Leaching of Rare Earth Elements from Phosphogypsum Using Mineral Acids

Rare earth elements (REEs) are critical metals for modern and emerging green technologies. Their increasing demand and limited supply have sparked the research on their recovery from secondary resources. The current study is focused on developing a hydrometallurgical process for the extraction of critical REEs from a waste byproduct, called phosphogypsum, and on elucidating the mechanism of the extraction process. Three types of mineral acids are used for the leaching, and a systematic study is utilized to assess the effect of operating parameters and to determine the optimum operating conditions. Thermodynamic modeling and solubility investigation shows the strong correlation between phosphogypsum solubility and leaching efficiency and the leaching process mechanism. Characterization results indicate that REEs can exist as isomorphous substitutions and/or separate phases inside phosphogypsum crystal. Based on these results, the destruction of phosphogypsum lattice is required to achieve improved extraction.