FI63442B - EXTRAKTIONSFOERFARANDE FOER SEPARERING AV EN KOBOLTPRODUKT SOMAER MYCKET REN FRAON NICKEL UR VATTENLOESNINGAR AV KOBOLT OH NICKEL - Google Patents

Description

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C ¢ 45 ^ Patent eviennet ly 10 06 1983 Parent uiodeC '^ at VTV ($ 1) Kvjk? /IM.a3 C 22 B 23/04 ENGLISH — FINLAND (21) Paunttflwkaiiw · - Pat «MaM6kiiinf 801709 p7) HikamlWW — AiwBknlnfidf .80 (23) Alkupttvi — eiklglMttdat 27.05.80 (41) Tulkit | ul kteelul - WMt offantiif 28.11. 8l ****** - j »reklrterih» llitu · / 44 ^ NikUvtkilpMeu (. KuUUiiiiulwn pvm.- P * tHb och ragietontyralMn '' AmMuii utlaf * ort uoXlIkM puMetad 28.02.83 (32) (33) (31) * n * "* r mmOmn prtortt · * (71) Outokumpu Oy, Outokumpu, FI; Töölönkatu U, 00100 Helsinki 10, Finland-FI (72) Bror Göran Nyman, Pori, Stig-Erik Hultholm, Pori, Matti Juhani Hämäläinen, Kokkola, Lars Gustav Jansson, Kokkola, Tom Olavi Niemi, Öja, Finland-Finland (Fl) (7M Berggren Oy Ab (5M This invention relates to a process for the separation of cobalt and nickel from aqueous aqueous solutions containing these metals by liquid-liquid extraction, Magnesium is either intentionally dissolved from the cobalt / nickel grade of the cobalt / nickel ore being treated. containing sodium and not removed in solution cleaning prior to liquid-liquid extraction or, if necessary, added before or during extraction. The object of the invention is to recover cobalt in good yield from cobalt- and nickel-containing solutions as a product with a high cobalt / nickel weight ratio. The aim is to extract more than 99% of the cobalt and at the same time increase the cobalt / nickel ratio of the recovered cobalt product by 1000-20 000 times the corresponding metal ratio of the extraction feed. Due to the improved separation, the method can also be applied to remove cobalt from solutions with a high nickel / cobalt ratio, for example from solutions of nickel processes for laterite, where the nickel / cobalt weight ratio may exceed 1000.

63442

The solution to the known difficult cobalt / nickel separation problem has previously been presented e.g. the use of concentrated chloride solutions to convert cobalt to the chloride-cobaltate form or the use of ammoniacal solutions to oxidize cobalt with air to the trivalent form, in both cases providing sufficient separation for the chemical behavior of cobalt and nickel to separate these metals using methods known to those skilled in metallurgy. However, such separation processes are a considerable process burden, unless it is also advantageous to carry out the leaching of the cobalt / nickel ore or concentrate to be treated in the form of chloride-based or ammonia, respectively.

For many process solutions, it would be more advantageous from an overall point of view if cobalt could be separated as a cation from that cobalt / nickel solution, whereby separation would be possible regardless of the anion species of the solution. This could then be, for example, sulphate, which would allow the use of sulfuric acid as a preferred dissolving chemical. U.S. Patent No. 3,399,055 discloses that cobalt can be separated from nickel by using organophosphoric acid in its alkali or ammonium salt form as an extractant. A possible salt is the ammonium salt of di- (2-ethylhexyl) -phosphoric acid, which acts as a cation exchanger by binding the extractable metal and releasing an equivalent amount of ammonium ion into the aqueous solution.

Finnish Patent Publication 51,110 shows that cobalt / nickel separation is improved when using organic phosphoric acid as an extractant if at least 5 g / l of magnesium is added to the cobalt / nickel solution before extraction. Magnesium co-extracts with cobalt at a slightly lower pH than nickel and displaces the nickel from the extraction solution as the metal content of the extraction solution increases. The result is better separation of cobalt and nickel. However, under the conditions shown, much of the added magnesium is extracted with the cobalt to be separated.

