Ion exchange properties of surface hydroxyl groups on lambda-MnO2 for sodium ion adsorption

Lambda-MnO2 has the ability to incorporate Li+ ions in solution selectively into its lattice vacancies, and can be applied as a sensor material for Li + ions and as an agent for recovering Li+ ions from seawater. The surface o f lambda -MnO2 in water is hydroxylated, and ion exchange reactions at surf ace hydroxyl groups may bring other ions into the recovered Li+ ions. The a mount of Na+ ions adsorbed by exchanges with surface hydroxyl protons was m easured by titration in NaNO3 solutions, and modeled by considering reactio n stoichiometry and equilibrium conditions with the Frumkin equation. The m odel equations reproduce the measured data, and can be used to estimate the amount of Na+ ions contaminating the recovered Li+ ions. A method for redu cing the contamination due to adsorbed Na+ is proposed.