CA2943483C - Copper removal method for aqueous nickel chloride solution - Google Patents

Abstract

Provided is a method for removing copper from an aqueous nickel chloride solution that includes separating and recovering cobalt and removing copper, zinc, and iron, from the aqueous nickel chloride solution containing cobalt, copper, zinc, and iron, by solvent extraction using, as an organic phase, an organic solvent containing a tertiary amine as an extractant and an aromatic hydrocarbon as a diluent, the method sequentially including: an extraction step (1), a stripping step (2), and a copper recovery step. In the copper recovery step, the organic phase is contacted with water or dilute hydrochloric acid having a pH of 1 or more to strip copper.

Description

COPPER REMOVAL METHOD FOR AQUEOUS NICKEL CHLORIDE SOLUTION
Technical Field [0001]
The present disclosure relates to a hydrometallurgical process of nickel and cobalt including separating and recovering cobalt from an aqueous nickel chloride solution containing cobalt by solvent extraction using an organic solvent formed by diluting a tertiary amine as an extractant with an aromatic hydrocarbon as a diluent.

[0002]
More specifically, the present disclosure relates to a method for removing copper from an aqueous nickel chloride solution in which an aqueous cobalt chloride solution having a low copper concentration is obtained as a stripped aqueous phase from an aqueous nickel chloride solution containing cobalt and having a high copper concentration by removing copper accumulated in an organic phase after stripping obtained by eliminating cobalt from an organic phase containing extracted cobalt to thereby reduce the copper concentration in an organic phase.
Background Art

[0003]
In smelting of nickel and cobalt, there has been produced nickel matte containing, as a main component, nickel sulfide such as Ni3S2 obtained by a so-called pyrometallurgical process, for example, nickel sulfide obtained by melting nickel sulfide ore in a blast furnace, nickel sulfide obtained by adding sulfur to nickel oxide ore and melting the mixture in an electric furnace, and the like.

[0004]
On the other hand, there has also been produced a mixed sulfide containing nickel and cobalt which contains a sulfide such as NiS as a main component (hereinafter, referred to as a mixed sulfide) obtained by subjecting nickel oxide ore having a low nickel grade to High Pressure Acid Leaching (HPAL for short) and removing impurities including iron from the HPAL solution, followed by wet sulfidation, for example, by blowing hydrogen sulfide gas into the leaching solution containing nickel ions and cobalt ions.

[0005]
Examples of practically used methods of refining nickel and cobalt using the above nickel matte and mixed sulfide as a raw material include a method of leaching the nickel matte and mixed sulfide with chlorine gas and subjecting the leached nickel ions and cobalt ions to electrowinning to be produced as electric nickel and electric cobalt, as described in Patent Literature I.

[0006]
In the method described above, the mixed sulfide is repulped in a chloride aqueous solution, and then chlorine gas is blown into the resulting slurry to thereby chlorine-leach nickel and cobalt into the chloride aqueous solution.
A ground nickel matte is brought into contact with the resulting chlorine leaching solution containing divalent copper-chloro complex ions as an oxidizing agent to perform displacement reaction between copper and nickel to thereby displace/leach nickel from the nickel matte into the solution.

[0007]
Subsequently, impurities such as iron, lead, copper, and zinc are removed from the resulting leachate after displacement leaching; cobalt in the leachate after displacement leaching is separated by a method such as solvent extraction; and then nickel is subjected to electrowinning to produce electric nickel.
Cobalt separated here is subjected to further removal of impurities in a processing route different from nickel and then subjected to electrowinning to be produced as electric cobalt.

[0008]
This method is simple and has achieved efficient and economical production; for example, chlorine gas generated in electrowinning is reused in leaching.
Further, in the technique of Patent Literature 1, copper contained in a very small amount in the raw material such as the nickel matte and mixed sulfide is an impurity for refining nickel and cobalt, but it is utilized as an oxidizing agent in the chlorine leaching step and the displacement leaching step and circulated between the chlorine leaching step and the displacement leaching step.

[0009]
In the displacement leaching step, nickel in the nickel matte is displaced/leached into the solution by performing displacement reaction between a divalent copper-chloro complex ion and Ni3S2 and Ni (metallic nickel) in the nickel matte; on the other hand, the copper-chloro complex ion becomes a solid in the form of Cu2S or Cu (metallic copper).

[0010]
That is, in the displacement leaching step, the removal of copper from a chlorine leaching solution is also performed at the same time, and the copper concentration in the leachate after displacement leaching will be 0.02 g/L or less. The copper carried in from the raw material is gradually accumulated in the chlorine leaching step and the displacement leaching step while it is circulated between the chlorine leaching step and the displacement leaching step. Therefore, in order to maintain the copper concentration in the chlorine leaching solution at an appropriate level in the range of 10 to 60 g/L, the copper balance is maintained by taking copper out of the system as copper powder, for example, by subjecting the chlorine leaching solution to copper removal electrolysis.

I

[0011]
Incidentally, in the hydrometallurgical process of nickel, the separation of nickel and cobalt which are contained in an acidic aqueous solution is the most important technical element.
For example, there has also been performed a method of adding chlorine gas as an oxidizing agent and a nickel carbonate slurry as a neutralizing agent to a nickel aqueous solution containing cobalt to separate cobalt as a trivalent hydroxide. However, in order to completely remove cobalt in the aqueous solution as a solid, nickel in an amount of about 3 times the weight of cobalt has also produced a trivalent hydroxide. Thus, since the separability of nickel and cobalt is poor, the above method cannot be said to be an efficient and economical method.

[0012]
So, a solvent extraction method with various organic extractants is mainly used at present for the separation of nickel and cobalt contained in an acidic aqueous solution.
In the solvent extraction method for separating nickel and cobalt, an acidic phosphate extractant such as D2EHPA (Di-(2-ethylhexyl)phosphoric acid) and an amine extractant such as TNOA (Tri-n-octylamine) are used as an organic extractant.

[0013]
Both the acidic phosphate extractant and the amine extractant which are used have excellent separation performance of nickel and cobalt. However, generally, the acidic phosphate extractant is used when an anion is a sulfate ion, and the amine extractant is used when an anion is a chloride ion.

[0014]
When a chloride ion concentration in a chloride aqueous solution of 200 g/L or more which is the chloride aqueous solution has a sufficiently high chloride ion concentration, cobalt forms a chloro complex ion, but nickel does not form a chloro complex ion. Therefore, the amine extractant has a higher separation factor of cobalt and nickel than the acidic phosphate extractant.

