Equilibrium and Thermodynamic Studies on Adsorption of Hexavalent Chromium from Aqueous Solution onto Low Cost Activated Carbon

Abstract

The removal of hexavalent chromium [Cr(VI)] is a challenging task due to its acute toxicity even at low concentration. In the present study, a low-cost activated carbon (LAC) was prepared from desert date seed shell by chemical activation with H 3 PO 4 and utilized for the removal of hexavalent chromium from aqueous solution. Batch experiments were conducted to investigate the influence of operating variables such as pH, contact time, adsorbent dosage, initial concentration, co-existing ions and temperature. The amount of Cr(VI) adsorbed was found to vary with solution pH and maximum adsorption was observed at a pH value of 2.0. The extent of chromium uptake (mg g-1) was found to increase with increase in initial concentration and contact time. The applicability of the four isotherm models for the present equilibrium data follows the sequence: Freundlich > Temkin > Langmuir > Dubinin-Radushkevich. The mean free energy from the Duninin-Radushkevic isotherm model hinted that the adsorption of Cr(VI) onto the adsorbent surface follows physisorption mechanism. Thermodynamic parameters related to adsorption, Gibbs free energy change (∆G°), enthalpy change (∆H°), entropy change (∆S°), were also calculated and the negative value of ∆H° indicates the exothermic nature of the adsorption process. The considerable adsorption capacity of 99.09 mg g-1 is a signifier of the suitability of the prepared adsorbent for commercial application. The findings implicated that the adsorbent can be employed in the treatment of Cr-bearing water and wastewater.

Simultaneous elimination of toxic dyes, ciprofloxacin and Cr(vi) contents from polluted water: escalating surface plasmon electrons of Ag cocatalysts on BiVO4 microstructures

“…Conversely, at high pH, the surface of the photocatalysts becomes negatively charged, and Cr exists as CrO 4 2− , so repulsion hinders the Cr(VI) reduction. 74,75 The results of the pH effect on Cr(VI) reduction are illustrated in Fig. 10c.…”