Investigations of Cr(VI) removal by millet bran biochar modified with inorganic compounds: Momentous role of additional lactate

In this study, millet bran biocharsmodified with inorganic compounds (H3PO4: P-BC, NaOH: Na-BC and K2CO3: KBC) were prepared and applied for Cr(VI) removal to evaluate the effects of modification on biochars' physicochemical properties. The results showed that Cr(VI) reduction capacity complied with the order of Na-BC > BC > P-BC > K-BC, and reductive groups such as -OH and -NH2 played considerable roles in electrons donating. Based on this, lactate was added for further investigation of electrons transferring. The results displayed that Cr(VI) removal of all biochars was enhanced tremendously and modified biochars exhibited better Cr(VI) reduction. This may be due to the bridging effect of lactate, which could not only chelate with Cr(VI) via -COOH (or -OH) but also form hydrogen bonds with oxygen or nitrogen containing groups on biochars through the other groups, thus facilitating electrons transferring between biochars and Cr(VI). This work provided an insight into evaluation of the influence of inorganic compounds modification on both electrons donating capability of biochars and electrons transferring potential of biochars combined with lactate in Cr( VI) removal. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

By modifying millet bran biochars with different inorganic compounds, this study found that the modified biochars exhibited better Cr(VI) reduction capacity. After adding lactate, the Cr(VI) removal efficiency of all biochars was significantly enhanced, possibly due to the bridging effect of lactate facilitating electron transfer between biochars and Cr(VI).