Study on the effect of active substances in molasses on the chemical reduction of Cr(VI).

Abstract

Industrial molasses has garnered significant attention in the fields of food, fermentation and environmental remediation due to its abundant nutrients and antioxidant substances. Cr (VI) can be rapidly reduced by molasses in an acidic environment. In this study, the reducing activity of molasses was systematically analyzed. At pH = 2, the reduction of Cr(VI) by molasses followed a second-order kinetic model. As the molasses concentration increased from 5 g/L to 10 g/L, the reaction rate constant rose from 0.43 to 5.21 mM^-1 h^-1, and 56 mg/L Cr(VI) was completely eliminated in both systems. The change in polyphenol content in molasses exhibited a consistent trend with the Cr(VI) concentration. Then multiple Cr(VI) spiking experiments demonstrated that molasses contains a variety of substances with different reactivity. The rate constant for the third spike with 10 g/L molasses was 0.18 mM^-1 h^-1, significantly lower than that of the initial molasses concentration of 5 g/L (0.43 mM^-1 h^-1) under similar polyphenol levels. Moreover, the amount of polyphenols consumed to reduce the same amount of Cr(VI) varied at different spiking stages. UV-Vis, FTIR and 2DCOS revealed that the phenolic hydroxyl groups were the primary active substances involved in the reduction reaction with Cr(VI), and the molar ratio of total polyphenols to Cr(VI) ranged between 0.1 and 0.2. This study provides valuable insights into the dosage of molasses and other parameters for the effective removal of Cr(VI) pollution.