Unveiling heavy metal removal mechanisms in mulberry and rice husk biochars via sacrificial mineral descriptors.

Rice husk biochar (RBC) and mulberry biochar (MBC) have gained significant attention in the removal of heavy metals in aquatic environments. Their easy affordability and eco-friendly nature make these biochar's a powerful adsorbent for sustainable water remediation applications. Although their heavy metal adsorption characteristics of individual biochar's have been widely studied, a clear understanding of how the inherited mineral composition in RBC and MBC influences Pb, Cd, and Zn removal in both deionized water (DIW) and Organization for Economic Co-operation and Development (OECD) water is currently lacking. In this study, heavy metal removal mechanisms of RBC and MBC in these water systems were investigated using various kinetic models and correlated them with their mineral composition. With the highest correlation coefficient of modified two-compartment first-order kinetic model (MTCFOKM), the measured q values highlight MBC as a promising candidate for heavy metal removal in both acidic and alkaline conditions. pH edge experiments revealed significant differences in metal removal efficiency between these biochars, despite their similar specific surface areas and surface charges (pH). XRD and FTIR characterization provided a strong support in explaining the high heavy metal removal ability of MBC stem from calcite mineral that inherited from biomass. Furthermore, the pH edge experiment combined with MINEQL speciation profiles revealed that heavy metal removal by MBC at low pH is linked to calcite leaching, shift in system pH, and heavy metal precipitation.