Overlooked mechanism of Pb immobilization on montmorillonite mediated by dissolved organic matter in manure compost

Abstract

In this study, three kinds of dissolved organic matter (DOM) derived from fresh chicken manure (FDOM), immature compost (IDOM) and mature compost (MDOM) were employed to compare their effects on Pb adsorption onto montmorillonite (MMT). The potential mechanism was revealed by characterization of mineral structure and calculation of interface force. The results demonstrated that the adsorption capacity (qmax) of Pb onto MMT was decreased by 14.3% and 29.8% in the presence of FDOM and IDOM, respectively, while increased by 44.4% in the presence of MDOM, resulting from the release or co-adsorption of DOM-Pb complexes. Parallel factor (PARAFAC) further indicated that Pb mainly bound to protein-like substances in FDOM and IDOM, and fulvic-like in MDOM. The X-ray diffraction (XRD) analysis proved that MDOM-Pb complex had a stronger ability to enter into the interlayer of MMT. The van der Waals force dominated the adsorption of FDOM-Pb and IDOM-Pb, while ligand exchange was involved in the case of MDOM-Pb. This study provided a comprehensive insight into the geochemical behavior of livestock manure and its compost as well as their interactions with heavy metal and soil mineral.