Investigation of Cr(VI) removal from aqueous solutions using different nanocomposites from agricultural waste charcoal

Water pollution caused by heavy metals constitutes an important place among the harms caused by industrial wastes to the environment. One of the most important causes of heavy metal pollution in wastewater is the presence of Cr (VI), a highly toxic ion, in the water. The aim of this thesis study is to synthesize an adsorbent that is natural, cheap, easy-to-find and has high Cr (VI) adsorption capacity from waste water. For this purpose, pyrolytic charcoal has been synthesized from the shell of cherry kernel. Composite beads were obtained using the synthesized cherry kernel shell pyrolytic charcoal (CKSC) and then the availability of pyrolytic charcoal and composite beads in Cr(VI) adsorption was investigated. Cherry kernel shell pyrolytic charcoal/chitosan composite (C-CKSC) and cherry kernel shell pyrolytic charcoal/chitosan/Fe2O3 nanocomposite (Fe-C-CKSC) were prepared as composite. Characterizations of the synthesized adsorbents were performed by SEM/EDX, BET, FTIR and elemental analysis. Adsorbent dosage, concentration, pH, contact time and temperature parameters affecting the adsorption were optimized as a result of batch adsorption experiments. The optimum adsorbent dosages for Cr(VI) adsorption from 55 mg/L Cr(VI) solution were found to be 5 g/L for CKSC,1.5 g/L for C- CKSC and 3 g/L for Fe-C-CKSC. Adsorption reached equilibrium at a contact time of 120 minutes for all adsorbents. The optimum initial pH values were found to be 1.56 for CKSC and 2 for C-CKSC and Fe-C-CKSC. With the increase in temperature, adsorption increased slightly. Langmuir, Freundlich, Scatchard, Dubinin-Radushkevich and Temkin isotherm models were applied with equilibrium data and the adsorption parameters were calculated. The adsorption equilibrium data fitted well with Langmuir isotherm model. The maximum adsorption capacities from this isotherm model were calculated as 14.455 mg/g for CKSC, 86.298 mg/g for C- CKSC and 47,576 mg/g for Fe-C-CKSC. As a result of calculations on the adsorption kinetics, adsorption was found to be consistent with the pseudo second order kinetic model. Thermodynamic calculations have shown that the adsorption is spontaneous and and has endothermic nature.