Adsorption of hexavalent chromium from aqueous solution by activated carbon prepared from almond shell: kinetics, equilibrium and thermodynamics study

Microporous activated carbon was prepared from almond shell powder and activated with H3PO4 and was used for the removal of Cr (VI). The characterization of activated carbon was done for Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer- Emmett-Teller (BET) surface area measurement and elemental analysis. The batch experiments were conducted to study the effects of contact time, solution pH, adsorbent dose, initial chromium concentration and temperature on removal of Cr (VI). The Cr (VI) removal was found to be 100% at an initial pH of 2. The equilibrium data for the adsorption of Cr (VI) on the adsorbent were fitted with Langmuir, Freundlich, Temkin and Dubinin-Radushkevich adsorption isotherm models. The Langmuir isotherm model fitted better and values of model parameters q(m), b, R-2 and R-L were found to be 195, 0.024, 0.98 and 0.45, respectively. Adsorption kinetics was analyzed for the pseudo first order, pseudo second order and intra-particle diffusion situations. Thermodynamic parameters revealed the spontaneous, endothermic and increased randomness nature of the adsorption process. The values of Delta H degrees and Delta S degrees were found to be 22.9 KJ/mol and 95.3 J/mol-K.