[0015]
Further, in the case of the acidic phosphate extractant, the cost of a neutralizing agent is required because protons are released from the extractant by the extraction of metal ions, and also a clad is often produced by the variation of pH.
The clad is a solid such as a metal hydroxide. Since the clad is stagnated and accumulated intermediate between an organic phase and an aqueous phase in an oil separator, it greatly inhibits the separation of oil and water which is an important technical element of solvent extraction.

[0016]
A method for separating cobalt with an amine extractant from an aqueous nickel chloride solution containing cobalt and other impurity elements is based on a technique as will be described below in a solvent extraction step comprising an extraction stage, a washing stage, and a stripping stage.

[0017]
As the extractant, it is more preferred to use a tertiary amine (R3N) than to use a primary amine (RNH2) or a secondary amine (R2NH) (wherein R represents an optional saturated or unsaturated hydrocarbon group).
The reason is that a tertiary amine is more polar, is highly reactive, and has a lower solubility in water.
When the tertiary amine is activated by adding hydrochloric acid thereto, it holds the extraction capability of metal-chloro complex ions and also has excellent separation characteristics of nickel and cobalt.

[0018]
In the above extraction stage, a metal species which forms a chloro complex ion, such as Co, Cu, Zn, and Fe, is extracted into an organic phase to produce an amine carrying a chloro complex ion of a metal element. Note that since nickel does not form a chloro complex ion, it remains in the extraction residual solution and is separated.
Therefore, when an aqueous nickel chloride solution contains a chloro complex ion of a metal which more easily forms a chloro complex ion than cobalt, that is, has a higher stability of a chloro complex ion than cobalt, for example, a chloro complex ion of copper, zinc, or iron, such a metal will also be extracted.

[0019]
A washing stage is optionally provided. In the washing stage, when a large number of entrainment in an organic phase after extraction, that is, impurities contained in fine waterdrops suspended in the organic phase, are present, the impurities are removed by dilution and removal treatment with washing water.

[0020]
Next, in the stripping stage, cobalt can be eliminated and transferred into an aqueous phase by bringing the washed organic phase, that is, the amine carrying the chloro complex ion of cobalt, into contact with a weakly acidic aqueous solution.
Here, the organic phase from which cobalt has been stripped, that is, the regenerated extractant, is returned again to the extraction stage and cyclically used. Thus, extraction, washing, and stripping will be repeated.

[0021]
However a metal which is more easily carried by amine as a chloro complex ion than cobalt, such as copper, zinc, and iron, is hardly eliminated under relatively weak stripping conditions for eliminating cobalt. Therefore, when the amine extractant is cyclically used in the solvent extraction step, copper, zinc, iron, and the like are gradually accumulated in the extractant.
If such accumulation of metal advances, an amino group which should contribute to extractive reaction will be occupied by the accumulated metal. Therefore, this will cause a sharp reduction in the extraction capability of an extractant. Further, since the viscosity of extractant increases, the increase will cause a reduction in oil-water separability.

[0022]
In order to cope with the above problem, a scrubbing stage has been provided to regenerate the extractant in order to separate and remove, for example, copper, zinc, iron, and the like from the amine extractant carrying a chloro complex ion of these metals.
For example, Patent Literature 2 describes a method including taking out a part of an organic phase after stripping, removing zinc contained in the organic phase as an impurity by neutralization treatment, then activating the extractant, and bringing the activated organic phase into contact with a stripped aqueous phase which is an aqueous cobalt chloride solution.

[0023]
The method of removing copper, zinc, iron, and the like contained in the amine extractant after stripping by neutralization treatment is based on a reaction accompanied by precipitate formation. Therefore, it is necessary to subject a mixture containing an organic phase, an aqueous phase, and a precipitate to solid-liquid separation with filtration equipment such as a filter press. The method is not only poor in filterability, handleability, and workability, but also has a safety problem in that a hazardous material is filtered with machinery and equipment. Therefore, the method is hardly said to be a preferred method.
Further, since the organic phase adheres to the precipitate, this problem leads to the loss of expensive extractant, causing an increase in the extractant cost.
And further, in the disposal of the mixture of the taken-out oil and the heavy metal, considerable technique and cost have been required in order to prevent an environmental problem from occurring.

[0024]
Therefore, an improved method shown in Patent Literature 3 is proposed and performed as a means to solve these problems.
This method includes subjecting an organic phase after stripping to alkali neutralization, taking out an organic phase which does not contain a precipitate by sedimentation from a mixture containing an organic phase, an aqueous phase, and a precipitate after alkali neutralization, and subjecting a mixture containing an aqueous phase, a precipitate, and the balance of the organic phase to acid dissolution.

[0025]
An aqueous phase containing copper, zinc, iron, and the like after acid dissolution is sent to a next treatment step such as a waste water treatment step, and an organic phase containing copper, zinc, iron, and the like is returned to the scrubbing stage.
This method has eliminated the handling of the precipitate mixed with the organic phase and the aqueous phase.

[0026]
In the scrubbing methods of the above Patent Literature 2 and Patent Literature 3, an alkali for neutralization and hydrochloric acid for activation are required. Therefore, a method which does not use these chemicals is also proposed, for example, in Patent Literature 4.
This is a method including washing an organic phase after stripping with water or an aqueous solution having a chloride ion concentration of 0 to 5 g/L so that a ratio (organic phase/aqueous phase) may be set to 1 to 10. This method is a method in which equipment is simple and which is advantageous in cost, as compared with the methods of Patent Literature 2 and Patent Literature 3.

[0027]
However, this method is a technique that is realized only under the conditions within a limited narrow range in which the solution to be extracted contains 25 mg/L or less of iron and 0.1 mg/L or less of zinc. Further, the target impurity metal is iron or zinc.

[0028]
Incidentally, in the process of leaching a nickel matte and a mixed sulfide with chlorine gas and subjecting leached nickel ions and cobalt ions to electrowinning to be produced as electric nickel and electric cobalt as described in Patent Literature 1, copper contained in a very small amount in the raw material such as the nickel matte and the mixed sulfide is utilized as an oxidizing agent in the chlorine leaching step and the displacement leaching step and circulated between the chlorine leaching step and the displacement leaching step.
Therefore, it is necessary to maintain the copper concentration in the chlorine leaching solution at an appropriate level in the range of 10 to 60 g/L.

