Rare earth elements leaching from phosphogypsum derived from magmatic and sedimentary phosphate ore

Phosphogypsum (PG), a by-product of wet-process phosphoric acid production, presents a promising secondary source of rare earth elements (REEs) due to its significant REEs concentrations and high production volumes. This study has two main objectives: first, to analyze and compare the chemical and mineralogical compositions of two PG types, magmatic PG (MPG) from the Wizów Chemical Plant in Poland and sedimentary PG (SPG) from the Jorf Lasfar plant in Morocco, using various characterization techniques; and second, to explore the leaching behavior of REEs from PG using different acids and additives. Leaching experiments were carried out with 2 M H₂SO₄ alone, as well as in combination with oxidizing agents (NaClO₃ and H₂O₂) and reducing agents (Fe and Zn), which are introduced here for the first time to improve REEs extraction from PG. The results demonstrated that MPG achieved a high REE recovery rate of 85% using 2 M H₂SO₄ alone. In contrast, SPG showed a lower recovery of 34% under the same conditions, which increased to 46% with H₂O₂ and 48% with Fe, while the combined use of NaClO₃ and Fe resulted in 47% recovery. These additives had no significant effect on MPG. Micro-EDXRF analysis revealed that the disparity in leaching performance is attributed to the differing REEs occurrences: MPG hosts REEs as soluble salts, whereas in SPG, REEs are structurally incorporated into the gypsum matrix via isomorphic substitution, making them less accessible. Effective REEs recovery from PG not only mitigates environmental contamination but also supports its valorization in agriculture and construction, aligning with circular economy and sustainability goals.