Adsorptive removal of As(V) by crawfish shell biochar: batch and column tests

As a toxic and metalloid substance, excess arsenic (As) can cause serious harm to the environment and public health. In this work, crayfish shell biochar (CFS450) and modified biochar (MCFS450) were prepared to remove As(V) from aqueous solutions under various conditions. Compared to CFS450, MCFS450 had a higher specific surface area, better pore structure, and higher As(V) adsorption capacity. Based on the Langmuir model, its maximum As(V) adsorption capacity was 17.2 mg/g. The biochar had a large number of surface functional groups such as C-O, O-H, and -OH. After modification, a certain mass of ZnO nanoparticles existed on MCFS450, which increased positive charge on the surface and promoted the adsorption of As(V). As the temperature rose, the adsorption capacity increased, suggesting the adsorption was endothermic. Under low PH conditions, the adsorption effect was better. When Cl^-, HCO₃^-, SO₄^2-, and PO₄^3- respectively existed, the adsorption capacity decreased, indicating that As(V) competed with other anions. The column adsorption experiments showed that Thomas, Yoon-Nelson, and Adams-Bohart models can be expressed as a unified model (EXY model). The EXY model can be used for the design of biochar-based filter for As(V) removal, providing a theoretical basis for practical production applications. Graphical abstract Experimental setup and results of column adsorption.