Synergic and competitive adsorption of Li–Na–MgCl2 onto lithium–aluminum hydroxides

Abstract

Layered lithium–aluminum hydroxides have been used for the lithium adsorption for its high selectivity and cyclic stability. The adsorption performances of lithium and sodium in the mixing solution with abundant magnesium chloride were investigated using batch system at 303 K. The lithium adsorption capacity was increased from 5.02 to 5.69 mg/g (initial lithium concentration is 350 mg/L) with the increasing of initial chloride ions concentration from 200 to 350 mg/L, while the sodium decreased. Both the adsorption capacities of lithium and sodium were lower in Li–Na–MgCl2 system than that’s in Li–MgCl2 and Na–MgCl2 system, which indicated the competitive effects between lithium and sodium ions. In addition, the Langmuir model could describe the isotherms of lithium and sodium well. Then, the homogeneous surface diffusion model (HSDM) was applied to represent the lithium adsorption kinetics. The surface diffusion coefficients of lithium were dependent on the initial concentration and affected by sodium ions. The Biot numbers were ranged from 25 to 40 confirming that the intraparticle diffusion is the limiting step. Breakthrough curves of lithium and sodium demonstrated the lithium could be enriched and obtained with fixed bed adsorption process, and verified the competitive adsorption phenomenon.