Chlor-alkali and sodium chlorate combined denitration process

Abstract

The invention discloses a sodium chlorate and chlor-alkali combined denitration process. Chlor-alkali light salt brine is subjected to secondary denitration through a chlor-alkali nanofiltration membrane and a sodium chlorate nanofiltration membrane, so that the content of sodium sulfate in an electrolyte is smaller than or equal to 6 g / L, the content of sodium chloride is increased to 100-120 g / L, the electrolytic efficiency is increased to 91-92%, the content of mirabilite in a sodium chlorate product is smaller than or equal to 0.02%, the content of sodium chlorate in a mirabilite product is smaller than or equal to 5 mg / kg, and the service life of the nanofiltration membrane is prolonged to 3 years. Chromium oxide / chromium hydroxide is used to replace heavy-toxicity sodium dichromate, and closed-loop recycling of chromium is achieved. The process is suitable for enterprises for preparing caustic soda from brine in northern dry areas. Pipeline-based salt supply is directly conducted on a sodium chlorate electrolysis system through light salt brine, and heat of low-grade electrolyte is fully utilized.

Description

technical field [0001] The invention belongs to the field of inorganic chemical industry and relates to a combined denitrification process of chlor-alkali and sodium chlorate. Background technique [0002] In the production of caustic soda by chlor-alkali ion membrane method, the raw salt contains a small amount of sodium sulfate, and sodium sulfite is also added to the pretreatment of light brine to remove free chlorine (because free chlorine Too high will destroy the internal structure of the secondary refining chelating resin tower, making it lose the chelating effect and affect the secondary refining effect), so there is a certain amount of sodium sulfate in the brine entering the tank for the production of caustic soda by the chlor-alkali ion membrane method. The light brine in the production of caustic soda by the chlor-alkali ion membrane method usually contains 190-210g / L sodium chloride, 8-15g / L sodium sulfate, and 1-16g / L sodium chlorate, and too high a concentrati...

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Problems solved by technology

[0003] Patent 201810454668.1 Evaporated crystallization mother liquor of light brine in chlor-alkali system, sodium chlorate product containing 2.4-3.0g / L sodium dichromate in sodium chlorate system, frozen crystallized Glauber's salt mother liquor common to chlor-alkali system and sodium chlorate system in the mixing tank Mixed in the medium, concentrated by nanofiltration membrane concentration system, frozen and crystallized to obtain Glauber’s salt, and its permeate enters the sodium chlorate system for utilization, but the patent also has the following problems: (1) The Glauber’s salt obtained by sodium chlorate freeze-crystallization contains quality Sodium dichromate with a percentage of 12% to 16% is difficult to handle; (2) due to the high concentration of sodium chlorate (175 to 185g / L) in the mixing tank, the concentrated solution concentrated by the nanofiltration membrane system is frozen and crystallized to obtain Glauber's salt Containing the sodium chlorate of mass percent 5.5~6.5% in it is not effectively recycled; (3) although the nanofiltration membrane system intercepts the sodium sulfate from 88~92% (mass percent) in the light brine of chlor-alkali system, but it passes through Also have the sodium sulfate of 8~12% (mass percentage) in the liquid to enter sodium chlorate system, have increased the sodium sulfate content of sodium chlorate system, influence the electrolysis efficiency of sodium chlorate electrolysis system; (4) sodium chlorate needs to replenish Industrial refined salt and hot water, a small amount of sodium sulfate in industrial refined salt is brought into the sodium chlorate system

[0004] Patent CN201911276725 A treatment process for sodium chlorate-containing chromium salt mud, only chromium salt treatment is performed, and there is still hexavalent chromium in the final solid waste, and chromium cannot be recovered

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