JP2011011155A - Method for removing copper ion from arsenic acid solution by using copper sulfide and single sulfur - Google Patents

Abstract

Provided is a method for removing Cu ions from a solution containing arsenic acid (pentavalent As) and Cu ions while suppressing the reduction of the arsenic acid (pentavalent As) to arsenous acid (trivalent As) as much as possible. .
SOLUTION SOLUTIONS << 3 >> or SO ₂ gas << 3 >> or a solution temperature of 60 ° C. or higher by adding simple sulfur (S ⁰ ) << 4 >> and copper sulfide << 5 >> to an arsenic acid solution << 1 >> containing Cu ions The present invention provides a method for removing Cu ions from an arsenic acid solution, in which a mixed gas << 3 ^* >> of SO ₂ gas and air is blown to remove the Cu ions as a recovered residue << 8 >> containing copper sulfide.
[Selection] Figure 4

Description

  The present invention relates to a method for removing Cu ions from a solution containing arsenic acid (pentavalent As) and Cu ions while suppressing reduction of the arsenic acid (pentavalent As) to arsenous acid (trivalent As).

Arsenic-containing intermediate products in copper smelting include arsenic sulfide recovered from sulfidation of sulfuric acid factory effluent and process water, and copper removal electrolytic slime generated in the electrolytic solution cleaning process at copper electrolysis factory. is there.
These arsenic intermediate products contain a considerable amount of Cu in addition to arsenic. Therefore, a considerable amount of Cu ions are dissolved in the arsenic acid solution prepared from these arsenic-containing intermediate products.

The concentrated arsenic acid solution is used as an original solution for producing scorodite when the arsenic is stabilized and stored as scorodite (FeAsO ₄ .2H ₂ O).
Here, as one method for producing scorodite, there is a method in which a divalent iron salt (Fe ²⁺ salt) is added to an arsenic acid solution and produced by an oxidation reaction at a high temperature.
However, when Cu, Zn, and Na coexist in the arsenic acid solution, the influence of these metal elements on scorodite crystal growth is shown. In particular, in the case of coexistence with Cu, Cu is taken into the crystal lattice of the scorodite particles, and it is said that caution is required because effects such as changes in particle morphology, changes in lattice constant, and increase in arsenic elution amount appear. Patent Document 1).

Kenno Tanno Resources and Materials Society 2008 Fall Meeting PY-40 p55

According to the study by the present inventors, Cu ions coexisting in the arsenic acid solution at the time of scorodite production act as an oxidation catalyst, and by promoting nucleation of scorodite, it is difficult to control the particle growth of scorodite crystals. I found out that
Therefore, when the concentrated arsenic acid solution is used as the original solution for scorodite production, it is preferable that the concentrated arsenic acid solution contains a smaller amount of Cu ions from the viewpoint of controlling particle growth of scorodite crystals.
Furthermore, in order to efficiently produce scorodite from the concentrated arsenic acid solution, the arsenic in the solution needs to be arsenic acid (pentavalent As). This is because arsenous acid (trivalent As) does not react and remains in the liquid. Therefore, the arsenic in the concentrated arsenic acid solution is required to be arsenic acid (pentavalent As) as much as possible. .

  The present invention has been made under such circumstances, and the problem to be solved is that a solution containing arsenic acid (pentavalent As) and arsenic acid (pentavalent As) from a solution containing arsenic acid (pentavalent As) and Cu ions. To provide a method for removing Cu ions while suppressing reduction to arsenous acid (trivalent As).

The present inventors have intensively studied a method that enables removal of dissolved Cu ions while suppressing reduction of arsenic acid (pentavalent As) to arsenous acid (trivalent As).
Then, elemental sulfur (S ⁰ ) and copper sulfide are added to an arsenic acid solution (pentavalent As solution) containing Cu ions, and at a liquid temperature of 60 ° C. or higher, SO ₂ gas or SO ₂ gas and air are added. By blowing the mixed gas, an innovative finding was obtained that dissolved Cu ions can be removed as copper sulfide while suppressing reduction of arsenic acid (pentavalent As) to arsenous acid (trivalent As).

That is, the first invention for solving the above-mentioned revision is
To the arsenic acid solution containing Cu ions, elemental sulfur (S ⁰ ) and copper sulfide are added, and the liquid temperature is set to 60 ° C. or higher, and SO ₂ gas or a mixed gas of SO ₂ gas and air is blown into the arsenic acid solution. A method for removing Cu ions from an arsenic acid solution, wherein Cu ions are removed as a deposit containing copper sulfide.

