In this study, Li+ uptake by ion sieves was studied in a fixed-pH aqueous phase using a pH 8.0 buffer solution of ammonia/ammonium Chloride. Two different spinet-type manganese oxide ion sieves were used to investigate the effect of intrinsic properties of ion sieves on Li+ uptake. The effect of ionic strength was also considered for potential recovery of lithium from seawater and brine. The results of Li+ uptake indicated that the sorption isotherms fit the Langmuir model well. The uptake was found to obey a pseudo-second-order rate. The thermodynamic parameters, Delta G(0), Delta H-0, and Delta S-0, were calculated, and the results indicated that the Li+ uptake by both ion sieves was endothermic. The influence of ionic strength was mainly found on the kinetics of Li+ uptake. Moreover, the global reaction rate is probably controlled by both intraparticle diffusion and boundary layer diffusion, and the extent of control is greater for intraparticle diffusion than for boundary layer diffusion for Sieve-1; the reverse is for Sieve-2. Finally, Sieve-2, with high 11 content and small grain size, was proposed as a more suitable absorbent for recovery of lithium from seawater or brine. (C) 2008 Elsevier Inc. All rights reserved.