Removal of methylene blue and crystal violet in binary aqueous solution by magnetic Terminalia catappa kernel shell biosorbent using Box–Behnken design

Due to their low cost, availability, and environmental friendliness, biosorbents derived from renewable sources are appropriate for wastewater treatment. This study proposes the Terminalia catappa fruit kernel shell-Fe3O4 as an effective biosorbent for the removal of Crystal Violet (CV) and Methylene Blue (MB) dyes from environmental fluids. The Box–Behnken design was used in conjunction with the surface response methodology to optimize the CV and MB absorption processes. Under the optimum conditions of pH 6.7, an adsorbent amount of 69 mg, a CV concentration of 30 mg/L, MB concentration of 26 mg/L, and contact time of 6 min, 92.61% and 90.89% of the CV and MB absorption efficiencies were observed. The development of isotherms in binary solution revealed that the Extended Langmuir multicomponent isotherm best described the adsorption process and was also consistent with quasi-quadratic kinetics. The biosorbent capacity does not reduce after five regeneration cycles and is still efficient.