Process for the preparation of phosphoric acid and calcium sulphate anhydrite as well as phosphoric acid and calcium sulphate anhydrite obtained by this process

摘要

Phosphate rock is digested with H.sub.2 SO.sub.4 into phosphoric acid and gypsum, the latter is separated off, washed and converted into anhydrite. After this first wash the gypsum is divided into a minor portion of fine crystals, which is discharged, and into a major portion of coarse crystals, which is subjected to a second wash, thereafter recrystallized into anhydrite by means of concentrated H.sub.2 SO.sub.4, the anhydrite being separated and washed and the recrystallization liquor returned to the digestion zone. The washing liquor obtained from the anhydrite wash is used for the second gypsum wash, the washing liquor obtained from this second wash is, together with water, used for the first gypsum wash, whereas the washing liquor obtained in this first wash is returned to the digestion zone. In this way practically all gypsum formed can be converted into anhydrite, while substantially all water can be functionally used without dilution of the H.sub.3 PO.sub.4 -product.