Natural phosphorus-ferromanganese ore-based composites for the simultaneous remediation of arsenic- and lead-co-contaminated groundwater: synergistic effectiveness, kinetics, and mechanisms.

Natural phosphorus-ferromanganese ore (NPO-NFMO) based composites by mechanical ball milling method, applying for the simultaneous remediation of arsenic (As) and lead (Pb) co-contaminated groundwater. Kinetic behavior adopted pseudo-second-order adsorption mechanism attaining equilibrium in 120 min over a wide pH range (2.0-6.0). NPO-NFMO realized higher adsorption capacity for As(III) (6.8 mg g) and Pb(II) (26.5 mg g) than those of single NPO (1.7 and 7.8 mg g) and NFMO (2.9 and 5.1 mg g), indicating that synergistic effects of NPO and NFMO considerably enhanced the adsorption capacity in mixed adsorption system. Fresh and used NPO-NFMO were characterized, and indicated that NPO-NFMO formed stable minerals of PbAsO and PbFe(AsO)(OH). The underlying adsorption mechanism indicated that As(III) and Pb(II) removal was involved with multiple mechanisms, including electrostatic adsorption, oxidation, complexation, and coprecipitation. The effects of key reaction parameters including mass ratios of NPO and NFMO, initial metal ion concentration, dosage, solution pH, and co-existing anions in groundwater were systematically investigated. The novel designed NPO-NFMO-based composites can be deemed as a promising amendment for simultaneous immobilization of As(III) and Pb(II) in co-contaminated soil and groundwater.