[0029]
On the other hand, since copper is an impurity in the refining of nickel and cobalt, the copper concentration in the displacement leaching solution needs to be 0.02 g/L or less.
In order to reduce the copper concentration in the displacement leaching soluLion to a level that is lower than the copper concentration in the chlorine leaching solution, there is required a nickel matte containing Ni and Ni3S2 which have a higher reducing power than that of NiS contained in the mixed sulfide.

[0030]
However, if the amount of the mixed sulfide treated is increased for increasing the production volume of nickel and cobalt, a situation of relative shortage of the nickel matte will also occur. Therefore, a technique that can flexibly respond to the change of the raw material composition ratio as much as possible has been required.
Specifically, it has been required to establish a technique of removing copper that can respond even if the copper concentration in a leachate after displacement leaching, that is, the copper concentration in a solution to be extracted in the solvent extraction step, has increased from 0.02 g/L to 0.2 g/L.

[0031]
Although copper accumulated in the extractant can be removed by a method of alkali neutralization in the above scrubbing stage as a countermeasure to the above problem, an alkali for neutralization and hydrochloric acid for activation are required, resulting in not only an increase in cost but also an increase in a scrubbing ratio of the stripped organic phase.

[0032]
Further, the alkali neutralization causes various problems: for example, an organic solvent is degraded and decomposed with a strong alkali to reduce the extraction capability of amine, and the concentration of the decomposed organic substance in the aqueous phase after scrubbing increases to increase the COD load to wastewater.

[0033]
Furthermore, since the above alkali neutralization process is a method in which zinc is the main target of removal, it has been required to establish a technique of selectively removing copper accumulated in the amine extractant independently from the method.
Citation List Patent Literature

[0034]
Patent Literature 1:
Japanese Patent Laid-Open No. 2012-026027 Patent Literature 2:
Japanese Patent Laid-Open No. S60-121236 Patent Literature 3:
Japanese Patent Laid-Open No. 2010-196162 Patent Literature 4:
Japanese Patent Laid-Open No. 2010-196122 Summary Technical Problem

[0035]
An object of selected embodiments is to provide method for removing copper from an aqueous nickel chloride solution including separating and recovering cobalt and removing copper, zinc, and iron, from an aqueous nickel chloride solution, by solvent extraction with an organic solvent formed by using a tertiary amine as an extractant and using an aromatic hydrocarbon as a diluent of the amine, the method being capable of preventing reduction in the extraction capability and oil-water separability of the organic solvent by selectively removing copper accumulated in the extractant, and, as compared with prior art, the method being capable of treating an aqueous nickel chloride solution having a high copper concentration without increasing chemical cost and without degrading and decomposing the extractant to increase the COD load of wastewater.
Solution to Problem [0035a]
Certain exemplary embodiments provide a method for removing copper from an aqueous nickel chloride solution including separating and recovering cobalt and removing copper, zinc, and iron, from the aqueous nickel chloride solution containing cobalt, copper, zinc, and iron, by solvent extraction using, as an organic phase, an organic solvent containing a tertiary amine as an extractant and an aromatic hydrocarbon as a diluent, the method sequentially comprising the following steps (1) to (3):
(1) an extraction step of extracting cobalt, copper, zinc, and iron from the aqueous nickel chloride solution that contains cobalt, copper, zinc, and iron and has a nickel concentration of 170 to 210 g/L, a cobalt concentration of 2 to 10 g/L, and a copper concentration of 0.01 to 0.2 g/L, into the organic phase to form a first organic phase containing cobalt, copper, zinc, and iron and obtain an aqueous nickel chloride solution from which cobalt, copper, zinc, and iron are removed; (2) a stripping step of bringing a weakly acidic aqueous solution into contact with the first organic phase containing cobalt, copper, zinc, and iron obtained in the step (1) to thereby eliminate cobalt from the first organic phase to obtain a second aqueous phase of an aqueous cobalt chloride solution and a second organic phase after the stripping, the second organic phase containing copper, zinc, and iron; and (3) a copper recovery step of mixing and contacting water or dilute hydrochloric acid having a pH
of 1 or more with the second organic phase after stripping to selectively strip copper in the second organic phase into a third copper-stripped aqueous phase to thereby recover copper from the second organic phase, wherein the extraction of step (1) is carried out using the third organic phase obtained after removal of copper in the step (3), a copper concentration in the second aqueous cobalt chloride solution obtained in the stripping step (2) is reduced to 0.3 g/L or less by the stripping of the first organic phase with the weakly acidic aqueous solution, thereby forming the second organic phase having copper therein and the second aqueous solution, whereby a copper concentration of 0.4 g/L or less in the third organic phase is achieved by producing the second aqueous solution having the copper concentration reduced to 0.3 g/L or less.

h

[0036]
In order to achieve the above object, the present inventors have paid attention to the point that when the concentration of chloride ions in an aqueous phase is low, copper accumulated in an extractant after stripping easily transfers to the aqueous phase as compared with zinc and iron, and have made intensive studies on extraction conditions such as the concentration of chloride ions in the aqueous phase, that is, the pH of dilute hydrochloric acid, to be mixed and brought into contact with the stripped organic phase and the 0/A ratio. As a result, the present inventors have found that, copper accumulated in the extractant after stripping can be selectively removed by mixing and contacting water or dilute hydrochloric acid having a pH of 1 or more with the stripped organic phase so that the 0/A ratio may be 1.5 or less, thereby completing the method described herein.

[0037]
Specifically, the first aspect of selected embodiments is a method for removing copper from an aqueous nickel chloride solution including separating and recovering cobalt and removing copper, zinc, and iron, from the aqueous nickel chloride solution containing cobalt, copper, zinc, and iron, by solvent extraction using, as an organic phase, an organic solvent containing a tertiary amine as an extractant and an aromatic hydrocarbon as a diluent, the method sequentially including the following steps (1) to (3).

