Effect of particle size on cesium exchange kinetics by K-depleted phlogopite

Cation exchange mechanism and rate of Cs⁺ exchange were investigated in < 2 μm and 20-2 μm particle size fractions of K-depleted phlogopite (Na-phlogopite). The K-depleted phlogopite was prepared from a natural phlogopite by a potassium removal method using sodium tetraphenylborate (NaTPB) at room temperature. X-ray diffraction (XRD) patterns revealed that interlayer K⁺ ions were completely replaced with sodium ions after the potassium removal treatment. Ion exchange isotherms and kinetics were determined for Na⁺ → Cs⁺ exchange with two particle size fractions. The isotherms indicated that both particle size fractions showed high selectivity for Cs⁺. Based on the isotherm tests, ΔG^o values of < 2 μm and 20-2 μm particle fractions were - 6.83 kJ/mol and - 7.08 kJ/mol, respectively. Kinetics of Cs exchange revealed that the 20-2 μm particle size fraction of the K-depleted phlogopite took up more Cs⁺ ions than the < 2 μm particle size fraction. Various kinetic models were applied to describe Na⁺ → Cs⁺ exchange process. Elovich model described the kinetic data of the < 2 μm particle size fraction well, while the modified first-order model or parabolic diffusion model described the data of the 20-2 μm particle size fraction well.