Note: Descriptions are shown in the official language in which they were submitted.
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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
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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
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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
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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
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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.
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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.
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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
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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
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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.
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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.
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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
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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
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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.
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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).
EXAMPLE 2
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
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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.
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