[0038]
(1) An extraction step of extracting cobalt, copper, zinc, and iron from the aqueous nickel chloride solution containing cobalt, copper, zinc, and iron into the organic phase to form an organic phase containing cobalt, copper, zinc, and iron and obtain an aqueous nickel chloride solution from which cobalt, copper, zinc, and iron are removed;
(2) a stripping step of bringing a weakly acidic aqueous solution into contact with the organic phase containing cobalt, copper, zinc, and iron obtained in the step (1) to thereby eliminate cobalt therein from the organic phase to obtain an aqueous phase of an aqueous cobalt chloride solution and an organic phase after stripping containing copper, zinc, and iron; and (3) a copper recovery step of mixing and contacting water or dilute hydrochloric acid having a pH of 1 or more with the stripped organic phase to strip copper in the organic phase into the aqueous phase to thereby recover copper, and using the organic phase containing zinc and iron from which copper has been removed as an organic solvent in the step (1).

[0039]
Next, the second aspect of the present invention is the method for removing copper from an aqueous nickel chloride solution according to the first aspect, wherein, in the extraction step (1), the aqueous nickel chloride solution containing cobalt, copper, zinc, and iron has a nickel concentration of 170 to 210 g/L, a cobalt concentration of 2 to 10 g/L, and a copper concentration of 0.01 to 0.2 g/L; and the copper concentration in the aqueous cobalt chloride solution obtained in the stripping step (2) is reduced to 0.3 g/L or less by removing copper in the organic phase containing cobalt, copper, zinc, and iron obtained in the step (1) until the copper concentration reaches 0.4 g/L or less.

[0040]
The third aspect of the present invention is the method for removing copper from an aqueous nickel chloride solution according to the first and second aspects, wherein, in the copper recovery step (3), the volume ratio of the organic phase to the aqueous phase is 1.5 or less.

[0041]
The fourth aspect of the present invention is the method for removing copper from an aqueous nickel chloride solution according to the first to third aspects, wherein the tertiary amine is tri-normal-octylamine (TNOA) or tri-iso-octylamine (TIOA).
Advantageous Effects of Invention

[0042]
According to the present invention, the reduction in the extraction capability and oil-water separability of the organic solvent can be prevented by selectively removing copper accumulated in the extractant; and even if the copper concentration in the solution to be extracted which is an aqueous nickel chloride solution increases from 0.02 g/L to 0.2 g/L, the copper concentration in an aqueous cobalt chloride solution obtained in the stripping step can be reduced to 0.3 g/L or less by removing copper in the organic phase until the copper concentration reaches 0.4 g/L or less.

[0043]
Further, as compared with the conventional art, since an alkali for neutralization and hydrochloric acid for activation are not required, the method of the present invention does not increase chemical cost and does not degrade and decompose the extractant to increase the COD
load of wastewater.

[0044]
Since the present invention is a simple method of mixing and contacting water or dilute hydrochloric acid having a pH of 1 or more with the stripped organic phase, a simple equipment modification is enough, and efficient operation can be achieved at a low cost and a low environmental load.
In addition to the above effects, the present invention can increase the raw material treatment ratio of a mixed sulfide to a nickel matte, and can increase the production volume of electric nickel and electric cobalt by increasing the treatment of the mixed sulfide.

Brief Description of Drawings

[0045]
Figure 1 is a schematic flow sheet of a nickel and cobalt smelting process including the present invention.
Figure 2 is a schematic flow sheet of the solvent extraction step in the copper removal method of the present invention.
Figure 3 is a view showing the relationship between the copper concentration in an organic phase and the copper concentration in an aqueous phase.
Figure 4 shows the relationship between the chloride ion concentration in an aqueous phase and the distribution ratio into an organic phase, with respect to copper, zinc, and iron.
Description of Embodiments

[0046]
Hereinafter, the method for removing copper from an aqueous nickel chloride solution of the present invention will be described in detail.
The method for removing copper from an aqueous nickel chloride solution of the present invention includes separating and recovering cobalt and removing copper, zinc, and iron, from an aqueous nickel chloride solution containing cobalt, copper, zinc, and iron, by solvent extraction using an organic solvent formed by using a tertiary amine as an extractant and an aromatic hydrocarbon as a diluent for diluting the extractant, the method including the following steps (1) to (3).

[0047]
(1) Extraction step An extraction step of extracting cobalt, copper, zinc, and iron from the aqueous nickel chloride solution containing cobalt, copper, zinc, and iron used as an aqueous phase to form an organic phase containing cobalt, copper, zinc, and iron and obtain an aqueous nickel chloride solution (aqueous phase) from which cobalt, copper, zinc, and iron are removed;
(2) Stripping step A stripping step of eliminating cobalt from the organic phase containing cobalt, copper, zinc, and iron with a weakly acidic aqueous solution used as an aqueous phase to obtain an aqueous cobalt chloride solution; and (3) Copper recovery step A copper recovery step of mixing and contacting water or dilute hydrochloric acid having a pH of 1 or more used as an aqueous phase with the stripped organic phase from which cobalt has been eliminated to strip copper from the organic phase into the aqueous phase and returning the organic phase from which copper has been removed to the extraction step (1).

[0048]
1. Nickel and Cobalt Smelting Process Figure 1 shows a schematic flow sheet of a nickel and cobalt smelting process including the present invention.

The present invention is a technique related to the scrubbing of the stripped organic phase in the solvent extraction step (the step shown in A in Figure 1) in all the steps of the nickel and cobalt smelting process.
However, the present invention is also a technique for achieving the total optimization with respect to the main elements of the nickel and cobalt smelting process, such as a raw material treatment ratio, chlorine leaching, displacement leaching (cementation), solution purification up to solvent extraction, and solvent extraction.
Therefore, each of the main elements will be described in detail with reference to Figure 1.

[0049]
(1) Raw Material There are two types of main raw materials, a nickel matte and a mixed sulfide.
The nickel matte refers to nickel sulfide obtained by a so-called pyrometallurgical process, such as nickel sulfide obtained by melting nickel sulfide ore in a blast furnace and nickel sulfide obtained by adding sulfur to nickel oxide ore and melting the mixture in an electric furnace.

[0050]
The nickel matte contains Ni3S2 and Ni (metallic nickel) as a main component, and the approximate chemical composition thereof is 65 to 80% by weight of Ni, about 1%
by weight of Co, 0.1 to 4% by weight of Cu, 0.1 to 5% by weight of Fe, and 20 to 25% by weight of S.

[0051]
A nickel matte using nickel sulfide ore as a raw material is characterized by higher impurity content as compared with a nickel matte using nickel oxide ore as a raw material, and the main input source of copper to the nickel and cobalt smelting process is the nickel matte using nickel sulfide ore as a raw material.
Therefore, the input amount of copper greatly varies with the treatment amount of the nickel matte using nickel sulfide ore as a raw material.

