CA2481729C

CA2481729C - Method for refining aqueous nickel chloride solution

Info

Publication number: CA2481729C
Application number: CA2481729A
Authority: CA
Inventors: Isao Nishikawa; Kazuyuki Takaishi; Nobuhiro Matsumoto; Nobumasa Kemori
Original assignee: Sumitomo Metal Mining Co Ltd
Current assignee: Sumitomo Metal Mining Co Ltd
Priority date: 2003-09-17
Filing date: 2004-09-15
Publication date: 2012-03-27
Anticipated expiration: 2024-09-15
Also published as: GB2406565B; AU2004208659B2; AU2004208659A1; JP4124071B2; JP2005089808A; GB0419262D0; CA2481729A1; GB2406565A

Abstract

A method for refining an aqueous nickel chloride solution to efficiently remove an impurity element, in particular zinc, which can form a complex with chlorine from the solution by a simple system at a low cost. More concretely, method for refining an aqueous nickel chloride solution containing zinc and one or more other impurity elements which can form a complex with chlorine, comprising a first step for oxidation/neutralization of the solution adjusted beforehand under given conditions with respect to Ni concentration, oxidation-reduction potential and pH to remove the impurity elements, and a second step for ion-exchanging the solution refined by the first step with an anion-exchange resin to remove zinc by adsorption.

Description

SPECIFICATION
METHOD FOR REFINING AQUEOUS NICKEL CHLORIDE SOLUTION
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a method for refining an aqueous nickel chloride solution, more specifically a method for efficiently removing an impurity element, in particular zinc, which can form a complex with chlorine from the solution by a simple system at a low cost.

DESCRIPTION OF THE PRIOR ART
The common starting material for nickel refining has been nickel matte, which is concentrated nickel sulfide produced from a nickel ore by a smelting process. Recently, new nickel-containing materials have been used as starting materials for nickel refining, as various scraps and intermediates produced in refining processes have been extensively recycled, and hydrometallurgical processes, e.g., sulfuric acid leaching for treating a laterite ore containing nickel at a low content, have been commercialized.

A nickel matte as the common starting material contains zinc as an impurity element in trace quantities, as zinc can be removed by a smelting process. On the other hand, new nickel starting materials contain zinc normally at several hundreds ppm to several per cents by weight together with other impurity elements, e.g., copper, cobalt and iron, since they are produced by a wet separation process, e.g., neutralization or sulfidation, as precipitates settled in a solution.

A hydrometallurgical process treating a new nickel starting material containing zinc and other impurity elements needs an additional step for removing zinc, when it involves leaching a nickel starting material in the presence of chlorine gas, refining the resultant aqueous nickel chloride solution and electrolysis to produce electrodeposited nickel, because zinc contained in the starting material cannot be sufficiently removed by the conventional nickel refining process.

In other words, zinc can form a complex with chlorine, e.g., ZnC142-, in an aqueous nickel chloride solution. Zinc is removed in the form of sulfide in the presence of hydrogen sulfide gas blown as a sulfidation agent into an aqueous nickel salt solution. However, removal of zinc from an aqueous nickel chloride solution is less efficient than from an aqueous nickel sulfate solution, and is accompanied by massive coprecipitation of nickel when zinc is to be completely removed. Moreover, it involves another problem of increased investment cost for an aeration step needed to treat the mother liquor containing hydrogen sulfide.

Zinc forms the hydroxide at a lower pH level than nickel, and can be removed by neutralization selectively to some extent. However, massive coprecipitation of nickel is inevitable also in this case when zinc is to be removed very deeply, because the solution should be kept at a pH level above 6. Therefore, neutralization is not a desirable process.
Zinc may be separated by solvent extraction. However, it is also not a desirable process, because it needs a large-size system and hence high investment cost.

As discussed above, the conventional techniques for removing zinc involve the problems resulting from a high investment cost required or greatly deteriorated nickel production yield.

Some methods which use an ion-exchange resin have been proposed to solve these problems. For example, JP-A-2001-20021 (pages 1 and 2) discloses a method in which an aqueous cobalt chloride solution is passed over an anion-exchange resin to remove metallic ions capable of forming a chloride complex, e.g., cobalt, zinc and iron ions, by adsorption while allowing nickel and the like to flow out.
Another method removes cobalt from an aqueous nickel chloride solution by oxidation/neutralization and then brings the treated solution into contact with an anion-exchange resin to remove zinc and chromium simultaneously by adsorption.
This method can deeply remove zinc from an aqueous nickel chloride solution.
However, it may involve problems of shortened service life of the anion-exchange resin and hence increased treatment cost, depending on type and concentration of an impurity element which can form a complex with chlorine, when it is present in the solution.

