FI59124B - ELEKTROLYTISK PROCESS FOER ELEKTROLYTISK UTFAELLNING AV METALLER - Google Patents

Description

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Patent mcddelat ^ T ^ (51) Kv.lk?/lnt.CI.3 C 25 C 7/00 SUOMI — FINLAND (21) PaMnttlhakwnu · - PatmtaraMwing 752059 (22) HaltamlapUv * - Anabknlngtdag l6.0T. 75 (23) AlkupUvl — Glltighatadag l6.07.75 (41) Tullut Julkisukal - Wivlt effamllg 17 * 01.76 «l- i. NkltvitallKu _ θΊ

Patent · och r «glitantyralMn '' Aitatta» utlagd och utMkrlfMn puMtc * r »« J 27 * 02. Ö1 (32) (33) 01) hrydttty utuelkaut — Buglrd prlorltut 16.07-71 *

England-England (GB) 3152U / 7U Proven— Styrkt (71) Parel Societe Anonyme, lU Rue Aldringen, Luxembourg, Luxembourg (LU) (72) Roger Griffiths, Southsea, Hampshire, England-England (GB),

This invention relates to an electrochemical process for the electrolytic deposition of a metal, such as cobalt or nickel, in an electrochemical process an electrolyte containing a solution of said metal salt through a layer of electrically conductive particles in the cathode space of the cathode-forming and two-part electrochemical cell, and in which method the acidic solution is circulated through the anode space of the cell and a potential difference is maintained between the electrode and the anode.

The majority of electrolytically produced cobalt is currently produced in Zaire and Zambia from copper and cobalt alloy sulphide ores or oxide ores. In the case of sulphide ores, it is standard practice to roast the ore sulphatically before extraction, whereas oxide ores can be extracted directly into an acidic solution.

59124

The extraction solution containing copper, cobalt and sulphate ions is then separated from the leachate by conventional liquid / liquid separation methods. The extraction residue is washed before being discarded. After the extraction solution has clarified, the copper is removed from the extraction solution electrolytically. The extraction solution can be subjected to "partial iron precipitation and washing" before clarification and electrolytic recovery of copper. When there is an acid deficiency in the extraction solution, e.g. when extracting oxide ores, part of the spent electrolyte of the copper electrolytic recovery step can be returned to the extraction liquid. The remainder of the spent electrolyte (containing cobalt but only a small amount of copper) is then purified to remove impurities such as iron, copper, and in some cases zinc, before the cobalt. precipitated or crystallized completely from solution. The solid cobalt thus formed is separated from the remainder of the solution, which is called waste liquid. In one method, the solid cobalt is then washed and redissolved in the spent electrolyte obtained from the subsequent electrolytic recovery of cobalt. The cobalt-rich solution obtained from this cobalt redissolution step is then passed, usually after clarification, to the cobalt electrolytic recovery step, where the cobalt is electrolytically precipitated. In some cases, the treatment involves additional purification steps before the cobalt mass is only partially dissolved in the solid cobalt in the redissolution step, and the resulting slurry containing dissolved cobalt and insoluble solid cobalt is electrolyzed in air-stirred cells. This is done so that the acid formed during the electrolysis is consumed by the insoluble solid cobalt in the slurry. When electrolytically doping cobalt, the temperature of the electrolyte has a significant effect on the electrolytic nature of the cobalt. l i n, especially the cathode ipotent and the internal stresses of the deposited cobalt as well as the hydrogen content. The electrolytic recovery step of cobalt is usually carried out by maintaining the electrolyte temperature at about 60 ° C.

In conventional electrolytic cobalt recovery, cobalt is generally deposited on "smooth" cathodes made of stainless steel. After the deposit has reached an acceptable strength, it is detached from these smooth cathodes. Removing this deposit from the smooth cathode can be difficult because the cobalt metal in some cases adheres firmly to the smooth stainless steel. Removal of cobalt from the 3 59124 stainless steel cathode is usually performed by hand using hammers and chisels. In this procedure, the cathodes themselves are often damaged, and the possible replacement of such cathodes as a result is expensive. The cobalt metal pieces removed from the cathodes are then reduced by crushing tu in other suitable ways, and then, before the cobalt metal is marketed, a vacuum treatment is usually performed to remove hydrogen remaining in the metal.