[0052]
On the other hand, the mixed sulfide refers to a mixed sulfide containing nickel and cobalt obtained by subjecting nickel oxide ore having a low nickel grade to high pressure acid leaching and removing impurities including iron from the high pressure acid leaching solution, followed by wet sulfidation, for example, by blowing hydrogen sulfide gas into the leaching solution containing nickel ions and cobalt ions.

[0053]
The mixed sulfide contains NiS and CoS as main components, and the approximate chemical composition thereof is 55 to 60% by weight of Ni, 3 to 6% by weight of Co, less than 0.1 by weight of Cu, 0.1 to 1% by weight of Fe, and 30 to 35% by weight of S.

[0054]
(2) Chlorine Leaching The mixed sulfide and a cementation residue to be described below is repulped in a chloride aqueous solution, and then chlorine gas is blown into the resulting slurry, thereby chlorine-leaching nickel and cobalt in the mixed sulfide and nickel and copper in the cementation residue into the chloride aqueous solution.

[0055]
In this step, chloro complex ions of divalent copper act as a direct leaching agent for dissolving a metal in the mixed sulfide and the cementation residue, and the chlorine gas indirectly participates in the leaching reaction by oxidizing monovalent ions of copper to divalent ions of copper.
Therefore, a certain amount of copper is indispensable in the chlorine leaching reactions, and it is important to maintain the copper concentration in the chlorine leaching solution at an appropriate level in the range of 10 to 60 g/L.
Main chlorine leaching reaction formulas are shown in the following formulas (1) to (4).

[0056]
[Formula 1]
NiS + 2CuC142- -+ Ni2+ + S + 2C1- + 2CuC132- ¨(1) Cu2S + 2CuC142- + 4C1- ¨> 4CuC132- + Su ¨(2) Cu + CuC142- ¨> 2CuC132- -= ( 3 ) 2CuC132 + C12 --> 2CuC142- -= (4)

[0057]
The chlorine leaching reaction conditions include an oxidation-reduction potential of the aqueous nickel chloride solution during the reactions of 480 to 550 mV
(based on Ag/AgC1 electrode) and a temperature of 105 to 115 C.

[0058]
(3) Displacement Leaching (Cementation) The displacement leaching step comprises two stages, a first displacement leaching step ("displacement leaching 1" in Figure 1) and a second displacement leaching step ("displacement leaching 2" in Figure 1).
In the first displacement leaching step, nickel and cobalt in the mixed sulfide is leached using the oxidizing power of chloro complex ions of divalent copper contained in the chlorine leaching solution.
In the displacement leaching solution obtained in the first displacement leaching step, the chloro complex ion of divalent copper is reduced to the chloro complex ion of monovalent copper.

[0059]
Next, in the second displacement leaching step, the displacement leaching solution obtained in the first displacement leaching step is brought into contact with a nickel matte to thereby perform the cementation reaction between copper ions in the displacement leaching solution and nickel in the nickel matte.

In the cementation reaction, solid nickel is eluted to form nickel ions, and copper ions in the solution which are electrochemically equivalent to the eluted nickel form a solid. Therefore, it can be said that the displacement leaching step is a copper removal step of removing copper contained in the chlorine leaching solution as a solid.

[0060]
Since the copper ions in the displacement leaching solution form a solid in the form of Cu2S or Cu metal, the copper concentration in the leachate after displacement leaching obtained in the second displacement leaching step is 0.02 g/L or less.

[0061]
In order to reduce the copper concentration in the leachate after displacement leaching, there is required a nickel matte containing Ni (metallic nickel) and Ni3S2 which have a higher reducing power than that of NiS
contained in the mixed sulfide.

[0062]
A cementation residue including insoluble residues of the mixed sulfide and the nickel matte and a solid containing copper obtained from the cementation reaction is subjected to solid-liquid separation from the leachate after displacement leaching obtained in the second displacement leaching sLep and sent to the chlorine leaching step.
Main displacement leaching reaction formulas are shown in following formula (5) to (7).

[0063]
[Formula 2]
Ni3S4 + 6CuC142- ¨> 3Ni2+ + 4S + 6C1- + 6CuC132- === (5) 4CuC132- + S ¨> Cu2S + 2CuC142- 4C1- ( 6) Ni + 2CuC132- -4 Ni2+
+ 20u + 6C1- (7)

[0064]
The displacement leaching reaction conditions include an oxidation-reduction potential of the aqueous nickel chloride solution during the reactions of 50 to 300 mV
(based on Ag/AgC1 electrode) and a temperature of 70 to 100 C.

[0065]
In the second displacement leaching step, the amount of copper to be removed from the solution is determined by the product of the amount of the chlorine leaching solution and the copper concentration in the chlorine leaching solution.
The amount of the chlorine leaching solution is determined by the amount of the mixed sulfide treated in the chlorine leaching step and the first displacement leaching step.
The copper concentration in the chlorine leaching solution will be a constant value because the concentration is maintained at an appropriate level in the range of 10 to 60 g/L in order to continue the optimum chlorine leaching operation.

[0066]
Therefore, when the treatment ratio of the nickel matte to the mixed sulfide is reduced, the nickel matte may be insufficient for the amount of copper to be removed.
In this case, the copper concentration in the leachate after displacement leaching obtained in the second displacement leaching step will increase.

[0067]
(4) Solution Purification A leachate after displacement leaching (solution after cementation) is sent to a solution purification step.
The solution purification step comprises an iron removal step, a solvent extraction step, a lead removal step, and a zinc removal step.

[0068]
In the iron removal step, the leachate after displacement leaching is subjected to a treatment in which chlorine gas as an oxidizing agent and a nickel carbonate slurry as a neutralizing agent are added to the leachate after displacement leaching to produce a precipitate containing ferric hydroxide as a main component to thereby reduce the iron concentration in the leachate after displacement leaching from 1 to 2 g/L to 15 mg/L or less.
Since the pH of the aqueous solution in the iron removal step is about 2.0 to 2.5, copper hydroxide is not produced in this step.
Further, since copper is not removed in the iron removal step, when the copper concentration in the leachate after displacement leaching increases, the copper concentration in the solution to be extracted to be supplied to the next solution purification step (solvent extraction) will increase.

