Optimization and modeling of aqueous Cr(VI) adsorption onto activated carbon prepared from sugar beet bagasse agricultural waste by application of response surface methodology

The sugar beet bagasse (SBB) agricultural waste was used as a precursor for production of highly microporous activated carbon (AC). The prepared activated carbon by sugar beet bagasse (ACSBB) was used for removal of Cr (VI) from aqueous solutions as an efficient adsorbent. The chemical structure, surface chemistry and morphology of the ACSBB were characterized by SEM-EDX, XRD, FT-IR, N-2 adsorption-desorption and TGA-DTG analyses. The response surface methodology (RSM) was applied for experimental design of Cr(VI) adsorption from aqueous solutions. The effect of three independent variables including pH, ACSBB dosage and Cr(VI) concentration on the Cr(VI) removal efficiency (R (%)) was studied in the ranges of 4-7, 0.1-2 g L-1 and 10-100 mg L-1, respectively. For this purpose, 20 runs of experiments that was designed by the Design-Expert software were performed. The optimum conditions for pH, ACSBB dosage and Cr(VI) concentration were found as 4.05, 1.49 g L-1 and 10.13 mg L-1, respectively. At these conditions, removal efficiency and desirability function were found to be 50.45% and 1.000, respectively. The results revealed that the thermodynamic study showed a spontaneous and exothermic nature for the adsorption process, experimental data well explained by the pseudo-second-order kinetic model and equilibrium data showed a good fit to the Langmuir isotherm model. The cost-benefit analysis indicated that the production cost of ACSBB from SBB based on the yield of 34% will be US $1.5/kg.