JPS6247813B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing arsenous acid from an arsenic sulfide-containing precipitate and a copper sulfate-containing aqueous solution. The roasting method has been used for a long time to produce arsenous acid, but since this is a dry method, construction costs are high.
There are also difficulties in environmental management. In the wet method, arsenic in various aqueous solutions is relatively simply precipitated and separated as arsenic sulfide by adding a sulfurizing agent. However, arsenic sulfide is not marketable. Therefore, it has been desired to establish a wet process for producing marketable arsenic acid from arsenic sulfide. The arsenic sulfide-containing precipitate used as a raw material in the arsenous acid manufacturing method according to the present invention is obtained by adding a sulfiding agent to the process liquid of a non-ferrous smelting factory, such as waste sulfuric acid generated from a non-ferrous smelting flue gas sulfuric acid manufacturing factory or the process liquid of a hydrometallurgical smelting process. Since it is a precipitate produced by adding it, it contains some impurities. In addition, an aqueous solution containing copper sulfate,
Since it is an aqueous solution in which crude copper sulfate recovered in the copper smelting process is dissolved or other intermediate process liquid, it contains impurities. Arsenous acid produced by mutually reacting these raw materials tends to contain copper, sulfur, compounds thereof, or other impurities, making it difficult to obtain a highly pure product. In the conventional method, the slurry concentration of the arsenic sulfide-containing precipitate during the mutual reaction between the copper sulfate-containing aqueous solution and the arsenic sulfide-containing precipitate is limited to a low concentration, and the
By strictly controlling the ratio of CuSC ₄ and As,
Moreover, by keeping the sulfuric acid concentration of the solution before arsenous crystallization low, it was possible to obtain high purity arsenous acid for the first time. Satisfying the above-mentioned conditions is not easily achieved in actual factory production management, and also results in a significant decline in process capability. The present inventors focused on the shortcomings of the above-mentioned conventional methods, and as a result of intensive research into a method for more efficiently producing high-purity arsenous acid from arsenic sulfide-containing precipitates and copper sulfate-containing aqueous solutions, they divided the reaction into two stages. In the first-stage arsenic elution reaction, the ratio of arsenic and copper in the reaction system is determined by the reaction equation.
As ₂ S ₂ +3CuSO ₄ +4H ₂ O=3CuS+2HASO ₂ +
3H ₂ SO ₄ is reacted while maintaining a state of excess copper and lack of arsenic, and then in the second step copper removal reaction, the reaction is carried out while maintaining a state of excess arsenic and lack of copper. As a result, it was discovered that high-purity arsenous acid could be produced at a high yield without satisfying the complicated operating conditions described above. That is, as described in the claims, the present invention provides a method for wet producing copper sulfide and arsenous acid by reacting an aqueous solution containing copper sulfate with a precipitate containing arsenic sulfide. Therefore, by reacting the copper sulfate-containing aqueous solution with the arsenic-containing copper sulfide produced in the copper removal step that follows the arsenic elution step, and separating the resulting slurry into solid and liquid, copper sulfide and the arsenic eluted solution are generated. Then, in a copper removal step, the arsenic elution solution and the arsenic sulfide-containing precipitate are reacted, and solid-liquid separation is performed to generate arsenic-containing copper sulfide and the copper removal solution, and the arsenic-containing Copper sulfide is repeatedly subjected to the arsenic elution step, and the copper-removed liquid is further reduced, concentrated and cooled to crystallize arsenous acid, and arsenous acid is produced by solid-liquid separation. The present invention provides a method for producing arsenous acid. Next, the content of the present invention will be explained in detail. The copper sulfate-containing aqueous solution may be an aqueous solution in which crude copper sulfate or purified copper sulfate is dissolved, or a hydrometallurgical process liquid, such as a copper sulfate manufacturing process liquid from copper electrolytic waste liquid. When applying to the present invention an aqueous solution in which electrolytically precipitated copper, which is an electrolytic deposit produced during electrolysis, is dissolved, the copper and arsenic in the aqueous solution are also separated at the same time, so the effect of killing two birds with one stone can be obtained. It will be done. As the arsenic sulfide-containing precipitate has been described above, it will not be described again. In the reaction of the arsenic elution step, it is necessary that the amount of copper be in sufficient excess with respect to the amount of arsenic. That is, if the amount of copper per atom of arsenic is less than 1.5 atoms, it is insufficient, and it is desirable that the amount of copper be present in an amount of 2.5 atoms or more per atom of arsenic. The upper limit of the amount of copper may be as long as it does not interfere with the next copper removal step, and there is no need to limit it numerically. In this step, the solid material is arsenic-containing copper sulfide produced from the next copper removal step, but there is no need to particularly limit the slurry concentration. However, in order to maximize the processing capacity with limited equipment, it is desirable to use a slurry concentration as high as possible, and as shown in Figure 1 and Table 1 of Examples, it is realistic to use a slurry concentration of 10% or more. It is true. The temperature and time of the reaction in this step may be about 70 to 90°C and about 90 to 150 minutes, respectively, and it is preferable to carry out the reaction with mechanical stirring. Solid-liquid separation after the arsenic elution reaction produces copper sulfide with a low arsenic content and an