MODIFYING METHOD OF GYPSUM FORMED IN PREPARING PHOSPHORIC ACID BY WET PROCESS AS BY-PRODUCT

摘要

PURPOSE:To modify gypsum formed as a by-product so as to be usable in the same manner as the natural gypsum, by treating the gypsum formed as the by-product in the form of an aqueous slurry with a hydrocyclone, separating particles of a given particle size, adding lime thereto, a drying the separated particles. CONSTITUTION:Gypsum formed as a by-product in preparing phosphoric acid by the wet process is stirred as an aqueous slurry, and treated with a hydrocyclone and disintegrated. Solid particles and soluble impurities finer than the gypsum particles are removed to give the separated particle size of about 5-20mu. Lime is then added to the separated gypsum particles to adjust to an alkaline pH of about 8-10 and fix the phosphoric acid content as a water-insoluble calcium salt. According to the method, the gypsum formed as a by-product can be modified to gypsum fit for cement without discharging an alkaline waste water.