Hexavalent chromium removal from simulated wastewater using biomass-based activated carbon: kinetics, mechanism, thermodynamics and regeneration studies

In this study, activated carbon (ACBA) was fabricated from Balanites aegyptiaca seed shell (BASS) using a two-step H3PO4 activation approach and was tested for the adsorption of toxic hexavalent chromium [Cr(VI)] from simulated wastewater. The surface properties, morphology, and elemental composition of the prepared ACBA were examined via Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) surface area analyses. The influence of various operating conditions such as pH, adsorbent amount, contact time and temperature was investigated. Kinetic studies indicated that the pseudo second order model was able to provide a realistic description of the adsorption kinetics and that film diffusion was the dominating mechanism of the sorption process. The adsorption activation energy evaluated using kinetic data suggested physical nature of Cr(VI) adsorption onto the carbon surface. Thermodynamic investigation confirmed that the adsorption was spontaneous and endothermic in nature. Regeneration tests demonstrated that 0.2 M NaOH can appreciably desorb Cr(VI) from Cr(VI)-loaded ACBA and the regenerated adsorbent can be used for six successive adsorption-desorption cycles while sustaining an adsorption efficiency of 80.10%. Altogether, the ACBA showed high adsorptive performance, fast kinetics and reuse potential, indicating the suitability of its application in wastewater treatment