| 摘要 |
1,162,514. Phosphoric acid and gypsum from phosphate rock. ALBATROS SUPERFOSFAATFABRIEKEN N.V. 6 Sept., 1966 [8 Sept., 1965], No. 38480/65. Heading C1A. Phosphoric acid and gypsum are obtained by acidulating phosphate rock with a mixture of phosphoric and sulphuric acids, to form a slurry of calcium sulphate hemihydrate crystals in a concentrated phosphoric acid solution, which latter is separated and withdrawn as product; the calcium sulphate hemihydrate crystals are washed with an aqueous liquid containing sulphuric acid with or without a minor amount of phosphoric acid, the composition and quantity of the washing liquid and the temperature being such as to prevent transformation of the hemihydrate to another crystal form and to make the liquid adhering to the washed crystals a suitable component for an aqueous recrystallization solution to which the hemihydrate is then transferred, and in which it is recrystallized to form gypsum. The recrystallisation solution, including the said component, contains 2 to 25% by weight of sulphuric acid, and less than 20% of phosphoric acid, calculated as P 2 O 5 . |
