FI81385C - Method of supplementing the nickel content of a spent nickel sulf atelectrolyte - Google Patents

Description

1 81385

Method for replenishing the nickel content of the nickel sulphate electrolyte used

The invention relates to a process for replenishing the nickel content of a spent sulphate-5 electrolyte by contacting the spent sulphate electrolyte with "green" nickel oxide, a substantially metal-free refractory product obtained by roasting sulphide-containing nickel to a sulfur content of less than about 0.1% by weight.

The basic premise of the present invention is that in order to be practical, the nickel electrical recovery process must be performed in the most economical way possible using commercially viable technology. Consideration of these 15 basic starting points is necessary to understand the difficulties involved in the seemingly simple task of replenishing the nickel content in a nickel-depleted electrical recovery bath.

Figure 1 of the drawings is a schematic overview of 20 simple nickel replenishment circuits. Figure 2 is a schematic representation of the nickel replenishment step. Figure 3 schematically illustrates electrolyte purification.

Figure 1 shows 11 electrical recovery units from which spent electrolyte passes through tube 12 to nickel 25 refill unit 13. The charged electrolyte is then transferred by pump 14 through purification unit 15 and through pipe 16 back to electrical recovery unit 11. This invention relates to nickel replenishment unit 13. activities. The spent electrolyte 30 entering the 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 to minimize corrosion difficulties 35 and to allow the use of relatively inexpensive anodes such as lead or Pb / Ti 2 81385 anodes in the electrical recovery unit 11. The difficulty in unit 13 is therefore simply how to dissolve nickel in a dilute, buffered aqueous solution.

5 Someone may be inclined to say that the answer is easy. Nickel can be extracted from metallic nickel or sulfur-poor metal rock. If metallic nickel is used, the cost is high due to the reduction cost. If a sulfur-poor metal rock is used, the extraction of Nikke-10 Iin is incomplete, leaving a residue of nickel sulfide that must be returned at an additional cost. The electrolyte used can be contacted with nickel (2) hydroxide or nickel (2) carbonate or basic nickel carbonate. This response to leaching difficulty requires the availability of large amounts of nickel ions in aqueous solution, the precipitation of this nickel ion content by alkali metal hydroxide or carbonate, and the washing of this precipitate substantially free of alkali metal ions. This can be done in the lab, so there is no need to think about costs or difficulties. However, when applied to a plant scale, the reagent costs for carbonate or alkali are significant and sometimes the washing of the gel-precipitated solid is expensive and in addition there are handling difficulties.

25 A much cheaper way to produce an oxide-nickel product in large-scale production is to roast nickel stone. Benzoni et al. CA Patent No. 914,701 of 1961 discloses a method for fluidized bed roasting of granulated nickel stone as an oxide product. The table in the middle of column 5 of this patent shows that the sulfur content of nickel rock roasted in a fluidized bed on a commercial scale is inversely proportional to the roasting temperature, i.

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Roasting temperature, ° C Total slag,%, in the roasting product 900 2.0 1000 1.0 1050 0.5 5 1122 0.15

From the above approximate equivalence, it can be seen that in order to prepare a low sulfur oxide product by the method disclosed in the Benzon 10 patent and the conditions set forth therein, the refrigeration temperature must be above about 900 ° C and preferably above about 1000 ° C. If nickel rock is roasted at these temperatures, we call the resulting product "hard-to-melt" nickel (2) oxide. This product is sometimes known as "green" nickel oxide, but the actual color of the material may be green to black depending on the amount and type of impurities (usually cobalt, copper and iron). The refractory nickel oxide to which the present invention relates is substantially stoichiometrically correct NiO as opposed to a) "black" nickel oxide, which contains more oxygen than stoichiometric material, and b) nickel oxide, which contains a material such as Li 2 O to form trivalent nickel sites. NiO crystal structure. A description of the solubility of "black" and "green" nickel oxides formed by the calcination of 25 high purity, dense nickel carbonates in a boiling solution containing 60 g / l sulfuric acid and water is given in "Production of Nickel Oxide from Ammoniacal Process Streams", CIM Transactions, VXIII, 30 pages 44-53, 1970). The following table, obtained from this publication, which refers to a very pure, non-sulphide nickel product, clearly shows the difference between "black" and "green" nickel oxide.

