JP2003137552A - Method for producing arsenious acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently producing arsenious acid at a low cost by preventing the lowering of reaction rate by controlling sulfuric acid concentration when solid arsenious acid extracted from an arsenic sulfied- containing material is oxidized and dissolved, and by generating a copper ion necessary as a catalyst instead of adding a copper sulfate solution in a system. SOLUTION: The method comprises a first step to recover a solid content which contains arsenious acid by cooling a slurry containing an extracted residue after extracting aresenic in the copper sulfate solution from the arsenic sulfied-containing material, a second step to oxidize trivalent arsenic to pentavalent arsenic whose solubility is large by aeration while controlling the sulfuric acid concentration to 70 g/L or less after copper oxide and a solution containing sulfuric acid are added to the solid content containing arsenious acid and a third step to deposit arsenious acid by reducing pentavalent arsenic in a solution after solid-liquid separation and to recover it.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for separating and refining arsenous acid from an arsenic sulfide-containing material and recovering it.

[0002]

2. Description of the Related Art As a method for purifying and recovering arsenous acid from an arsenic sulfide-containing material such as a sulfurized starch produced as a copper smelting intermediate, there is a method described in JP-B-60-46048.

In this method, as shown in FIG. 2, in a first step, an arsenic sulfide-containing substance such as a sulfide compound is reacted with an aqueous solution containing copper sulfate in a warmed state to convert arsenic into arsenite ions in the liquid. Is dissolved in and extracted, and the slurry containing the extraction residue is cooled to recover the solid content containing arsenous acid.

In the next second step, the recovered solid content containing arsenous acid is repulped into a slurry to aerate in the presence of 1 g / l or more of copper ions to oxidize most of the arsenic acid to arsenic acid. Dissolve in solution. After that, in the third step, arsenic acid in the solid-liquid separated solution is reduced with sulfurous acid gas (SO ₂ ) to precipitate as arsenous acid.

According to this method, the recovery rate of arsenic is 70%.
As described above, impurities such as Zn are discharged from the filtrate out of the system when solids are obtained in the second step, whereby concentration can be prevented and high-quality arsenous acid can be recovered.

[0006]

[Problems to be Solved by the Invention] Japanese Patent Publication No. 60-4
In the method for producing arsenous acid described in JP-A-6048, since copper ions are supplied to the first step for extracting arsenic, in another copper extraction step, a sulfuric acid-containing solution (the first step indicated by * in FIG. 2 is used). Copper sulfate is extracted from copper oxide to produce a copper sulfate solution by using the replacement final solution, the final reduction solution of the third step, the cleaning solution of the residue of the second step, etc.).

However, at the same time, since copper ions required as a catalyst for the oxidation reaction are supplied to the second step, a low-concentration copper sulfate solution having a different concentration from the high-concentration copper sulfate solution for arsenic extraction in the first step is used. It had to be manufactured separately. For this reason, two kinds of copper sulfate solutions having different concentrations had to be produced in the copper extraction step, which was extremely uneconomical.

Further, the sulfuric acid concentration in the slurry has an adverse effect on the oxidation reaction rate in the second step.
It is desirable to control the operation at 0 g / l or less. However, it is difficult to control the sulfuric acid concentration because the sulfuric acid concentration in the slurry in the second step is determined by the arsenic grade in the sulfurized starch treated in the first step.

Specifically, the higher the arsenic grade of the sulfided starch in the first step, the more the consumption of copper sulfate and the amount of sulfuric acid produced as a by-product increase. Most of this sulfuric acid is separated as a filtrate, but since the water content attached to the residue is about 50%, the sulfuric acid content brought into the second step increases. This sulfuric acid content may be neutralized with an alkali such as NaOH or Ca (OH) _2. However, contamination of the product with Na or scaling due to gypsum precipitation poses a problem and increases the cost of the unnecessary neutralizing agent. It was difficult to put it into practice.

