FI83672C - SAETT ATT AVLAEGSNA FOERORENINGAR UR ANVAEND SULFATELEKTROLYT. - Google Patents

Description

1 83672

The method of removing impurities from the sulphate electrolyte used

Separated from patent application 852546 5

The invention relates to a method for removing impurities from a spent sulphate electrolyte containing cobalt, copper and iron in a process in which the nickel content of the sulphate electrolyte used is supplemented by contacting the spent sulphate electrolyte with at least a small amount of the solubility of "green" nickel oxide.

The method according to the invention is characterized by what is stated in the characterizing part of claim 1. Figure 1 of the drawings is an overview of a simple nickel replenishment circuit.

Figure 2 is a schematic representation of the nickel replenishment step.

Figure 3 schematically illustrates electrolyte purification.

Figure 1 shows 11 electrical recovery units 25, from which the spent electrolyte passes through a pipe 12 to a nickel content replenishment unit 13. The replenished electrolyte is then transferred by a pump 14 through a cleaning unit 15 and back through a pipe 16 to an electrostatic recovery unit 11. The invention is based on nickel. the activities of the supplementary unit 13.

The spent electrolyte entering unit 13 generally has a pH of about 0.5 to 1.5 and a free acid content (assumed to be sulfuric acid) of about 25 to 60 grams per liter (g / l). The electrolyte is mainly a sulphate electrolyte and only a small amount of chloride ions is present in it to minimize the corrosive effect and to allow the use of relatively cheap anodes such as lead or Pb / Ti anodes in the electroconversion unit 11. Electrolyte recovery of the nickel electron recovery method from the electrical recovery unit 11 at a pH of about 0.5 to 1.5 and contains about 25 to 60 g / l of sulfuric acid which is not chemically bound to metallic substances. This spent electrolyte at a temperature of about 60 ° C is a liquid supply to the replenishment unit 13. As the solid supply 10, it is preferable to use "green" or refractory nickel oxide prepared by roasting a primary nickel melt. The general composition of this commercially available oxide is shown in Table I as a percentage by weight (unless otherwise stated).

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Table i__ Range Typical

Ni,% 65-79 75.5

Co,% 0-3 1.05

Cu,% 0-10 0.65 20 Fe,% 0-2 0.4 total sulfur,% 0.01 max. 0.015

Ni (soluble in Br2 / CH3OH),% 1 max. 0.1

Ni / 0> 1 25

The purification procedure applied in the electrocold recovery method of the present invention begins in a dissolution operation. Essentially all of the "green" nickel oxide iron is transferred to insoluble substances. Iron 30 as hydrated fine ferric hydroxide moieties, insoluble at pH 3 and above, is removed from the extraction circuit along with a small amount of cobalt. Further purification depends on the degree of purity required for the nickel metal 35 formed in the electrical recovery unit 11. For example, if not more than 2% of cobalt can be accepted in the nickel produced, then when using the typical green oxide defined in Table I, it is not necessary to remove the cobalt from the supplemented electrolyte. A particular and preferred feature of the present invention is the use of a sufficient amount of perdisulfate in the extraction tanks 17 and 29 not only to accelerate the extraction of "green" nickel oxide but also to convert all cobalt to an insoluble, trivalent, solid oxide form. By adding this amount of perdisulfate to the extraction tanks, the acidity of the accelerator and the accompanying sulfuric acid is used to dissolve the "green" nickel oxide. Provided that the pH in the extraction tank 29 is kept lower than about 3.5, most of the cobalt remains in solution. After the solid / liquid separation in the cone settler 32, the cobalt can be removed as a cobalt-rich nickel / cobalt hydroxide precipitate by raising the pH in the cone overflow to about 4-5. If possible, too high a pH value should be avoided, because the more copper is allowed to precipitate with cobalt, the higher the pH value is allowed to rise. This implementation of cobalt removal is shown schematically in Figure 2 by means of a branch line 35A, indicated by broken lines, through which the solution flows to the cobalt recovery unit 56, from which the cobalt-free solution exits through line 57 and solid cobalt-containing product 25 is removed through means 58.

