Highly selective and rapid removal of metal ions from ionic liquids solutions through size-sieving and ion-exchange strategy

The introduction of metal ion impurities into ionic liquids (ILs) when serving as solvents and catalysts is inevitable, thus the purification and recovery of ILs is essential in view of the quality control of the final products and cost. However, the highly efficient removal of impurity with minimal IL loss is challenging. In this work, the adsorption of metal ions from 1-ethyl-3-methylimidazolium diethyl phosphate ([Emim]Dep) solution generated in the cellulose spinning process was investigated. Based on the size-sieving and ion-exchange strategy, the modified molecular sieves (MMSs) were used and the effect of particle size on the adsorption performance was systematically studied. Batch adsorption showed that the MMSs with the smaller size of 1.6 mm exhibited the superior advantages over metal ions with fast removal kinetic and higher selectivity. The removal ratio of K+, Ca2+, Mg2+, Cu2+ and Zn2+ could reach 88.9 %, 98.4 %, 98.9 %, 99.6 % and 99.9 %, respectively. Benefiting from the size-sieving effect, the loss ratio of [Emim]Dep was lower than 0.7 %. Fixed-bed adsorption experiments further suggested the benign long-term separation performance of metal ions from [Emim]Dep aqueous solution. Moreover, the high removal ratios of metal ions from the actual [Emim]Dep aqueous solutions indicated the potential application in the purification of real ionic liquids.