The second invention is
The reaction for removing the Cu ions as a precipitate containing copper sulfide is terminated when the Cu ion concentration becomes 1 g / L or less. Cu from the arsenic acid solution according to the first invention This is a method for removing ions.

The third invention is
Cu ions from the arsenic acid solution according to the first or second invention, wherein the total amount of SO ₂ gas blown is equal to or less than an equimolar amount of the total molar amount of Cu ions dissolved in the arsenic acid solution. This is a removal method.

The fourth invention is:
The method for removing Cu ions from an arsenic acid solution according to any one of the first to third inventions, wherein the copper sulfide is added to the arsenic acid solution in an amount of 10 g / L or more.

The fifth invention is:
The first to fourth inventions are characterized in that the above-described removed copper sulfide-containing material is added as copper sulfide and elemental sulfur (S ⁰ ) in the next and subsequent methods of removing Cu ions from the arsenic acid solution. Or a method for removing Cu ions from the arsenic acid solution.

By adding elemental sulfur (S ⁰ ) and copper sulfide to an arsenic acid solution in which Cu ions are dissolved, and blowing a mixed gas of SO ₂ gas or SO ₂ gas and air at a predetermined liquid temperature, While suppressing the reduction of the arsenic acid to trivalent As (arsenous acid), the dissolved Cu ions could be removed to a level suitable for scorodite production.

It is a graph showing the relationship between the SO ₂ gas blowing time and Cu ion removal rate. SO 2 ₊ is a graph showing the relationship between the mixed gas blowing time and pentavalent As air ratio. SO 2 ₊ mixed gas blowing time of the air and is a graph showing the relationship between the dissolved Cu ion concentration. It is a process flow figure of the removal method of Cu ion concerning the present invention.

The form for implementing this invention is demonstrated referring an Example and FIG. FIG. 4 is a process flow diagram of the Cu ion removal method according to the present invention.
The copper sulfide and SO ₂ gas to be added to the arsenic acid solution will be described in detail, and the recycling of the sediment containing simple sulfur (S ⁰ ) and copper sulfide generated by the implementation will be described. explain.

(1) Embodiment in which elemental sulfur (S ⁰ ) and copper sulfide are present in an arsenic acid solution containing Cu ions, and SO ₂ gas is blown into the arsenic acid solution to perform a sulfurization reaction. <1> Contains Cu ions Preparation of arsenic acid solution sample 99.45 g of reagent 60% arsenic acid solution and 16.8 g of reagent copper sulfate pentahydrate (purity 99.5% or more) were weighed. The 60% arsenic acid solution 99.45 g has a volume of about 63 cc.
Therefore, the 60% arsenic acid solution 63 cc, the wet water of wet copper sulfide described later, and the water (pure water) as the solvent were weighed into water as the solvent adjusted to 700 cc per sample. A 60% arsenic acid solution and reagent copper sulfate pentahydrate were added to prepare 700 cc of an arsenic acid solution << 1 >> sample containing Cu ions. In addition, according to the said preparation, it becomes about 45 g / L as a density | concentration of the pentavalent As solution obtained.

<2> Copper sulfide used in the present embodiment The copper sulfide << 5 >> used in the present embodiment is preferably copper sulfide having low crystallinity. The low-crystallinity copper sulfide can be easily produced by a wet process in which a sulfide is added to Cu ions in an aqueous solution to produce copper sulfide. Furthermore, the copper sulfide produced in the wet process is recovered as a wet filter residue. The wet state is preferable for the copper sulfide used for the reaction. This is because repulp mixing into the liquid to be treated is facilitated, and there is no need for drying.
In the present invention, for example, copper sulfide having low crystallinity produced by the wet process may be referred to as “wet copper sulfide”.

<3> Wet process for producing wet copper sulfide Hereinafter, a wet process for producing wet copper sulfide << 5 >>, a wet process of adding reagent sodium hydrosulfide (NaSH) as a sulfiding agent to a reagent copper sulfate solution. The process will be described as an example.
As a reaction apparatus, a 10-liter beaker and four two-stage turbine blades with baffles were prepared.
First, a copper solution and a sodium hydrosulfide solution were prepared.
1) Preparation of copper solution 900 g of the reagent copper sulfate pentahydrate was weighed, and this was added to 4,000 cc of pure water at a temperature of 60 ° C.
To prepare a copper solution.
2) Preparation of sodium hydrosulfide solution 260 g of reagent 70% sodium hydrosulfide (flakes) was weighed and dissolved in pure water to make a final liquid amount of 900 cc to prepare a sodium hydrosulfide solution.

