Removal of Cr(VI) from aquatic solutions with agricultural based biomass mixture and activated carbon prepared from them

Adsorption, which is considered to be easy to apply and environmentally friendly, is one of the most frequently applied treatment methods in the advanced treatment of wastewater. It has been a preferred process with the use of cheap and abundant agricultural wastes and effective adsorbents produced from them. In this study; a triple mixture of apricot and almond shells and peach stones that are produced in significant quantities due to the prevalence of agricultural activities in our country and processed in agro-indutries, and an activated carbon (AC) obtained from the triple mixture chemically activated with KOH by prolysis were prepared. Each adsorbent were characterized with ash content, elemental analysis, BET surface area, pore volume, pHzpc, FT-IR, Boehm titration and SEM analysis. In order to demonstrate the adsorbing efficiency of each adsorbent and to compare them with commercial AC, Cr(VI) adsorption experiments were carried out with each adsorbent separately. Effects of initial pH, adsorbent dosage, contact time, temperature, initial Cr(VI) concentration and presence of foreign ions on Cr(VI) adsorption were investigated. The obtained results were applied to adsorption isotherms and kinetic models, and the Cr(VI) adsorption capaties and some thermodynamic parameters were calculated. The adsorbent directly prepared from the triple mixture has a surface area of 5.32276 m2/g and a pore volume of 0.0048 cm3/g. New AC with the best properties was obtained from the triple mixture chemically activated with KOH/triple mixture ratio of 6/40 followed by pyrolysis. It was determined that the obtained new AC had a surface area of 1413 m2/g and a pore volume of 0.5937 cm3/g. The optimum pH, adsorbent dosage and equilibration time for the removal of 50 mg-Cr(VI)/L with the each adsorbent were found to be pH 2, 4 g/L adsorbent dosage and 30 min for new AC, pH 2, 5 g/L adsorbent dosage and 90 min for commercial AC, pH 2, 20 g/L adsorbent dosage and 60 min for triple mixture. It was determined that the kinetic data fit to the first order in the triple mixture and fit the second order kinetic equations for the new AC and commercial AC. The activation energies for each adsorbents were calculated to be 19.499, 37.956 and 69.24 kJ/mol, respectively. The data showed that Cr(VI) adsorption fit the Langmuir isotherm, and thermodynamic parameters showed that the adsorption is exothermic and occurre by a spontaneous mechanism.