Phosphate Removal from Water Using Novel ${\mathsf{Fe}}^{\mathsf{2}\mathsf{+}}\text{-}{\mathsf{KMnO}}_{\mathsf{4}}$ Process: Significant Role of In Situ–Formed Fe(III)

This paper investigated the phosphate removal from aqueous solutions using the ${\mathrm{Fe}}^{2+}\text{-}{\mathrm{KMnO}}_4$ process. Results indicated that the reaction of ${\mathrm{Fe}}^{2+}$ and ${\mathrm{KMnO}}_4$ in the ${\mathrm{Fe}}^{2+}\text{-}{\mathrm{KMnO}}_4$ process could synergistically increase the removal of phosphate compared with those achieved by Fe(III) coagulation and ${\mathrm{MnO}}_2$ adsorption at $\mathrm{pH}\ge 7$. It was necessary that the optimal Fe/P molar ratio was above 3 for effective phosphate removal because of effects of coexisting substances. At pH 7.0, phosphate removal approached a maximum within approximately 5 min. Competing effects of sulfate, bicarbonate, and silicate on phosphate removal were slight. The presence of ${\mathrm{Ca}}^{2+}$ and ${\mathrm{Mg}}^{2+}$ had limited effects on phosphate removal at $\mathrm{pH}\le 4$ but resulted in a significant increase at $\mathrm{pH}\ge 5$. Coprecipitation was considered as the dominant mechanism about phosphate removal in the ${\mathrm{Fe}}^{2+}\text{-}{\mathrm{KMnO}}_4$ process. Fe(III) formed in situ was primarily responsible for phosphate removal. Additionally, in-situ-formed ${\mathrm{MnO}}_2$ also contributed to the phosphate removal through complexation adsorption. The ${\mathrm{Fe}}^{2+}\text{-}{\mathrm{KMnO}}_4$ process had the potential to be utilized in natural water and municipal wastewater treatment for phosphate removal.