Adsorption and desorption properties of Li+ on PVC-H1.6Mn1.6O4 lithium ion-sieve membrane

A series of PVC-Li_1.6Mn_1.6O₄ precursor membranes were prepared by the solvent exchange method using spinel-type lithium manganese oxide powder (Li_1.6Mn_1.6O₄) as the precursor, poly(vinyl chloride) (PVC) as the binder, and N,N-dimethyl acetamide (DMAc) as solvent. The Li⁺ of the precursor membrane was extracted by treated with HCl solution to obtain PVC-H_1.6Mn_1.6O₄ lithium ion-sieve membrane adsorbent. The preparation conditions were investigated by changing the concentration of PVC and Li_1.6Mn_1.6O₄, and the thickness of liquid film. The structure, morphology and adsorption properties of PVC-H_1.6Mn_1.6O₄ lithium ion-sieve membrane were carried out by scanning electron microscope and atomic absorption spectrophotometer. The adsorption capacity depended on the preparation conditions. The membrane prepared with concentration of 10 wt% PVC and 15 wt% Li_1.6Mn_1.6O₄ in DMAc and liquid film thickness of 0.30 mm is optimum for the adsorption of Li⁺ from aqueous solution. The thickness of membrane prepared under above conditions is about 0.1 mm. Repeated adsorption-desorption test indicates that the PVC-H_1.6Mn_1.6O₄ lithium ion-sieve membrane can be effectively regenerated with HCl solution and reused for Li⁺ adsorption without significant loss in the adsorption capacity. Li⁺ adsorption experiments confirm that the PVC-H_1.6Mn_1.6O₄ lithium ion-sieve membrane possesses high selectivity for Li⁺ in the presence of Na⁺, K⁺, Ca²⁺ and Mg²⁺. According to the coefficients, the isothermal data correlated with the Langmuir model better than the Freundlich model, and the adsorption process follows a pseudo-second-order kinetic model.