Simultaneous removal of Na, Ca, K and mg from synthetic brine and seawater using Fe₂ O₃ –Sio₂ mixed oxide nanostructures: Kinetics and isotherms studies

In the study, Fe₂O₃–SiO₂ nanocomposite (prepared using sol–gel method), was used as an adsorbent for the removal of Na, K, Ca and Mg ions from synthetic brine solutions. The structural and surface characteristics of the nanoadsorbent were investigated by N₂ adsorption–desorption, transmission electron microscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and powder X-ray diffraction spectroscopy. The batch adsorption technique was used for removal of major cations from the synthetic samples. Experimental parameters (such as pH, initial concentration, adsorbent mass and contact time) affecting the removal of Na, K, Ca and Mg were optimized using response surface methodology. Equilibrium isotherms for the simultaneous adsorption of Na, K, Ca and Mg onto Fe₂O₃–SiO₂ nanocomposite were analyzed by the Freundlich, Langmuir, Dubinin–Radushkevich (D–R) and Temkin isotherm models. Adsorption isotherm studies indicate that the simultaneous adsorption of Na, K, Ca and Mg ions onto Fe₂O₃–SiO₂ nanocomposite followed models in the order Langmuir > Temkin ≈ Dubinin–Radushkevich (D–R) > Freundlich model. The kinetic study of adsorption shows that the batch adsorption system followed pseudo-second-order kinetic model. The isotherm and kinetic studies confirmed that the adsorption of major cations was based on physical adsorption mechanism.