The use of a phosphoric acid ester as a cobalt-nickel separating extractant is also disclosed in Finnish patent application 780072. According to this method, cobalt is extracted at an elevated temperature of 3 63442, with a lower limit of 40 ° C, while raising the cobalt content of the extraction solution to 11-16 g / l. To adjust the pH of the cobalt / nickel solution, the phosphoric acid ester in question, di- (2-ethylhexyl) -phosphoric acid, has been used in its sodium salt form.

According to German application 2820841, an alkylphosphonic acid monoalkyl ester is used as an extractant to separate cobalt and nickel. This extractant, which is proposed for use in the ammonium salt form, has been able to extract cobalt more selectively from cobalt / nickel sulphate solutions than is possible with the corresponding extractant of the di-alkylphosphoric acid type.

The main object of the present invention is to considerably improve the cobalt / nickel separation from the level provided by the prior art methods, and the main features of the invention appear from the appended claim 1.

According to the invention, cobalt is extracted from magnesium-containing cobalt / nickel solutions under conditions such that cobalt, while being separated from nickel, is also separated from most of the magnesium. Since it has been considered important that cobalt can be extracted as a cation regardless of the anions present in the cobalt / nickel solution, only cation exchangers with DCo> DMg> DNi <denote in this case the partition coefficient of the metal in question, which indicates the concentration ratio for the metal under consideration. in two equilibrated solution phases. The notation org is abbreviated to the organic phase and the notation aq is the aqueous phase when "is greater than".

The extractant may be considered useful for the purpose of this invention provided that technically feasible conditions are found for the extractant under consideration in which, as the pH of the cobalt / magnesium / nickel solution is raised, cobalt begins to extract more strongly than nickel, which is more strongly extracted than nickel. The cobalt-magnesium separation factor SCq, which refers to the ratio of the partition coefficients of cobalt to magnesium, should be at least 1.5 in order to avoid the extraction of most of the 63442 magnesium from the multi-stage technical countercurrent extraction of cobalt. A higher SCq Mg value would be more advantageous if the SCq Ni ~ value were correspondingly higher. For example, when the SCQ M 2 rises to 10, it would be advantageous if XT. nousi-

CO / N X

si to 100 or greater.

Useful extractants are, for example, di- (alkyl) -phosphoric acids, which have the general structural formula

R - O O

P or (1)

R - θ '' ^ OH

alkylphosphonic acid monoalkyl esters of the general formula R + O ^ p '/ \ R - O OH or (2) alkylphosphinic acid monoalkyl esters of the general formula

R O

Noh

In the disclosed compounds, the organic radicals R may be the same or different alkyl groups containing at least five carbon atoms so that the compounds are not significantly soluble in aqueous solutions. Corresponding alicyclic or aromatic compounds containing a cyclic hydrocarbon or aryl radical instead of one or both alkyl groups are useful under conditions in which dCq>>

Dn ^. It has not been considered appropriate to list dozens of examples of each group of compounds, including the corresponding alicyclic and aromatic compounds, but to state that the most preferred radical so far is 2-ethyl-1-hexyl, because its structurally available compounds have average or above-average extraction properties.

The spent extractant is diluted as an organic solvent to adjust the physical properties of the resulting extractant to 63442 5 to suit the operating temperature in question. Aliphatic, alicyclic, aromatic or chlorinated hydrocarbons can be used as diluents, which have a low viscosity so low as not to adversely slow the separation of the mixed solution phases after extraction contact and which have a flash point safely away from the operating temperature used. Hydrocarbons distilling between 190 and 250 ° C with a viscosity of the order of 1-2 cP at room temperature are suitable for this purpose. It is often also necessary to add 0.5 to 15% by volume of an emulsion-reducing agent. Such are the higher alcohols such as isodecanol or dodecanols and organic phosphates and phosphonates such as tri-n-butyl phosphate and tri-n-butyl phosphonate.

It is most preferred to separate cobalt from a cobalt / magnesium / nickel solution having a cobalt / magnesium weight ratio of 1-2. Even 1 g / l magnesium clearly improves cobalt / nickel separation, although it is generally preferable to use macpesium concentrations above 3 g / l. Thanks to magnesium, the cobalt / nickel ratio in the separated cobalt product easily rises tenfold compared to where it would rise when cobalt is separated from a similar solution with virtually no magnesium.

