Performance and mechanisms for remediation of Cd(II) and As(III) co-contamination by magnetic biochar-microbe biochemical composite: Competition and synergy effects

Contaminations by heavy metals in the environment always exist as a mixture of both metal and metalloid. Thus, it is a challenge to simultaneously remove both components due to their adverse chemical behaviors. Herein, effective cadmium (Cd) and arsenic (As) removal in aqueous solution was achieved by use of a novel composite, which was synthesized by Bacillus sp. K1 loaded onto Fe₃O₄ biochar (MBB). The combination with Bacillus sp. K1 provided new biosorption sites such as amine and hydroxyl groups in the composite surface, which significantly increasing the removal capability of Cd(II) by 230% when compared with the raw magnetic biochar. Both competition and synergy effects were found in binary system. Adsorption of As(III) extended active sites for capturing Cd(II), which appeared on the surface of the MBB as type B ternary surface complexes. The maximum adsorption capacity of Cd(II) and As(III) reached 25.04 and 4.58 mg g^-1 in a binary system, respectively. In summary, this environmentally friendly composite is promising for simultaneous Cd(II) and As(III) remediation.