Effective retention of inorganic Selenium ions (Se (VI) and Se (IV)) using novel sodalite structures from muscovite; characterization and mechanism

Abstract

Muscovite flakes were applied in the synthesis of three types of sodalite with different morphologies by hydrothermal processes for 24 h, 48 h, and 72 h. The synthetic sample after 72 h (S-72) showed the best surface area (105 m2/g), morphological features, and ion exchange capacity (71.3 meq/100 g). The S-72 was applied for effective retention of both Se (VI) and Se (IV) ions in batch adsorption studies. The retention capacities of Se (VI) and Se (IV) ions using S-72 sodalite are 149 mg/g and 255 mg/g, respectively after an equilibration time of 300 min and 360 min. The kinetic assessment suggested Pseudo-second order behavior for the retention of both Se (VI) and Se (IV). The equilibrium studies of their retention reactions demonstrated Langmuir isotherm behavior and monolayer form for the homogeneously adsorbed Se (VI) and Se (IV) ions on the surface of sodalite. The Gaussian energies (> 8 KJ/mol), enthalpies (< 80 KJ/mol), and Gibbs free energies (< 40 KJ/mol) for both Se (VI) and Se (IV) suggested physical reactions related to coulumbic attractive forces or ion exchange process. Based on the thermodynamic investigations, the Se (VI) and Se (IV) retention reactions are of exothermic, favourable, and spontaneous properties. The removal percentages of Se (VI) and Se (IV) ions by sodalite in the coexisting of Pb2+, Zn2+, PO4−3, and NH4+ ions are of significant values either in pH 2 or pH 7.