Sodium-Modified Vermiculite for Calcium Ion Removal from Aqueous Solution

The treatment and recuperation of hydric resources portray recurrent challenges and demand alternative processes and technologies. The removal of hardness and metal ions from water are necessary in certain sources of human consumption and for industrial purposes. In this work, sodium-modified vermiculite was investigated toward the removal of calcium ions in aqueous medium. The effects of adsorbent dosage, contact time, initial concentration of calcium ions, initial pH, and temperature were systematically studied for both raw and modified vermiculite. pH 10 was shown to be the most appropriate to conduct the experiments. Raw, sodium-modified, and postadsorption vermiculite were characterized by microstructure analysis (scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray fluorescence, and X-ray diffraction). The maximum adsorption capacity was found in sodium-modified vermiculite, resulting in about 80 mg g–1. Kinetic studies were carried out to relate the experimental data to pseudo-first-order, pseudo-second-order, and Elovich models. Isotherm models (Freundlich, Langmuir, and Redlich–Peterson) were employed to describe the softening process, and thermodynamic parameters ΔG°, ΔH°, and ΔS° were determined. Results revealed a spontaneous endothermic adsorption process with pseudo-second-order kinetics and corroborated the sodium-modified vermiculite adequacy for water softening.