Investigating Leaching Parameters for Enhanced Rare Earth Elements Sustainability and Recovery from Phosphogypsum

Substantial volumes of phosphogypsum (PG) are generated globally as a by-product in phosphoric acid production, categorizing it as a widespread waste. Managing such substantial amounts of PG poses challenges due to its composition containing various pollutants, including persistent rare earth elements (REEs) with non-biodegradable characteristics. Conversely, an encouraging approach for valorizing PG involves extracting REEs, as these elements play a critical role in diverse modern technologies. However, any recovery process must be cost-effective and environmentally compliant. This research aims to enhance leaching efficiency and explore the correlation between the extraction efficiency of REEs from PG and gypsum solubility. The results reveal that the leaching efficiency of REEs increases with higher acid concentration, extended leach duration, and an optimized solid/liquid ratio, primarily due to the improved solubility of phosphogypsum. Notably, hydrochloric acid ( \({\text{HCl}}\) $\text{HCl}$ ) leaching exhibits superior efficiency at ambient temperatures, presenting advantages in terms of lower industrial energy demand and reduced cost.Furthermore, the addition of ammonium chloride or sodium chloride to HCl as a leaching agent significantly enhances the leaching efficiency of REEs from PG. The optimal content of sodium and ammonium (ion-exchangeable) for achieving the highest REEs leaching efficiency was found to be 2% and 4%, respectively. The highest leaching efficiency for the combined elements Nd, Y, and La in hydrochloric acid was achieved with an acid concentration of 3 mol L⁻¹, and a solid/liquid ratio of 1/40, and a temperature of 25 °C. These promising results are noteworthy, especially considering that no heating system is required for REEs extraction from PG, aligning with the circular economy goals and environmental protection. High recovery efficiency achieved (about 87%) while minimizing costs is essential for the economic viability of REEs extraction.