15 cobalt 91 g / l nickel 1.5 g / l lead 12 mg / l iron 0.2 g / l copper 15 mg / l 20 zinc 5 rag / l

Lead was removed from the slurry by adding barium carbonate in an amount corresponding to 0.5 g / l of slurry, which reduced the amount of lead in the solution after 30 min to less than 0.1 mg / l. The slurry was then neutralized to pH 5.5 by adding 25 L of CoCO 3 slurry containing about 150 g / L of cobalt. The latter consisted in part of recycled cobalt in that it was prepared by treating the discharge stream of purified electrolyte with sodium carbonate. After filtration of the neutralized slurry, 17.8 liters of filtrate were obtained, containing: cobalt 99.5 g / l nickel 1.27 g / l lead <0.1 mg / l 35 iron 0.3 mg / l copper 1, 8 mg / l zinc 3.8 mg / l

Cl "30 mg / 1 10 66920

The solid extraction residue, after being filtered off, contained cobalt in an amount representing 1.5% of the cobalt present in the feed cake.

Example 2 An experiment similar to that described in the previous example was performed to investigate the use of methanol as a reducing agent during extraction. In this case, S, 2 kg of wet cobalt oxide hydrate cake containing 25%

Co and 0.1% Cl were slurried with 36 L of cobalt-10 sulfate electrolyte containing: cobalt 54.6 g / L nickel 0.18 g / L lead 2 mg / L sulfuric acid 85 g / L 15 39 min air blasting after 65 ° C it was found that 90% of the chloride was released leaving an electrolyte containing 45 g / l Co, 0.8 g / l Ni and 20 mg / l Cl-.

Pure methanol was added to the dechlorinated slurry at a rate of 15 ml / h of slurry. After 20 min, corresponding to the addition of 0.17 moles of CH 3 OH per mole of cobalt in the feed cake, the pH of the slurry had risen from 0.6 to 1.6. At this point, the sample of the slurry filtrate contained 89.5 g / l Co, indicating an extraction rate of about 25% of the co-25 bol in the feed. The addition of methanol was stopped, and instead sulfur dioxide was added to the slurry at a rate of 0.21 mol / h / l slurry for 100 min, indicating that the extraction was completed as the redox potential dropped from + 700 mV to + 440 mV at pH 2.3. Extraction was followed by blowing air for 20 min to remove dissolved Si 2, during which time the redox potential rose to + 690 mV. Analysis of the extraction solution gave the following results: cobalt 98.2 g / l 35 nickel 1.12 g / l lead 10 mg / l 11,66920 iron 0.11 g / l copper 15 mg / l zinc 4 mg / l

Removal of lead from this solution required repeated additions of BaCO 3. The first addition of 0.5 g BaCO 2 per liter of slurry reduced the lead content to 0.4 ml / l after 15 min. Another identical addition reduced the lead to 0.2 mg / L over the next 15 min.

The resulting slurry was neutralized to pH 5.4 by adding 1 liter of CoCO 3 slurry containing about 100 g / L of cobalt. After filtration, 40 liters of electrolyte containing 0.3 mg / l Fe and 3 mg / l Cu were obtained, whereby the separated residue represented 0.95% of the cobalt in the feed cake.

15 Example 3

The following experiments describe the removal of zinc by ion exchange from electrolytes with high concentrations of cobalt and high ionic strength.

A cobalt sulphate electrolyte containing 120 g / l of 20 Co, 1.2 g / l of Ni, 0.020 g / l of Zn and about 50 g / l of Na2SO4 and having a pH of 5.5 measured at 22 ° C was treated with 50 ml " Lewatit OC1062 "resin. The resin, as mentioned above, comprising a copolymer containing 150 g of D2EHPA resin layer per liter was poured into a column of columns having a diameter of 1.7 cm and a height of 3 cm. The column was subjected to a flow of 2 m of solution per square meter (m / m / h) of cross-section of the bed, maintaining a temperature of 50 ° C. After treatment with 0.5 liters of solution, i.e. 10 bed volumes (B.V.), the effluent from column 30 was found to contain less than 0.2 mg / l Zn.

This represents a ratio of Co: Zn in the purified electrolyte greater than 6 x 10 ^: 1.

On a larger scale, containing 100 g / l Co, 1 g / l Ni, 0.005 g / l Zn and 100 g / l Na 2 SO 4, and having a pH of 35 5.0 measured at 22 ° C, was purified on a column with a diameter of 4 , 1 cm and length 79 cm, and containing 12 66920 1 liter of "Lewatit OC 1026" resin. The column was operated at 60 ° C and 4.5 m / m / h to treat a volume of 213 liters (i.e. 213 B.V) of solution, at the end of which the effluent contained only 0.7 mg / l Zn. This represents a 5 Co / Ni ratio greater than 1 x 10 2: 1 in the purified electrolyte.

It is clear that D2EHPA, which contains a resin, provides an effective method for removing zinc from the concentrated electrolytes of the invention. The extraction should be performed at a pH of -10a, which is not lower than about 2.5, and preferably the pH should be initially adjusted, if necessary, to a range of 4-6. The loaded resin layer # can be eluted with dilute mineral acid and then reused to further remove zinc.

After feeding through the resin layer, the electrolyte may contain some D2EHPA, due to the slight solubility of the latter in aqueous solutions. To remove small amounts of extraction from the electrolyte, the latter is preferably passed through a column of activated carbon.

20 Example 4

The following experiments describe the removal of nickel by ion exchange from electrolytes with high concentrations of cobalt and high ionic strength.

