Spatial confinement and ion exchange synergetic strategy for highly selective removal of metal ions from the spinning solution containing ionic liquids

The accumulation of metal ions (Na+, K+, Ca2+, Mg2+, Fe3+, Cu2+ and Zn2+) in the coagulating and water baths generated during the spinning process using ionic liquids (ILs) as solvent seriously affects the strength and textile performance of regenerated cellulose fibers, and make a huge challenge for the recycling and reuse of ILs. In this work, a spatial confinement and ion exchange synergetic strategy was adopted and the molecular sieves with proper pore size and exchangeable structural metal ions were used. Batch adsorption demonstrated the superior removal efficiency and high selectivity of the 10X molecular sieve towards different metal ions. As a result, the highest removal ratios of 82.7%, 95.2%, 93.5%, 97.3%, 99.1% were achieved for K+, Ca2+, Mg2+, Cu2+ and Zn2+, respectively, and that for IL (1-ethyl-3-methylimidazolium diethyl phosphate, [Emim]Dep) was below 0.6%. Moreover, the adsorbed 10X could be facilely eluted and reused by the HCl solution. The fixed-bed experiments found that the 40.2 BV [Emim]Dep solution could be entirely purified at a contact time of 10 min, further indicating its favorable removal efficiency and long-term application perspective. All these results confirmed that this commercial and cost-effective molecular sieve could be used in the efficient separation of trace metal ions from the aqueous solutions with high IL concentration produced during the cellulose spinning process.