Phosphate coprecipitation affects reactivity of iron (oxyhydr)oxides towards dissolved iron and sulfide

Iron (Fe) cycling exerts strong control on the mobility and bioavailability of key nutrient phosphate (PO4) in soils sediments. Coprecipitation PO4 is known to alter structure Fe (oxyhydr)oxides (FeOx), however environmental fate PO4-bearing FeOx not well-understood. Here, with 9 mol% coprecipitated were prepared by Fe(III) hydrolysis Fe(II) oxidation presence dissolved PO4, addition pure synthesized PO4-free solutions. The subsequently exposed different concentrations sulfide (2 10 mmol L?1). Mineral transformations tracked over 7–14 days wet chemical techniques (including sequential S extraction) synchrotron-based K-edge X-ray absorption spectroscopy. affected rate extent transformation differently for sulfide. Poorly-ordered was preserved while ferrihydrite nearly completely transformed into goethite 7 days. By contrast, coprecipitation rendered more reactive towards compared FeOx. Reaction resulted formation non-sulfidized or under high low Fe/sulfide ratio, respectively. Under Fh PO4-bearing, poorly-ordered sulfidized after 14 Sulfidation led efficient release solution, at ratio released than expected based sulfidation. results suggest feedback mechanisms relevance: strongly-sorbing species such as disrupts structure, which affects reactivity overall contaminant retention capacity sediments depending ambient redox conditions. Specifically, switch from reducing sulfidic conditions may be associated disproportionate nutrients contaminants.