Natural Promotion of Reactive Oxygen Species Generation Based on Manure Derived Dissolved Organic Matter Influence on Clay Mineral for Mercury Binding

Abstract

This study reports the mercury binding by bentonite clay under the influence of 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 Hg 2+ up to five days. We speculated that reactive functional species in DOM would direct the extent of binding with bentonite-DOM. The binding kinetics of Hg 2+ to the resulting composite was studied (Metal= 350 µM/L, pH 5.2). Bentonite-DOM bound much more Hg 2+ than original bentonite and accredited to the establishment of additional binding sites by the DOM. On the other hand, the presence of DOM in aqueous media was found to decrease the Hg 2+ binding on the clay surface, specifically, the percent decrease of metal with increasing DOM concentration in aqueous solution. Post to binding of DOM with bentonite resulted in increased particle size diameter (~33.37 - ~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 than that of the bentonite. Carboxyl, hydroxyl and oxygen vacancies on the surface were found actively involved in Hg 2+ uptake by bentonite-DOM composite. Furthermore, DOM increased the content of Hg 2+ binding by ~10% (Pseudo-second-order q e = 90.9 – 100.0) through boosting up Fe 3+ reduction with the DOM. The quenching experiment revealed that more oxygen functionalities were generated in bentonite-DOM, where OH was found to be dominant specie for Hg 2+ 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.

Keywords: Bentonite binding, Manure DOM, Oxygen functional groups, Metal-complex