Different adsorption behavior of inorganic and organic phosphorus on synthetic schwertmannite: Assessment and mechanism of coexistence

Abstract

Schwertmannite (Sch) is a common secondary-iron (Fe)-hydroxylsulfate mineral that is found in acidic environments containing high concentrations of iron and sulfate (SO42-). The presence of Sch affects the occurrence states, mobility, transportation pathways, and transformation processes of elements. To understand the interaction between Sch and different forms of phosphorus in the hydrosphere, the inorganic phosphorus (iP) and organic phosphorus (oP) were selected as adsorbates to investigate their adsorption behavior on synthetic Sch. The results showed that iP and oP have good adsorption effects on Sch; the maximum adsorption capacities of iP and oP were 87.9 mg·g−1 and 18.4 mg·g−1 (as P), respectively. Their adsorption processes can be effectively described by the Langmuir isotherm. Both iP and oP were competitively adsorbed onto Sch, but the adsorption affinity of iP was greater than that of oP. The adsorption of iP occurred by the exchange of SO42- ions on the surface and in the tunnels of Sch, whereas oP was adsorbed primarily by the exchange of SO42- ions on Sch surface. These results showed that, the formation of Sch in acidic environments can influence the mobility and transport of various forms of P and inhibit the eutrophication of water bodies.