Response surface modeling and optimization of hexavalent chromium adsorption onto eucalyptus tree bark-derived pristine and chemically-modified biochar

Abstract

Biochar can be used as an adsorbent to remove hexavalent chromium (Cr(VI)) from water containing pollutant due to its low cost of production, non-toxicity, improved textural qualities and high adsorption capacity. This study was aimed to examine and compare the adsorption behaviour of unmodified biochar (BC) and ZnCl2-modified biochar (ZMBC) obtained from eucalyptus tree bark for the removal of Cr(VI) from aqueous solutions. The BC and ZMBC adsorbents were evaluated by various characterization techniques (TGA/DTA, SEM, FTIR, XRD, BET and pHpzc). Optimization by response surface methodology was used in investigating the influence of process factors (Cr(VI) concentration, adsorbent quantity, and pH) on Cr(VI) uptake. Various isotherm (Langmuir, Freundlich, and Temkin) and kinetic (pseudo-first-order (PFO) and pseudo-second-order (PSO)) models were used to test the adsorption experimental data. Under the optimal adsorption conditions (i.e., at 99.9 mg/L Cr(VI) concentration, 1.00 g/L sorbent amount and pH of 9.31), the removal efficiency attained 81.22±0.87% and 97.14±0.32% when BC and ZMBC were used, respectively. A higher surface area, well-developed porous structure, and dominance of active surface functional groups, validated by BET, SEM, and FTIR, contributed to the ZMBC's outstanding performance over BC. Freundlich isotherm and PSO models adequately agreed with the experimental data.