JPS5825049B2 - Arsenous acid oxidation method - Google Patents

Description

Detailed Description of the Invention The present invention provides a method for producing arsenic acid by oxidizing arsenous acid, by adding activated carbon to a pulp solution containing arsenous acid and reacting it at high temperature and under high oxygen pressure using a pressure cooker. ,
The present invention provides a method for producing arsenic acid by oxidizing arsenous acid extremely efficiently.

Conventionally, there are various methods for producing arsenic acid by oxidizing arsenous acid, but generally a method using an oxidizing agent such as nitric acid, chlorine, or hydrogen peroxide, or a wet method using electrolytic oxidation is employed.

In the oxidation method using nitric acid, air is blown into the reaction to suppress the loss of nitric acid, and the oxidation rate of arsenous acid increases in proportion to factors such as the concentration of nitric acid, oxygen pressure, and residence time. There are problems with the materials used and measures against NOx generated during the reaction.

In addition, when oxidizing with chlorine, dichromic acid, permanganate, etc. as an oxidizing agent, the arsenic acid produced has a high solubility, so it is difficult to separate the ions of the salts used from the arsenic acid, so it is not used as an oxidizing agent. The high cost of these chemicals makes it extremely disadvantageous for industrial implementation.

Furthermore, although the method of using hydrogen peroxide as an oxidizing agent is relatively superior in terms of oxidation reactions and environmental pollution, it is unsuitable for industrial use because of the problem of the cost of chemicals.

Although the electrolytic oxidation method has no problems in terms of cost, there are problems in terms of environmental pollution due to the hydrogen arsenide generated during the reaction, and there are many problems in using it industrially.

There is also a method of air oxidation with a neutral solution, but the reaction is slow and the drop in pH caused by the arsenic acid produced must be neutralized with an alkaline agent before oxidation, so the salts used for neutralization must be separated from the arsenic acid. becomes extremely difficult.

As mentioned above, each of the conventional methods has many problems.
At present, no industrially advantageous method has been proposed.

The present invention is an extremely excellent method that solves the problems of these conventional methods. Pulp containing arsenous acid is introduced into a pressure cooker, activated carbon is added to the liquid as an oxidation catalyst to raise the temperature, and oxygen is forced into the liquid. The present invention relates to a method for converting arsenous acid into arsenic acid by reaction.

The reagents used in the method of the present invention are only activated carbon as an oxidation catalyst and oxygen gas, and there are no problems such as separation of the generated arsenic acid from other salts or environmental pollution, and it can be purified with very simple operations. arsenic acid can be produced.

Next, the method of the present invention will be described in detail.

An arsenous acid-containing pulp of about 200 fi/II to 300 g/13 is made, the pulp is charged into a pressure cooker, and about 5% activated carbon is added.

The pulp is heated to 100 to 250°C, preferably 150 to 200°C.
Heating to about ℃, oxygen pressure 3 to 15 kg/c4, preferably 5
The reaction is carried out while maintaining the ratio at about 9/ffl.

As the reaction progresses and arsenic acid begins to be produced, arsenous acid dissolves and the pH decreases due to the arsenic acid. By the end of the reaction, all the arsenous acid crystals have been dissolved, and the pH was initially around 7, but it has decreased to approximately It decreases to about 1.5.

After completion of this reaction, the liquid is taken out from the pressure cooker and subjected to solid-liquid separation to separate activated carbon, which is then used again.

On the other hand, pure arsenic acid crystals can be obtained by heating and concentrating the separated liquid.

Activated carbon as an oxidation catalyst used in the method of the present invention may be a commonly used commercially available one.If activated carbon is not used, the oxidation rate is low, but when about 5% activated carbon is added, the reaction improves rapidly. However, the reaction time can be extremely shortened.

As mentioned above, activated carbon can be recycled after being separated from the arsenic acid solution, and even after repeated use, the activated carbon does not deteriorate and can be used as an excellent catalyst.

In addition, the reaction temperature may be 100 to 250°C, or about 150°C.
The oxidation reaction rapidly progresses from around ℃ and is accelerated in proportion to the temperature and oxygen pressure.

As described above, the present invention is an excellent method that can easily oxidize arsenous acid using only oxygen and generate arsenic acid very efficiently by adding activated carbon as an oxidation catalyst.

Example 1 200! Activated carbon was added in an amount of 5% to a pulp solution containing l/13 arsenous acid, and the mixture was introduced into a pressure cooker and the oxygen pressure was increased to 9/a to 5.0.
The reaction was carried out at rt and a temperature of 180° C. for 5 hours.

The oxidation rate of arsenous acid was 100%.

After reacting the pulp solution containing arsenous acid of Comparative Example 20011/11 in a pressure cooker at an oxygen pressure of 5.0 kg/crit and a temperature of 180° C. for 5 hours, the oxidation rate of arsenous acid was 22.8%.

Example 2 The same experiment as in Example 1 was conducted using a pulp solution containing 200 g/13 arsenic acid, the arsenic acid solution and activated carbon were separated in the furnace, and the activated carbon was reused.

Activated carbon was used 10 times, but the oxidation rate of arsenous acid was 100% all 10 times, and no deterioration of the activated carbon was observed.

Claims (1)

[Claims] 1. A method for producing arsenic acid by oxidizing arsenous acid, which is characterized by adding activated carbon as an oxidation catalyst to a pulp solution containing arsenous acid, introducing the solution into a pressure cooker, and causing the reaction to occur at high temperature and under high oxygen pressure. oxidation method of arsenous acid. 2. The method for oxidizing arsenous acid according to claim 1, wherein the temperature in the pressure cooker is 100 to 250°C and the oxygen pressure is 3 to 15 kg/cJ.