Preparation,Characterization And Molecular Simulation For Potassium Ionic Sieve

Adsorption capacity of potassium adsorbed by zeolite is lower in the technology of extracting potassium from seawater and brine. To solve the problem, merlinoite, which has higher adsorption capacity for potassium, was prepared by hydrothermal method using Na₂SiO3·9H₂O and NaAlO₂ as the raw materials. The influence of gel compositions on preparation factors and crystallity of zeolite synthesized were investigated; crystallization field of merlinoite were determined. Furthermore, merlinoite was characterized by X-ray diffraction（XRD）, Fourier transform infrared spectrum（FT-IR）, scanning electron microscopy（SEM） as well as Energy dispersive X-ray spectrometry（EDS）. The sample was modified successively with NH4 Cl and NaCl heated solution, next, adsorption tests of separating potassium from solution with the sample modified were investigated. Meanwhile, the process of cations exchange in MER type zeolite was simulated by molecular simulation method. The study is a significant theoretical foundation for preparation and cations exchange of MER type zeolite.The results show:（1） Compared with gel without sodium, the plot of crystallization field of merlinoite is significantly reduced using Na₂SiO₃·9H₂O and NaAlO₂ as the raw materials. By increasing the SiO₂/Al₂O₃ at high K₂O/SiO₂ ratio, the crystallinity of the zeolite synthesized increased, while at low alkalinity, the crystallinity decreased. Increasing alkalinity when SiO₂/Al₂O₃ is a constant, the Si/Al of zeolite framework increased.（2） Merlinoite modified has the same framework structure as the synthetic merlinoite. Adsorption capacity of potassium adsorbed by Na-merlinoite in the KCl solution, seawater, Manas Lake and Lop Nur Lake respectively is 185.5 mg/g, 52.8 mg/g, 70.1 mg/g and 85.1 mg/g. The adsorption ratio of potassium from simulated seawater for NH₄^-merlinoite is more rapid than that for Na-merlinoite. In addition, the adsorption kinetics of the merlinoite was best described by pseudo-second-order kinetic equation and the ion exchange process was controlled by liquid film diffusion.（3） A preferential siting of Al is in MER type zeolite framework site T₂ and the minimum Si/Al of zeolite framework is 1.67. There are three kinds of sites located by extra-framework K⁺, Na⁺ and NH4+ and K⁺ sites are priority in buckled rings. From the point of binding energy, the preferable cation absorbed by zeolite is K⁺, followed by Na⁺ and NH4+, in addition, the cations located in the site III firstly exchange with other cations, followed by site I and II. The process of K⁺-Na⁺ and K⁺-NH4+ ion exchange for Na-MER and NH₄^-MER type zeolites respectively is the exothermic reaction, however, the process of Na⁺-NH4+ ion exchange for NH₄^-MER type zeolite is the endothermic reaction. The hydrogen-bonded network of potassium and water forms a structure-directing agent that acts as an inorganic template in the formation of MER type zeolite. Increasing the temperature, the diffusion coefficients of water confined in MER type zeolite increase. The order of diffusion activation energy of water confined in the different kinds of cation MER type zeolite is K-MER type zeolite >Na-MER type zeolite >NH₄^-MER type zeolite.