Single and Binary Adsorption Behaviour and Mechanisms of Cd 2+ , Cu 2+ and Ni 2+ onto Modified Biochar in Aqueous Solutions.

The chitosan–EDTA modified magnetic biochar (E–CMBC) was successfully used as a novel adsorbent to remove heavy metals. The adsorption behaviour and mechanisms of E–CMBC to Cd²⁺, Cu²⁺ and Ni²⁺ were performed in single and binary system in aqueous solutions. In single–metal system, the adsorption process of Cd²⁺, Cu²⁺ and Ni²⁺ on E–CMBC fitted well with the Avrami fractional–order kinetics model and the Langmuir isotherm model. The measured maximum adsorption capacities were 61.08 mg g⁻¹, 48.36 mg g⁻¹ and 41.17 mg g⁻¹ for Cd²⁺, Cu²⁺ and Ni²⁺, respectively. In binary–metal system, coexisting ions have obvious competitive adsorption behaviour on E–CMBC when the concentration of heavy meal beyond 20 mg L⁻¹. The maximum adsorption capacities of the heavy metals were found to be lower than that in single–metal system. The order of the competitive adsorption ability was Cu²⁺ > Ni²⁺ > Cd²⁺. Interestingly, in Cd²⁺–Cu²⁺ system the earlier adsorbed Cd²⁺ could be completely replaced by Cu²⁺ from the solution. Different competitive adsorption ability of those heavy metal were due to the characteristics of heavy metal and resultant affinity of the adsorption sites on E–CMBC. The adsorption mechanism indicated that chemical adsorption played a dominating role. Therefore, E–CMBC could be a potential adsorbent for wastewater treatment. [ABSTRACT FROM AUTHOR]