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Effect of calcination temperature on acid solubility of nickel oxide

Calcination- Excess Color Dissolved nickel temperature oxygen content,% 5 ° C atomic% 315 4.3 very 100 black 425 1.9 black 100 10 540 0.50 greyish black 100 650 0.26 black gray 99.9 760 0.16 gray 99.4 870 0.08 greenish 91.3 15 gray 980 0.04 gray-green 70.0 1090 0.015 green 4.8

If nickel oxide is doped with lithium oxide, such a material is not suitable for the purposes of the present invention because it is expensive and its use would cause lithium to accumulate in the electrolytic electrolyte. The nickel oxide to which the present invention is directed is a material whose commercial value is considerably lower than that of a non-stoichiometric or alloyed material. Hardly digestible nickel oxide is not readily soluble in dilute aqueous sulfuric acid. A difficulty that has been observed and now resolved is the development of a replenishment method for nickel recovery in which electrolyte replenishment 30 is performed using "green", i. difficult-to-melt nickel oxide at a temperature below 100 ° C without significantly adding impurities to the electrical recovery system.

The object of the present invention was to develop a new, advantageous process for the use of nickel sulphate

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5 81 385 to supplement the nickel content of the trolyte.

The process according to the invention is characterized in that the sulphate electrolyte used is contacted with finely divided "green" nickel oxide when the sulphate electrolyte contains at least a small amount of material which effectively improves the solubility of "green" nickel oxide and belongs to the group of acidic and normal perdisulphate ions. and normal per-monosulfate ions, trivalent nickel, and ionic or molecular species obtained by oxidizing the spent sulfate electrolyte with ozone for a time sufficient to dissolve the "green" electrolyte nickel oxide and raise the pH of the resulting solution to at least about 3.

For the purposes of the present invention, it is important that virtually all of the free acid be neutralized in the leaching process, as any acid that is not neutralized must be neutralized prior to electrical recovery using a much more expensive neutralizing agent (e.g., nickel carbonate).

The nickel sulphate electrolyte replenishment circuit is schematically shown in Figure 1, as mentioned above, and the invention relates mainly to the replenishment unit 13. The electrolyte used in the normal operation of the nickel electron recovery method 25 exits the electrode recovery unit 11 at a pH of about 0.5 to 1.5. - 60 g / l of sulfuric acid not chemically bound to metallic substances. This spent electrolyte at a temperature of about 60 ° C is a liquid-30 feed to the replenishment unit 13. It is preferable to use "green" or "difficult-to-melt" nickel oxide prepared by roasting nickel stone as the solid feed. 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

Area Typical

Ni,% 65-79 75.5

Co,% 0-3 1.05 5 Cu,% 0-10 0.65

Fe,% 0-2 0.4 total sulfur,% 0.01 max. 0.015

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

Ni / 0> 1 10

An oxide pulp having the composition shown in Table I is preferably prepared by roasting and re-roasting nickel rock, i. a metal rock obtained in a metal stone separation process as disclosed in CA-15 Patent No. 542,861. Roasting is performed in a fluid bed roaster at a temperature of about 1160 ° C using air or slightly oxygen-enriched air as the fluidizing agent. The solid product from the roaster is then re-roasted in a fluidized bed reactor using 20 air or partially combustion air as the fluidizer at a temperature of about 1220 ° C. The product obtained from re-roasting is then ground, for example by means of wet milling, in a ball mill to a finely divided shape. Preferably, substantially all of the powder particles pass through a 44 μm screen-25 size. Care must be taken to separate metallic impurities that may be present as a result of grinding.

