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.
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