Exploring different mechanisms of biochars in removing hexavalent chromium: Sorption, reduction and electron shuttle

The role of different biochars in Cr(VI) removal process is not clear. Two raw materials with distinct components were prepared into biochars at various pyrolysis temperatures. The biochar derived from cotton stark (with less lignin than walnut shell) always had more surface functional groups. The pyrolysis temperature had a significant effect on the biochar. In the sorption experiments, the fitting results of two compartment models showed that slow compartment dominated by surface functional groups plays a leading role in the Cr(VI) removal by lowtemperature char, while the contribution of the rapid or slow compartment to the process of high-temperature char was equal. In the experiment of biochar mediated the lactate to reduce Cr(VI), the biochar derived from walnut shell (richer lignin) had better conductivity due to its highly aromatic structure, which could directly transfer electrons. This study indicated that various biochars may play different roles in the Cr(VI) removal process.

Automated summary

The role of different biochars in Cr(VI) removal process varies depending on their source materials and pyrolysis temperatures. Surface functional groups of biochar are influenced significantly by pyrolysis temperature, affecting their efficiency in Cr(VI) removal. The conductivity and aromatic structure of biochar play important roles in mediating the reduction of Cr(VI).