The present invention has been made in view of such conventional circumstances.
Japanese Patent Publication Sho-60- for refining and recovering arsenous acid from arsenic sulfide-containing materials
The method described in JP-A-46048 is improved so that the sulfuric acid concentration can be controlled in order to prevent a reduction in the rate of the oxidation reaction in the second step, and copper ions necessary as a catalyst for the oxidation reaction in the second step are generated in the system. By omitting the production and supply of the low-concentration copper sulfate solution to the second step, it is an object of the present invention to provide an efficient and low-cost production method of arsenous acid.

[0011]

In order to achieve the above object, the present invention extracts arsenic as arsenite ions from an arsenic sulfide-containing material in a copper sulfate-containing aqueous solution, and cools a slurry containing an extraction residue to remove arsenite. The first step of recovering the solid content containing is added, the copper oxide and the sulfuric acid-containing solution are added to the recovered solid content containing arsenous acid, and the copper sulfate extraction reaction and the arsenic oxidation reaction are simultaneously performed by aeration to produce trivalent arsenic. The method is characterized by including a second step of oxidizing to pentavalent with high solubility and dissolving in a solution, and a third step of reducing pentavalent arsenic in the solid-liquid separated solution to precipitate and recover arsenous acid. .

In the method for producing arsenous acid of the present invention, the concentration of sulfuric acid in the solution in the second step is 70 g /
The addition amount of copper oxide is controlled based on the sulfuric acid concentration of the sulfuric acid-containing solution so as to be 1 or less.
Further, in the second step, the copper ion concentration in the solution during the oxidation reaction is controlled to be in the range of 1 to 30 g / l.

[0013]

DETAILED DESCRIPTION OF THE INVENTION A process diagram of the method of the present invention is shown in FIG. Further, the reaction formulas of the respective steps are shown in the following chemical formulas 1 to 3, and the first step and the third step are the same as those described in JP-B-60-4604.
The method is the same as that described in 8.

In the first step of the method of the present invention, the arsenic in the arsenic sulfide-containing material is extracted as arsenite ions with an aqueous solution containing copper sulfate. The slurry containing the extraction residue is cooled, and the solid content containing arsenous acid is collected as the replacement residue.
The copper sulfate solution used in the first step is produced in the copper extraction step shown in FIG. 1, and the sulfuric acid-containing solution used in this case is the replacement final solution in the first step, the reduction final solution in the third step, and the second step. The cleaning solution for the residue (shown by * in FIG. 1) and the like can be repeatedly used.

In the second step, copper oxide and a sulfuric acid-containing solution are added to the solid content containing arsenous acid recovered in the first step, and 2
By raising the temperature to 0 ° C or higher and performing aeration, 3
Valence arsenic (arsenous acid) is oxidized to pentavalent (arsenic acid) having high solubility and dissolved in the solution. After this is filtered and solid-liquid separated, in the third step, a reducing agent such as SO ₂ is added to the separated solution to reduce pentavalent arsenic, and arsenous acid is deposited and recovered. As the copper sulfate solution used in the second step,
The replacement final solution in the first step, the reduction final solution in the third step, the residue cleaning solution in the second step, and the like can be repeatedly used.

[0016]

Embedded image First step: As ₂ S ₃ + 3CuSO ₄ + 4H ₂ O = 2HAsO ₂ +
3CuS + 3H ₂ SO ₄

[0017]

Embedded image Second step: CuO + H ₂ SO ₄ = CuSO ₄ + H ₂ O As ₂ O ₃ + O ₂ + 3H ₂ O = 2H ₃ AsO ₄

[0018]

Embedded image Third step: 2H ₃ AsO ₄ + 2SO ₂ = As ₂ O ₃ + 2H ₂ SO ₄
+ H ₂ O

In the method of the present invention, in the second step, as a copper ion which acts as a catalyst for the oxidation reaction, a solution containing sulfuric acid together with copper oxide is added instead of the copper sulfate solution in the conventional method. At the same time that the copper sulfate extraction reaction takes place in situ in the system, arsenous acid is oxidized.
Therefore, only the high-concentration copper sulfate solution to be supplied in the first step of arsenic extraction needs to be manufactured, which is much more economical than the conventional method.

