A high-efficiency purification method of waste phosphogypsum via hydrodynamic cavitation pretreatment and froth flotation

The presence of hazardous impurities such as phosphorus, fluoride and silicon in phosphogypsum (PG) is a significant obstacle to its large-scale utilization, and the conventional method of stirring water washing (SWW) is often ineffective in removing these impurities. This study innovatively applies hydrodynamic cavitation pretreatment (HCP) combined with froth flotation to purify PG. Computational fluid dynamics was used to determine the optimal parameters for the cavitation tube. During the pretreatment stage, HCP significantly outperformed SWW in removing soluble phosphorus and fluoride. When combined with flotation for further removal of undissolved silicon, HCP continued to play a more positive role. The proposed novel method increased the purity of PG from 81.0 % to 97.27 % with a recovery rate of 83.81 %, obtaining acceptable gypsum products. Analytical tests indicate that HCP effectively disrupts the crystal structure of PG. In addition, HCP enhanced the adsorption amount of collectors on the target mineral surfaces. Molecular dynamics simulations further confirm that both 1231 and DDA exhibit higher adsorption energies on the surfaces of quartz and PG with HCP. Thus, this study proposes a novel approach for the green and efficient treatment of PG, laying the theoretical and technical foundation for the high-value unitization of massive solid waste.