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

Area of Science:

• Geochemistry
• Materials Science
• Mining Engineering

Background:

• Rare earth elements (REEs) are vital strategic resources for high-tech applications.
• In situ leaching (ISL) of REEs faces challenges due to reverse adsorption of leached ions onto low-grade ore layers.
• Understanding REE reverse adsorption mechanisms in low-grade ores is critical for optimizing extraction efficiency.

Purpose of the Study:

• To investigate the reverse adsorption behavior and characteristics of key rare earth ions (La³⁺, Y³⁺, Dy³⁺) onto low-grade ore.
• To elucidate the influencing factors (initial concentration, pH) on rare earth reverse adsorption.
• To determine the adsorption mechanism and identify the primary adsorption sites and bonding in low-grade ores.

Main Methods:

• Systematic study of La³⁺, Y³⁺, and Dy³⁺ reverse adsorption using low-grade ore as the adsorbent.
• Experimental analysis of adsorption capacity under varying initial concentrations and pH levels.
• Isothermal adsorption modeling (Langmuir model) to determine adsorption characteristics and mechanism.

Main Results:

• Reverse adsorption capacity increases with initial rare earth ion concentration, eventually plateauing.
• Adsorption capacity is higher for light rare earths (e.g., La³⁺) compared to medium and heavy rare earths (e.g., Y³⁺, Dy³⁺).
• Both adsorption capacity and rate increase with pH, with diminishing returns after pH > 3.
• Langmuir model fitting (R² > 0.99) indicates monolayer adsorption of rare earths onto clay minerals.
• Surface hydroxyl groups (e.g., Al-OH) are identified as primary adsorption sites, forming ≡Al-O-RE bonds with rare earth ions.

Conclusions:

• Low-grade ores exhibit significant reverse adsorption of rare earth ions, primarily through monolayer adsorption governed by the Langmuir model.
• Surface hydroxyl groups on clay minerals are key active sites for rare earth ion complexation.
• The findings provide a crucial theoretical foundation for mitigating reverse adsorption and enhancing rare earth recovery efficiency in in situ leaching operations.