[0069]
Although details will be described below, in the solvent extraction step, TNOA which is an amine extractant is mixed and brought into contact with an iron-removed solution having a nickel concentration of 170 to 210 g/L, a cobalt concentration of 2 to 10 g/L, a copper concentration of 0.02 g/L or less, a zinc concentration of 0.01 to 0.03 g/L, and an iron concentration of 15 mg/L or less, thereby transferring cobalt, copper, zinc, and iron from the aqueous phase to the organic phase.

[0070]
In the lead removal step, chlorine gas is added as an oxidizing agent and a nickel carbonate slurry is added as a neutralizing agent, thereby removing lead in the nickel chloride solution after solvent extraction as lead oxide, in the same manner as in the iron removal step.
Since the pH of the extraction residual solution in the lead removal step is 4 to 5, a part of nickel also forms a precipitate as a trivalent hydroxide.

[0071]
In the zinc removal step, the chloro complex ion of zinc remaining in a very small amount of about 0.1 mg/L in a de-leaded solution after lead removal is removed by being adsorbed onto a weakly basic anion exchange resin.

[0072]
2. Solvent Extraction Step Next, the solvent extraction step constituting the copper removal method according to the present invention and constituting a part of the above solution purification step (4) will be described in detail.

[0073]
(1) Constitution of Solvent Extraction Step Figure 2 shows a schematic flow sheet of the solvent extraction step according to the present invention. The flow sheet also shows the flow of the copper removal method according to the present invention.
A multistage countercurrent system is employed in the solvent extraction, and the system comprises an extraction stage, a washing stage, a stripping stage, and a copper recovery stage.
An extraction apparatus of a mixer settler system is used, and in Examples used for describing the present invention, the extraction stage is constituted by three stages, the washing stage is constituted by three stages, the stripping stage is also constituted by three stages, and the copper recovery stage is constituted by one stage.
Note that, in order to remove zinc and iron in the stripped organic phase in the stripping stage, a zinc removal stage is preferably provided in parallel or in series with the copper recovery stage.

[0074]
That is, when the copper recovery stage and the zinc removal stage are independently operated, copper, zinc, and iron in the organic phase can be efficiently removed:
the copper recovery stage including taking out a predetermined amount of the stripped organic phase depending on the copper concentration in the solution to be extracted, and mixing and bringing the taken-out organic phase into contact with water or dilute hydrochloric acid having a pH of 1 or more to strip copper in the organic phase into the aqueous phase; and the zinc removal stage including a predetermined amount of the stripped organic phase depending on the degree of enrichment of zinc or iron in the stripped organic phase, and neutralizing the taken-out organic phase with an alkali to remove zinc and iron in the organic phase.

[0075]
Since zinc and iron are input from a mixed sulfide, the zinc concentration in the solution to be extracted is influenced by the zinc content in the mixed sulfide and the treatment amount of the mixed sulfide.
Since iron is removed in the iron removal step, the iron concentration of the solution to be extracted is always constant.
On the other hand, the copper concentration in the solution to be extracted is determined by the treatment ratio of the nickel matte to the mixed sulfide.

[0076]
That is, since the zinc concentration and the copper concentration in the solution to be extracted independently vary, and particularly the width of variation of the copper concentration is large, it is more efficient to independently operate the removal of zinc and the removal of copper in the organic phase.

[0077]
Further, the cost can be reduced also by a serial arrangement, that is, by a method including mixing and contacting water or dilute hydrochloric acid haying a pH
of 1 or more as an aqueous phase with an organic phase a stripped to strip copper from the organic phase a into the aqueous phase and then neutralizing an organic phase b after copper recovery with an alkali to remove zinc and iron in the organic phase, because the amount of the alkali used in the zinc removal stage can be reduced consistent with the amount of copper.

[0078]
(2) Extractant and Reaction A tertiary amine is used as an extractant, and tri-normal-octylamine (TNCA) or tri-iso-octylamine (TIOA) is preferably used.
An aromatic hydrocarbon is used as a diluent of the extractant.
In order to adjust the viscosity of an organic phase, the extractant concentration in the organic phase (extractant and diluent) is set to 20 to 40% by volume.

[0079]
The tertiary amine is activated by the addition of hydrochloric acid according to the following formula (8).
Thereby, the tertiary amine holds the extraction capability of metal-chloro complex ions as shown in formula (9) and formula (9') and has excellent separation characteristics of nickel and cobalt.

[0080]
[Formula 3]
R3N: + HC1 -* R3N:HC1 (8) 2R3N:HC1 + MC142 -* (R3N:H)2MC14 + 2C1- -.(9)

[0081]
M in the above formula (9) represents a metal species which forms a chloro complex ion, such as Co, Cu, and Zn.
Since the form of the chloro complex ion is different depending on the valence of a metal ion, the following formula (9') is valid, for example, in the case of Fe (trivalent).
Note that ":" in formula (8), formula (9), and formula (9') represents the unshared electron pair of a nitrogen atom.

[0082]
[Formula 4]
R3N:HC1 + FeC14 R3N:HFeC14 + Cl-

[0083]
In the extraction stage, a metal species which forms a chloro complex ion, such as Co, Cu, Zn and Fe, is extracted into an organic phase by the reaction shown by formula (9) or formula (9') to produce an amine carrying a chloro complex ion of the metal element. In this regard, since nickel does not form a chloro complex ion, it remains in the extraction residual solution and is separated.
Therefore, when an aqueous nickel chloride solution contains a chloro complex ion of a metal which more easily forms a chloro complex ion than cobalt, that is, has a higher stability of a chloro complex ion than cobalt, for example, copper, zinc, or iron, such a metal will also be extracted.

[0084]
On the other hand, in the stripping stage, cobalt can be eliminated and transferred into an aqueous phase according to the following formula (10) which is a reverse reaction of formula (9) by bringing the organic phase after washing, that is, the amine carrying the chloro complex ion of cobalt, into contact with a weakly acidic aqueous solution.

[0085]
[Formula 5]
(R3N:H)2CoC14 -* 2R3N:HC1 + CoC12 -(10)

[0086]
3. Copper Removal by Solvent Extraction The main function of solvent extraction is to extract and separate cobalt from a solution to be extracted (mixed solution of nickel chloride and cobalt chloride) in the first place. However, if copper can be selectively eliminated from the stripped organic phase as further function, the role of a step of removing copper in the solution to be extracted can also be played.