Wet copper sulfide to be used for the test was prepared by adding the sodium hydrosulfide solution of 2) to the copper solution of 1) above while stirring while maintaining the liquid temperature at 60 ° C. using the above-described reaction apparatus. Produced. Specifically, first, 95% sulfuric acid was added to the copper solution to adjust the pH to 1.5, and then the addition of the sodium hydrosulfide solution was started. The addition of sodium hydrosulfide was carried out over 15 minutes, and stirring was continued for 15 minutes after the addition to complete the reaction (pH at the end of the reaction was 1.1).
The produced copper sulfide pulp was subjected to filtration to recover the copper sulfide deposit. Since the unreacted Cu ions are attached to the recovered copper sulfide deposit, it is repulped with 5,000 cc of pure water, subjected to filtration again, and wet copper sulfide << 5 >> after the repulp washing is used. It was collected.
The repulp washing was carried out twice, and the finally recovered wet copper sulfide after repulp washing was 915 wet · g. Table 1 shows the quality of the wet copper sulfide << 5 >>. In the table according to the present invention, “Total-S” is the total sulfur content.

<4> Examination of Addition Amount of Wet Copper Sulfide The effect of addition of wet copper sulfide << 5 >> added to the arsenic acid solution << 1 >> was confirmed, and a preferred addition amount was further examined.
Specifically, the pulp concentration of the wet copper sulfide << 5 >> to be added is converted into a dry amount (converted into a dry amount), and 0 dry · g / L (test A), 2 dry · g / L (test B), 10 dry, respectively. -Four-level tests were conducted with g / L (Test C) and 70 dry. G / L (Test D).
In addition, in tests A to D, the addition amount of reagent sulfur powder, which is elemental sulfur (S ⁰ ) << 4 >>, was unified to 8.6 g. The sulfur powder addition amount 8.6 g is 4 times equivalent (4 times mole amount) of the total Cu ion mole amount of the reaction shown in the following formula (1).
Cu ²⁺ + S ⁰ → CuS (1)
That is, the amount of Cu in 16.8 g of copper sulfate pentahydrate is 4.255 g, which is 0.06696 mol. Therefore, it can be understood that the added amount of 8.6 g of elemental sulfur (S ⁰ ) is 4 times equivalent to the total molar amount of Cu ions by the following formula (2).
8.6 g ÷ 32.06 (atomic weight of S) ÷ 0.06696 (molar amount of Cu ion) = 4 times equivalent (2)
Table 2 shows sample preparation compositions according to tests A to D.

<SO ₂ gas blowing amount>
In each sample of Tests A to D, SO ₂ gas << 3 >> was blown at a rate of 100 cc / min. Of the SO ₂ gas "3", as a measure of the total amount of SO ₂ gas was blown into each elapsed time "3", the molar amount of the total amount of blown the SO ₂ gas "3", then dissolved in each sample Table 3 shows how many times the total molar amount of Cu ions is.

In each sample of Tests A to D, since the amount of copper sulfate added to the sample solution is 16.8 g, the Cu amount is 4.255 g, which is 0.06696 mol.
Therefore, the amount of SO ₂ gas << 3 >> which is equimolar to the Cu ion molar amount is (0.06696 (mol) × 22.4 (L / mol) × 1000 (cc / L) = 1500 cc. From Table 3, it can be understood that when the SO ₂ gas << 3 >> is blown for 15 minutes, the molar amount is equal to the molar amount of Cu ions in the sample solution.

  Here, a test apparatus was prepared in which four baffle plates were provided in a 1 liter beaker and two-stage turbine blades that were stirred at 500 rpm were provided. The gas was blown from the bottom of the beaker through a glass tube.

After each test sample was sufficiently stirred and mixed at room temperature, the temperature was started to rise, and when the liquid temperature reached the test set temperature (75 ° C.), 10 cc was sampled and the composition analysis of each test sample liquid was performed.
Next, blowing of SO ₂ gas (purity 99.9%) << 3 >> into each sample was started, and the start of the blowing was defined as the start of reaction. The amount of SO ₂ gas << 3 >> blown was 100 cc / min, and the reaction was continued while maintaining a liquid temperature of 75 ° C. And 10 cc was sampled at the time of 15 minutes from the start of blowing SO ₂ gas << 3 >>, and the composition analysis of each test sample solution was performed.
During this time, the reaction was continued while the SO ₂ gas << 3 >> was continuously blown and the liquid temperature was maintained at 75 ° C. Then, the reaction was terminated when 30 minutes had elapsed from the start of blowing the SO ₂ gas << 3 >>, 10 cc was sampled, and the composition analysis of each test sample solution was performed.

