Research on the Reverse Adsorption Process of Rare Earth Ions on Low-Grade Minerals

Rare earths play an irreplaceable role in high-tech fields as key strategic resources. It is of importance to achieve efficient recovery of rare earth elements. During the in situ leaching process, the already leached rare earth ions are reverse-adsorbed to low-grade ore layers, which seriously restrict the rare earth leaching efficiency. To explore the reverse adsorption behaviors and characteristics of rare earths in low-grade ore layers, this paper used low-grade ore as the adsorbent and systematically studied the reverse adsorption behaviors of La³⁺, Y³⁺, and Dy³⁺. The results showed that the reverse adsorption capacity increased first and then tended to level off with the rise of the initial concentration, and the adsorption capacity for light rare earths was stronger than that for medium and heavy rare earths. The reverse adsorption capacity and reverse adsorption rate increased with the enhancement of pH, and the growth slowed down after pH > 3. Through isothermal adsorption model fitting, it was found that the reverse adsorption of rare earths by clay minerals all conformed to the Langmuir model, with R² > 0.99, indicating that the reverse adsorption process of rare earths by low-grade ores is monolayer adsorption. The analysis indicated that surface hydroxyl groups such as Al-OH are the main adsorption sites, and rare earth ions chemically coordinate with the mineral surface by forming ≡Al-O-RE bonds. This study revealed the reverse adsorption mechanism of rare earths by low-grade ores, providing a theoretical basis for optimizing the in situ leaching process and suppressing reverse adsorption.