Mechanism of oxidation and catalysis of organic matter abiotic humification in the presence of MnO.

Humification plays a critical role in the environmental fate of organic wastes, and MnO holds great promise for enhancing this reaction. However, the effects of MnO on the enhancement of the humification reaction remain ambiguous. To better reveal the mechanism by which MnO enhances the reaction and investigate the fate of the humification products, abiotic humification experiments were performed using increasing concentrations of dissolved organic matter (DOM) to a fixed amount of MnO. DOM was represented by model humic precursors consisting of catechol, glucose and glycine. The results indicate that the reduction of MnO played a dominant role in the formation of fulvic-like acids (FLAs), and the subsequent reduction products, MnOOH and Mn(II), acted as catalysts in the formation of humic-like acids (HLAs). Moreover, CO release occurred during the formation of FLAs, and a strong linear correlation between CO release and the formation of FLAs was observed (p < 0.01), where 0.73-1.87 mg of CO was released per mg dissolved organic carbon (DOC) FLAs. Furthermore, the concentration of MnO had a pronounced influence on the product behavior, where a lower MnO concentration decreased the quantity of FLAs produced.