Synthesis Of MnO₂-Type Potassium Ion-Sieve And Study On Ion Exchange Action For K⁺

Potassium ion-sieve CRYMO-H was synthesized with manganese sulfate and potassium permanganate as the main materials. Via orthogonal experiment (L9 (34)) conditions obtaining CRYMO-H were: the concentration of KMnO₄ was 0.5 mol·L^-1. the concentration of MnSO4 was 2.0 mol·L^-1. nKMNO₄/nMnSO₄ was 1:2, reaction temperature was 75℃. and the concentration of nitric acid remodeling was 5.0 mol·L^-1. Its crystal structure was determined by XRD and the result showed that its crystal structure wasα-MnO₂.The saturation exchange capacity of CRYMO-H to potassium ion (in the solution which concentration of K⁺ was 0.lmol·L^-1) was 181.54mgK⁺·g-1. The result of pH titration curve experiment and saturated ion exchange capacity was consistent. The selectivity of potassium ion-sieve CRYMO-H for alkali ions was: K⁺>Na+>Rb+>Li+>Cs+Saturation exchange capacity of potassium ion-sieve CRYMO-H for K⁺ in seawater was 6.1.17mg·g-1 and K⁺ was enriched 166 times.The exchange isothermal curves of H⁺-K⁺ on CRYMO-H were mensurated at 15℃,25℃,35℃,45℃respectively. Using Pitzer electrolyte solution theory, activity coefficients of the system were calculated, and then Kielland diagrams of the ion exchange system were obtained. Ion exchange free enthalpy of CRYMO-H for K⁺ was negative. This indicated that ion exchange process of CRYMO-H for K⁺ was a spontaneous process.Ion exchange kinetics of potassium ion-sieve CRYMO-H for K⁺ was determined at 25℃, and using shrinking core model its reactive control step could be estimated: the reactive control step was not one of liquid membrane diffusion control, particle diffusion control, chemical reaction control but two or three control together. Langmuir model, Elovich model and Bangham model were used to describe ion exchange kinetics of potassium ion-sieve for K⁺. The result showed using Elovich model precision was high and linear regression was good. Ion exchange kinetics equations for K⁺ were obtained in different concentration of K⁺ solution. Linear correlative coefficients were higher than 0.97.Granulation was put up with DMF-PVC-H2O system for potassium ion-sieve CRYMO-H precursor and did pole exchange experiment using seawater. The result showed adsorption quantity for K⁺ was 58.25mg·g^-1.