Hexavalent chromium [Cr(VI)] removal by acid modified waste activated carbons.

Fresh activated carbon (AC) and waste activated carbon (WAC) were pretreated by heating with mineral acids (sulfuric acid and nitric acid) at high temperature to prepare several grades of adsorbents to evaluate their performance on Cr(VI) removal from aqueous phase. Effects of temperature, agitation speed and pH were tested, and optimum conditions were evaluated. Kinetic study was performed under optimum conditions with several grades of modified adsorbents to know the rates of adsorption. Batch adsorption equilibrium data followed both, Freuindlich and Langmuir isotherms. Maximum adsorption capacity (q(max)) of the selected adsorbents treated with sulfuric acid (MWAC 1) and nitric acid (MWAC 2), calculated from Langmuir isotherm are 7.485 and 10.929 mg/g, respectively. Nitric acid treated adsorbent (MWAC 2) was used for column study to determine the constants of bed depth service time (BDST) model for adsorption column design.