Method for controlling coarse crystallization of semi-hydrated gypsum

Abstract

The invention discloses a method for controlling coarse crystallization of semi-hydrated gypsum, which comprises the steps of 1, firstly feeding phosphorite into a premixing area, mixing with returned acid, and quickly decomposing; 2, feeding the slurry discharged from the premixing area into a dissolving area, and fully dissolving the slurry in the presence of returned acid and sulfuric acid to avoid generating a compact calcium sulfate wrapping film; 3, feeding the reaction slurry discharged from the dissolving area into a crystallization area, and crystallizing and growing in the presence of concentrated sulfuric acid; and 4, feeding the reaction slurry out of the crystallization region into a curing region, and further growing the semi-hydrated gypsum crystals. The method is simple, easy to control, high in yield and capable of effectively obtaining coarse and large semi-hydrated gypsum crystals with good uniformity.

Description

technical field [0001] The invention relates to the field of phosphoric acid production, in particular to a method for controlling the coarse crystallization of hemihydrate gypsum used in the hemihydrate-dihydrate wet-process phosphoric acid process. Background technique [0002] The production technology of the semi-water-dihydrate method is to control the reaction conditions, first crystallize to form calcium sulfate hemihydrate, accompanied by high concentration of phosphoric acid, then change the reaction conditions, hydrate and recrystallize to form calcium sulfate dihydrate, which is called hemihydrate-dihydrate law craft. In the traditional hemihydrate-dihydrate wet-process phosphoric acid semi-water process, phosphoric acid is dissolved and crystallized in sequence to obtain hemihydrate gypsum, [0003] Since the semi-water-dihydrate process has P 2 o 5 High yield, high concentration of phosphoric acid product, good acid quality, good quality of phosphogypsum, low...

AI Technical Summary

Problems solved by technology

In the actual operation of the above process, it is found that the following problems still exist: (1) The crystallization control of hemihydrate gypsum is unstable, the crystal size is generally 40-60um, and the filtration strength of hemihydrate gypsum slurry is generally 3.0-3.7tP 2 o 5 / m 2 / d, leading to low filtration rate and blockage of semi-water filter cloth, which is not conducive to the improvement of system operating rate

(2) The control of sulfuric acid concentration is not precise and stable, and a dense calcium sulfate-coated film is easily formed on the surface of phosphate rock, which hinders the decomposition of phosphate rock. The vicious cycle may even force the car to stop for adjustment.

Images