Cobalt / nickel ores and concentrates generally do not contain soluble magnesium to such an extent that their dissolution treatment directly results in a solution with a sufficient magnesium content for the separation of this invention. The magnesium level can advantageously be raised by using an appropriate amount of magnesium oxide as a neutralizing agent, either in the cobalt extraction or in one of the preceding process steps. Alternatively, the extractant to be partially cobalt-separated can be partially pre-converted to the magnesium salt form, with correspondingly less or no magnesium required in the cobalt / nickel solution of the process in question.

By performing the cobalt / nickel separation by the addition of magnesium according to the present invention, a cobalt product having a nickel content of less than 0.1% per cobalt can be easily separated. In the best case, the separation factor SCq Ni rises to 100-500, making it possible to reduce the nickel content of the cobalt product to less than 0.01%, if necessary. The cobalt / nickel separation does not require as close monitoring of the separation conditions as the cobalt / magnetic sieve, which is simultaneously targeted. The latter determines at which pH and at which solution volume flows this separation must be carried out. With a cobalt / magnesium weight ratio of 1-2, the nickel content of the solution has virtually no effect on cobalt extraction. When the cobalt / magnesium weight ratio of the cobalt product is between 50 and 100, the corresponding cobalt / nickel weight ratio generally rises between 5,000 and 30,000, according to the test results.

The most preferred type of liquid-liquid extractor is a mixer-settler, which, in addition to the appropriate solution / solution contact, provides good possibilities to control the separation of cobalt from magnesium and at the same time also from nickel. Using the pH adjustment procedure described in Finnish Patent Publication No. 49,185, which is based on the direct dosing of the neutralizing agent into the mixer based on the measurement pulses of the pH electrodes placed in the dispersion, these metal separations can be directed in the desired direction by selecting appropriate pH guide values for those mixer-settler cells. to which there is a need to add a neutralizing agent. Such direct pH control improves the controllability of the separation process in question, while in this way, in an advantageous manner, the extractant can be used in the acid form as it is after back-extraction with the acid solution. It is not necessary to convert the extractant to the sodium or ammonium salt form as required by the separation methods described above. According to the most preferred separation procedure, the pH of the aqueous solution is raised to between 4.5 and 5.5 in the last extraction cell, to which the extraction solution is introduced after back-extraction. As the anti-pH base, a suitable neutralizing chemical such as sodium hydroxide solution, sodium carbonate solution or slurry, ammonia water or gas, calcium hydroxide or magnesium oxide slurry can be used. With a similar one-way pH adjustment, the drop in pH below the set values is also prevented in the second to last extraction step and, if necessary, in the third to last extraction step. In other extraction steps where the pH drop is no longer strong, no pH adjustment is usually required.

The invention is described in more detail below by means of examples.

\ 63442

Example 1

A series of extraction experiments were performed using a di- (2-ethylhexyl) -phosphoric acid solution as the extractant, mixing this with cobalt and nickel or a solution containing cobalt, nickel and magnesium. In separate extraction experiments, the pH of the sulfate solutions was raised to between 3.5 and 5.5 at either room temperature or an elevated temperature of 55 ° C. The metal concentrations of the second sulphate solution were Co 11.0 g / l and Ni 10.5 g / l and the other Co 11.0 g / l, Ni 10.2 g / l and Mg 10.2 g / l. The composition of the extraction solution used was 20% by volume of di- (2-ethylhexyl) -phosphoric acid, 5.0% by volume of tri-n-butyl phosphate and 75% by volume of kerosene containing 20% by weight of aromatics. The mixing ratio vorg / Vag was 1.33 before raising the pH. A lye solution containing 120 g / l NaOH was used to raise the pH. The pH of this sulfate solution was raised stepwise using a stirring time of 10 minutes after each rise before the mixed dispersion was sampled for chemical analysis.

