In this paper, FeS_m/BC composites were prepared using coconut shell biochar (BC) as the carrier. FeS_m on FeS_m/BC is preferentially oriented along the (001) crystal plane and exhibits a uniform honeycomb morphology. It has a high specific surface area and a small pore size distribution, which is more suitable as a heavy metal ion removal material. The results show that Cr(Ⅵ) can be almost completely removed within 120 min under acidic conditions with an initial concentration of 10 mg/L of Cr(Ⅵ), a temperature of 20 ℃, and a dosage of 0.6 g/L of adsorbent. Where pH was the main factor influencing the removal of Cr(Ⅵ):pH affects Cr(Ⅵ) removal by changing the form of Cr(Ⅵ) in the solution, adsorption free energy, redox potential, charged species on FeS_m/BC surface, and the reduction properties of Fe~(2+) and S~(2-), low pH value is more favorable for Cr(Ⅵ) removal. Coexisting anions in solution inhibit Cr(Ⅵ) removal due to competitive adsorption, but coexisting cations have no effect. The adsorption process of Cr(Ⅵ) by FeS_m/BC follows the pseudo-second-order kinetics and Langmuir adsorption isotherm model, indicating that the adsorption process is a mon-olayer surface adsorption controlled by the chemical adsorption mechanism and involves electron sharing or exchange between adsorbent and adsorbate. Thermodynamic study shows that the adsorption process is a spontaneous entropy-increasing process, and raise the temperature is beneficial to the adsorption. The removal of Cr(Ⅵ) by FeS_m/BC is the synergistic effect of adsorption, reduction, and co-precipitation.
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