Controlling phosphate release from phosphate-enriched sediments by adding various iron compounds

In a laboratory experiment, different ironsalts (FeCl2, FeCl3, FeSO4) andFe2O3 were added to a phosphateenriched silty loam sediment in order to studytheir effect on phosphate mobilisation.Phosphate concentrations in sediment pore waterwere not reduced by the addition ofFe2O3. Addition of both ironchlorides, however, resulted in a strongdecrease of phosphate levels in sediment porewater. A similar but less pronounced effect wascaused by the addition of iron as iron(II)sulphate. Sulphate appears to counteract theimmobilisation of phosphate brought about byiron(II). Phosphate release from the sedimentappeared to be determined by the iron/phosphateratio in the sediment pore water. The additionof Fe2O3 barely affected thephosphate release from the sediment whereas theaddition of iron salts was effective inpreventing phosphate release. Increased amountsof iron added to the sediment resulted in adecreased phosphate release.