JPH06171946A - Production of high purity diarsenic trioxide - Google Patents

Abstract

PURPOSE:To produce high purity diarsenic trioxide suitable for use as a reference substance by a wet process using a material contg. highly diarsenic trioxide as a starting material and simple appliances and facilities. CONSTITUTION:A satd. aq. soln. of a material contg. highly diarsenic trioxide and impurities such as diarsenic pentoxide is prepd., a reducing agent is added to the soln. and this soln. is heated to reduce pentavalent arsenic to trivalent arsenic. At the same time, the soln. is concd. by evaporation to prepare a satd. aq. soln. of diarsenic trioxide again. This soln. is rapidly added to cooling water or ethanol under vigorous stirring to deposit fine diarsenic trioxide crystals and these crystals are separated by filtration, washed with cooled pure water and satisfactorily dried until sticking water is removed.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY In the present specification, "high-purity diarsenic trioxide" means an AS ₂ O ₃ content of 99.95 wt% or more. Also, "high content diarsenic trioxide" means AS ₂ O
_{3 It} means that the content is 98.0 wt% to 99.0 wt%. TECHNICAL FIELD The present invention relates to a method for producing high-purity diarsenic trioxide from arsenic trioxide containing impurities, and particularly to a method for producing high-purity diarsenic trioxide suitable as a standard substance.

[0002]

[Prior Art and Problems] Diarsenic trioxide (AS ₂ O ₃ )
Is obtained by burning metal arsenic or an arsenic compound in air. Industrially, a large amount is produced as a by-product at the time of baking of Ryuhitetsu ore and smelting of copper ore containing arsenic. However, the arsenic trioxide thus obtained generally contains a large amount of impurities and cannot be used as it is, and it is necessary to increase the content ratio of arsenic trioxide.

The following methods are known as methods for increasing the content of arsenic trioxide. Diarsenic trioxide containing impurities is dissolved in hydrochloric acid, and the resulting solution containing diarsenic trioxide is distilled to add a large amount of water to the solution, which is hydrolyzed to separate diarsenic trioxide. To further enhance the quality, sublimate diarsenic trioxide for purification. Redistributed arsenic trioxide solution and sublimation purification of arsenic trioxide are repeated to produce high content arsenic trioxide. The obtained high-content diarsenic trioxide is used as a raw material for high-purity metal arsenic having a purity of 6 to 9 Nine. The arsenic trioxide obtained by this method is very small as an impurity as shown in Table 1. However, the content of arsenic trioxide is about 98% to 99%, and as a high-purity diarsenic trioxide for a standard substance, I can not use it.

[0004]

[Table 1]

Also, at the Osaka Industrial Testing Laboratory (currently the Osaka Institute of Industrial Technology), for more than 10 years since the early Showa period,
High purity diarsenic trioxide was prepared as a volumetric standard reagent and the method was as follows. That is, after the pharmacopoeia diarsenic trioxide is dissolved in a sodium hydroxide solution, carbon dioxide gas is passed to precipitate the diarsenic trioxide. This operation is repeated for purification. The purified arsenic trioxide is then dissolved in hydrochloric acid. Add water to hydrolyze to precipitate arsenic trioxide, and repeat this procedure for purification. Further, the sublimation purification operation was repeated, and the arsenic trioxide content was determined by an iodine titration method.
The product which guarantees 9.98% or more was obtained.

Incidentally, in the currently used Japanese standard (JIS K8005-1992) standard material for volumetric analysis, the quality of arsenic trioxide is specified as follows. Purity 99.95% or more Aqueous ammonia solution 10 g of ammonia water (2 + 3) was added to 1 g of the test-compatible sample, dissolved by heating, cooled, and adjusted to 20 ml with water to be clear. Ignition residue (sulfate) 01% or less Chloride (Cl) 0.001% or less Sulfide (S) 0.001% or less Copper (Cu) 5 ppm or less Lead (Pb) 5 ppm or less Antimony (Sb) 0.001% or less Iron (Fe) 5 ppm or less

As explained above, arsenic trioxide produced as a raw material for high-purity metal has a different purpose, and has the drawback that it cannot be used as high-purity diarsenic trioxide for standard substances. The purification method is extremely long,
It is not practical when the currently produced high content diarsenic trioxide is used as a raw material. And although there is a regulation on the quality of arsenic trioxide as a standard substance in the Japanese standard, the current situation is that domestic products are not manufactured at all and all are imported. Incidentally, according to the announcement by the Trade and Industry Inspection Office of the Ministry of International Trade and Industry, diarsenic trioxide, which has been guaranteed as a standard substance for volumetric analysis in the past 10 years, has not been produced.

