Method for continuously neutralizing and decontaminating sodium chromate alkali solution

Abstract

The invention relates to a method for continuously neutralizing and decontaminating a sodium chromate alkali solution. The method comprises the following step of: adding a neutral aqueous solution containing sodium chromate and an optional crystal seed which are used as bottom materials in a neutralization reactor for realizing neutralization and decontamination based on carbon dioxide as a neutralizing agent or chromium-containing acidic wastewater which is produced in the process of producing sodium bichromate from sodium chromate, a pre-acidification solution, an acidification solution, a sodium bichromate mother liquid, a sodium dichromate aqueous solution and inorganic acid, or any mixture of the former neutralizing agents. Through the control over the concentration, temperature, pH value and stirring speed of a reaction liquid, precipitate obtained by the method is large in particle and rapid in sedimentation speed; aluminum mud is good in filtering property and is easy to wash; and the content of hexavalent chromium in the aluminum mud in greatly reduced, thereby reducing the discharge amount of the aluminum mud. In addition, the neutralization reactor the upper part of which is provided with an overflowing port is adopted for neutralization reaction, so that the automation and continuty of the neutralization and decontamination process of the sodium chromate alkali solution are realized.

Description

technical field [0001] The invention relates to a method for continuously neutralizing and removing impurities of sodium chromate alkaline liquid. Background technique [0002] Sodium red alum is a basic inorganic chemical raw material, mainly used in the manufacture of chromic anhydride, basic chromium sulfate, chromium oxide green and other chromium salt products, widely used in printing and dyeing, electroplating and other industries. [0003] The production of sodium bauxite mainly includes the preparation of sodium chromate and the conversion of sodium chromate into sodium bauxite. At present, most domestic manufacturers still use dolomite, limestone and chromium slag as auxiliary materials, oxidize and roast chromite and soda ash at high temperature, leach sodium chromate alkaline solution, and then use sulfuric acid to decompose chromic acid Sodium is transformed into sodium rubidin. [0004] In the production process of sodium red alum, the sodium chromate alkaline...

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Problems solved by technology

[0011] (2) The concentration of sodium chromate alkaline solution should not be too high during the neutralization reaction. If the concentration of the feed solution is too high, extremely dispersed aluminum hydroxide colloids will be generated during the reaction, which will deteriorate the filtration performance and the hexavalent aluminum hydroxide in the aluminum sludge will Increased chromium strip loss

[0015] U.S. Patent No. 3,899,568 adopts the mother liquor of red vitriol sodium as a neutralizing agent. This method adopts segmental operation and cannot carry out continuous production, and the neutralization time of this method is as long as 4-12h, and the yield is low. The obtained aluminum sludge is a colloid, which is not fundamentally Solve the belt loss problem of aluminum mud

Chinese patent application publication CN1069711 uses sodium bisulfate for neutralization, and the resulting aluminum sludge precipitates as an extremely dispersed colloid. The aluminum sludge has poor filtration performance and is difficult to wash, and its hexavalent chromium band loss is high

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