FIELD: chemistry.
SUBSTANCE: invention relates to a method of producing phosphoric acid and obtaining, at the same time, alpha-hemihydrate gypsum I, as well as alpha-hemihydrate gypsum II as by-products. Method includes the following stages, at which: (1) mixing phosphoric acid and phosphate rock powder; performing the extraction reaction while stirring; when reaction is completed, sulphuric acid solution is added; solid and liquid phases of the extract suspension are separated to obtain an extract solution A of phosphoric acid and slag suspension B; wherein the amount of added sulphuric acid solution is controlled such that from 10 to 50 % of calcium ions are converted to dihydrate gypsum, and remaining 50–90 % of calcium ions are in form of primary calcium dihydrogen phosphate; (2) mixing solution A of phosphoric acid obtained at step (1) and a solution of sulphuric acid, performing a decalcification reaction; upon completion of reaction, solid and liquid phases are separated to obtain solid phase C and filtrate D; (3) a crystalline form conversion reaction is carried out using solid phase C obtained at step (2), a portion of filtrate D obtained in step (2), a solution of sulphuric acid and an additive for controlling conversion of crystalline forms; upon completion of the reaction, solid and liquid phases are separated to obtain alpha-hemihydrate gypsum II, as well as filtrate F; (4) a crystalline form conversion reaction is carried out using slag suspension B obtained at step (1), a portion of filtrate D obtained in step (2), a solution of sulphuric acid and an additive for controlling conversion of crystalline forms; upon completion of the reaction, the solid and liquid phases are separated to obtain alpha-hemihydrate gypsum I and filtrate J, where the purity of alpha-hemihydrate gypsum II is higher than that of alpha-hemihydrate plaster I.
EFFECT: technical result consists in simultaneous production of extraction phosphoric acid and different types of gypsum.
15 cl, 2 dwg, 7 ex
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