The results summarized in Table 1 show that the effect of magnesium addition on cobalt / nickel separation is strongly temperature dependent. At room temperature 20 ° C, the addition of magnesium corresponding to 10.2 g / l Mg raises the separation factor from 1.6 to 2.5 to 2.1 to 3.2, with a corresponding increase at 55 ° C from 5.9 to 8, 0 between 10-98. The corresponding increase in the separation factor SCq M ^ is in turn between 0.39-1.6 and 0.80-1.72. It is found that the addition of magnesium is particularly advantageous at elevated temperatures when raising the pH to between 5.0 and 5.5. This also improves the separation of cobalt from magnesium to the extent that most of the magnesium is not extracted in a multi-stage countercurrent separation of cobalt and nickel.

63442 8

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Example 2

The effect of magnesium on the separation of cobalt and nickel using 20% by volume of 2-ethylhexyl-phosphonic acid mono-2-ethylhexyl ester as the extraction solution - 5% by volume of tri-n-butyl phosphate - 75% by volume of aliphatic kerosene has been demonstrated by extraction of cobalt amounts of magnesium-containing nickel sulphate solutions. The metal contents of the sulphate solutions used in the extraction experiments were 10.0-10.3 g / l of cobalt, 9.5-9.8 g / l of nickel and 0-18.6 g / l of magnesium. The mixing ratio VQ / V was 1.33 when, in the experiments, the pH of the metal sulfate solution in question was gradually raised with an alkali solution containing 120 g / l of sodium hydroxide. After the pH reached the set point, stirring was continued for 10 minutes before a dispersion sample was taken for phase metal analysis and the pH was continued to the next set point. The experiments were performed at room temperature.

Looking at the results shown in Table 2, it is found that a relatively small addition of 4.5 g / l of magnesium is sufficient to increase the separation factor between 61-74.

CO / NX

105-190 in the pH range of 4.7-5.5 at which cobalt extraction is intensified, with a higher magnesium addition of 9.8 g / l raising this separation factor to 135-450. A rising coefficient of more than 100 between cobalt and nickel provides good opportunities for sharp cobalt extraction in a multi-stage technical countercurrent separation process. At the same time, a satisfactory difference between cobalt and magnesium is obtained, since the separation factor SCq surprisingly turned out to be clearly higher than when a di- (2-ethylhexyl) -phosphoric acid solution was used as the extraction solution. SCq Mg values of 7.6-9.9 allow the cobalt / magnesium weight ratio in the separated cobalt product to be increased relatively easily between 50-100.

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63442 11

Example 3

Continuous countercurrent extraction of cobalt was performed at room temperature from a nickel sulfate solution / in which magnesium was also dissolved. Mixer-settler cells were used as extraction contactors, of which five U1-U5 were in the extraction circuit, four in the P1-P4 wash circuit and two in the Tul and Tu2 back-extraction circuit. The extraction cell coupling used is shown in Table 3, which also shows the driving conditions and the corresponding separation results. The extraction solution was 20% by volume of 2-ethylhexyl-phosphonic acid mono-2-ethylhexyl ester - 5% by volume of tri-n-butyl phosphate - 75% by volume of kerosene, the former component in acid form being recycled directly from the back-extraction. The pH was maintained at the reference value 5.0 in step U5 and at the reference value 4.9 and 4.7 in steps U4 and U3, respectively, using the pH measurement pulses obtained from the respective mixer dispersions for the automatic addition of neutralizing agent. The neutralizing agent was a lye solution containing 200 g / l sodium hydroxide. The pH of the other steps was allowed to drop freely.

A back-extract solution neutralized to pH 4.0 with sodium hydroxide and analyzed by cobalt 81.0 g / l, nickel 0.002 g / l and magnesium 1.09 g / l was used as the washing solution. During the washing, the cobalt content of the solution decreased to 25.3 g / l, the nickel content increased to 0.43 g / l and the magnesium content to 27.4 g / l, the pH remaining almost unchanged.

