Wet Process Phosphoric Acid Removal Process

Abstract

The invention discloses a process for removing arsenic by wet-process phosphoric acid. 2 S gas with a concentration of 35‑45% P 2 o 5 The wet-process phosphoric acid is countercurrently contacted in a two-stage arsenic removal tower. In the arsenic removal tower, H 2 S dissolves in wet-process phosphoric acid and ionizes to S 2+ , ionized S 2+ As in phosphoric acid 3+ Generate As 2 S 3 Arsenic slag, As 2 S 3 The arsenic slag crystallizes and grows into a crystal. After the reaction, the wet-process phosphoric acid containing arsenic slag is filtered to remove the arsenic slag, and then sent to the stripping tower to strip the H dissolved in the acid. 2 S gas, the dearsenic acid after stripping is sent to the follow-up device as a finished product; compressed air is introduced into the stripping tower as stripping gas to contact with the phosphoric acid after deslagging in countercurrent. The invention has the advantages of simple process, high arsenic removal efficiency, small consumption of arsenic removal agent, good air stripping effect, and residual H in the product phosphoric acid 2 S is low, the process is environmentally friendly, and the production and operation costs are low.

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...

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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

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