Aqueous Cr(VI) removal by biochar derived from waste mangosteen shells: Role of pyrolysis and modification on its absorption process

A series of mangosteen-derived biochars were produced by several modifiers (HCl, KOH and ZnCl2), in different preparation conditions (i.e. pyrolysis temperature, pyrolysis process and impregnation ratio). It indicated that the Z2PT350-700 presented excellent ability for Cr(VI) removal. The physical/chemical properties of the prepared biochar are reflected by the electrostatic interaction, surface complexation, ion exchange occupied primary position in the process of adsorbing Cr(VI). Besides, the effects of reaction time, pH, adsorbent dosage and initial adsorbate concentration on Cr(VI) removal were evaluated. The sorption process of Cr(VI) could be described by the pseudo-second order (PSO) kinetic model and Sips isotherm model. In optimal reaction condition, the surface of Zn2MB350-700 was composed of homogeneous and heterogeneous adsorption and the chemical adsorption dominated in the adsorption process. Therefore, the results suggested that Zn2MB350-700 could be used as an inexpensive and highly efficient adsorbent for Cr removal from water environment.