Distribution, occurrence, and extraction of rare earth elements in phosphogypsum

The extraction of rare earth elements (REEs) might become a vital way to reuse phosphogypsum (PG), which might be a meaningful method to solve the problems of REE resource shortage and PG environmental pollution. REEs in PG primarily exist within the gypsum lattice through isostructural substitution, followed by independent REE minerals (i.e., monazite), and reside a little in compounds (such as sulfates, phosphates, and silicates). Currently, there are advantages and disadvantages to the REE extraction methods (including direct acid leaching, enhanced acid leaching, organic acid leaching, organic solvent extraction, salt solution leaching, and bioleaching) of PG. Employing microwave or ultrasonic technologies, promising applications, to enhance REE extraction could significantly improve efficiency. Bioleaching is more environmentally friendly and demonstrates better selectivity and extraction efficiency for low-concentration REEs, making it a promising approach for the REE extracting of PG. The recovery of REEs from PG should not only focus on the efficiency of the single leaching stage but also consider the subsequent separation and purification of REEs and the value of by-products. Achieving a comprehensive and fully integrated solution that is technically feasible, economically efficient, and environmentally friendly for the REE extracting of PG should be the direction for future efforts.