Ca2+removal from water by the use of Na-palygorskite for potential water softening

Abstract

Sodium-treated palygorskite (Na-Pal) sample was investigated for the sorption of Ca2+ions with the aim of treating water hardness. The effective modification of the mineral with Na was verified by XRD and FT-IR techniques. Batch kinetic experiments in standard solutions were performed proving that 30 g/L of Na-Pal were highly satisfactory as the Ca2+removal reached the 85% for 100 mg/L Ca2+initial concentration, which is very promising for the softening of moderate or hard waters. The Ca2+removal found to be pH and temperature independent, with high removal rates at room temperature and common pH values of water samples (pH 4-12), rendering these circumstances ideal for the low-cost maintenance of the procedure that took place within the first 5 min. The linear form of the Langmuir isotherm model expressed better (R2 = 1) the Ca2+sorption, which means that takes place at specific homogeneous sites of Na-Pal. Thermodynamic analysis proved the non-spontaneous (positive ΔG0), physical, and exothermic nature (ΔH0=_10.8197 kJ/mol) of the reaction, while the kinetic models proved the chemisorption of Ca2+by Na-Pal.