High-yield hydrated crystalline phase reconstruction wet-process phosphoric acid production technology

Abstract

The invention discloses a high-yield hydrated crystalline phase reconstruction wet-process phosphoric acid production technology. The technology comprises a semi-hydrated reaction filtration process and a dihydrate reaction filtration process, and the semi-hydrated reaction filtration process comprises the steps of premixing, dissolving, crystallizing, curing and semi-hydrated filtration; and the dihydrate reaction filtration process comprises a conversion step and a dihydrate filtering step. According to the invention, through gradient control of the relationship between the sulfate ion concentration and the CaO concentration in different stages of the semi-hydrated reaction, the crystal size is increased, the crystal is kept stable, and the semi-hydrated gypsum crystal with uniform particle size is obtained; by changing the circulation path of the slurry, the reaction retention time is prolonged, and the growth of semi-hydrated gypsum crystals in a relatively stable environment is ensured; coarse, uniform and stable dihydrate gypsum crystals are obtained by controlling the degree of supersaturation of a dihydrate reaction, the filtering performance is good, the content of water-soluble phosphorus in the dihydrate gypsum is reduced, and the filtering yield is improved; and by reasonably utilizing the filtrate and the flushing water, the wastewater discharge is reduced, and the total yield of P2O5 is increased.

Description

technical field [0001] The invention relates to the field of phosphoric acid production, in particular to a high-yield hydrated crystal phase reconstruction wet-process phosphoric acid production 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, because the semi-hydrate-dihydrate process has P 2 o 5 High yield, high concentration of phosphoric acid product, good acid quality, good quality of phosphogypsum, low energy consumption and less environmental pollutio...

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.

(3) In the process of operation, the problem of acid accumulation in the filter plate of the filter sometimes occurs, causing the filter plate of the filter to overflow and make the conversion area P 2 o 5 Concentration increases beyond the standard, resulting in the increase of soluble phosphorus in dihydrate gypsum

(4) When the crystallization of hemihydrate gypsum is poor, the hemihydrate gypsum crystals are fine, the liquid holding capacity of the hemihydrate filter cake is high, and the dihydrate slurry phase P 2 o 5 The concentration is easy to rise rapidly to 30%, resulting in long dihydrate conversion time and intergranular P in gypsum. 2 o 5 Increased loss, difficulty in filtering and washing dihydrate slurry, etc.

If the dihydrate gypsum transportation is designed as a wet discharge method, the hemihydrate gypsum will reabsorb water in the dihydrate re-slurry pipeline and convert it into dihydrate gypsum, which will harden and scale and cause pipeline blockage

(6)P 2 o 5 The yield still needs to be further improved

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