[Problems to be Solved by the Invention]

The present invention solves the above problems.
The object of the present invention is to use a high content of arsenic trioxide as a starting material,
99.99% by the wet method using simple equipment and facilities
The purpose is to produce high-purity diarsenic trioxide having the above content.

[Means for Solving the Problems]

In the present invention, a certain amount of arsenic trioxide with a high content is dissolved by heating with water to form a thermally saturated solution of arsenic trioxide, to which a certain amount of a reducing agent such as saturated aqueous solution of sulfite is added. High-purity diarsenic trioxide is obtained by heating and reducing pentavalent arsenic to trivalent arsenic, and then adding this to a quenching or cold ethanol solution with stirring to precipitate diarsenic trioxide by a simple wet process. (The content rate is 99.99% or more).

As the reducing agent, conventional ones such as aqueous sulfite and hydrazine solution can be used. The amount of the reducing agent used varies depending on the amount of diarsenic pentoxide contained in the raw material arsenic trioxide, and is used in an amount sufficient to reduce pentavalent arsenic to trivalent arsenic.

The present invention will be described below with reference to examples.

Example 1 High content diarsenic trioxide (98.0%) 90
1000 ml of pure water was added to g and dissolved by heating while gently stirring until dissolved. Then saturated saturated sulfite water 1
After adding 00 ml with stirring, the mixture was continuously heated and evaporated to concentrate until just before arsenic trioxide crystals were precipitated. The solution was placed in ice-cold water with vigorous stirring to cool rapidly and kept as cold as possible. Next, suction filtration was performed using a glass filter. 100 ml of cooled pure water was added to the filter and suctioned to wash the crystals. This cleaning operation 2
Repeated ~ 3 times. The crystals were transferred to a container, dried at about 100 ° C. until there was no non-adhered water, then lightly ground in a clean aluminum oxide mortar, and again about 150 to 20.
It was dried at 0 ° C. The product was titrated several times by the iodine titration method with the arsenic trioxide content of 99.95% as the standard, and the results were 99.99% in all cases. The yield of high purity diarsenic trioxide was about 70% in several experiments.

[0012]

Example 2 The same operation as in Example 1 was carried out, and the obtained saturated diarsenic trioxide solution was added little by little to ethanol (98%) which was cooled and stirred, and hydrolyzed to give fine crystal dioxide trioxide. Arsenic was deposited. Then, suction filtration was performed using a glass filter. 100 ml of cooled pure water was added to the filter and suctioned to wash the crystals. This washing operation was repeated 2-3 times. The crystals were transferred to a container and gradually heated in a dryer to be dried at about 70 ° C. for about 1 hour. Continue to increase the temperature to about 1
The temperature was raised to 00 ° C and dried. Then, the same operation as in Example 1 was performed. The content of arsenic trioxide in the obtained crystals was 99.9.
At 9%, the yield was about 80% or higher.

[0013]

According to the present invention, a high-purity diarsenic trioxide that can be sufficiently used as a standard substance can be produced by a wet method with a simple operation.

Claims (1)

[Claims] 1. A saturated aqueous solution of diarsenic trioxide with a high content containing impurities such as diarsenic pentoxide is prepared, and a reducing agent is added to this solution and heated to reduce the pentavalent arsenic to trivalent arsenic. The solution is concentrated by evaporation again to a saturated solution of arsenic trioxide, and then the saturated solution is rapidly cooled or added to ethanol with vigorous stirring to precipitate fine crystals of arsenic trioxide. Is filtered, washed with cold pure water, and then dried sufficiently until there is no attached water. A method for producing high-purity diarsenic trioxide.