The sample of Tests A to D was blown with SO ₂ gas << 3 >> for 30 minutes, and the pH value, total arsenic concentration, trivalent arsenic concentration, and pentavalent arsenic at 0, 15, and 30 minutes. The concentration, pentavalent arsenic ratio, Cu ion concentration, and Cu ion removal rate were measured. The measurement results are shown in Tables 4 to 7. In addition, a graph was prepared with the Cu ion removal rate on the vertical axis and the elapsed time on the horizontal axis. Test A is-◆-, Test B is-■-, Test C is-▲-, and Test D is-●- And plotted in FIG.

<Conclusion>
From Tables 4 to 7 and FIG.
When copper sulfide << 5 >> coexists in the arsenic acid solution << 1 >> sample containing Cu ions at the start of the reaction (tests B to D), the removal of Cu ions proceeds from the start of the reaction. In addition, the coexistence of the copper sulfide << 5 >> has dramatically improved the reactivity, and furthermore, the effect of suppressing the reduction of arsenic acid (pentavalent As) to arsenous acid (trivalent As) could be found. .
On the other hand, when copper sulfide << 5 >> was not present in the arsenic acid solution << 1 >> sample containing Cu ions at the start of the reaction (test A), the removal of Cu ions hardly proceeded. In addition, reduction of arsenic acid (pentavalent As) to arsenous acid (trivalent As) has progressed, and the original purpose could not be achieved. With regard to this phenomenon, the present inventors made it possible for SO ₂ gas << 3 >> to be preferentially consumed for reduction of arsenic acid (pentavalent As) by making copper sulfide << 5 >> exist in the liquid at the beginning of the reaction. suppressing, and, by promoting the reaction between Cu ion and S ^0, are presumed to be allowed to proceed removal of Cu ions.

The existence effect of copper sulfide << 5 >> could be confirmed even at a concentration of 2 dry · g / L (Test B). The presence effect of copper sulfide << 5 >> increased with the concentration of copper sulfide << 5 >>, but the concentration was 70 dry · g / L (test D), which was close to 10 dry · g / L (test C). Met.
Then, if the concentration of copper sulfide "5" 10dry · g / L or more, at the time point (time point 15 min) was blown a SO ₂ gas "3" of the total molar amount equimolar amount of dissolved Cu ions, initially dissolved 90% or more of the Cu ions were removed, and the arsenic acid (pentavalent As) ratio was 85%.

(2) blowing SO ₂ gas, effect test methods to replace the mixed gas of SO ₂ gas and air, described above, "(1) Cu elemental sulfur in the arsenic acid solution" 1 "containing the ions ( S ⁰ ) << 4 >> and copper sulfide << 5 >> and SO ₂ gas << 3 >> is blown into this embodiment, but the copper sulfide concentration is 70 dry · g / L and the sampling interval is The interval was 5 minutes and the process was completed until the end of 30 minutes.

<Mixed composition of blowing gas>
99.9% SO ₂ gas simple (same as (1) described above) << 3 >> 100 cc / min (Test E)
99.9% SO ₂ gas and air mixed (SO ₂ : air = 1: 1) gas << 3 ^* >>, SO ₂
100cc / min + air 100cc / min (Test F)
Mixing of 99.9% SO ₂ gas and air (SO ₂ : air = 1: 5) gas << 3 ^* >>, SO ₂ 100 cc / min + air 500 cc / min (test G)
In addition, SO ₂ gas and air were blown out from the blown glass tube after cutting out and mixing predetermined amounts from the respective compression cylinders.

Table 8 shows changes in pH value and arsenic acid (pentavalent As) ratio for each sampling time of tests E to G, and Table 9 shows changes in dissolved Cu ion concentration and dissolved Cu ion removal rate. In addition, a graph with the vertical axis representing the arsenic acid (pentavalent As) ratio and the horizontal axis representing the elapsed time is plotted, with test E plotted as-◆-, test F as-■-, and test G as-▲-. 2 and plotting the dissolved Cu ion concentration on the vertical axis and the elapsed time on the horizontal axis, and plotting Test E with-◆-, Test F with-■-, and Test G with-▲- did.