Under these circumstances, there have been demands for methods for efficiently removing an impurity element, in particular zinc, which can form a complex with chlorine from an aqueous nickel chloride solution by a simple system at a low cost.

SUMMARY OF THE INVENTION

The present invention provides a method for efficiently removing an impurity element, in particular zinc, which can form a complex with chlorine from an aqueous nickel chloride solution by a simple system at a low cost, in consideration of the problems involved in the background art.

The inventors of the present invention have found, after having extensively studied a method for refining an aqueous nickel chloride solution containing zinc and one or more other impurity elements which can form a complex with chlorine to achieve the above object, that impurity elements, in particular zinc, which can form a complex with chlorine can be efficiently removed by treating the solution adjusted under specific conditions in two steps, oxidation/neutralization and ion-exchange with an anion-exchange resin, achieving the present invention.

The present invention provides a method for refining an aqueous nickel chloride solution containing zinc and one or more other impurity elements which can form a complex with chlorine, comprising:

a first step for oxidation/neutralization of the solution under given conditions with respect to a Ni concentration, an oxidation-reduction potential and a pH to remove the other impurity elements, and a second step for ion-exchanging the solution refined by the first step with an anion-exchange resin to remove zinc by adsorption.

Preferably, the first step is conducted at a Ni concentration of 90 to 130 g/L, an oxidation-reduction potential of 600 to 1200 mV (determined using a silver/silver chloride reference electrode) and a pH of 4.0 to 6Ø

Preferably, the process comprises an additional step for treating the solution refined by the first step with active carbon prior to the second step.

The method of the present invention for refining an aqueous nickel chloride solution can efficiently remove an impurity element, in particular zinc, which can form a complex with chlorine from the solution by a simple system at a low cost, and is of very high industrial value.

In one aspect, the invention relates to a method for refining an aqueous nickel chloride solution containing, as impurities, zinc and at least one other element selected from the group consisting of copper, cobalt and iron all in their chloride form, the solution having a concentration of the other element of 0.01 g/L or more and an Ni concentration of 90 to 130 g/L, which method comprises: (1) a first step comprising: (a) an oxidation of the aqueous nickel chloride solution by blowing chlorine gas into the solution so that the aqueous nickel solution has an oxidation-reduction potential of 600 to 1200 mV as determined by using a silver/silver chloride reference electrode, and (b) a neutralization of the aqueous nickel chloride solution oxidized as defined above, to a pH of 4.0 to 6.0 to precipitate only the other impurity element in a hydroxide form, followed by a separation of the other impurity element so precipitated, thereby reducing the concentration of the other impurity element to 0.01 g/L or less while maintaining a concentration of zinc unchanged, wherein nickel hydroxide, basic nickel carbonate or nickel carbonate is used to neutralize the aqueous nickel chloride solution; and (2) a second step for ion-exchanging the solution refined by the first step, with an anion-exchange resin at a pH of 4.0 to 6.0 and at an adsorption temperature of 30 to 70 C, to remove zinc by adsorption.

DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention for refining an aqueous nickel chloride solution is described in more detail.
The method of the present invention for refining an aqueous nickel chloride solution is for refining an aqueous nickel chloride solution containing zinc and one or more other impurity elements which can form a complex with chlorine, comprising a first step for oxidation/neutralization of the solution adjusted beforehand under given conditions with respect to Ni concentration, oxidation-reduction potential and pH to remove the impurity elements, and second step for ion-exchanging the solution refined by the first step with an anion-exchange resin to remove zinc by adsorption.

It is of essential significance for the present invention to remove by oxidation/neutralization an impurity element, other than zinc, which can form a complex with chlorine from an aqueous nickel chloride solution as a starting material adjusted beforehand under given conditions with respect to Ni concentration, =oxidation-reduction potential and pH in the first step, prior to the second step which removes zinc by ion-exchange with an anion-exchange resin. This can greatly improve service life of the anion-exchange resin for the second step, and efficiently remove zinc. In other words, an impurity element, other than zinc, which can form a complex with chlorine is adsorbed on the anion-exchange resin during the ion-exchange step together with zinc to cause. a breakthrough point in a shorter time, when it is present in the solution. Removal of such an element prior to the second step prevents the above problem.