Because the electrolytically produced cobalt must be of acceptable purity, and if lead anodes are used, the lead content of the precipitated cobalt is often higher than acceptable, and therefore anodes made of cobalt-silicon-manganese alloy are usually used. Such anodes are expensive and susceptible to breakage due to their fragile structure. The cost of such alloy anodes is a substantial part of the total cost of conventional cobalt electrolytic recovery methods.

The mutual location of cobalt and hydrogen in the electrochemical series may lead to the simultaneous discharge of these elements. This is relevant e.g. because it may adversely affect the quality and physical properties of the electrolytically deposited metal. As is usually the case with other electrolytic recovery methods, it is desirable to achieve good current efficiency in the electrolytic production of cobalt as well as to produce cobalt with acceptable physical and chemical properties. Unfortunately, the conditions required in the methods described above for precipitating cobalt with good current efficiency do not promote the precipitation of cobalt into a layer with acceptable physical properties. When a conventional cell is used at a pH above 2.5 and at a temperature of about 60 ° C, the layer tends to have a high internal stress and the layer itself is often brittle. Indeed, the internal stresses are sometimes so high that the layer tends to peel off the "smooth" cathode and this can cause a short circuit between the cathode and the anode. In order to obtain a layer on the planar cathode with acceptable physical properties, the electrolysis should be performed at pH values below 2.0 at a temperature of about 60 ° C. In conventional cobalt electrolytic recovery, the acid concentration of the cell electrolyte is as high as 15 g / l sulfuric acid, and the current efficiency may be only about 80%. In addition, as the acidity of the electrolyte increases, the current efficiency decreases due to the evolution of hydrogen at the cathode, and therefore, in conventional methods, the acidity of the electrolyte is usually limited to 8-15 g / l of sulfuric acid. This in turn limits the amount of cobalt that can be precipitated per unit volume of cobalt catalyst. The depletion of cobalt per unit volume of catholyte is only about 7 g / l of a solution containing about 40 g / l of cobalt.

In practice, the maximum cathode current density in the electrolytic production of cobalt is limited by the diffusion rate of cobalt ions from the electrolyte to the cathode surface, and in the known methods described above the current density is practically limited to about 400 A / m, sometimes as low as 300 A / m.

Many of the disadvantages of the cobalt electrolysis methods described above are also found in the methods used in the electrolytic production of metals such as nickel and zinc.

The present method is characterized by (a) placing an anion exchanger film between the cathode space and the anode space of the electrochemical cell to prevent cations from passing from the anode space to the cathode space, and (b) adjusting and maintaining a potential difference an acidic solution having a pH sufficient to transport the anions into the anode space at a rate such that the pH of the cathode space solution can be adjusted and maintained at the desired value.

The anion exchange membrane may be any material that is permeable to anions but impermeable to cations. Anion exchange films manufactured by Asahi Glass Co Ltd in Japan, referred to as AMV anion exchange films, and anion exchange films manufactured by Ionac Chemical Co., designated MA 3148 and MA 3475 anion, have been used as films having satisfactory results in the process and electrolysis cell of the present invention.

5,591 24

The particulate cathode may be of the type described, for example, in British Patent Specification 1 VI4 181, but is preferably of the type described in Belgian Patent Publication 818 453.

In particular, the present invention is used for the electrolytic production of cobalt from electrolytes containing sulfate ions or chloride ions or mixtures of these ions, and the present invention will be further described by describing the electrolytic production of cobalt from a cobalt sulfate electrolyte. To this end, the cathode and anode compartments of the electrochemical cell of the present invention were separated by an anion exchanger membrane, and separate catholyte and anolyte were passed through the respective cathode and anode compartments. During the electrolysis, cobalt was deposited on a cathode of the particulate electrode type described in e.g. Belgian Patent 818,453, and sulfate ions passed through the anion exchanger membrane into the anode compartment.