<Conclusion>
From Tables 8 and 9 and FIGS.
Whether pure SO ₂ gas << 3 >> was blown into the arsenic acid solution << 1 >> sample containing Cu ions or a mixed gas << 3 ^* >> of SO ₂ gas and air was blown, the dissolved Cu ions Although there is almost no difference in removal capability, it has been found that the arsenic acid (pentavalent As) ratio can be maintained high when a mixed gas <3 ^* > of SO ₂ gas and air is blown. That is, by blowing a mixed gas of SO ₂ gas and air << 3 ^* >>, arsenic acid (pentavalent As) is reduced to arsenous acid (trivalent As) compared to the case where pure SO ₂ gas << 3 >> is blown. Cu ions can be removed while being suppressed.

SO ₂ in the gas and air mixture gas "3 ^*", and in the time considered range, the difference in reactivity by mixing amount of the difference between the SO ₂ gas and air was observed. However, if the amount of gas to be blown is large, it is disadvantageous in terms of calorie (heat is taken away to the outside), and (SO ₂ + air) is preferably (1 + 1).
From the above, it was found that by using a mixed gas << 3 ^* >> of SO ₂ gas and air, the pentavalent As ratio can be kept high while maintaining the Cu removal ion ability.

On the other hand, when manufacturing scorodite << 10 >> from filtrate << 7 >> which is an arsenic acid concentrated solution in actual operation, the present inventors have a Cu ion concentration coexisting in the arsenic acid concentrated solution at 1 g / L or less. If it exists, the control of the particle growth of the scorodite << 10 >> crystal | crystallization to produce | generate could be made steady, and the knowledge that the said scorodite << 10 >> manufacture could be performed stably was acquired.
Then, it was found that the pentavalent As ratio can be secured at 90% or more by terminating the de-Cu ion reaction at a stage where about 0.5 to 1 g / L of dissolved Cu ions remain.
Administration of the reaction is blown SO ₂ gas "3", or, easily controlled can be in an amount of mixed gas ^{"3 *"} of the SO ₂ gas and air.

(3) Cyclic reuse of the wet recovery deposit containing copper sulfide produced Copper sulfide << 5 >> is present in the arsenic acid << 1 >> solution containing Cu ions, and SO ₂ gas << 3 >><< 3 ^* When the reaction in the form of blowing is completed, the wet collection residue << 8 >> mainly composed of copper sulfide is recovered. This wet collection thing << 8 >> becomes a copper smelting raw material << 11 >>. Further, the recovered residue << 8 >> includes unreacted elemental sulfur (S ⁰ ) << 4 >>.
Therefore, in the subsequent round of the reaction, the recovered gluteal product "8", using Te repeated "9" as the copper sulfide source and S ⁰ source and consider cyclical reuse.

<First reaction, preparation of temple samples>
Elementary sulfur (S ⁰ ) << 4 >> and copper sulfide << 5 >> are present in the arsenic acid solution << 1 >> containing Cu ions described in (1) above, and SO ₂ gas << 3 >> In the embodiment, wet copper sulfide << 5 >> was added at 70 dry · g / L, and the elemental sulfur (S ⁰ ) << 4 >> having a molar amount 4 times the total molar amount of Cu ions was added. Similarly, the reaction conditions were a liquid temperature of 75 ° C., an SO ₂ gas << 3 >> blowing rate of 100 cc / min, and the reaction was completed in 15 minutes.
The composition of the initial reaction is shown in Table 10.

  After completion of the first reaction, the product was filtered << 6 >> to obtain a filtrate << 7 >> and a recovered residue << 8 >>. The filtrate << 7 >> was subjected to composition analysis. On the other hand, the post-reaction liquid is attached to the recovered residue << 8 >>, and the attached post-reaction liquid is mixed into the next step. Here, from the viewpoint of accurately grasping the reaction in the next step, using 600 cc of pure water heated to about 40 ° C., the recovered pulp << 8 >> is repulped and subjected to filtration again. A 175 wet · g wet collection << 8 >> was recovered. When 5 wet · g was collected from the collected residue << 8 >> and the moisture was measured, the moisture was 65% by mass. Table 13 shows the composition analysis result of the filtrate << 7 >>.

<Repeated first reaction>
The total amount of the washed wet recovered product << 8 >> recovered in the first reaction in the arsenic acid solution << 1 >> containing Cu ions described in (1) above, and the total molar amount of Cu ions An equimolar amount of S ⁰ << 4 >> was added, and similarly, the reaction was terminated for 15 minutes at a liquid temperature of 75 ° C. and a SO ₂ gas << 3 >> blowing rate of 100 cc / min.
In addition, Table 11 shows the composition of the first repeated reaction.