[0087]
Therefore, although the removal of copper from the chlorine leaching solution in the nickel and cobalt smelting process is basically performed in the displacement leaching (cementation) step, the removal of copper by solvent extraction will exhibit an effect when the copper concentration in the leachate after displacement leaching greatly varies or increases due to the shortage of a nickel matte and the like.

[0088]
It is the first feature of the present invention to use the solvent extraction as a copper removal step.
In the extraction stage, even if the copper concentration in the solution to be extracted is as high as 0.2 g/L, almost the whole amount of copper ions can be extracted into the organic phase.
This is because the chloride ion concentration in the solution to be extracted is as high as 200 to 250 g/L, and copper forms a stable chloro complex ion.

[0089]
On the other hand, in the stripping stage for recovering cobalt as an aqueous cobalt chloride solution, the chloride ion concentration is 70 to 100 g/L, which is lower than that in the extraction stage.

Therefore, when the chloride ion concentration is 70 to 100 g/L, the copper-chloro complex ion in the organic phase will be unstable, and a part of copper is stripped into the aqueous phase.
Since the copper concentration in the aqueous phase is proportional to the copper concentration in the organic phase, the copper concentration in the aqueous cobalt chloride solution will increase when the copper concentration in the organic phase increases.
When the copper concentration in the aqueous cobalt chloride solution increases, the solution purification (copper removal) load of a subsequent aqueous cobalt chloride solution will increase, and the copper content in electric cobalt as a product may be increased.

[0090]
Figure 3 shows the relationship between the copper concentration in an organic phase and the copper concentration in an aqueous phase in the stripping stage.
The data in Figure 3 is the operation data when an organic solvent, containing 20% by volume or 30% by volume of tri-normal-octylamine (TNOA) as an extractant and 80%
by volume or 70% by volume of an aromatic hydrocarbon as a diluent, is used in the solvent extraction step of a multistage countercurrent system, comprising three extraction stages, three washing stages, and three stripping stages.

[0091]
The solution to be extracted (mixed aqueous solution of nickel chloride and cobalt chloride) has a nickel concentration of 170 to 210 g/L, a cobalt concentration of 2 to 10 g/L, and a copper concentration of 0.02 to 0.2 g/L; and the stripping residual solution (aqueous cobalt chloride solution) has a cobalt concentration of 50 to 70 g/L.

[0092]
Figure 3 shows that although the inclination of a regression line, that is, the distribution ratio, changes with the concentration of the extractant, the copper concentration in the aqueous cobalt chloride solution can be reduced to 0.3 g/L or less by reducing the copper in the organic phase down to a copper concentration of 0.4 g/L or less.
It is the second feature of the present invention to produce the aqueous cobalt chloride solution having a low copper concentration.

[0093]
The copper recovery stage of the present invention is a step of selectively separating and removing copper from copper, zinc, and iron concentrated in the organic phase into the aqueous phase.
The stability of copper, zinc, and iron in the organic phase is the stability of the chloro complex ion of a metal, and the stability is positively correlated with the chloride ion concentration in the aqueous phase.

[0094]
Figure 4 shows the relationship between the chloride ion concentration in the aqueous phase and the distribution ratio into the organic phase, with respect to copper, zinc, and iron.
Here, among copper, zinc, and iron, copper has the lowest stability in the organic phase and tends to be distributed into the aqueous phase.
Therefore, if an aqueous phase having a low chloride ion concentration is mixed and brought into contact with the stripped organic phase, copper in the organic phase can be selectively eliminated and transferred into the aqueous phase.

[0095]
As a result of intensive studies on the stripping behavior of the chloride ion concentration and copper, the present inventors have been able to find that water or dilute hydrochloric acid having a pH of 1 or more is suitable as a solution before stripping.
Among these, copper is easily eliminated from the organic phase when water is used, but the use of hydrochloric acid having a pH of 1 is favorable because the elimination of hydrochloric acid from the organic phase can be prevented, and a subsequent activation treatment of the extractant with hydrochloric acid is not required.

[0096]
According to the present invention, a solvent extraction step as shown in Figure 2 is constituted to adjust the copper concentration in the organic phase to 0.4 g/L or less. Thereby, a solution to be extracted having a copper concentration of up to 0.2 g/L can be treated, and the copper concentration in the aqueous cobalt chloride solution after stripping can be reduced to 0.3 g/L or less.
In other words, it is possible to cope with the copper load 10 times the conventional art (zinc removal stage by alkali neutralization).

[0097]
In the present invention, since copper is recovered without using an alkali, it is possible to achieve cost reduction as compared with a zinc removal stage of conventional art in which zinc and iron in the organic phase are removed, for example, by alkali neutralization.

[0098]
Further, since the organic phase is not brought into contact with strong alkali, the COD components produced by the decomposition of the organic phase are present in the copper recovery solution only in a low concentration, and the COD load to a post step can be reduced.
That is, various problems of conventional art (zinc removal stage by alkali neutralization) can be solved by performing weak elimination using water having a pH of from 1 to a neutral region instead of or in combination with conventional strong elimination using an alkali.
Note that the elimination of hydrochloric acid from the organic phase can also be suppressed by using dilute hydrochloric acid having a pH of about 1 for a solution before copper recovery.
Examples

[0099]
Next, the present invention will be further described using Examples.
Example 1

[0100]
In a solvent extractor using a mixer settler of a multistage countercurrent system comprising three extraction stages, three washing stages, and three stripping stages, solvent extraction operation was performed using an organic solvent containing 20% by volume of tri-normal-octylamine (TN0A) which is a tertiary amine as an extractant and 80% by volume of an aromatic hydrocarbon as a diluent.

[0101]
The solution to be extracted (mixed aqueous solution of nickel chloride and cobalt chloride) has a nickel concentration of 170 to 210 g/L, a cobalt concentration of 2 to 10 g/L, a copper concentration of 0.01 to 0.02 g/L, a zinc concentration of 0.02 to 0.03 g/L, and an iron concentration of 10 to 14 mg/L; and the stripping residual solution (aqueous cobalt chloride solution) has a cobalt concentration of 50 to 70 g/L and a copper concentration of 0.1 to 0.2 g/L.
With respect to each flow rate, the flow rate of the organics is 1000 to 1300 L/min; the flow rate of the solution to be extracted is 1300 to 1600 L/min; and the flow rate of the solution before stripping is 140 to 170 L/min.

