Abstract:

In order to speed up the comprehensive utilization of fluorine resource,by-product of phosphate fertilizer and solve the problems of large land occupation and water pollution caused by the stacking of electric lime.Silicon tetrafluoride was prepared by the reaction of fluorosilicic acid,by-product of phosphate fertilizer,and electric lime to prepare fluoride and by-product of calcium fluoride with high added value and high quality.The effect of the proportioning ratio of calcium chloride to fluorosilicic acid,reaction temperature,calcium chloride solution concentration and mother liquor circulation on the yield of calcium fluorosilicate were studied.At the same time,the effect of calcium fluorosilicate pyrolysis temperature on the quality of silicon tetrafluoride products were also analyzed.The results showed that calcium chloride was concentrated to 60%,and the single batch yield of calcium fluorosilicate could reach 86% at temperature of 55 ℃ and the ratio of calcium chloride to fluorosilicic acid of 2∶1.Calcium fluorosilicate was statically decomposed at 350 ℃ for 1 h,the decomposition rate reached 99%,and the the quality of as-prepared silicon tetrafluoride products met the requirements of preparation of silane and anhy-drous hydrogen fluoride,and the quality of the by-product calcium fluoride met the requirements of the industry standard（YB/T 5217—2019 Fluorite）.The fluorine and silicon resources could be fully utilized in the process research,and the process was simple,easy to operate,and easy to industrialized production,which provided certain guidance for the comprehensive utilization of phosphate fertilizer by-product fluorosilicic acid.

Key words: by-product of phosphate fertilizer, fluorosilicic acid, silicon tetrafluoride, electric lime