arsenic elution solution containing a large amount of copper and arsenic. Copper sulfide may be treated in a dry copper smelting process. The solution after arsenic elution is processed in the next copper removal step. In the copper removal step, the arsenic sulfide-containing precipitate is added to the solution after arsenic elution and caused to react, thereby reducing the amount of copper in the solution as much as possible. As the amount of copper in the solution decreases, the arsenic in the arsenic sulfide-containing precipitate dissolves, and solid-liquid separation after the reaction completes the separation of the decoppered solution, which has a high arsenic content and an extremely low copper content, from the initial copper-free solution. Copper sulfide containing arsenic is produced in which part of the arsenic and copper are substituted for the arsenic sulfide-containing precipitate. In the reaction system of the copper removal process, it is necessary that arsenic be in excess of copper. That is, the amount of copper per atom of arsenic must be 1.5 atoms or less. Although the slurry concentration is not particularly limited, 10% or more is realistic when considering downsizing of equipment. The temperature is
The reaction may be carried out at 70 to 90°C for 90 to 150 minutes, preferably with mechanical stirring. The arsenic copper sulfide produced in this step is treated in the arsenic elution step described above. Since the copper-removed solution is an arsenic-containing solution with an extremely low copper content, high-purity arsenous acid can be produced from this solution. First, a reducing agent is added to the solution after copper removal to reduce pentavalent arsenic present in the solution to trivalent arsenic. The reducing agent in this case may be a relatively weak reducing agent, and SO ₂ -containing gas is used in non-ferrous smelting plants. Of course, liquid sulfurous acid or sulfurous acid water may be used.
This is because when these reducing agents are used, it is advantageous that only sulfuric acid is produced as a by-product during the reaction. If there is no problem even if alkali ions are mixed into the system, an aqueous solution of alkali sulfite or acidic alkali sulfite, such as sodium sulfite or acidic sodium sulfite, may be used. The reduced arsenic-containing solution is heated or evaporated under reduced pressure and then cooled to crystallize arsenic acid and undergo solid-liquid separation to recover high-purity arsenic acid. In the concentrated liquid before arsenous acid crystallization, the sulfuric acid concentration increases because sulfuric acid derived from SO ₂ blown for reduction is added to sulfuric acid derived from the raw material copper sulfate solution. As shown in FIG. 2, the higher the sulfuric acid concentration, the lower the solubility of trivalent arsenic and therefore the higher the crystallization rate of arsenous acid, which is preferable. Therefore, as shown in Table 1, a sulfuric acid concentration of about 300 g/m is suitable. If the sulfuric acid concentration before arsenous acid crystallization is less than 250 g/min, as described above, the crystallization rate will be low, and the amount of liquid handled before and after the crystallization process will increase, and the direct recovery rate of arsenous acid will decrease, which is not efficient. According to the method of the present invention, arsenous acid of sufficiently high purity can be produced even if the sulfuric acid concentration of the pre-crystallization solution exceeds 250 g/ml. Of course, it contains a high concentration of sulfuric acid, and contains Cu and impurities.
If a solution containing tens of grams of Fe, Ni, etc. is heated and concentrated, the impurities such as sulfates will precipitate, so care should be taken to avoid this. The liquid after crystallization of arsenous acid is dilute sulfuric acid that contains some arsenic, so it may be partially repeated into the system of this process, but since doing so will accumulate sulfuric acid in the system, the process of dissolving intermediate products such as dust is necessary. Alternatively, it is reasonable to add it to a process that requires dilute sulfuric acid, such as a gas cleaning process. Examples are shown below. Example: Arsenic sulfide precipitate produced by sulfiding arsenic waste acid discharged from a copper smelting flue gas sulfuric acid factory,
Regarding an example in which high-purity arsenous acid was manufactured and tested by the method of the present invention using a sulfur-brewed copper aqueous solution as a raw material, the flow is shown in Figure 1, and the amount and composition of each process product are shown in Figure 1.
Shown in the table. Effects As can be seen from Figure 1 and Table 1, using arsenic sulfide-containing precipitates and copper sulfate-containing aqueous solutions as raw materials, the quality
Arsenous acid of 99.5% or more can be produced with a high yield of 90% or more using compact equipment based on a wet process. 【table】

[Brief explanation of the drawing]

FIG. 1 is a flow sheet in an example of the present invention, and FIG. 2 is a graph showing the relationship between the solubility of trivalent arsenic in a sulfuric acid solution and the temperature or free sulfuric acid concentration.

Claims (1)

[Claims] 1. In a method for wet production of copper sulfide and arsenous acid by reacting an aqueous solution containing copper sulfate with a precipitate containing arsenic sulfide, an aqueous solution containing copper sulfate and a copper-removal process subsequent to the arsenic elution step are used in an arsenic elution step. Copper sulfide and arsenic eluted solution are produced by reacting with arsenic-containing copper sulfide produced in the process and separating the resulting slurry into solid and liquid. After reacting the arsenic sulfide-containing precipitate, solid-liquid separation is performed to generate arsenic-containing copper sulfide and a post-copper removal solution, and the arsenic-containing copper sulfide is repeatedly subjected to the arsenic elution step, and further A method for producing arsenous acid, characterized in that arsenous acid is produced by reducing, concentrating and cooling a copper-removed solution to crystallize arsenous acid, and performing solid-liquid separation.