Synthesis of a new low-cost activated carbon from activated sludge for the removal of Cr (VI) from aqueous solution: Equilibrium, kinetics, thermodynamics and desorption studies

Elimination of Cr (VI) from aqueous solution was investigated by a new low cost activated carbon developed from aerobically digested activated sludge (ADAS). The adsorbent demonstrated remarkable characteristics such as high surface area of 760m(2)center dot g(-1) and large total pore volume of 0.8383 cm(3)center dot g(-1). The maximum equilibrium uptake of Cr (VI) was 70.15 mg center dot g(-1) at optimum pH 2.0. Interpretation of equilibrium data revealed that the best description was provided by the Freundlich isotherm. The kinetics of Cr (VI) adsorption was well described by the pseudo-second order equation. Calculation of thermodynamic parameters revealed that the adsorption process was endothermic, spontaneous and feasible. The adsorbent was regenerated using NaOH and it was found to be suitable for reuse in successive adsorption-desorption cycles. The desorption efficiency of Cr (VI) ion was up to 78%. Finally, comparison of Cr (VI) adsorption capacity of the developed adsorbent with commercial activated carbon demonstrated its higher performance.