Sorption Characteristics of Dissolved Phosphorus Compounds onto Iron (Oxy)hydroxides in Seawater

Abstract

Sorption of phosphorus (P) compounds by iron (Fe) (oxy)hydroxides significantly influences dissolved P concentrations in marine environments. This research offers comparisons of the kinetics and extent of the sorption of phosphate (PO4), adenosine monophosphate (AMP), adenosine triphosphate (ATP), and glucose 6-phosphate (G6P) onto the Fe phases ferrihydrite, goethite, and hematite. Isotherm experiments were conducted in which artificial seawater solutions containing various concentrations of a single P compound were mixed with a single Fe-phase and allowed to equilibrate for three days. Kinetics experiments in which several identical samples were shaken at a constant temperature and sacrificed in a time series were also carried out. For all P compounds, the extent and rate of uptake from solution was in the order ferrihydrite ≫ goethite > hematite. The extent of uptake of P onto ferrihydrite and goethite was of the order PO4 >G6P>ATP>AMP, while for hematite the order was ATP>PO4 >AMP>G6P. While PO4 and organic P compounds displayed similar sorption behavior, there exist differences in the sorption capacities and affinities of different P compound/Fe-phase combinations. The different sorption behavior for the various P compound/Fe-oxide combinations has important implications for the potential release of sorbed P compounds and the bioavailability of P in aquatic systems.