When replenishing the spent nickel sulfate electrolytic electrolyte using the "green" nickel oxide defined in Table I, it is preferable to add perdisulfate ions or acidic perdisulfate ions obtained from perdi sulfuric acid (H2S208) to the spent electrolyte. Perulfuric acid (sometimes referred to as "peroxydulphuric acid") can be prepared by electrolysis of a relatively concentrated aqueous sulfuric acid solution using a smooth platinum anode and below about 25 ° C.

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7 81385. An anode provided with cooling coils circulating cold water is preferred. A review of the preparation of this peroxyacid is described in "A Comprehensive Treatise on Inorganic and Theo-5 retical Chemistry" (J.W. Mellor, Longmans, Green and Co., 1930, Vol. 10, pp. 453-456) and other literature sources. It has also been found that perdisulphates can be prepared with smooth platinum anodes by electrolysing a nickel sulphate electrolyte, especially kept in the vicinity of the anode 10 at a temperature below about 40 ° C.

In the simplest embodiment of pererculphuric acid, for the extraction of green nickel oxide, i.e., supplementing the nickel sulphate electrolytic solutions used with at least about 0.1 g / l perulfuric acid is preferably carried out at a temperature of about 80 to 95 ° C, for example 80 ° C. Preferably, about 0.2-5 g / L perdulfuric acid is used to extract the "green" nickel oxide. Since the spent electrolyte leaves the electrical recovery cells at a temperature of about 60 ° C, it may be necessary to heat the electrolyte. The preferred extraction temperature is about 75 to 90 eC. Because dissolution is an exothermic event, only minor external heating is usually required to reach the extraction temperature. If the sulfur and metallic nickel contents of the "green" nickel oxide are assumed to be low, about 0.2 g / l perdi-30 sulfuric acid in the electrolyte used causes the nickel to dissolve from the oxide into the electrolyte used. A larger amount of perulfuric acid than the above can be used, with the advantage of accelerating the dissolution of "green" nickel oxide without significant disadvantages (except for 35 which is shown below).

8,81385 The preferred shape of the refill unit 13 is shown in Figure 2 of the drawings. As described therein, the tube 12 containing the spent electrolyte enters the refill unit 13 at two points. A portion of the tube 12 feeds to a first extraction tank 17 equipped with a stirrer 18, a sulfuric acid tube 19 and a return fan 20. A second portion of the tube 12 enters an oxide mixing tank 21. The oxide mixing tank is provided with a stirrer 22, a feed port 23 (through which solid oxide 10 is fed from the tank 24) and recirculation pipe 25. Recirculation pipe 25 is provided with a slurry pump 26 for recirculating sludge through pipe 25 and oxide mixing tank 21 and through branch pipe 27 to feed first extraction tank 17. Excess liquid and solids 15 from first extraction tank 17 are transferred to each extraction tank 29 by overflow means 28 the extraction tank 17 is provided with a stirrer 18A and a return ventilation unit 20A. The second extraction tank 29 uses means 30 for adding nickel carbonate 20 to adjust the pH as needed. The overflowing liquid and solids are transferred from the second extraction tank 29 via the overflow means 31 to a conical settling unit 32 provided with return ventilation means 20B. The alite from the cone settling unit 32 passes through the pipe 33 to the first extraction tank 17 under the action of the pump 34. The excess from the cone settling unit 32 passes through the pipe 35 to the tank 36 and then, forced by the pumps 37 and 40, through the pipe 38, if desired through the filter 39 to the storage tank 41.

Referring to Figure 2, those skilled in the art will recognize that variations and modifications to this dissolution / replenishment method are possible. Modifications that are particularly directed to the present invention alternatively or additionally include the addition of solid 35 "green" nickel oxide directly to the extraction tank.

