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

Area of Science:

• Environmental Chemistry
• Soil Science
• Geochemistry

Background:

• Livestock manure and compost are significant sources of dissolved organic matter (DOM).
• DOM can influence the fate and transport of heavy metals in soil environments.
• Montmorillonite (MMT) is a clay mineral with high adsorption capacity relevant to soil contaminant interactions.

Purpose of the Study:

• To investigate the effects of different dissolved organic matter (DOM) types from chicken manure and compost on lead (Pb) adsorption onto montmorillonite (MMT).
• To elucidate the underlying mechanisms of Pb adsorption influenced by DOM through mineral structure and interface force analysis.

Main Methods:

• Characterization of dissolved organic matter (DOM) from fresh chicken manure (FDOM), immature compost (IDOM), and mature compost (MDOM).
• Adsorption experiments of Pb onto montmorillonite (MMT) in the presence and absence of different DOM types.
• Analysis of mineral structure using X-ray diffraction (XRD).
• Calculation of interface forces and Parallel Factor Analysis (PARAFAC) to identify DOM-Pb binding characteristics.

Main Results:

• FDOM and IDOM decreased Pb adsorption capacity on MMT by 14.3% and 29.8%, respectively.
• MDOM increased Pb adsorption capacity on MMT by 44.4%.
• Pb predominantly bound to protein-like substances in FDOM/IDOM and fulvic-like substances in MDOM.
• MDOM-Pb complexes showed greater ability to intercalate MMT layers.
• Van der Waals forces governed FDOM-Pb and IDOM-Pb adsorption, while ligand exchange was key for MDOM-Pb.

Conclusions:

• The type and maturity of organic matter significantly alter Pb adsorption onto MMT.
• Mature compost DOM enhances Pb immobilization on MMT through complexation and interlayer intercalation.
• Understanding DOM-MMT-Pb interactions is crucial for managing heavy metal contamination from livestock waste.