Alternatively, simultaneous dissolution of nickel from green nickel oxide and precipitation (or perhaps non-dissolution) of trivalent cobalt in the spent electro-30 recovery electrolyte in nickel sulfate can be used. If an additional amount of perdisulphate ions of the order of about 1.5 g / l perdulfuric acid is used in the leaching operation, nickel tends to dissolve from the "green" nickel oxide, but under certain conditions the cobalt contained therein is not prone to dissolve but precipitates as trivalent cobalt. in the extraction solution. Such precipitation readily occurs in the extraction tank 29 if, either naturally or by the addition of nickel carbonate, the pH rises to greater than about 3.5. In the special case where an excess of persulfate ions is used and the pH is allowed to rise above about 3.5, the liquid in the storage tank 41 is partially or completely purified with respect to cobalt. As specifically shown in Figure 2, the replenished but impure nickel sulfate electrolytic uptake electrocyte storage tank 41 is considered to contain copper, iron, lead, and minor amounts of other impurities.

A relatively complete purification treatment is shown schematically in Figure 3. Referring to Figure 3 below, a supplemented but impure nickel sulfate electrolytic electrolyte from the storage tank 41 arrives at the copper precipitation unit 42 via line 43. Nickel metal is fed as a powder to the precipitation unit 42 by means 44. The nickel-contaminated copper precipitate 20 is removed from the precipitation unit 42 by means 45, and the replenished nickel sulfate electrolytic electrolyte from which the copper has now been removed passes through a pipe 46 to a copper purification unit 47, although not normally used when the copper is removed by precipitation. ions by means of 48 so that the residual copper co-precipitates with the other elements in the supplemented electrolyte, the solubility of which is very low. Copper sulfide, together with other such sulfides, is removed by means 49. The partially purified nickel sulfate electrolyte is then passed through line 50 to an oxidizing hydrolysis unit 51. In unit 51, the residual iron is oxidized to the trivalent state and hydrolyzed from solution as a hydroxy-type precipitate. The oxidation can be performed using air, oxygen, ozone, permonosulfate, perdisulfates, sulfur dioxide / air (or oxygen) mixtures, chlorine, or the like, as is well known in the art. If the electron recovery procedure is required to be performed without chlorides, the use of chlorine, hypochlorite, chlorates or the like in the oxidative hydrolysis process can, of course, be avoided. Barium carbonate, barium hydroxide or other soluble salts of barium are also added to unit 51 for co-precipitation of residual lead as the insoluble (Ba, Pb) -SO 4 salt. The product leaving the oxidizable hydrolysis unit 51 via the means 52 consists mainly of a ferric hydroxide precipitate and a barium / lead sulphate precipitate and passes to the electron recovery unit 11. Those skilled in the art will recognize that several changes can be made to the purification procedure schematically shown in Figure 3 of the drawings. oxidative hydrolysis of cobalt may follow the removal of copper using nickel black, ozone, perdisulphate, permonosulphate or similar substances as oxidants at pH values higher than 3,5 to precipitate trivalent cobalt and iron: nickel-rich metal rock may be used instead of nickel to precipitate copper, where the copper content of the impure electrolyte is low, copper can be removed by sulfide precipitation alone.

In the following example, the re-roasted and ground primary melt feed was used to continuously replenish the nickel sulfate electrolyte. Roast (roasted and re-roasted first melt) with analysis 30: 70% Ni, 3% Cu, 1.05% Co and 0.38% Fe, 700 ppm Pb, 260 ppm As, 10 ppm Zn, 6 ppm Se and 230 ppm total sulfur, was screened so that about 86% of the material was less than 25 μm in diameter and about 28% was less than 6 μm. Extraction of this calcine was carried out continuously using a residence time of one hour in one of 6,83672 compartments at 90 ° C together with 525 g / l of solids kept in a sub-cycle by means of a cone settler. The roast was added to about 39 g / L of spent electrolyte. About 2.4 g / l of S 2 O 8 = ions were added to the electrolyte used. In the cone settling device placed in the pipe behind the extraction tank, the upward flow velocity at the crossing was about 0.19 m / h. The average amount of the excess was 1.29 g / l solids and the alite contained an average of 49% 10 solids and the pH of the excess was about 3.0. The solids in the excess contained essentially all of the iron feed as well as most of the other insoluble impurities such as lead, arsenic, and silicon.

