Process method for removing arsenic from feed-grade calcium hydrogen phosphate prepared from wet-process phosphoric acid

Abstract

The invention relates to a process method for removing arsenic from feed-grade calcium hydrogen phosphate prepared from wet-process phosphoric acid. The process method comprises the following steps of: 1) adding a sodium sulfide or calcium sulfide solution into neutralized slurry by using an adjustable pressure metering pump until the solution reaches a position which is 50cm away from the liquid level of the neutralized slurry; 2) desulfurizing by an air stripping method, namely removing hydrogen sulfide (H2S) from slurry at the bottom of a thickener by using a desorption tower; 3) recovering the H2S in tail gas to generate a mixed solution of calcium sulfide and sodium sulfide by using lime water and liquid caustic soda in a molecular ratio of Ca(OH)2 to NaOH of 1:1 as washing water of a tail gas washing tower, wherein the washing water of the tail gas washing tower is used as a raw material of an arsenic remover for the neutralized slurry in a section I and recycled after the concentration of the washing water is qualified; and 4) adding the sodium sulfide or calcium sulfide solution into the last one or two reaction tanks for one-stage neutralization of the wet-process phosphoric acid. The process method has the advantages that the content of the H2S in the slurry is reduced to about 3ppm, and the slurry does not have the odor of the H2S; and arsenic removal cost is reduced by more than half compared with that of a treatment method in which lime is not used.

Description

technical field [0001] The invention relates to the technical field of a process for removing arsenic and sulfur from a wet-process phosphoric acid neutralization solution. Background technique [0002] In the process of producing feed-grade calcium hydrogen phosphate with sulfuric acid and phosphoric acid as raw materials, certain arsenic impurities are brought in from phosphate rock or smelting sulfuric acid, so that the arsenic in calcium hydrogen phosphate products exceeds the standard requirements of the product (feed grade Dibasic calcium phosphate standard requires the arsenic content in the product to be less than 30ppm). [0003] At present, most calcium hydrogen phosphate enterprises and industrial-grade phosphate production enterprises mainly use sodium sulfide or phosphorus pentasulfide to remove arsenic from hot-process or wet-process phosphoric acid. The method for removing arsenic in feed calcium hydrogen phosphate enterprises is mainly to use sodium sulfide ...

AI Technical Summary

Problems solved by technology

The method for removing arsenic in feed calcium hydrogen phosphate enterprises is mainly to use sodium sulfide to remove arsenic from wet-process phosphoric acid, one-stage or two-stage neutralization slurry, and the hydrogen sulfide in the waste gas generated during the dearsenic removal process is not recycled. And direct discharge, resulting in high consumption of sodium sulfide for arsenic removal, high production cost of treatment

At the same time, because the exhaust gas contains a certain amount of toxic hydrogen sulfide gas, it will cause varying degrees of harm to the surrounding environment and the health of the operators on the job.

Although some enterprises wash and recover the hydrogen sulfide gas in the tail gas with liquid alkali or clear water, the cost of arsenic removal treatment is high, and the washing effect on hydrogen sulfide in the tail gas is poor. 5%), the removal effect of hydrogen sulfide in the tail gas is getting worse and worse, because the smell of hydrogen sulfide in the washing water is relatively strong during the production process, which brings a lot of inconvenience to the production operation

[0004] Some enterprises often have product quality accidents due to failure to remove arsenic from wet-process phosphoric acid or neutralized slurry, which has caused great losses to the enterprise

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