Quantitative Insights into Phosphate-Enhanced Lead Immobilization on Goethite.

Despite extensive study, geochemical modeling often fails to accurately predict lead (Pb) immobilization in environmental samples. This study employs the Charge Distribution MUlti-SIte Complexation (CD-MUSIC) model, X-ray absorption fine structure (XAFS), and density functional theory (DFT) to investigate mechanisms of phosphate (PO) induced Pb immobilization on metal (hydr)oxides. The results reveal that PO mainly enhances bidentate-adsorbed Pb on goethite via electrostatic synergy at low PO concentrations.

Carbon sequestration in paddy soils: Contribution and mechanisms of mineral-associated SOC formation.

In this work, comparative study of paddy and upland soils were carried out to unravel mechanisms of enhanced soil organic carbon (SOC) sequestration in paddy soils using fractionation methods, C NMR and Nano-SIMS analysis, as well as organic layer thickness calculations (Core-Shell model). The results showed that although there is a strong increase in particulate SOC in paddy soils compared to that in the upland soils, the increase in mineral-associated SOC is more important, explaining 60-75% of SOC increase in the paddy soils. In the wet and dry alternate cycles of paddy soil, iron (hydr)oxides adsorb relatively small and soluble organic molecules (fulvic acid-like), promote catalytic oxidation and polymerization, thus accelerating formation of larger organic molecules.