5a The technical backgrounds of breakthrough point at an ion-exchange resin are described in detail. Two types of test solutions were prepared using a base solution containing Ni at 120g/L, and cobalt, copper, iron and zinc each at 0.001g/L or less; one was the base solution adjusted to contain zinc at 0.005g/L, and cobalt, copper and iron each at 0.001g/L or less, and the other was the base solution adjusted to contain zinc at 0.005g/L, and cobalt and iron each at 0.5g/L, to follow removal of zinc from these test solutions by ion-exchange with an anion-exchange resin. Zinc chloride, cobalt chloride and ferric chloride, all of reagent grade, were used for these solutions to adjust the zinc, cobalt and iron concentrations.

Each of these test solutions (250mL each) was separately put in a glass beaker, incorporated with 15mL of an anion-exchange resin (Amberlite IRA400, supplied by Organo Corp.) and stirred by a stirrer at 50 C, to analyze zinc concentration of the final solution. It was found that zinc was removed to 0.0001g/L or less with the solution of lower cobalt and iron concentrations, and only to 0.001g/L with the solution of higher cobalt and iron concentrations. In order to keep zinc concentration at l0ppm or less in electrodeposited nickel produced by electrolysis, it is necessary to decrease zinc concentration at 0.0001g/L or less in the aqueous nickel chloride solution to be treated by the electrolysis. In other words, it is essential to remove an impurity element, other than zinc, which can form a complex with chlorine prior to ion-exchange with anion-exchange resin.

(1) Aqueous nickel chloride solution The aqueous nickel chloride solution for the present invention is not limited, and an aqueous nickel chloride solution containing zinc and one or more other impurity elements is used. Of aqueous nickel chloride solutions useful for the present invention, one of the preferable ones is an aqueous *Trade-mark nickel chloride solution produced by a hydrometallurgical process which treats a nickel starting material by leaching with chlorine gas, refining the resultant aqueous nickel chloride solution and electrolysis to produce electrodeposited nickel. The aqueous solution produced contains impurity elements, e.g., zinc, cobalt, copper, iron and a noble :metal, which can form a complex with chlorine.

(2) First step The first step for the present invention treats an aqueous nickel chloride solution by oxidation/neutralization, after it is adjusted under given conditions with respect to Ni concentration, oxidation-reduction potential and pH to remove impurity elements in the form of hydroxides.
Ni concentration of the aqueous nickel chloride solution for the first step is not limited. However, it is preferably 90 to 130g/L, more preferably 100 to 120g1L. An aqueous nickel chloride solution produced by leaching a nickel starting material with chlorine gas normally contains nickel at around 170g/L. It is treated by oxidation/neutralization after being diluted to a chlorine ion concentration at which chlorine complexes of impurity elements, e.g., cobalt, copper and iron, become unstable.

This is to utilize difference among the impurity elements in stability while they form a chlorine complex in an aqueous nickel chloride solution.
Decreasing chlorine ion concentration makes cobalt, copper and iron complexes with chlorine less stable and more easily removed by the oxidation/neutralization. It should be noted, however, that increasing extent of dilution increases the diluent quantity and hence system capacity.
Therefore, the Ni concentration is set at 90g/L, which corresponds to the minimum chlorine concentration at which zinc can form a complex with the chlorine ion, or more. At above 130gIL, on the other hand, cobalt, copper and iron concentrations cannot be removed to a level, e.g., 0.01 g/L
or less, at which the adverse effects of retarding zinc adsorption in the second step can be controlled to a minimum acceptable level. It is preferable to recycle the spent solution discharged from the electrolysis step as the diluent for the aqueous nickel chloride solution.
Oxidation-reduction potential of the aqueous nickel chloride solution for the first step is not limited.
It is however preferably 600 to 1200 mV (determined using a silver/silver chloride reference electrode), more preferably 1000 to 1200 mV. At below 600 mV, the oxidation proceeds insufficiently to satisfactorily remove cobalt, copper and iron. At above 1200 mV, on the other hand, oxidation of nickel is accelerated to increase coprecipitated Ni quantity. The oxidant for the first step is not limited.
One of the preferable ones is chlorine gas, which causes little accumulation of the impurity elements.

In the first step, the pH level of the aqueous nickel chloride solution to be adjusted is not limited.

