SU63473A1 - The method of producing ammonium thiosulfate - Google Patents

Description

In photography, sodium thiosulfate is usually used as a fixer. It is more convenient, because of the faster fixing effect, to use ammonium thiosulfate. However, the preparation of crystalline thiosulfate in its pure form presents significant technological difficulties.

Methods are known for the preparation of high percentage ammonium thiosulfate solutions by the exchange reaction between sodium thiosulfate and ammonium salts, but the solutions obtained contain, in addition to ammonium salts and sodium salts (thiosulfate and chloride or sulfate).

Ammonium crystalline thiosulfate is also prepared on the basis of the above exchange reaction, followed by separation of the resulting sodium sulfate by cooling and evaporation of the mother liquor under vacuum. However, this method makes it possible to obtain only a 90% product. To obtain ammonium thiosulfate-free impurities from ammonia, sulfur dioxide and hydrogen sulfide, followed by crystallization of the product from (the solution, the authors of the present invention propose to react the hydrogen sulfide with sulfuric acid salts in two stages: first saturate the sulfite solution with hydrogen sulfide at temperatures up to 50 and then After adding ammonia and sulfurous acid to the thiosulfate solution, saturate the solution with hydrogen sulfide at temperatures higher than 50 °.

The ammonium thiosulfate solutions obtained in this way contain 64–67% (NH4) 2 S, 0: j. These solutions can be subjected to direct crystallization with the release of crystalline ammonium thiosulfate.

An obstacle to the use of crystalline ammonium thiosulfate in photography is that it is difficult to obtain it free from sulfur contamination. This is due to the easy degradability of ammonium thiosulfate to form elemental ceipbi.

In order to obtain a sulfur-free product, concentrated ammonium thiosulfate solutions are proposed to be treated with ammonia after binding by excess methods of hydrogen sulfide by known methods.

to pH 7.5-9.0. This technique, i.e., can be applied to any method of producing crystalline ammonium thiosulfate.

Example. In 100 kg of concentrated ammonia solution, 45 kg of sulfur dioxide are introduced and the resulting solution is saturated with hydrogen sulfide at a temperature / D below 50 °. Then another 18 kg of gaseous NHs and 45 kg of SO2 or the corresponding amount are added. salt se) rni-. acid resistant The solution is heated to 60 ° and again saturated with hydrogen sulfide. After binding the excess hydrogen sulfide in the usual way, the solution is alkalinized with ammonia, filtered and crystallized. The yield of crystalline product is 15 kg. The mother liquor is returned to the process.

Inventory 1t inventions

1. A method of producing ammonium thiosulfate from ammonia, sulfur dioxide and hydrogen sulfide, followed by crystallization of the product from solution, characterized in that, in order to obtain an impurity-free crystalline P-product, the reaction of hydrogen sulfide with ammonium sulfate is carried out in two stages, first saturating the solution of sulfites with hydrogen sulfide at temperatures up to 50 ° C, and then, after adding ammonia thiosulfate and sulfurous acid to the resulting solution, saturating the solution with hydrogen sulfide at higher temperatures 50 ° C.

2. Acceptance of the method according to claim 1, characterized in that, in order to obtain a sulfur-free product, ammonium thiosulfate solution is treated with ammonia to pH 7.5 -9.0 prior to its crystallization.