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9 81385 17 or 29, placing one or more additional extraction tanks in series or in parallel, contacting the "green" nickel oxide with the spent electrolyte countercurrently, using pre-prepared nickel perdisulphate as extraction accelerator instead of perdic sulfuric acid and replacing it with alternative equipment mixers, settling In particular, in industrial use, the conical settler 32 may be replaced with a hydrocyclone or similar device to minimize residence time in solid / liquid separation and thus minimize the amount of unnecessary dispersion of perdisulfate ions that occurs in the solid / liquid separation event.

The purification procedure of the electron recovery method starts in 15 dissolution events. Substantially all of the iron in "green" nickel oxide is transferred to insoluble matter. Iron 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 formed in the electrical recovery unit 11. For example, if no 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 definite and advantageous 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 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, 35 cobalt remains largely in solution. After the solid / liquid ίο 813 8 5 separation in the cone settler 32, cobalt can be removed as a cobalt-rich nickel / cobalt hydroxide precipitate by raising the pH of the cone overflow to about 4 to 5. If possible, avoid too high a pH of 5, as copper precipitates the more with cobalt, the higher the pH 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 the solid cobalt-containing product is removed by means 58.

Alternatively, simultaneous dissolution of nickel from green nickel oxide and precipitation of trivalent cobalt (or perhaps not dissolving it) in the spent nickel sulfate electrolytic electrolyte can be used. If an additional amount of perdisulphate ions of the order of about 1.5 g / l perdic sulfuric acid is used in the leaching operation, the nickel tends to dissolve from the 20 "green" nickel oxides, but under certain conditions the cobalt contained therein does not tend to dissolve but precipitates as a trivalent cobalt. Such precipitation easily 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 excess persulfate ions are used in the process of the present invention 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 electrolyte storage electrolyte in the storage tank 41 is considered to contain copper, iron, lead, and minor amounts of other impurities.

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The particular electrical recovery carried out in the electrical recovery unit 11 can be performed in any suitable manner according to the general teachings of the prior art. These methods are disclosed in writings and patents, for example, U.S. Patent Nos. 1,577,422, 3,928,153; 4,087,338 and 4,210,653 and in The Winning of Nickel, Boldt-Queneau, Van Nostrans Company Inc., C 1967, pp. 369-374. We recommend electrical recovery using lead anodes at a temperature of about 60 ° C with a current density of about 200 A / m 2 of an electrolyte containing about 100 g / l of nickel, about 100 g / l of sodium sulfate and about 5 g / l of boric acid. Under these conditions, we have achieved approximately 97% power efficiency.

The method of the present invention has been particularly disclosed with respect to the use of perdisulfate to improve or more properly allow the dissolution of nickel from "green" (refractory) nickel oxide to replenish the spent nickel recovery electrolyte. Table II shows the amounts of material and the degree of extraction that have been found to allow the replenishment of spent nickel electrolyte from "green" nickel oxide in accordance with the present invention. Table IIA shows the comparison results obtained outside the scope of the present invention. The tests on which Table II is based have all been performed using real or synthetic spent nickel sulphate electrolyte containing about 50 g / l of free sulfuric acid in contact with 60 g / l of identical samples of "green" nickel oxides at 90 ° C.

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Table II

Material Concentration (g / l) Extraction rate, sulfuric acid neutralized in 2 hours (%) 5 perdisulphate 1 95 H2SO3 0,60 85

Ni *** 0.45 75 03 0.2 * 97

10 Table IIA

Material Concentration (g / l) Extraction rate, sulfuric acid neutralized in 2 hours (%) 5 15 02 saturated 15 ** H 2 O 2 0, 18 10 * cumulative concentration added in 2 hours **% oxide dissolved in 3 hours 20 Tables II and IIA show that the "green" Nikke oxide is substantially insoluble in aqueous sulfuric acid and that the selected reagents can substantially alter this property of the "green" nickel oxide in small amounts.

To demonstrate the effectiveness of perdic sulfuric acid by supplementing the electrolytic electrolyte with nickel sulfate using "green" nickel oxide, an experiment was performed in which roasted nickel rock was extracted countercurrently in two steps. The results of this experiment, together with the materials and experimental conditions, are shown in Table III.

