Phosphogypsum (PG) is a by-product of producing fertilizer from phosphate rock. By 2020, there will be over 600 Mt of PG in storage, with 75 Mt produced annually. However, a limited amount is reused. The majority of PG is stored in enormous stacks on surfaces. Due to the rapid increase of demand for rare earth elements (REEs), studies for secondary sources have received extensive research, and PG is one of the promising secondary sources of REEs owing to its significant content of REEs such as yttrium (Y), lanthanum (La), and neodymium (Nd).
The study investigated microwave-assisted extraction (MAE) for recovery of Y, La, and Nd from PG, while phosphorus (P) recovery was also assessed. The effects of acid type (HCl, H2SO4, HNO3), reaction temperature (100-150oC), acid concentration (0.25-1.0 N), solid concentration (10-40 g/L), and reaction time (5-30 min) on leaching efficiency were investigated. The addition of H2O2 was also investigated for possible applications of advanced oxidation processes (AOP) for REEs recovery from waste.
When using 1.0 N HCl, solid concentration of 20 g/L, 100oC, and reaction time of 5 min, leaching efficiency of 106.3% for Y, 102.0% for La, 99.8% for Nd, and 87.0% for P was found. The addition of H2O2, however, decreased leaching efficiency due to surface passivation by an oxide layer of zirconium (ZrO2). Simulation results also showed that recovery of P via selective precipitation was not feasible due to the high amount of Ca that interferes with the formation of struvite.

Phosphogypsum (PG) is a by-product of producing fertilizer from phosphate rock. By 2020, there will be over 600 Mt of PG in storage, with 75 Mt produced annually. However, a limited amount is reused. The majority of PG is stored in enormous stacks on surfaces. Due to the rapid increase of demand for rare earth elements (REEs), studies for secondary sources have received extensive research, and PG is one of the promising secondary sources of REEs owing to its significant content of REEs such as yttrium (Y), lanthanum (La), and neodymium (Nd).
The study investigated microwave-assisted extraction (MAE) for recovery of Y, La, and Nd from PG, while phosphorus (P) recovery was also assessed. The effects of acid type (HCl, H2SO4, HNO3), reaction temperature (100-150oC), acid concentration (0.25-1.0 N), solid concentration (10-40 g/L), and reaction time (5-30 min) on leaching efficiency were investigated. The addition of H2O2 was also investigated for possible applications of advanced oxidation processes (AOP) for REEs recovery from waste.
When using 1.0 N HCl, solid concentration of 20 g/L, 100oC, and reaction time of 5 min, leaching efficiency of 106.3% for Y, 102.0% for La, 99.8% for Nd, and 87.0% for P was found. The addition of H2O2, however, decreased leaching efficiency due to surface passivation by an oxide layer of zirconium (ZrO2). Simulation results also showed that recovery of P via selective precipitation was not feasible due to the high amount of Ca that interferes with the formation of struvite.

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