The redox chemistry of phosphate complexed green rusts: Limited oxidative transformation and phosphate release

The reductive dissolution of ferric (hydr)oxide-phosphate (P) complex is believed to be responsible for P release under anoxic conditions. Although it has been observed that P release may not correlate to the oxygenation concentrations of bottom waters, the evidence and related mechanism are still missing. In this work, the release of P from green rust (GR)-P complex under low/high pO(2) levels and in the presence of high-valent metal oxidants [Cr(VI)] was studied. It was found that high oxidant concentrations led to a fast release rate and a high released amount of P from the GR-P complex. A high amount of adsorbed P retards the oxidation of GR, which inhibits the P release process. A higher Fe(II)/Fe(III) ratio in GR leads to stronger P fixation ability. GR in GR-P complex was transformed to ferrihydrite and then to lepidocrocite and goethite, depending on the oxidation conditions. Our results demonstrate that the increased redox potential introduced by oxidants leads to the release of P from the GR-P complex, which deepens our understanding of the relationship between redox potential and the P fixation by iron-bearing minerals.

Automated summary

The reductive dissolution of ferric (hydr)oxide-phosphate complex is believed to be responsible for P release under anoxic conditions. Our results demonstrate that the increased redox potential introduced by oxidants leads to the release of P from the GR-P complex, which deepens our understanding of the relationship between redox potential and the P fixation by iron-bearing minerals.