Chromium (VI) removal by using peach stone and polymer based activated carbon

Chromium compounds which are used in several industry such as leather, textile, metal plating, battery and pigments exist in two stable oxidation states as Cr(III) and Cr(VI). Cr(III) is relatively innocuous and essential trace element for living organisms. Because of its toxicity and carcinogenic nature, Cr(VI) compounds must be removed before discharging to the environment. Although the use of activated carbons for removing chromium from wastewater has been received a great attention, the application in this field is not common because of limited adsorption capacity and high cost of commercial activated carbons. In this study, activated carbons with high Cr(VI) sorption capacity were obtained by using different precursors.Experimental studies were investigated in two main parts as activated carbon production by using two different precursors and Cr(VI) sorption. Turkey is the fifth peach producer in the world. Peach stone and crosslinked macro porous acrylonitrile divinyl benzene copolymer were used as precursor. Steam and potassium hydroxide activation were applied for production of peach stone based activated carbon while air oxidation was used for production of polymer based one. Obtained activated carbon samples were characterized bu using N2 adsorption measurements, FTIR Spectroscopy, Boehm?s titration, SEM, pH titration analysis, zeta potential measurements, elemental analysis and kjeldahl nitrogen analysis.Cr(VI) removal from aqueous solution was investigated by using peach stone based (KSN), polymer based (PAK) and commercial activated carbon (Chemviron, CPG-LF) in batch and continuous flow system. Sorption capacity alters in order by CPG-LF >=KSN > PAK and maximum Cr(VI) removal was obtained at pH 2. Equilibrium adsorption data were applied to Langmuir and Freundlich adsorption model; all data were fitted to Freundlich model. Cr(VI) uptake was described by pseudo second-order rate model. Regeneration of chromium loaded activated carbon samples was carried out by using different strength of acid and alkali solution and variation of sorption capacity was investigated during the five cycles of adsorption/desorption experiments. Activation energy, mean free sorption energy, isosteric adsorption heat and thermodynamic parameters like ? G°, ? H°, ? S° were calculated. In addition, Cr(VI) sorption mechanism were explained by using XPS (X-ray Photoelectron Spectroscopy).