Harmless treatment technology of phosphogypsum: Directional stabilization of toxic and harmful substances

Phosphogypsum is one of the typical by-products of phosphorus chemical industry. As a strategic industry related to the national livelihood of China, phosphorus chemical industry has accumulated and produced a significant amount of phosphogypsum. In general, phosphogypsum contains approximately 80%–95% calcium sulfate dihydrate, and less than 5% toxic and harmful elements. In this paper, toxic and hazardous components in phosphogypsum were efficiently solidified and stabilized by highly targeted solidification and stabilization technology. Calcium carbide slag or lime was used as an alkali-base neutralizer of phosphogypsum, and polymeric ferric sulfate or polymeric aluminum chloride as a directional solidification stabilizer to analyze the leaching toxicity of the mixed powder in 1, 3, 5 and 15 days. The experimental results demonstrate excellent solidification and stabilization effect with the leaching pH of 6–9, the leaching concentration of P, F and heavy metals of less than 0.5 mg/L, 10 mg/L and 0.1 mg/L, respectively, which meets the requirements of relevant international standards. Mechanistic analysis indicates that the solidification and stabilization of toxic and hazardous substances in phosphogypsum is perfectly achieved owing to the generation, adsorption and encapsulation of insoluble substances. This technology can reduce the costs and difficulty in the phosphogypsum treatment, and has extensive application potentials.