Preliminary Study of Enhanced Removal of Phosphate by Iron Oxides Formed in situ through Reducing Fe (VI) with Fe (II)

Phosphorous removal in secondary by ferric (Fe(III)) was investigated in presence of ferrate (Fe(VI))/ferrous(Fe(II)). In the raw water, adding Fe(VI) or Fe(VI)+Fe(II) could increase the phosphorous removal in comparison to Fe(III) coagulation. For initial phosphate concentration of 2.5 mg P/L, phosphate removal rates of about 15-30% were observed. But the increasing removal rate was not associated with the dosage of total Fe. At the same dosage of total Fe, about 10% increasing was observed. The experimental data of synthetic water demonstrated that Fe(VI) and Fe(II) form freshly amorphous hydrated iron oxides which had much more adsorptive capacity due to theirs small size and amorphous state, therefore they had much affinity for ligand phosphate. The dominant mechanism for the phosphate removal with Fe(VI) + Fe(II) was adsorption firstly, then co-precipitation.