Effects of nFe3O4 capping on phosphorus release from sediments in a eutrophic lake

This study applied the techniques of high-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) to explore the effects and the behind mechanism for inhibition phosphorus (P) releasing from sediments by nFe3O4 capping. The highest decreasing rates of SRP and labile P (i.e., 49% and 47%, respectively) and the decreased flux of SRP showed that nFe3O4 capping can successfully control sediment internal P release. Adsorption by Fe(III) hydroxides with the oxidation of Fe(II) was one of the reasons for the decrease of P concentrations in nFe3O4 capping sediments. This was supported by the increase of Eh and significant negative correlation between Eh with Fe(II) (soluble and labile Fe(II)) and P (SRP and labile P) and significant positive correlation between Fe(II) and P in sediments by nFe3O4 capping. An outer-sphere complex between positively charged nFe3O4 surface groups and P formation was the other reason to decrease the concentrations of P in the nFe3O4 capping sediments. This was supported by the decrease of pH value in sediments by the capping of nFe3O4. This study shows that nFe3O4, when used as capping agent, can effectively control the sediment internal P release, which is expected to be used as a potential material for repairing lake eutrophication.