After settling of the supplemented electrolyte, cobalt was precipitated in four compartments at 90 ° C with a total residence time of about 5.3 hours. Alkaline nickel carbonate was added to 2.7 g / L in the first compartment to maintain a pH of 4.35 and sodium carbonate was added to 0.7 g / L in the second compartment to maintain a pH of 4.35 in this compartment. The cone supernatant contained about 370 mg / L of cobalt, which was reduced to about 30 mg / L in a four-compartment precipitator. The cobalt filter cake obtained in this precipitation contained on average about 35% solids.

Copper was removed from the supplemented electrolyte using impure nickel powder that had been mechanically ground to pass through a 250 μm sieve and about 50% remained on the 50 μm sieve. Precipitation was carried out continuously on a column containing a 500 ml bed volume, using an upward flow of 5 m / h and feeding 200 ml / min of supplemented nickel electrolyte with a residence time of 2.5 minutes. The first column was used approximately 500 minutes before the breakthrough. The operation of the column involved gentle mixing and

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7 83672 fluidization combination. Without agitation, channelization occurred in the nickel particle layer. The stirring intensity was adjusted so that without upward flow, the bed settled. The purified electrolyte leaving the copper precipitation unit contains on average about 0.4 ppm copper, less than 0.2 ppm selenium and has a pH of about 5.2 at 90 ° C.

The electrolyte was finally purified by oxidation to remove residual iron and co-precipitated materials at high pH.

The cobalt precipitate, which by analysis contained 42.6% nickel, 7.56% copper, 12.4% cobalt, 4.4% iron and 0.5% lead, was redissolved at 60 ° C using sulfuric acid and sodium sulfite to give the re-15 dox potential was kept at +400 mv (SCE). The liquid was analyzed to contain 17.6 g / l Co, 41.3 g / l Ni and 9.3 g / l Cu. The residue, which was analyzed to contain 11% iron and 37% nickel, was extracted for 6 hours with sulfuric acid at pH 3 and 90 ° C with the addition of 2.5 g / l S 2 g-10. The final analysis of the residue gave 18.6% iron, 23.3% nickel, 1.64% cobalt and 1.65% copper, corresponding to total changes of nickel, cobalt and copper of 99.4%, 97% and 99% respectively. . 1

Claims (8)

1. A method of removing contaminants from a spent sulfate electrolyte in a process in which the nickel content of a spent sulfate electrolyte is supplemented by contacting the spent sulfate electrolyte with atomized "green" nickel oxide, which is a substantially metal-free, hot-melt product. prepared by rusting sulfide-containing nickel to a sulfur content below about 0.1% by weight, characterized in that the spent sulfate electrolyte is contacted with the finely divided "green" nickel oxide since the sulfate electrolyte contains at least a small amount of a material which improves efficiently. the solubility of the "green" nickel oxide and belonging to the group of acidic and normal horse disulfate ions, acidic and normal permonosulfate ions, trivalent nickel and ionic and molecular species obtained by oxidizing the spent electrolyte with ozone, for a time sufficient to dissolve it. "green" electrolyte the loxide and raise the pH of the obtained solution to at least a value of about 3, and that after complete contact with the "green" nickel oxide, the pH is less than about 3.3 and then the pH is raised to a range of 4-5 to precipitate the trivalent cobalt. 25 2. A method according to claim 1, characterized in that, after removal of the cobalt, the supplemented electrolyte is treated to remove copper. 3. A method according to claim 2, characterized in that the copper is removed in the form of metallic copper by precipitation with metallic nickel. 4. A method according to claim 2, characterized in that the copper is removed in the form of a sulphide precipitate. Il 11 83672 5. A method according to claim 1, characterized in that the copper is removed by precipitation with a nickel-rich, sulfur-poor metal stone. 6. A method according to claim 1, characterized in that the copper is removed from the supplemented electrolyte prior to the precipitation of nickel, and that as a small amount of the material which improves the solubility of the "green" nickel oxide, at least about 0.1 g / l per-disulfate ions. 10 Process according to Claim 6, characterized in that, after the copper has been removed from the supplemented electrolyte, a material belonging to the group of nickel black, ozone, horse disulfate ions and permonosulfate ions is added to a pH 15 above 3.5 to precipitate. cobalt and iron. 8. A method according to claim 6, characterized in that the copper is removed by precipitating with a nickel-rich, sulfur-low metal stone.