Process for removing arsenic from wet-process phosphoric acid

Abstract

The invention discloses a process for removing arsenic from wet-process phosphoric acid. H2S gas with pressure and wet-process phosphoric acid with the concentration of 35-45% P2O5 are subjected to countercurrent contact reaction in a two-stage dearsenification tower, H2S is dissolved in the wet-process phosphoric acid and ionized into S<2+> in the dearsenification tower, the ionized S<2+> and As<3+> in the phosphoric acid generate As2S3 arsenic slag, the As2S3 arsenic slag is crystallized and grows into crystals, the arsenic slag in the wet-process phosphoric acid containing arsenic slag after reaction is filtered by a filter, then the phosphoric acid is fed into a gas stripping tower to carry out gas stripping on the H2S gas dissolved in the acid, and the arsenic-removed acid after gas stripping is fed into a subsequent device as a finished product, and compressed air is introduced into the gas stripping tower to serve as gas stripping gas to be in countercurrent contact with the phosphoric acid subjected to slag removal. The method is simple in process, high in arsenic removal efficiency, small in arsenic removal agent consumption, good in gas stripping effect, low in residual H2S in the product phosphoric acid, environmentally friendly and low in production and operation cost.

Description

technical field [0001] The invention relates to a wet-process phosphoric acid process, in particular to a process for removing arsenic from wet-process phosphoric acid. Background technique [0002] At present, the removal of arsenic by wet-process phosphoric acid is one of the requirements for moderate purification of wet-process phosphoric acid. The arsenic in wet-process phosphoric acid exists in the form of arsenous acid or arsenic acid, and the methods for removing arsenic are mainly chemical methods. [0003] The chemical method of arsenic removal is to convert arsenic in phosphoric acid into As 2 S 3 The form of precipitation separation, usually adding sodium sulfide aqueous solution, P 2 S 5 solid. [0004] P 2 S 5 Solid and aqueous sodium sulfide react with phosphoric acid to form H 2 S, generated H 2 S then reacts with arsenic in phosphoric acid to generate H2S with low partial pressure, poor arsenic removal efficiency, and surplus H 2 S is difficult to re...

AI Technical Summary

Problems solved by technology

[0006] (1) It is generally believed that the higher the concentration of phosphoric acid is conducive to the removal of arsenic, such as in this scheme with H 2 The phosphoric acid concentration of S reaction is as high as 85%, but finds in inventor's actual research, the viscosity of high-concentration phosphoric acid is big, can influence H 2 The solubility of S in phosphoric acid leads to limited arsenic removal efficiency, which can easily lead to unqualified products; (2) the general arsenic removal reaction includes three processes, H 2 S dissolves in phosphoric acid and ionizes to S 2+ , ionized S 2+ with As 3+ The reaction produces As 2 S 3 Arsenic slag, As 2 S 3 The arsenic slag crystallizes and grows into large particles. If the three processes in this scheme are completed in one arsenic removal reactor, the effect is limited; (3) The reactor has stirring facilities, which is not conducive to H 2 S dissolves in phosphoric acid, resulting in a long reaction time; (4) Blow off the residual H in the acid by air bubbling and negative pressure suction 2 S gas, cannot effectively replace dissolved H in phosphoric acid 2 S gas, resulting in H 2 S is reduced to elemental S in phosphoric acid, reducing product quality

Images