Comparative study of calcium alginate, ball-milled biochar, and their composites on aqueousmethylene blue adsorption

In this work, a novel composite, ball-milled biochar (BMB) encapsulated in calcium-alginate (CA) beads (CA-BMB), was synthesized as an alternative adsorbent for the removal of methylene blue (MB) from an aqueous solution. Sorption performance was compared among CA, BMB, and CA-BMB composite with batch adsorption experiments. With 25% BMB and 75% alginate, the new composite resembled CA in MB adsorption. With an initial MB concentration of 50mgL(-1), kinetics studies showed that 74% MB removal by CA-BMB was achieved within 8h, followed by slow kinetics reaching 91% removal in 16h. The adsorption kinetics was well explained by the Ritchie's kinetic model, indicative of energetically heterogeneous solid surface of the composite. Adsorption isotherms of BMB, CA, and CA-BMB can all be fitted with the Langmuir models; the adsorption capacity of CA-BMB (1210.7mgg(-1)) was close to that of CA (1282.2mgg(-1)) and much higher than that of BMB alone (184.1mgg(-1)). The outstanding adsorption performance suggested that CA-BMB can serve as a low-cost and eco-friendly adsorbent for MB removal from an aqueous solution.