Research progress on comprehensive utilization of phosphogypsum and heavy metal gypsum slag

With the acceleration of industrialization, the production of various industrial by-products of gypsum slag is increasing year by year. As a large agricultural country and a non-ferrous metal smelting country, China produces a large amount of solid waste with CaSO4·2H2O as the main component in both phosphate fertilizer production and dirty acid neutralization process, and accelerating the comprehensive utilization of both is crucial for resource recovery and environmental protection. At present, phosphogypsum has a wide range of applications in the fields of construction, chemical industry and agriculture, and is widely used in the preparation of cement retarder, quicklime, road base material, soil conditioner, etc. However, its comprehensive utilization rate is only about 40%, and there is still a large amount of phosphogypsum stockpiled, expanding the market demand for phosphogypsum applications is crucial. Heavy metal gypsum, on the other hand, is difficult to handle due to the presence of toxic elements such as arsenic, cadmium, lead, etc., and is now mainly disposed of by recovery of valuable metals and solidification/stabilization. However, due to the complex composition and low content of its valuable metals, the economic benefits of recovery are insufficient and it is difficult to realize industrialization. In this paper, combined with domestic and international research, the current status of comprehensive utilization of phosphogypsum and heavy metal gypsum is reviewed, the advantages and disadvantages of disposal and utilization technologies are analyzed, and suggestions and prospects are put forward. For phosphogypsum, green and efficient deep decontamination methods should be explored to ensure the quality of products in the fields of construction, agriculture and chemical industry, and at the same time, the development of emerging fields such as preparation of gypsum whiskers and synthesis of new chemical raw materials should be explored, so as to expand the scale of high-value utilization of phosphogypsum and to achieve large-scale elimination of phosphogypsum. For heavy metal gypsum, the future development trend is proposed: 1) continue to develop green and efficient valuable metal element recovery technology, and realize large-scale industrialization application, 2) strengthen the exploration of the synergistic use technology of heavy metal gypsum and other solid wastes, and synergistically treat gypsum slag with other solid wastes before combining it with other methods such as flotation to realize its resource utilization, 3) carry out long-term research on solidification/stabilization to prevent the phenomenon of “anti-solution”, 4) research and development of a new process for the treatment of polluted acid, to achieve the reduction of heavy metal gypsum slag production.