However, it is preferably 4.0 to 6.0, more preferably 4.0 to 5Ø The solution prior to the first step normally has a pH
lower than 4Ø At below 4.0, the neutralization proceeds insufficiently to satisfactorily remove cobalt, copper and iron. At above 6.0, on the other hand, neutralization of nickel is accelerated to increase coprecipitated Ni quantity. The pH adjusting agent for the first step is not limited, but an alkaline compound is normally used. The preferable alkaline compounds include alkaline nickel compounds such as nickel hydroxide, basic nickel carbonate and nickel carbonate, which cause little accumulation of the impurity elements.

Before the first step, the solution has a total concentration of the other impurities of higher than 0.01 g/L, often 0.1-2 g/L, and more typically 0.2-1 g/L, and a zinc concentration of 0.1-5 g/L, more typically 0.3-2 g/L.
In the first step, the aqueous nickel chloride solution adjusted above, is subjected to oxidation/neutralization, in a manner well. known in the art.
For example, a chlorine gas may be blown into the aqueous nickel chloride solution as an oxidant. Other known oxidants may be used instead. Then the solution may be neutralized by adding a pH adjusting agent, e.g., the alkali salt. By adjusting the pH for example to 4.0-6.0, preferably 4.2-4.8, the other impurities (e.g., copper, cobalt and iron) precipitate in their hydroxide form. The precipitate may be removed, for example, by filtration.
After the first step, the resulting solution has a total concentration of the other impurities of 0.01 g/L or less, preferably 0.002 g/L or less, while the concentration of zinc is virtually unchanged.

(3) Second step The second step for the present invention is for ion-exchanging the solution refined by the first step with an anion-exchange resin to remove zinc by adsorption. The aqueous nickel chloride solution is refined in the first step to remove the impurity elements, e.g., cobalt, copper and iron, to 0.01 g/L or less, in order to minimize their adverse effects of retarding adsorption of zinc in the second step. The resin which adsorbs zinc is cleaned with a hydrochloric acid solution, and then subjected to an elution procedure with water, after the aqueous nickel chloride solution deposited thereon is recovered.

In the second step, a pH level is not limited.
However, preferably it is set at 6.0 or less, at which neutralization of nickel tends to be controlled. In other words, the solution refined in the first step is directly used for the second step without the pH level being adjusted.

Adsorption temperature in the second step is not limited, but preferably 30 to 70 C.

The procedure for the second step is not limited.
It is however preferably carried out in a column packed with a commercial anion-exchange resin, because of its high efficiency resulting from the liquid being continuously passed over the resin at a given rate until the adsorption breakthrough occurs.

(4) Treatment with active carbon In the present invention, the aqueous nickel chloride solution may be treated with active carbon, as required, after being refined in the first step and before being charged to the second step. This removes dissolved chlorine or trace quantities of a noble metal by adsorption on active carbon, when present in the refined solution, and thereby more efficiently controls deterioration of zinc adsorption capacity in the second step, because dissolved chlorine and a noble metal have an adverse effect on zinc 9a adsorption capacity of the ion-exchange resin.

The procedure for the treatment with active carbon is not limited.
However, it is preferable to use commercial active carbon of wood, coal, coconut or the like packed in a column.
An aqueous nickel chloride solution containing impurity elements which can form a complex with chlorine, e.g., cobalt, copper, iron and zinc, can be refined by these steps to be suitable for electrolysis of nickel, substantially free of these impurity elements.

EXAMPLES
The present invention is described in more detail by EXAMPLES, which by no means limit the present invention. Metals were analyzed by atomic absorption spectrometry in EXAMPLES.

EXAMPLE I
An aqueous nickel chloride solution produced by leaching a nickel starting material with chlorine was treated by the following first and second steps for a hydrometallurgical process involving oxidation/neutralization and then electrolysis to produce electrodeposited nickel.
(1) First step First, the aqueous nickel chloride solution was diluted with the spent solution discharged from the electrolysis step to have a nickel concentration of 120g/L before it was treated by oxidation/neutralization. Then, it was incorporated with a given quantity of zinc chloride of reagent grade, to adjust the starting aqueous nickel chloride solution under given conditions, and treated by oxidation/neutralization under the following conditions.
The resulting precipitate was separated by filtration, and the filtrate as the refined solution was analyzed for its composition. The results are given in Table 1, which also shows composition of the starting aqueous nickel chloride solution.

[Oxidation/neutralization conditions]
(1) Oxidation condition: Oxidation-reduction potential was set at 1000mV
(determined using a silver/silver chloride reference electrode) with chlorine gas as an oxidant blown into the system.
(2) Neutralization condition: pH level was adjusted at 4.5 with nickel carbonate (Sumitomo Metal Mining) as a pH adjusting agent.

