SU1452784A1 - Method of producing sodium dithionite - Google Patents

Abstract

The invention relates to chemical technology of inorganic salts. The purpose of the invention is to enhance. total product yield. The method is carried out as follows. A suspension of zinc powder in water, taken in a weight ratio of 1: (2-4.5), is treated with sulfur dioxide. The resulting zinc dithionite solution is added to the sodium hydroxide solution simultaneously with the first wash water from the previous operation. The suspension is separated on a filter, the precipitate is washed with a second wash water from the previous operation. The resulting first and second wash waters are used in the interaction of the following portions of zinc dithionite with caustic soda and the first wash of the next precipitate, respectively. Washed zinc hydroxide is dried. The sodium dithionite dihydrate is salted out with sodium chloride from the filtrate while cooling, part of the mother liquor is separated, and the remaining suspension is heated to 55-60 ° C, followed by separation of the crystals of anhydrous sodium dithionite and drying. The target product contains 96.0- 96.2% by weight of the base material. Yield 65.0 - 67.1%. 1 hp, f-ly, 1 ta bl. i 4 01 Yu “

Description

The invention relates to chemical technology of inorganic salts, in particular, to methods for producing sodium dithionig.

The purpose of the invention is to increase the yield of the target product.

The method is carried out as follows.

A suspension of zinc powder in water, taken in a mass ratio of 1:: (2-4.5), is treated with sulfurous gas. The resulting zinc dithionite solution is added to the sodium hydroxide solution simultaneously with the first industrial water from the previous operation and fresh water. In the resulting suspension, the content of sodium dithionite in the solution is 220-280 g / l. The suspension is separated on a filter, the precipitate is washed with a second wash water from the previous operation. The resulting first and second wash waters are used in the interaction of the next portion of zinc dithionite with caustic soda and the first wash of the next sludge, respectively. Washed zinc hydroxide is dried.

From the filtrate, salt is salted out while cooling the sodium dithiotite dihydrate, part of the mother liquor is separated, and the remaining suspension is heated to 55-60 ° C after-; separating the crystals of anhydrous sodium dithionite and drying them. Get the target product with the content of the basic substance / v96,0- 96,2 wt.% Yield 65,0-67,1%.

Example 1 A suspension of 340 kg of zinc powder in water with a mass ratio of 1: 4.5 is treated with sulfur dioxide. The resulting zinc dithionite solution was prepared to a solution of sodium hydroxide (42%) simultaneously with 300 l of the first wash water from the previous operation. In the liquid phase of the resulting suspension, the sodium dithionite content is 260 g / l. The suspension is separated on a filter, the precipitate is washed with a second wash water from the previous operation in the amount of 1300 l and fresh water in the amount of 1300 l. The resulting first and second wash waters are used in the interaction of the next portion of zinc dithionite with caustic soda and the first wash of the next sludge, respectively. The washed zinc hydroxide is dried. From the filter solution

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salt is cooled with sodium dithionite dihydrate while cooling, part of the mother liquor is removed, the remaining suspension is heated to 55-60 ° C, the resulting crystals of anhydrous sodium dithionite are separated and dried. 595 kg of sodium dithionite are obtained, containing 96% of the basic substance, which corresponds to a yield of 67.1%. The content of the basic substance in zinc oxide (calculated on the dry product) is 95.7%.

PRI mme R 2. A suspension of 340 kg of zinc powder of the specified quality in water with a mass ratio is treated with sulfur dioxide. The resulting zinc dithionite solution is added to the caustic soda solution simultaneously with 1500 liters of the first wash water. In the liquid phase of the resulting suspension, the sodium dithionite content is 220 g / l. The suspension is separated on a filter, the precipitate is washed with 1500 liters of second wash water and 1500 liters of fresh water. The resulting washing solutions are used in the interaction of the next portion of zinc dithionite with caustic soda. The washed zinc hydroxide is dried, and sodium dithionite is obtained from the solution separated on the filter press as in Example 1.

615 kg of sodium dithionite, containing 90% of the basic substance, are obtained, which corresponds to a yield of 65%. The content of the basic substance in zinc oxide (calculated on the dry product) is 96.7%.

EXAMPLE 3 A suspension of 380 kg of zinc powder of the specified quality in water with a mass ratio of 1: 3.2 is treated with sulfur dioxide and anhydrous sodium dithionite is obtained in the same way as in Example 1, adding 1400 liters of first wash water simultaneously with a solution of zinc dithionite. The content of sodium dithionite in the liquid phase of the suspension is 280 g / l. 670 kg of sodium dithionite are obtained, containing 93.5% of the basic substance, which corresponds to a product yield of 66.2%. The basic substance in zinc oxide is 96.2%.

Examples of the implementation of the method in the claimed limits, outside the specified limits and by a known method are presented in the table.

As follows from the above data, carrying out the process of obtaining sodium dithionite according to the proposed method (examples 1-3) allows increasing the yield of sodium dithionite by 2-7%, the content of the basic substance in zinc oxide by 1-2% and reducing expenditure ratios 3-5% compared with the known method (example 8). An increase in the mass ratio of zinc powder and water to 1: 1.5 (Example 4) leads to a sharp decrease in the yield of the product due to the deterioration of the conditions for the interaction of sulfur dioxide and zinc powder and its incomplete consumption. With a 1: 5 mass ratio of zinc powder and water (Example 5), the product yield is slightly reduced due to the partial decomposition of sodium dithionite during storage of the first wash water until the next operation, which is not compensated (as in Examples 1-3) by salting out a more concentrated solution. When rinsing dithionite of zinc is introduced into caustic soda (Example 6), anhydrous sodium dithionite crystals are formed, which do not have time to dissolve when rinsing water is supplied and remain on the filter along with zinc hydroxide, which leads to a decrease in the yield of the product and a decrease in the content of the main substance in zinc oxide. The introduction of wash water into caustic soda before feeding zinc dithionite (example 7) causes partial decomposition of dithionite nat

ri, contained in the wash water, in a significant excess of alkali.

Thus, the use of the method proposed for the preparation of sodium dithionite provides, in comparison with the known method, an increase in the yield of the target product to 65.0-67.1%.

Formula inventions

Claims (2)

1. A method of producing sodium dithionite, comprising treating an aqueous suspension of zinc powder with sulfur gas with dithionite zinc, the interaction of the latter with caustic soda, separating the precipitate obtained zinc hydroxide from the mother liquor and washing it with water, returning the wash water to the process, salting out sodium dihydrate sodium chloride from the mother solution, discharging part of the mother liquor and heating the remaining suspension with obtaining a precipitate of anhydrous sodium dithionite, separating it and drying, characterized in that, in order to increase the yield of the target product, the processing of a zinc suspension the powder with sulfur dioxide is carried out at T: W 1: 2-4.5, and the washing water from the stage of washing of zinc hydroxide is returned to the stage of interaction of zinc dithionite with caustic soda. 2. A method according to claim 1, characterized in that the wash water is introduced simultaneously with dithionite at the stage of interaction. fo i CNI + O. r -IO i.n J3 YU in CO CXJ VO cn Vd