Comparative study on the uranium removal performance of common minerals: performance, kinetics and mechanism

This study evaluated the uranium removal performance and mechanisms of six minerals: zeolite, montmorillonite, bentonite, phlogopite, sodium bentonite (Na-bentonite), and potassium feldspar (K-feldspar). When the initial uranium concentration was 10 mg/L, montmorillonite exhibited the highest uranium adsorption capacity, reaching 64.9%, followed by bentonite (63.3%), zeolite (57.2%), phlogopite (53.3%), Na-bentonite (37.3%) and K-feldspar (35.7%). The adsorption process was pH-dependent, with bentonite and zeolite showing enhanced adsorption at higher pH levels, while other minerals exhibited complex trends due to changes in uranium speciation and mineral surface properties such as electronegativity. Mechanistic analysis revealed that zeolite, phlogopite and K-feldspar removed uranium mainly through chemical adsorption, such as structural incorporation and surface complexation, whereas montmorillonite, bentonite and Na-bentonite mainly removed uranium via physical adsorption such as ion exchange and electrostatic attraction. Phlogopite exhibited strong uranium retention via interlayer adsorption, whereas Na-bentonite and K-feldspar exhibited weaker adsorption due to lower cation exchange capacity and surface interactions. Thermodynamic studies indicated that adsorption onto montmorillonite, bentonite, zeolite, and phlogopite was spontaneous and exothermic, whereas Na-bentonite and K-feldspar showed endothermic behaviour. Stability tests in bicarbonate solution confirmed phlogopite's highest uranium retention, whereas bentonite and montmorillonite released more uranium due to bicarbonate complexation. These findings provide insight into uranium adsorption mechanisms and serve as a reference for the selection of materials for radioactive waste disposal repositories.