Table 1 Concentration (g/L) Ni Co Cu Fe Zn Starting aqueous nickel chloride 120 0.3 0.007 0.2 0.7 solution Solution refined in the first step 120 0.001 <0.001 <0.001 0.7 As shown in Table 1, cobalt, copper and iron were removed to 0.001g/L
or less, whereas zinc was not.

(2) Second step The solution refined in the first step, i.e., the aqueous nickel chloride solution oxidation/neutralization-treated, was incorporated with zinc chloride of reagent grade to prepare the starting adsorption solution. Its composition is given in Table 2.

Table 2 Concentration (g/L) Ni CO Cu Fe Zn Solution for the second step 115 0.002 0.0001 0.0003 0.003 The solution was passed through a column packed with 200mL of an anion-exchange resin (Amberlite IRA400, supplied by Organo Corp.). The adsorption conditions were liquid space velocity (]liquid volume/hour/resin volume): 5 and temperature: 50 C. The treated solution was analyzed for zinc concentration. The results are given in Table 3.

Table 3 Liquid rate (BV) 5 100 200 253 306 Zinc concentration (mg/L) <0.1 <0.1 <0.1 <0.1 <0.1 As shown in Table 3, the solution was highly purified to contain zinc at 0.lmg/L or less until it was passed over the anion-exchange resin to 306 multiples of bed volume (BV).

An aqueous nickel chloride solution produced by leaching a nickel starting material with chlorine was treated by the first and second steps for a hydrometallurgical process involving oxidation/neutralization and then electrolysis to produce electrodeposited nickel, where the effect of treating the solution with active carbon was verified.

The solution refined in the first step was passed over active carbon.
Each of the solutions, one treated with active carbon and the other not, was *Trade-mark incorporated with zinc chloride of reagent grade at 0.003g/L as zinc.
Each of these solutions was passed through a column packed with 200mL of an anion-exchange resin (Amberlite IRA400, supplied by Organo Corp.) at a space velocity of 2 (SV2) to about 300 multiples of BV. Next, the resin was washed with water at a space velocity of 2 (SV2) to 5 multiples of BV to elute out the adsorbed zinc. The adsorption/elution cycles were repeated 50 times.

For the solution not treated with the active carbon, the adsorption-treated liquid volume until zinc was detected at 0.0001g/L or more (hereinafter referred to as breakthrough BV) decreased gradually, to about 70% of the initial level at the 50 cycles.

For the solution treated with the active carbon, on the other hand, the anion-exchange resin exhibited the adsorption performance substantially unchanged throughout 50 cycles, with decreased breakthrough BV not confirmed. Therefore, treatment with active carbon controls decrease in breakthrough BV in the adsorption/elution cycles in the ion-exchange step, decreasing elution frequency, and hence both waste liquid treatment cost and waste liquid treatment investment cost.

The method of the present invention is useful for refining an aqueous nickel chloride solution for the nickel refining area, in particular suitable for refining an aqueous nickel chloride solution containing at a high content an impurity element which can form a complex with chlorine.

*Trade-mark

Claims

CLAIMS:

1. A method for refining an aqueous nickel chloride solution containing, as impurities, zinc and at least one other element selected from the group consisting of copper, cobalt and iron all in their chloride form, the solution having a concentration of the other element of 0.01 g/L or more and an Ni concentration of 90 to 130 g/L, which method comprises:

(1) a first step comprising:

(a) an oxidation of the aqueous nickel chloride solution by blowing chlorine gas into the solution so that the aqueous nickel solution has an oxidation-reduction potential of 600 to 1200 mV as determined by using a silver/silver chloride reference electrode, and (b) a neutralization of the aqueous nickel chloride solution oxidized as defined above, to a pH of 4.0 to 6.0 to precipitate only the other impurity element in a hydroxide form, followed by a separation of the other impurity element so precipitated, thereby reducing the concentration of the other impurity element to 0.01 g/L or less while maintaining a concentration of zinc unchanged, wherein nickel hydroxide, basic nickel carbonate or nickel carbonate is used to neutralize the aqueous nickel chloride solution; and (2) a second step for ion-exchanging the solution refined by the first step, with an anion-exchange resin at a pH of 4.0 to 6.0 and at an adsorption temperature of 30 to 70°C, to remove zinc by adsorption.

2. The method according to claim 1, which further comprises:

an additional step for treating the solution refined by the first step with active carbon, prior to the second step.