Bentonite binding with mercury(II) ion through promotion of reactive oxygen species derived from manure-based dissolved organic matter

This study reports the mercury binding by bentonite clay influenced by cattle manure-derived dissolved organic matter (DOM). The DOM (as total organic carbon; TOC) was reacted with bentonite at 5.2 pH to monitor the subsequent uptake of Hg2+ for 5 days. The binding kinetics of Hg2+ to the resulting composite was studied (metal = 350 mu M/L, pH 5.2). Bentonite-DOM bound much more Hg2+ than original bentonite and accredited to the establishment of further binding sites. On the other hand, the presence of DOM was found to decrease the Hg2+ binding on the clay surface, specifically, the percent decrease of metal with increasing DOM concentration. Post to binding of DOM with bentonite resulted in increased particle size diameter (similar to 33.37-similar to 87.67 nm) by inducing the mineral modification of the pore size distribution, thus increasing the binding sites. The XPS and FTIR results confirm the pronounced physico-chemical features of bentonite-DOM more than that of bentonite. Hydroxyl and oxygen vacancies on the surface were found actively involved in Hg2+ uptake by bentonite-DOM composite. Furthermore, DOM increased the content of Hg2+ binding by similar to 10% (pseudo-second-order q(e) =90.9-100.0) through boosting up Fe3+ reduction with the DOM. The quenching experiment revealed that more oxygen functionalities were generated in bentonite-DOM, where hydroxyl was found to be dominant specie for Hg2+ binding. The findings of this study can be used as theoretical reference for mineral metal interaction under inhibitory or facilitating role of DOM, risk assessment, management, and mobilization/immobilization of mercury in organic matter-containing environment.

Automated summary

This study investigates the influence of cattle manure-derived dissolved organic matter (DOM) on the binding of mercury by bentonite clay. The results show that the presence of DOM enhances the binding of mercury to bentonite, but at the same time, it decreases the binding of mercury on the clay surface. The binding of DOM with bentonite increases the number of binding sites, resulting in higher binding capacity. XPS and FTIR analysis confirm that bentonite-DOM has distinct physico-chemical features compared to bentonite alone. DOM also promotes the reduction of Fe3+ and increases the binding of mercury by about 10%. These findings provide important insights into the interaction between mineral metals and DOM in organic matter-containing environments.