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Table III

Roast: nickel sulphide rock fluid bed roasted at 1200 ° C

at temperature (%): 75.5 Ni, 1.05 Co, 0.65 Cu, 0.40 Fe,

0.015 S

5 ground: 5.5% 0 74 pm, 2.47% + 37 pm

Synthetic electrolyte used (g / 1: 60 Ni as NiSO4, 100 Na2SO4, 5 H3BO3, 50 H2SO4

First extraction step: 600 g of ground roast 15 L of second stage filtrate at 80 ° C 10 added 0.14 g / l S 2 O 6 =

Time Redox H2SO4 min mV (SCE) pH g / 10 +410 1.6 20.6 60 +530 1.75 12.7 15 120 +795 2.4 4.0 180 +760 2.95 0, 6 Residue = 357 g

Filtrate (g / l): 90 Ni, 0.42 Co, 0.24 Cu, 0.07 Fe 2 O 2 Extraction step: 357 g of the residue from the first extraction step 15 l of electrolyte used at 80 ° C Time added Redox H 2 SO 4 min S, 0a g / 1 mV (SCE) g / 1 0 0.07 +295 45.1 25 60 0.14 +405 45.1 120 0.21 +410 36.8 240 0.28 +415 27.0 360 0, 28 +460 20.6 Residue = 45 g (total weight loss 92.5%) 30

In the following example, a re-roasted and ground metal rock feed was used to continuously replenish the nickel sulfate electrolyte. Roast (calcined and re-roasted metal rock) with analysis of: 70% 35 Ni, 3% Cu, 1.05% Co and 0.38% Fe, 700 ppm Pb, 260 ppm 14 81 385

As, 10 ppm Zn, 6 ppm Se and 230 ppm total sulfur, were 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 compartment at 90 ° C together with 525 g / l of solids kept by means of a cone settler in a sub-cycle. The roast was added to about 39 g / L of spent electrolyte. About 2.4 g / l of S 2 O 8 ions 10 was added to the electrolyte used. In the cone settler placed in the pipe after 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% 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 filtration cake obtained in this precipitation contained on average about 35% solids.

The copper was removed from the replenishment electrolyte using precipitated 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 with a bed volume of 500 ml, 35 using an upward flow of 5 m / h and feeding 200

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15 81 385 ml / min of replenished nickel electrolyte with a residence time of 2.5 minutes. The first column was used approximately 500 minutes before breakthrough. The operation of the column involved a combination of gentle mixing and fluidization. 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 precipitated materials at high pH.

15 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 sulphite, whereby the re-dox potential was kept at +400 mv (SCE). Liquid 20 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 O 8 = ions. The final analysis of the residue was 18.6% iron, 23.3% nickel, 1.64% cobalt and 1.65 copper, corresponding to a total extraction of nickel, cobalt and copper of 99.4%, 97% and 99% respectively. .

Claims (3)

A method of supplementing the nickel content of a spent sulfate electrolyte by contacting the spent sulfate electrolyte with "green" nickel oxide, which is a substantially metal-free, non-molten product prepared by rusting sulfur-containing nickel to a sulfur content below about 0. , 1 wt.%, Characterized in that the spent sulfate electrolyte is burned in contact with finely divided "green" nickel oxide where the sulfate electrolyte contains at least a small amount of a material which effectively improves 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 the "green" nickel oxide electrolyte and raising the obtained the pH of the solution to at least a value of about 3. 20 2. A process according to claim 1, characterized in that the horse disulfate is used in an amount of at least about 0.1 g / l of electrolyte consumed. 3. A process according to claim 1, characterized in that sufficient horseradish sulfate is added to the spent electrolyte to improve the solubility of the "green" nickel oxide and to oxidize the cobalt present in the "green" nickel oxide, wherein the cobalt is obtained in the form of a trivalent oxide solid.