Since most of the sulfate ions generated in the cathode compartment by cobalt precipitation were removed from the cathode compartment through the anion exchanger membrane, much less acid remained in the cathode compartment, and it was therefore possible to produce more cobalt metal per unit volume

At any cobalt concentration of the catholyte, using a given current density, it has been found that the pH of the cathode compartment depends on the hydrogen ion concentration of the anode compartment. By selecting a certain hydrogen ion concentration in the anolyte and maintaining this concentration by removing the acid from the anolyte and replacing this acid with water, it is possible to perform the cathode reaction in the preferred pH range. As cobalt precipitates from the catholyte, its concentration in the catholyte decreases and in some cases the pH range acceptable for its precipitation can be maintained by keeping the acid concentration of the anolyte at the desired fixed value.

The fact that the anolyte is separated from the catholyte makes it possible to use alternative anode materials other than expensive Co-Si-Mn alloy anodes. Anodes of stable size, such as a platinum-coated titanium plate, are preferred, especially when operating at high current densities.

6 59124

When cobalt precipitates on the mainly spherical particles of the particulate cathode, the disadvantages associated with the stresses in the deposits or the fragility of the deposits are not significant. As a result, when a particulate electrode is used as the cathode, greater pH variations in the catholyte can be allowed. In the preparation of cobalt, the pH of the catholyte varies from 1.2 to 2.50. An additional advantage of using a particulate cathode is that a large cathode surface area is included in the small cell volume, and therefore high current densities relative to the active film surface area or cell volume can be used. Thus, it is possible to work with a current density of up to 10,000 A / m relative to the active film surface area, although the optimum current density is usually in the range of 1,500 to 5,000 A / m.

In addition, the size and shape of the product obtained from the particulate cathode do not require reduction, as the product is already of a size suitable for marketing.

To facilitate understanding of the invention and to illustrate its application, reference is made to the drawings, in which:

Figure 1 is a vertical section of an electrochemical cell according to the invention.

Figure 1 shows an electrolytic cell having a cathode compartment 30 from which an anode compartment 32 has been separated, and a separator 33, which is an AMV anion exchange membrane, manufactured by Asahi Glass Company, is arranged between them. The cathode compartment has a current feeder 34 and a layer 36 of copper particles as a particulate cathode of the type described in Belgian Patent 818 453. The anode compartment has an anode 38 formed by a titanium plate partially coated with platinum 39. The device also includes an anolyte feed 40, anolyte outlet line 42, catholyte supply line 44 and catholyte outlet line 46. The composition of the anolyte is controlled by anolyte outlet 48 and water supply 50. The operating power is obtained from the rectifier 52.

When the device is operating, the catholyte is passed through the cathode compartment of the cell and an anolyte of different composition is passed through the anode compartment. A potential difference is maintained between the electrodes of the cell and this allows metal to precipitate on the cathode and anions to pass through the anion permeable membrane.

7 59124 The electrolysis process of the present invention is illustrated by the following examples.

Example 1

Four experiments were performed with the cell of Figure 1 using a current of about 30 amps (corresponding to a current density of about 3,000 A / h with respect to the active surface of the film). 15 liters of catholyte were prepared from technical grade CoSO 4. 7 μl of crystals and the solution was acidified with ^ SO 2. 8 liters of anolyte (100 g / l h2so4) were prepared.

The two solutions were passed through the respective compartments of the cell while maintaining the potential difference between the electrodes. Electrolytic precipitation of cobalt on the cathode copper particles occurred with a particle size in the range of 420 to 1,400 μm.

During the experiment, the voltage was approximately constant at 4.5 volts while the pH of the catholyte was constant at 1.7 volts. The course of the four experiments is shown in the following Tables I to IV.

Table I

Time Temperatures. Power Cell- pH Co-pit ..