[0102]
Subsequently, a part of the stripped organic phase was sent to the copper recovery stage (one stage) using a mixer settler as in the extraction stage and the like, and mixed with neutral water.
The flow rate of the organic phase was set to 48 to 54 L/min; the flow rate of the aqueous phase was set to 48 to 54 L/min; and the 0/A ratio was set to 0.9 to 1.1.

[0103]
The results are shown in Table 1, which reveals that the copper in the organic phase is selectively stripped into the aqueous phase.
In this regard, the COD in the aqueous phase after copper recovery was 20 mg/L.
In Tables 1 and 2, "Stripping organic" represents the organic phase "a" after the stripping in Figure 2, and "Copper recovery organic" represents the organic phase "b"
after the copper recovery in Figure 2.

[0104]
[Table 1]
Stripping organic Copper recovery organic Cu (g/L) Fe (g/L) Zn (g/L) Cu (g/L) Fe (g/L) Zn (g/L) 0.29 0.43 0.87 0.07 0.24 0.82 Example 2

[0105]
Solvent extraction operation was performed under the same conditions as in Example 1 except that an organic solvent containing 30% by volume of TNOA and 70% by volume of an aromatic hydrocarbon was used.
Subsequently, the organic phase and the aqueous phase were mixed at an 0/A ratio of 0.9 to 1.1 in the same manner as in Example 1 except that a part of the stripped organic phase was sent to the copper recovery stage, and dilute hydrochloric acid having a pH of 1 was used as the aqueous phase.

[0106]
The results are shown in Table 2, which revealed that copper in the organic phase was selectively stripped into the aqueous phase even with hydrochloric acid having a pH
of 1 in a manner similar to neutral water.

[0107]
[Table 2]
Stripping organic Copper recovery organic Cu (g/L) Fe (g/L) Zn (g/L) Cu (g/L) Fe (g/L) Zn (g/L) 0.14 0.93 2.00 0.01 0.61 1.70

[0108]
(Comparative Example 1) Solvent extraction was performed under the same conditions as in Example 1, and a part of the stripped organic phase was then sent to the zinc removal stage (one stage) comprising three 3-m3 FRP tanks and mixed with dilute caustic soda in a neutralization tank which is the first tank. Here, the dilute caustic soda used has a caustic soda concentration of 118 g/L.
Subsequently, from a mixture containing an organic phase, an aqueous phase, and a precipitate after alkali neutralization, the organic phase which does not contain the precipitate was taken out by overflow, and a mixture containing the aqueous phase, the precipitate, and the balance of the organic phase was sent to an acid dissolver which is the second tank to be subjected to acid dissolution with 35% hydrochloric acid.

[0109]
Note that the flow rate of taking out the organic phase was set to 48 to 54 L/min, and the flow rate of the dilute caustic soda was set to 48 to 54 L/min. The amount of the 35% hydrochloric acid used was set to 15 L/min.

[0110]
The resulting COD concentration in the aqueous phase after zinc removal by alkali neutralization was 230 mg/L.

[0111]
Thus, copper in the organic phase can be selectively removed to reduce copper to a target concentration by treating the stripping organic in the copper recovery stage, and the copper concentration in the stripped organic phase is adjusted to 0.4 g/L or less by adjusting the amount of the organic solvent taken out, that is, the treatment amount in the copper recovery stage.

[0112]
Further, as compared with Comparative Example (conventional method), neither caustic soda for neutralization nor hydrochloric acid for acid dissolution is required, and the COD concentration in the aqueous phase after treatment can be reduced to about 1/10.
Note that since when the copper concentration in the organic phase is further increased, the copper concentration in the aqueous phase will increase with the increase, the amount that is removed from the organic solvent will increase.
Reference Signs List

[0113]
a Organic phase after stripping Organic phase after copper recovery

Claims (4)

Claims

1. A method for removing copper from an aqueous nickel chloride solution including separating and recovering cobalt and removing copper, zinc, and iron, from the aqueous nickel chloride solution containing cobalt, copper, zinc, and iron, by solvent extraction using, as an organic phase, an organic solvent containing a tertiary amine as an extractant and an aromatic hydrocarbon as a diluent, the method sequentially comprising the following steps (1) to (3):
(1) an extraction step of extracting cobalt, copper, zinc, and iron from the aqueous nickel chloride solution that contains cobalt, copper, zinc, and iron and has a nickel concentration of 170 to 210 g/L, a cobalt concentration of 2 to 10 g/L, and a copper concentration of 0.01 to 0.2 g/L, into the organic phase to form a first organic phase containing cobalt, copper, zinc, and iron and obtain an aqueous nickel chloride solution from which cobalt, copper, zinc, and iron are removed;
(2) a stripping step of bringing a weakly acidic aqueous solution into contact with the first organic phase containing cobalt, copper, zinc, and iron obtained in the step (1) to thereby eliminate cobalt from the first organic phase to obtain a second aqueous phase of an aqueous cobalt chloride solution and a second organic phase after the stripping, the second organic phase containing copper, zinc, and iron; and (3) a copper recovery step of mixing and contacting water or dilute hydrochloric acid having a pH of 1 or more with the second organic phase after stripping to selectively strip copper in the second organic phase into a third copper-stripped aqueous phase to thereby recover copper from the second organic phase, wherein the extraction of step (1) is carried out using the third organic phase obtained after removal of copper in the step (3), a copper concentration in the second aqueous cobalt chloride solution obtained in the stripping step (2) is reduced to 0.3 g/L or less by the stripping of the first organic phase with the weakly acidic aqueous solution, thereby forming the second organic phase having copper therein and the second aqueous solution, whereby a copper concentration of 0.4 g/L or less in the third organic phase is achieved by producing the second aqueous solution having the copper concentration reduced to 0.3 g/L or less.

2. The method for removing copper from the aqueous nickel chloride solution according to claim 1, wherein, in the copper recovery step (3), a volume ratio of the second organic phase to the second aqueous phase is 1.5 or less.

3. The method for removing copper from an aqueous nickel chloride solution according to claim 1, wherein the tertiary amine is tri-normal-octylamine (TNOA) or tri-iso-octylamine (TIOA).

4. The method for removing copper from an aqueous nickel chloride solution according to claim 1, further comprising a zinc removal step in parallel with the copper recovery step (3), in which zinc removal step, the second organic phase after stripping containing copper, zinc, and iron or the third organic phase after removal of copper in the copper recovery step (3) is neutralized with an alkali to remove zinc and iron therefrom.