Preparation, characterization and application of activated clay biochar composite for removal of Cr(VI) in water: Isotherms, kinetics and thermodynamics

This study explored the feasibility of employing a new activated clay mineral biochar composite produced from simultaneous pyrolysis of Macadamia nutshells/groundnut shells biomaterials and calcination of attapulgite clay in the adsorptive removal of Cr(VI) from contaminated water. Fourier transform infrared spectroscopic analysis revealed the presence of absorption peaks at 1139 and 1027 cm(-1) attributed to the biochar C-O and fingerprints of attapulgite. The parameters influencing the adsorption of chromium on the adsorbent surface were investigated, and it was shown that pH 3, contact time of 40 min, adsorbent mass of 100 mg and concentration of 2.5 mg L-1 were the optimal parameters. The removal mechanism involved adsorption of Cr(VI) through electrostatic attraction and/or subsequent reduction of Cr(VI) to Cr(III). At low Cr(VI) initial concentrations, the removal mechanism was dominated by chemisorption while at higher concentrations physisorption was more pronounced. The adsorption isotherm was best fitted with the Freundlich model. Thermodynamic data indicated the endothermic nature of adsorption process which was feasible and spontaneous. The achieved equilibrium adsorption capacity of 6.1 mg g(-1) is comparable with the values reported for other adsorbents in literature.