The washing solution used was combined with the cobalt / magnesium / nickel solution fed to the extraction. Starting from a feed containing 7.0 g / l of cobalt, 4.46 g / l of nickel and 6.0 g / l of magnesium, a solution containing more than 100 g / l of cobalt with a cobalt / nickel ratio of 25,000 and a cobalt / magnesium ratio of 60 and a nickel solution containing 0.025 g / l of cobalt with a nickel / · cobalt ratio of 160. In this mode of operation, the dynamic viscosity of the extraction solution remained below 12 cP even in the wash.

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Example 4

In a series of extraction experiments with 20% by volume of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester -5% by volume of tri-n-butyl phosphate - 75% by volume of kerosene, the pH of the other metals more strongly extracted than cobalt was monitored: as a function of n are partitioned between the organic phase in question and the metal-containing aqueous solution brought into contact with it. The pH dependence of the resulting partition coefficient D for the metals in question is shown in Figure 1. It can be seen that the extraction or back-extraction equilibrium in the pH range 2.0-3.5 prevents most of the cobalt extraction or allows most of the cobalt to regress while the metals in question are significantly transferred to the extraction solution or, accordingly, remain in this phase. By using selective back-extraction, the purity of the cobalt product obtained can be increased. Based on the presented result, it is possible for a person skilled in the art to calculate which pH is preferably used in each case for the back-extraction of selective cobalt. At pH 2.5-3.0, for example, cobalt can be separated from calcium and metals that extract more strongly.

Claims (19)

A process for separating cobalt from magnesium and nickel by extraction by contacting the magnesium-containing aqueous solution containing cobalt and nickel with a solution containing an organic di- (alkyl) -phosphoric acid, alkylphosphonic acid monoalkyl ester or alkylphosphinic acid monoalkyl ester, characterized in that the extraction is carried out under conditions in which the cobalt distribution factor is at least 1.5 times greater than the magnesium distribution factor and at the same time eating at least 30 times greater than the nickel distribution factor, whereby the cobalt / magnesium ratio of the aqueous solution before extraction or during extraction is adjusted to 0; 2-2. Process according to claim 1, characterized in that di- (2-ethylhexyl) -phosphoric acid is used as an extractant at a temperature of 40-80 ° C. Process according to claim 1 or 2, characterized in that the temperature is 50-60 ° C. Process according to claim 2 or 3, characterized in that the di- (2-ethylhexyl) phosphoric acid is diluted in a hydrocarbon containing at least 20% by weight of aromatics. Process according to any of the preceding claims, characterized in that the organic solution contains 5-20% by volume of tri-n-butyl phosphate or tri-n-butyl phosphonate. Process according to any of the preceding claims, characterized in that the pH of the aqueous solution is 4.5-5.5. Process according to claim 1, characterized in that 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester is used as extractant. Process according to claim 1, characterized in that 2-ethylhexylphosphinic acid mono-2-ethylhexyl ester is used as extractant. 17 63442 Method according to claim 7 or 8, characterized in that the temperature is 20-80 ° C. Process according to claim 7, 8 or 9, characterized in that the extractant is diluted in an organic hydrocarbon. Process according to any of claims 7-10, characterized in that the organic solution contains 0-20% by volume of tri-n-butyl phosphate or tri-n-butyl phosphonate. Process according to any of claims 7-11, characterized in that the pH of the aqueous solution is 4.0-6.0. Process according to any of the preceding claims, characterized in that the magnesium content of the aqueous solution containing cobalt and nickel is increased in the leaching or solution purification which precedes the cobalt extraction by dissolving magnesium-containing raw materials and adding a soluble magnesium compound, respectively. Process according to claim 13, characterized in that the soluble magnesium compound is a magnesium oxide. Process according to any of the preceding claims, characterized in that the magnesium content of the aqueous solution containing cobalt and nickel is increased at the cobalt extraction. Method according to claim 15, characterized in that the extractant is used in acid form and the protons released in the cobalt extraction are neutralized with magnesium oxide. Process according to claim 15, characterized in that the extraction agent used in the cobalt extraction before the extraction was partially converted to magnesium salt form. 18. A process according to claim 13, characterized in that the extractant is used in acid form and for neutralization of protons released during the extraction, a base is added at least to the two or three last extraction steps. Process according to claim 18, characterized in that the base is sodium hydroxide or ammonia *