USAGE OF BY-PRODUCT ALPHA-HEMIHYDRATE GYPSUM INVOLVED IN PHOSPHORIC ACID MANUFACTURING PROCESS

摘要

PROBLEM TO BE SOLVED: To provide the subject usage comprising adding α-hemihydrate gypsum as a by-product through manufacturing wet phosphoric acid by decomposing igneous rock-type phosphate rock with sulfuric acid by dihydrate-hemihydrate method to anhydrous gypsum to remarkably shorten the anhydrous gypsum's setting time. ;SOLUTION: This usage comprises the following practice: the above-mentioned by-product α-hemihydrate gypsum is washed and dried by specified means and pulverized so as to adjust its specific surface area; for anhydrous gypsum, if it is incorporated with an alkali for its neutralization, it is usable without question; it is preferable that 5-50 pts.wt. of the α-hemihydrate gypsum is used based on 100 pts.wt. of the anhydrous gypsum; when the anhydrous gypsum incorporated with the α-hemihydrate gypsum is kneaded with water, the resultant slurry comes to pH 8.5-12 due to an alkali incorporated therein beforehand; owing to the alkali, the hydration of the α-hemihydrate gypsum is promoted, resulting in advancing the α-hemihydrate setting and in running to a pseudoset state as a whole in an early stage; thereby, through mixing the two kinds of gypsum together, the setting time can be remarkably shortened.;COPYRIGHT: (C)2000,JPO