Technology for recycling by-product fluosilicic acid of wet process phosphoric acid

Abstract

The invention relates to a technology for recycling a by-product fluosilicic acid of wet process phosphoric acid. The technology comprises the following steps: washing and absorbing fluorine-containing gas produced in a production process of the wet process phosphoric acid so as to form a fluosilicic acid solution, and then enabling the fluosilicic acid solution and ammonia water to be subjected to a preneutralization reaction so as to generate an ammonium fluosilicate solution; primarily mixing the ammonium fluosilicate solution with the wet process phosphoric acid to obtain mixed acid liquor; then, secondarily mixing the mixed acid liquor with potassium hydrogen sulfate to obtain compound fertilizer mixed acid slurry; enabling the compound fertilizer mixed acid slurry and gaseous ammonia to be subjected to a neutralization reaction to obtain compound fertilizer neutralized slurry; or enabling the mixed acid liquor and the gaseous ammonia to be subjected to a neutralization reaction to obtain ammonium phosphate neutralized slurry, and concentrating the ammonium phosphate neutralized slurry to obtain concentrated slurry; carrying out slurry-spraying granulation on the compound fertilizer neutralized slurry or the concentrated slurry, drying, screening and enveloping to obtain sulfur-based compound fertilizer or ammonium phosphate. The technology reduces the volatilization of the fluorine-containing gas of the fluosilicic acid solution, reduces the corrosivity of the solution, reduces pollutant emission and improves the ecological environment.

Description

technical field [0001] The invention relates to a recycling process of fluosilicic acid, a by-product of wet-process phosphoric acid. Background technique [0002] Phosphate rock contains 2.5% to 4.0% fluorine. During the production process of wet-process phosphoric acid, part of the fluorine escapes as silicon tetrafluoride gas and hydrogen fluoride gas. After being absorbed by water, a fluorosilicic acid solution with a concentration of 8% to 12% is obtained. At present, most phosphate and compound fertilizer enterprises in China use the recycled fluosilicic acid solution to produce sodium fluosilicate, sodium fluoride and other products, but the sodium ion-containing waste water generated in the production process of sodium fluosilicate and sodium fluoride is recycled to wet The production of farphosphoric acid leads to fouling of the system. Therefore, it is necessary to study a new method to reuse the fluosilicic acid recovered from washing in the production process of...

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Problems solved by technology

[0003] Generally, fluorine-containing by-products need to be disposed of by factory-set recycling devices or sent to manufacturers with fluorine-containing waste treatment qualifications for recycling according to national environmental protection requirements. Use it to produce sodium fluoride, aluminum fluoride, cryolite, sodium fluoride and other products, but in the production process of wet-process phosphoric acid, the concentration of fluosilicic acid solution obtained from the extraction section is low, the content of silica gel is high, and the content of impurities is high. , when used in the production of fluorine-containing products, the impurity removal process is long, the cost is high, and the economic benefit is low. Generally, manufacturers who recycle fluorine-containing waste have higher requirements on the impurities and concentration of the by-product fluorosilicate solution of phosphorus and compound fertilizers. However, in order to ensure that the tail gas discharges up to the standard when producing wet-process phosphoric acid when using medium and low-grade phosphate rock, it is difficult for the recovered fluosilicic acid solution to meet the requirements for external sales or to be directly used for raw sodium fluoride, aluminum fluoride, cryolite, Requirements for products such as sodium fluoride, so it is necessary to study new methods to solve the problem of recycling fluosilicic acid in wet-process phosphoric acid

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