After completion of the first reaction repeatedly, the product was filtered << 6 >> to obtain a filtrate << 7 >> and a recovered residue << 8 >>. The filtrate << 7 >> was subjected to composition analysis, while the recovered residue << 8 >> was subjected to repulp washing in the same manner as the first reaction and again subjected to filtration. In this way, 167 wet · g wet collection << 8 >> was recovered. When 5 wet · g was collected from the wet collection residue << 8 >> and the water content was measured, the water content was 61% by mass.
Table 13 shows the composition analysis result of the filtrate << 7 >>.

<Repeated second reaction>
In the arsenic acid solution << 1 >> containing Cu ions described in (1) above, the total amount of the wet-recovered wet collection << 8 >> recovered by the first reaction described above, and the total Cu ions A molar amount and an equimolar amount of S ⁰ << 4 >> were added, and similarly, the reaction was terminated at a liquid temperature of 75 ° C. and an SO ₂ gas << 3 >> blowing rate of 100 cc / min for 15 minutes.
In addition, Table 12 shows the composition of the repeated second reaction.

  After the second reaction was repeated, the product was filtered << 6 >>, and the wet collection residue << 8 >> was washed with the same repulp as described above to recover a 164 wet · g wet collection residue << 8 >>. When 5 wet · g was collected from the wet collection residue << 8 >> and the moisture was measured, the moisture was 58% by mass. In addition, the composition of the filtrate << 6 >> was also analyzed. Table 13 shows the composition analysis result of the filtrate << 6 >>.

<Conclusion>
From the results shown in Table 13, there is a difference between the newly produced wet copper sulfide << 5 >> and the wet recovered residue << 8 >> even when the Cu ion removal performance and the arsenic acid (pentavalent As) ratio are compared. Absent. Thus, cyclical reuse of copper sulfide and S ⁰ is generated as wet recovered gluteal product "8" is believed to be and effective.
Specifically, in the initial reaction, the newly produced wet copper sulfide << 5 >> and the elemental sulfur (S ⁰ ) << 4 >> having a molar amount 4 times the total molar amount of Cu ions contain Cu ions. Add to arsenic acid solution << 1 >>. And the wet collection thing << 8 >> after completion | finish of the said first reaction is cyclically reused as copper sulfide in reaction after the next time. By this cyclic reuse, the addition of new copper sulfide << 5 >> and the addition of elemental sulfur (S ⁰ ) << 4 >> is equivalent to the total molar amount of Cu ions. It is possible to continue. As a result, drug costs and product processing costs can be significantly reduced.

<< 1 >> Arsenic acid solution << 2 >> Sulfurization reaction << 3 >> SO ₂ gas << 3 ^* >> Mixed gas of SO ₂ gas and air << 4 >> Single element sulfur (S ⁰ )
"5" Copper sulfide "6" Filtration "7" Filtrate "8" Recovery residue "9" Repeated "10" Scorodite "11" Copper smelting raw material

Claims (5)

To the arsenic acid solution containing Cu ions, elemental sulfur (S ⁰ ) and copper sulfide are added, and the liquid temperature is set to 60 ° C. or higher, and SO ₂ gas or a mixed gas of SO ₂ gas and air is blown into the arsenic acid solution. A method for removing Cu ions from an arsenic acid solution, wherein Cu ions are removed as a deposit containing copper sulfide.   2. The Cu ion from the arsenic acid solution according to claim 1, wherein the reaction of removing the Cu ion as a precipitate containing copper sulfide is terminated when the Cu ion concentration becomes 1 g / L or less. Removal method. _3. The removal of Cu ions from the arsenic acid solution according to claim 1, wherein the total amount of SO ₂ gas blown is equal to or less than an equimolar amount of the total molar amount of Cu ions dissolved in the arsenic acid solution. Method.   The method for removing Cu ions from an arsenic acid solution according to any one of claims 1 to 3, wherein the copper sulfide is added in an amount of 10 g / L or more to the arsenic acid solution. 5. The method according to claim 1, wherein the copper sulfide containing the removed copper sulfide is added as copper sulfide and elemental sulfur (S ⁰ ) in the next and subsequent methods of removing Cu ions from the arsenic acid solution. A method for removing Cu ions from the arsenic acid solution according to claim 1.

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