Separation of chromium from water samples using eggshell powder as a low-cost sorbent: kinetic and thermodynamic studies

Chromium is one of the hazardous pollutants in industrial effluents. The aim of this research is to investigate feasibility of using waste eggshells for the removal of Cr(VI) ions from its aqueous solutions. Characterization of crushed and sieved eggshell have been carried out using scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray fluorescence, etc. analysis. The effect of pH, Cr(VI) ions concentration, amount of eggshell, contact time, temperature, etc. parameters have been investigated on the adsorption and it has been found that the maximum removal (about 93%) of Cr(VI) onto eggshells can be achieved at 25 degrees C and pH 5 in 90 min. Freundlich and Langmuir adsorption isotherm models e have been verified using experimental data. Results also include calculation of thermodynamic parameters like, change in enthalpy (Delta H-0), change in entropy (Delta S-0), and change in free energy (Delta G(0)) of the ongoing adsorption process. Chromium sorption kinetics is also found to be fitted in pseudo-first-order kinetic model. Results clearly indicate that the waste material eggshell, a solid waste from the food industry, can be very effectively used as a sorbent for the removal of chromium ions from its aqueous solutions.