(min.) (° C) (a) voltage (g / l) 0 21 30 6.5 2.9 30, 0 30 28 30 5.8 2, 4 29, 5 60 40 30 5.8 2, 2 30, 0 97 43 30 5.7 2, 0 30.0 127 45 30 5.5 1.9 28.6 159 47 30 5.3 1.8 28.5 188 49 30 5.3 1.8 26 8 21 8 50 30 5, 2 1, 8 26, 0 248 52 30 5.2 1.8 25.5 278 52 30 5.2 1, 7 24.8 308 52 30 5, 2 1, 7 24.8 340 52 30 5.4 1.7 24.8 368 52 30 5.4 1, 8 24.5 β 59124

Experiment 2 Table II

---------, -Ί ---- f "..... '-----------------,

Time Temperatures. Power Cell pH Co-pit.

(min.) (° C) (a) voltage (g / l) 0 48 30 5.0 2.8 '. 40.9 30 50 30 5.0 2.4 38.9 60 51 30 4.9 2.5 38.0 90 51 30 5.1 2.1 37.9 135 51 30 5.0 2.0 36 9,180 52 30 5.0 · 2.0 35.0 210 52 30 5.0 1.7 35.1 240 52 30 5.2 1.8 35.1 300 52 30 5.2 1.7 34.8 . t 330 52 30 5.1 1.7 35.0 360 52 30 5.0 1.8 35.1 390 52 30 5.0 1.8 33.8

Table III

Experiment 3 ------ p-p - rt-- v Temperatures. * Power Cell-Co-pit.

'<ppm-) (° C) (A). voltage__Cg / I) _ O 60 30 4.6 6.5 39.6 45 65 30 4.7 2.6 38.4 90 62 30 4.7 1.9 38.4 135 63 30 4.6 1.7 37.7

192 64 30 4.6 1.7 36.4 I

237 65 30 4 ^ 6 1.7 35.3 282 65 30 4.6 1.7 34.7 348 65 30 4.6 1.7 34.0 9 59124

Koe M ·

Time Temperatures. Power Cell pH Co-pit.

(min.) (° C) (A) voltage (g / l) 0 65 30 4.5 4.0 41.1 45 65 30 4.5 2.6 40.0 90 65 30 4.5 2.3 38.8 1 35 65 30 4.4 2, 1 38.9 1 80 65 30 4.3 2, 0 37.9 225 64 30 4.5 1, 9 37, 0 273 64 30 4.5 1, 8 36, 1

Example 2

An experiment similar to that described in Example 1 was performed using a higher pH of the catholyte, namely pH 3. In this case, the composition of the anolyte was maintained at 30 g / l The cobalt content of the catholyte decreased from 50 to 35 g / l in 12 hours, indicating that the average current efficiency was about 80%. Up to 80% of the acid theoretically formed in the cathode compartment can be recovered from the anolyte.

Example 3

Four experiments were performed with the cell shown in Figure 1 using a current density of 4,000 A / m relative to the active surface area of the film. Anolyte and catholyte with different initial acid and cobalt contents were prepared and passed through the respective anode and cathode compartments. The experimental conditions and the results obtained are shown in Table V below.

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The following Example 4 describes the electrolytic recovery of nickel.

Example 4 2 Using again a current density of about 3,000 A / m, the nickel sulfate catholyte was treated for six days, reducing the nickel content from 80 g / l to 30 g / l. The composition of the anolyte was maintained at 30 g / l 2 SO 4 and as a result the pH of the catholyte was about 3. The current efficiency varied between 100%, at the beginning of the experiment, and about 80%, at the end of the experiment. The cell voltage varied considerably (7.5 V + 0.6 V).

Claims (2)

12,591 24 An electrochemical method for electrolytically precipitating a metal such as cobalt or nickel, the method comprising circulating an electrolyte containing a solution of said metal salt through a layer of electrically conductive particles in the cathode space of a cathode-forming and two-part electrochemical cell, and recycling the acid solution through the cell, a potential difference between the cathode and the anode of the electrochemical cell, characterized in that (a) an anion exchange membrane is placed between the cathode space and the anode space of the electrochemical cell to prevent cations from passing from the anode space to the cathode space; to form an acidic solution in the anode space with a pH sufficient to transport the anions to the anode space at a rate such that the pH of the cathode space solution can be adjusted. a to keep it at the desired value. Process according to Claim 1, characterized in that the density of the cathode current during the electrolysis is between 1,500 and 2,500 A / m with respect to the active surface area of the anion exchange membrane.