The effect of sulfate ion on the oxidation reaction in the second step has already been described in the above-mentioned JP-B-60-46048. The relationship between the sulfuric acid concentration at the initial stage of the oxidation reaction and the oxidation reaction rate in the plant currently operating is shown in FIG. In this oxidation reaction, the required rate is determined according to the scale of the equipment such as the reaction tank. To achieve a reaction rate of 1 g / l · hr or more, which is necessary for the liquid treatment capacity of the plant, the sulfuric acid concentration should be 70 g from FIG. It turns out that it is necessary to make it less than / l.

In carrying out the method of the present invention, 70 g of the target sulfuric acid concentration in the oxidation reaction is obtained in order to obtain an oxidation rate which does not exceed the residence time calculated from the size of the reaction tank.
It may be set at less than / l. Also, the lower the sulfuric acid concentration, the faster the oxidation rate, and if the oxidation rate doubles, the equipment required for the oxidation reaction requires only half the capacity. Therefore, the lower the sulfuric acid concentration, the more economically advantageous.

However, when copper sulfate is produced in situ from a solution containing copper oxide and sulfuric acid by the method of the present invention, an amount of copper ions corresponding to the reduction of the sulfuric acid content is produced in the liquid. Therefore, if the copper concentration rises too much, there is a concern that the amount of copper mixed in the product may increase when the arsenic acid is reduced and crystallized to arsenous acid in the third step.
The copper grade, which is a trace impurity in arsenous acid, is assumed to exist mainly in the adhered water.

Impurities can be reduced by increasing the particle size of arsenous acid or by cleaning for a long time. However, when the concentration of copper ions in the solution exceeds 30 g / l, the cleaning time becomes long and the amount of treatment liquid increases, which leads to enlargement of equipment and the amount of liquid to be discharged to the outside of the process increases. Inconveniences such as lowering the recovery rate of
Therefore, in order to reduce the copper quality of arsenous acid to 10 ppm or less, it is usually desirable to set the copper ion concentration to about 1 to 30 g / l.

Therefore, the addition amount of copper oxide to be supplied in order to obtain the target sulfuric acid concentration may be calculated by the following calculation, and optimum values may be selected as the copper ion concentration and the sulfuric acid concentration. Therefore, when the arsenic sulfide-containing material is a sulfurized starch produced in the heavy metal separation process by the formation of sulfurized precipitate in copper smelting, even if the arsenic sulfide grade of the sulfurized starch varies, the optimum copper ion concentration and sulfuric acid concentration are always maintained. Can be stably obtained.

Reduced sulfuric acid concentration (g / l) = sulfuric acid concentration at the initial stage of oxidation
(g / l) -Target sulfuric acid concentration (g / l) Required Cu addition amount (kg) = Reduced sulfuric acid concentration (g / l) x Treatment liquid amount (m
³ ) ÷ 98 × 63.5 Copper oxide addition amount (kg) = Required Cu addition amount (kg) ÷ Copper oxide Cu
Grade (%) Copper concentration increase (g / l) = Required Cu addition amount (kg) ÷ Treatment liquid amount (m ³ )

[0026]

EXAMPLE According to the process shown in FIG. 1, first, in a first process, a copper sulfate solution and water were added to an arsenic sulfide precipitate to form a slurry, and arsenic was extracted by stirring while heating at 70 to 75 ° C. The whole was cooled to room temperature and solid-liquid separated, and the solid content containing arsenous acid was recovered. In the copper extraction step, only the high-concentration copper sulfate solution supplied to the first step was manufactured.

