| 摘要 |
Concentrated phosphoric acid and calcium sulfate hemihydrate are directly produced by sulfuric acid attack upon calcium phosphate, the improvements comprising (i) continuously conducting the acid attack reaction, with concomitant formation of crystalline calcium sulfate hemihydrate, in but a single, homogeneous liquid reaction medium comprising the products of reaction, (ii) maintaining constant the temperature of the reaction medium as to effect formation of hemihydrated calcium sulfate, (iii) controlling the amount of reactants introduced to the reaction medium such as to maintain essentially constant, in liquid phase, a determined sulfate ion content, said content being at least 5 g/l and said determined content increasing with decreasing concentrations of P2O5 at a given temperature, and (iv) withdrawing a fraction of reaction effluent, including the concentrated phosphoric acid, and individually separating and recovering hemihydrated calcium sulfate from said reaction effluent fraction. Advantageously, the hemihydrate is recrystallized into a marketable gypsum by means of a treatment liquid which is subsequently recycled, preferably first to wash the hemihydrate and thence for purposes of the phosphate attack. |