A solution of 125 g / l Co, 2.04 g / l Ni and about 50 g / l Na 2 SO 4 and having a pH of 6.1 measured at 22 ° C was treated with Dow's bis (2-picolyl) with an amine resin in a solid layer having a diameter of 5 cm and a height of 3 cm and containing 6 liters of resin. The solution to be purified was run upwards through a resin column at a temperature of 50 ° C and a rate of 3 m / m / h. Samples of the effluent, taken after running different bed volumes of solution, were analyzed for nickel. The results showed that after running the two bed volumes of the solution, the sample from the effluent from the bed contained only 35 33 mg / l nickel, i.e. the Co / Ni ratio of the electrolyte was greater than 3000: 1. Analysis of a sample from the effluent that 13 66920 came from about 4 B.V. after driving, showed a nickel content of 490 mg / l. By determining the average value for the entire collected effluent, it was determined that with such a starting solution up to 6 B.V. could be treated in 5 columns to purify an electrolyte in which the amount of nickel did not exceed about 0.5 g / l, i.e. The Co / Ni ratio was at least 200: 1. Such an electrolyte allows the electrical recovery of high purity cobalt.

10 The ion exchange treatment described above is effective in removing not only nickel but also all the copper in the electrolyte. Removal of copper from a picolylamine resin is more difficult to perform than removal of nickel from a loaded resin. Therefore, it is preferred to remove the copper before using this resin. The removal of copper can be carried out in many known ways, such as using special copper-selective ion exchange resins or solvent extracts such as carboxylic acid or oxime-type extractants.

20 Example 5

Purified electrolyte containing: cobalt 89 g / l nickel 20 mg / l lead 0.4 mg / l 25 zinc 1.3 mg / l iron 0.3 mg / l copper 0.1 mg / l was used for electrical recovery of cobalt 2 , In 5-liter laboratory cells as well as in a larger 16-liter ken-30. The electrodes in these cells were 10 x 15 cm and 10 x 35 cm, and the anodes were in a lead alloy containing 0.05% calcium and 0.5% tin. The cathodes were made of stainless steel. Each anode was surrounded by a diaphragm that separated the anolytic compartment, while the rest of the space in the 35 cells consisted of a standard catholyte compartment.

14 66920

A small amount of 20-30 mg / L sodium lauryl sulfate was added to the electrolyte to act as an anti-corrosion and anti-fogging agent. The electrolyte was then fed through the cells at a rate such that the amount of cobalt remained at 41 g / l, with a current density of about 200 h / τα2. The cell temperature was 55 ° C and the pH of the catholyte was 2.1.

Cobalt was galvanized for 171 h with a current efficiency of 92%.

The deposited substances were found to contain the following impurities, in parts per million: 10 nickel 87 ppm lead 6 ppm zinc 11 ppm iron 16 ppm copper 2.5 ppm 15 The following electrical recovery was performed using a similar process except for the following differences. The electrolyte had a different level of impurity, the results were: cobalt 93 g / l nickel 0.24 g / l 20 lead 0.2 mg / l zinc 1 mg / l iron 0.2 mg / l copper 0.3 mg / l

The cathodes were also covered, revealing only 25 round islets in them, in which separate cobalt deposits formed. The achieved concentration was 46 g / l cobalt with a catholyte pH of 2.3 and a current efficiency of 91%.

After 167 h of electrical recovery, the deposit was found to contain: 30 nickel 252 ppm lead <4 ppm zinc 10 pp, iron <8 ppm copper <7 ppm 35 By testing the efficiency of variations in the electron recovery parameters, the following conditions were found to be desirable and preferred: 15,66920

Feed composition: 85-105 g / l Co, preferably about 100 g / l Co;

Amount of cobalt: 35-60 g / l, preferably more than 45 g / l 5 Consumption of electrolyte consumed: * 40 g / l Co, preferably> 50 g / l Co;

Current density: 100-300 A / m2, preferably about 200 A / m2; Temperature: 50-60 ° C, preferably about 55 ° C;

Catholyte pH: 2-3, preferably about 2.5 L

The amount of cobalt should be at least 35 g / l to avoid sludge formation problems. This need for a minimum of 15 is illustrated by the results of the following comparative test.

Identical electroconversion experiments were performed under similar conditions as in the other of the two electroconversion experiments mentioned above, except that the amount was arranged to be 45 g / l in one case and only 12 g / l in the other case. The feed electrolytes were selected to ensure that in both cases the same level of cobalt (500 mg / l) was present in the consumed electrolyte.

After 167 h of electrical deposition, the total amount of sludge collected from the anode box and the electrolyte consumed was 13.0 g using a lower amount of material.

However, it is not possible to select a concentration of more than about 60 g / l without inconvenience to work, because at excessive amounts the pH of the catalyst drops below 2, and this causes both a decrease in current efficiency and a puncture score. Thus, a comparative experiment in which a cobalt content of 75 g / l was achieved showed only 55% current efficiency. In addition, a large number of point deposits were found after 100 h, despite the presence of sodium lauryl sulfate.

35 The work steps described in the form of batches can be carried out continuously or semi-continuously.

Claims (2)

16 66920 An electrolytic cobalt recovery method, wherein a cobalt material comprising a cobalt oxide hydrate precipitate is dissolved in a spent sulfate electrolyte obtained from the cobalt electroprecipitation step, and wherein the cobalt material to be fed and / or the spent electrolyte is a time sufficient to release gaseous chlorine from substantially all chloride ions in the slurry, substantially all of the cobalt in the dechlorinated slurry is dissolved by treating the slurry with a reducing agent such as sulfur dioxide, hydrogen peroxide or an organic reagent suitable to substantially reduce the cobalt to divalent; to obtain a solution from which cobalt is recovered electrolytically. A method according to claim 1, wherein the electrolyte used initially contains chlorate ions as an impurity, characterized in that the electrolyte used is treated with a reducing agent which reduces chlorate ions to chloride ions before slurrying the cobalt material with the electrolyte.