Synthesis of ferrate (Fe(vi))-coated sand for stabilized reactivity and enhanced treatment of phenol

Abstract

Ferrate (Fe(VI)) is a multifunctional water treatment agent of interest due to its benign environmental impact yet effective disinfecting, coagulating, and oxidizing capabilities. Fe(VI) decomposition in water produces short-lived Fe(V) and Fe(IV) intermediates which are highly effective oxidants. Studies report that the addition of SiO₂ gels during Fe(VI) application can facilitate Fe(V) and Fe(IV) generation, and stabilize Fe(VI) reactivity for enhanced treatment. However, the application of SiO₂ gels is impractical and requires post-treatment disposal. This study leverages SiO₂ stabilization and catalytic effects on Fe(VI) reactivity to develop a Fe(VI)-coated sand water treatment media. The Fe(VI)-coated sand was synthesized by coating potassium ferrate onto sand modified with a tetraethyl orthosilicate precursor. The mass of Fe(VI) leached from the media surface increased with increasing pH (pH 7–9). Furthermore, Fe(VI) decay was faster in a borate buffer (k = 2.22 mg L⁻¹ h⁻¹) than in a phosphate buffer (k = 3.39 mg L⁻¹ h⁻¹). Removal of 219 ± 12 μg per L phenol—a representative wastewater organic compound—was achieved at a faster rate by the composite than by application of aqueous K₂FeO₄ powder (51% removed after 5 min compared to 37%). Decomposition of Fe(VI) from the composite surface in the presence of methyl phenyl sulfoxide (PMSO) suggests that reactive Fe(V) and Fe(IV) formation occurs at a faster rate than with K₂FeO₄ powder addition. In the presence of PMSO, phenol treatment was approximately 1.1 times higher, which suggests Fe(V)/Fe(IV) involvement. This novel, cost-effective and eco-friendly media presents a viable alternative for more feasible deployment of Fe(VI) in water treatment systems.