Synthesis Of Doped-Type Ion Exchanger And Study Of Its Exchange Property

A series of Ni-doped lithium manganese oxide LiNixMn2-xO4(x=0.00, 0.05, 0.10, 0.20) were synthesized as lithium ion-sieve precursors by a sol-gel method using acetic lithium, nickel and manganese as raw materials. The optimum conditions of preparing lithium ion-sieve precursors were: citric acid as chelating agent, calcining heat 700℃, calcining time 8h, amount of x 0.05, which were obtained by orthogonal experiments. Their spinel structures and acidic stability were studied. The lithium ion-sieve noted as LiNiMn-H was obtained by acid-modifying the gained LiNi0.05Mn1.95O4 by 0.5 mol/L (NH4)2S2O8. The ion-exchange properties of LiNiMn-H such as its saturation capacity for alkali mental ions and the pH titration curves for Li+, Na+ and K+ were determined.The results showed that the dissolving ratio of Mn2+ from the obtained spinel LiNi0.05Mn1.95O4 was only 0.31% during the acid-modified process and the saturated ion-exchange capacity of the obtained lithium ion-sieve LiNiMn-H for 0.1mol/L Li+ solution was 5.29 mmol (36.72mg)Li+/g , which showed a high selectivity for Li+.The ion-exchange thermodynamics of lithium ion-sieve was determined. The exchange isothermal diagrams of H+-Li+ on lithium ion- sieve were measured at 15℃, 25℃, 35℃and 45℃respectively. The average activity coefficients of the electrolyte and the Kielland diagrams were calculated by using Pitzer electrolyte solution theory, then the other thermodynamic constants such as equilibrium constant K a,ΔG0,ΔH0andΔS0during the exchange process were computed. The ion exchange free enthalpy of lithium ion-sieve for Li+ were negative, which indicated that its selectivity for Li+ was higher than the original ion H+, the ion exchange process carried out spontaneously (ΔG0<0), and the exchange process was exothermic. The ion-exchange dynamics of lithium ion-sieve was studied at 25℃. The kinetics curves of lithium ion-sieve for Li+ during the ion-exchange process were measured in 0.005, 0.025和0.050mol/L Li+ solutions respectively. The shrinking-core model was choosen to deal with the dynamics dates of the ion exchange process, and the kinetics controlled step was determined to be particle diffusion control (PDC). Besides, the kinetics equations and diffusion coefficients (De) of the lithium ion-sieve for Li+ were obtained at the experimental conditions .