Method for preparing phosphogypsum whiskers by secondary crystallization

Abstract

The invention discloses a method for preparing phosphogypsum whiskers by secondary crystallization. The method comprises the steps of weighing dried phosphogypsum, adding a sulfuric acid solution, performing stirring reaction in a water bath, filtering when being hot, abandoning insoluble substances, cooling filtrate at room temperature for crystallization, performing suction filtration, and then retaining a filter cake; adding the sulfuric acid solution and a crystallization promoting agent, namely magnesium salt, performing stirring reaction in the water bath, naturally cooling the solution in the water bath for crystallization, performing suction filtration to obtain the whiskers, washing till neutrality and drying. The crystallization promoting agent is not used in primary crystallization in the method disclosed by the invention, the solid-liquid ratio of raw materials has a good effect, the reaction temperature and the stirring rotational speed are reasonably designed, the secondary crystallization method is created, the problems of short length-diameter ratio, low yield, difficulty in production under non-high pressure conditions and difficulty in succeeding without pretreatment of the phosphogypsum whiskers in the prior art are solved, the problems of phosphorus residue and the like can be solved by recycling a solvent, and the sustained cyclic production can be further realized. The length-diameter ratio of the whiskers produced by the method disclosed by the invention is more than 100, the whiteness is not less than 95%, and the product yield is improved by 10%-15%.

Description

technical field

[0001] The invention relates to a method for preparing phosphogypsum whiskers by secondary crystallization. Background technique

[0002] For every 1 ton of phosphoric acid produced in my country, 4.5-5 tons of phosphogypsum will be discharged. Phosphogypsum is divided into dihydrate gypsum (CaSO 4 2H 2 O) and hemihydrate gypsum (CaSO 4 1 / 2H 2 O), mostly gypsum containing two waters. At present, the total annual output of wet-process phosphoric acid in the world is about 270 million tons (in P 2 o 5 Calculated), the by-product phosphogypsum is about 150 million tons, and the utilization rate is only 4.3% to 4.6%. It is estimated that the demand for phosphate fertilizer in my country will exceed 130 million tons in 2015, and the annual discharge of phosphogypsum will exceed 20 million tons, of which the utilization rate is only about 5%. The natural stacking of phosphogypsum has become the main treatment method, which not only costs a lot of money and ...

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