In the next second step, this solid content was added to a sulfuric acid-containing solution together with copper oxide to be repulped, and air was blown in while aerating by heating at 70 to 75 ° C.
The slurry was filtered and solid-liquid separated. In the third step, SO ₂ gas was supplied to the obtained solution to reduce it, and the precipitated arsenous acid was filtered and recovered. Incidentally, as the sulfuric acid-containing solution used in the second step, a reduction final solution containing sulfuric acid by-produced in the third step,
The in-system repeating solution used in the copper extraction step, such as the final substitution solution obtained in the first step and the washing solution for the residue obtained in the second step, was added as it was.

For each of Samples 1 to 10 in the present invention, the rate of the oxidation reaction in the second step was compared with the conventional example carried out by the method of Japanese Patent Publication No. 60-46048 along with the copper concentration and the sulfuric acid concentration. The results are shown in Table 1 below.
In Table 1, the average value and standard deviation of the oxidation rate, the copper concentration, and the sulfuric acid concentration were calculated for each sample and are shown together.

[0029]

[Table 1]

In each of the samples of the present invention, it can be seen that the sulfuric acid concentration can be suppressed to a target value of 70 g / l or less, and the copper concentration is also controlled to 30 g / l or less. On the other hand, in the conventional example, since there is no means for controlling the sulfuric acid concentration, the sulfuric acid concentration is extremely high. At this time, the rate of the oxidation reaction of the example of the present invention is obviously higher than that of the conventional example.

[0031]

According to the present invention, since only the copper sulfate solution supplied to the first step has to be produced in the copper extraction step, the agitator and pump power can be reduced, and arsenous acid can be produced at low cost. can do.

In the second step of oxidizing and dissolving arsenous acid into arsenic acid, copper oxide is added to the slurry together with the sulfuric acid-containing solution, so that the extraction reaction of copper sulfate and the oxidation reaction of arsenic proceed at the same time. The sulfuric acid content is reduced by the amount consumed in the copper extraction reaction. Therefore, the sulfuric acid concentration in the second step, which was conventionally uncontrollable, can be arbitrarily controlled, and the desired oxidation reaction rate can be stably maintained.

[Brief description of drawings]

FIG. 1 is a process drawing of the method of the present invention.

FIG. 2 is a process diagram of a conventional method.

FIG. 3 is a graph showing the relationship between the sulfuric acid concentration and the oxidation rate in the second step.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuhiko Kamada             3-5-3 Nishihara-cho, Niihama-shi, Ehime Sumitomo Kin             Besshi Works, Inc. (72) Inventor Harumasa Kurokawa             3-5-3 Nishihara-cho, Niihama-shi, Ehime Sumitomo Kin             Besshi Works, Inc. F term (reference) 4G048 AA02 AB02 AB08 AE01 AE05

Claims (4)

[Claims] 1. A first step in which arsenic is extracted as arsenite ions from an arsenic sulfide-containing material into a copper sulfate-containing aqueous solution, and a slurry containing an extraction residue is cooled to recover a solid content containing arsenous acid; A solution containing copper oxide and sulfuric acid is added to the solid content, and the copper sulfate extraction reaction and the arsenic oxidation reaction are simultaneously performed by aeration to oxidize trivalent arsenic into pentavalent one having high solubility and dissolve it in the solution. A method for producing arsenous acid, comprising: two steps; and a third step of reducing pentavalent arsenic in a solid-liquid separated solution to precipitate and recover arsenous acid. 2. The addition amount of copper oxide is controlled based on the sulfuric acid concentration of the sulfuric acid-containing solution so that the sulfuric acid concentration in the solution in the second step is 70 g / l or less. The method for producing arsenous acid according to claim 1. 3. The method for producing arsenous acid according to claim 1, wherein in the second step, the concentration of copper ions in the solution during the oxidation reaction is controlled within the range of 1 to 30 g / l. . 4. The arsenous acid-containing substance according to claim 1, wherein the arsenic sulfide-containing substance is a sulfided starch produced in a heavy metal separation step by sulfide precipitation formation in copper smelting. Production method.