Removal of chromium by riverbed sand from water and wastewater: Effect of important parameters

Application of riverbed sand, a non-toxic substance for the removal of Cr(VI) for aqueous solutions has been investigated. Removal of Cr(VI) was dependent on initial concentration and removal increased from 43.2% to 74.3% by decreasing initial concentration from 7.5 × 10−5 M to 1.0 × 10−5 M at 25 °C, 1.0 × 10−2 M NaClO4 ionic strength and 100 rpm. Higher removal was obtained at particles of smaller sizes of the adsorbent. Removal decreased from 74.3% to 40.7% by increasing temperature from 25 °C to 35 °C exhibiting exothermic nature of the process of removal. Thermodynamic parameters, namely change in free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°), were calculated and were found to be −0.81 kcal mol−1, −17.21 kcal mol−1 and 56.94 cal mol−1, respectively at 25 °C. pH of the solution has pronounced effect on the removal and higher removal was obtained in acidic pH ranges, maximum (74.3%) being at 2.5 pH.