Recycling of waste gypsum from αlpha-hemihydrate phosphogypsum: Based on the atmospheric hydrothermal process

Phosphogypsum (PG) is a typical solid waste in the phosphorus chemical industry, which restricts the sustainable development of the phosphorus chemical industry. From the perspective of green manufacturing in the whole life cycle, this paper puts forward the hydrothermal recycling and utilization of waste gypsum (WG) from αlpha-hemihydrate phosphogypsum (α-PGHH). It is revealed that the raw material characteristics of WG will lead to the crystal fine fragmentation of the product, which will lead to the significant deterioration of the strength and filtration performance of the hardened paste. The increase of the acidity of the reaction medium is proposed to weaken the negative effect of the crystal modifier on crystal phase transition, so as to obtain recycled αlpha-hemihydrate gypsum (α-HH) with better crystal integrity and macroscopic performance. It was proved that when the pH value was controlled at 4.5, the comprehensive properties of the product were good, and the 2 h bending strength and 3 d compressive strength were 4.1 MPa and 29.2 MPa, respectively. The preparation of recycled α-HH from WG produced by α-PGHH can be achieved through the atmospheric hydrothermal process.