JPS6221728B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for separating and removing arsenic from an acidic solution containing arsenic. The smoke generated in the copper smelting process contains volatile components such as arsenic, cadmium, zinc, and lead in addition to copper, which is the main component of the raw material. Leaching with sulfuric acid is generally performed to recover valuables such as copper and separate impurities such as arsenic from this smoke ash.
When smoke ash is leached with sulfuric acid, lead becomes lead sulfate and is insoluble in sulfuric acid solution, so it is separated as a residue and used as a lead raw material. On the other hand, copper, arsenic, cadmium, zinc, etc. are leached out by sulfuric acid and enter the solution. The present invention relates to a method for efficiently separating and removing arsenic from this solution. Conventionally, as a method for recovering arsenic from solutions containing copper, arsenic, cadmium, zinc, etc., the valuable copper is first converted into copper sulfide or precipitated copper using neutralizing agents such as hydrogen sulfide, iron powder, and calcium carbonate. Separate and collect. Next, a neutralizing agent is further added to the copper-depleted liquid to raise the pH to 4 or higher, and if there is little iron in the liquid, an iron salt is added, and the PH of the liquid is maintained at 4 or higher. A commonly used method is to perform air oxidation while separating and removing arsenic as iron arsenate.
However, these known methods not only have the drawback of requiring a copper removal step before arsenic separation, resulting in a large number of steps, but also have the disadvantage that the separation of arsenic particles is difficult due to PH.
Since it is carried out at a temperature of 4 or higher, a large amount of precipitated products will be produced.
The arsenic content of iron arsenate is also low, at less than 10%, and the subsequent disposal of the large amount of iron arsenate generated is a problem. Furthermore, when the liquid contains cadmium, a pH of 4 or more has the disadvantage of causing precipitation of cadmium in the iron arsenate. In this way, when separating arsenic from a solution containing arsenic and other heavy metals, if precipitation is caused at a pH of 4 or higher, arsenic can be completely separated from the solution, but if there is copper in the solution, It is necessary to separate this in advance, and if cadmium is present in the liquid, there is a drawback that cadmium will precipitate together with arsenic. Furthermore, since the pH during precipitation and separation of arsenic is as high as 4 or more, there is also the drawback that the amount of arsenic precipitates increases. For this reason, engineers in this field are researching various techniques for precipitation and separation of arsenic from solutions containing heavy metals such as copper in acidic regions with low pH. On the other hand, according to Japanese Patent Publication No. 56-6356, in order to precipitate and separate arsenic at a pH of 2.0 to 3.2, sulfuric acid is added to a sulfuric acid solution containing arsenic and heavy metals.
A treatment method is disclosed in which iron is added and then heated in a high-pressure vessel under oxygen pressure or air pressure. According to this method, arsenic can be separated by precipitation from pH 2.0.
3.2, it is said that arsenic and other heavy metals can be separated well. However, as seen in the examples, the treatment is carried out at a high temperature of 130° C. in a container pressurized to 1.5 kg/cm ² G with industrial oxygen, which has the disadvantage of requiring expensive equipment. There is also the operational disadvantage of handling acidic solutions in high-pressure vessels. Furthermore, 0.14 to 0.39 g of arsenic still remains in the filtrate after arsenic has been precipitated, indicating that the precipitation and separation of arsenic is not complete. As described above, it is said that it is extremely difficult to efficiently precipitate and separate arsenic from other heavy metals in an acidic region with a pH of 3 or less, but the inventors have solved this drawback and simplified the process. After conducting various research on how to efficiently separate arsenic from acidic solutions containing other heavy metals using iron arsenate with an arsenic content of 10% or more, we succeeded in developing the following process. The method will be explained below. In acidic solutions containing arsenic and heavy metals such as copper, cadmium, and zinc, arsenic is dissolved in trivalent or pentavalent form. Since trivalent arsenic is difficult to separate by precipitation, an oxidizing agent is first added to the liquid to oxidize trivalent arsenic to pentavalent arsenic. The oxidizing agent used at this time includes potassium permanganate, hydrogen peroxide, chlorine, etc., and it is sufficient that the amount added is twice the chemically required amount of trivalent arsenic. After the oxidation of arsenic is completed, the pH of the liquid
is adjusted to 1.5 to 3.0, ferrous salt is added to this,
While maintaining the pH of the liquid at 1.5 to 3.0, preferably 2.0 to 2.6, oxidation is carried out with air, industrial oxygen, or an oxidizing agent such as those exemplified above to oxidize ferrous iron to ferric iron and remove arsenic. is precipitated and separated as iron arsenate. This method not only efficiently separates arsenic from other heavy metals such as copper, but also allows the reaction to occur at a pH of 2.0.
Since it is carried out in the acidic region of ~2.6, the arsenic content is
More than 10% iron arsenate can be obtained. The temperature of the solution during the above reaction treatment may be at room temperature or in a heated state below the boiling point at atmospheric pressure. Examples of the present invention are shown below. Example 3.6 g of potassium permanganate is added to 1 liter of a sulfuric acid acidic solution having a pH of 1.7 containing the ingredients shown in Table 1 below, and the mixture is stirred. Since this oxidation is completed in a short time, the stirring time may be several minutes.

[Table] Next, a small amount (3.4 g) of calcium carbonate was added to this solution to adjust the pH of the solution to 2.0-2.6.
After further adding 25g of ferrous sulfate (calcium carbonate and ferrous sulfate may be added first), air oxidation is performed while maintaining the pH of the liquid at 2.0 to 2.6, and the ferrous sulfate is replaced with ferrous sulfate. Oxidizes to iron, precipitates arsenic as iron arsenate, and performs filtration separation. The components of the filtered iron arsenate and the filtrate are shown in Table 2.

[Table] By adding an oxidizing agent to the solution in Table 1, arsenic is removed only by air oxidation of ferrous salt as in the conventional method, without oxidizing trivalent arsenic to pentavalent arsenic. When the pH is in the range of 1.5 to 3.0, arsenic precipitation is insufficient, and the arsenic content in the filtrate after iron arsenate removal is, for example, 0.7 g/residual when the pH is 2.5. , the purpose of arsenic removal is not achieved. On the other hand, in order to completely remove arsenic, if the pH of the liquid is raised to 4.1 and air oxidized as in the conventional method, the arsenic in the filtrate will be less than 0.1g/, and the purpose of arsenic removal will not be achieved. Instead, the copper content in iron arsenate
5.2%, cadmium content is as high as 0.2%,
Separation of copper, cadmium and arsenic becomes worse. As can be seen from the above results, by the method of the present invention, arsenic can be efficiently separated from heavy metals such as copper and cadmium when the pH of the liquid is in the range of 1.5 to 3.0. In addition, in this method, the amount of iron used for precipitation is less than 10 parts per 1 part of arsenic (about 10 parts in the example).
Since the amount of iron arsenate precipitate is extremely small (2.2 parts), it has the advantage of reducing the amount of iron arsenate precipitate, and it is also extremely simple in terms of equipment, requiring only a container equipped with a simple stirrer.

Claims (1)

[Claims] 1 Add an oxidizing agent to an acidic solution containing heavy metals such as copper, cadmium, zinc, etc. and arsenic to oxidize the trivalent arsenic in the solution to pentavalent arsenic, then add a ferrous salt, and then By oxidizing ferrous iron with air, oxygen, an oxidizing agent, or a combination of two or more of the above while maintaining the pH of the solution between 1.5 and 3.0, arsenic is converted into iron arsenate with a high arsenic content. A method for separating arsenic, which comprises performing precipitation separation from a solution containing the heavy metal.