Phosphate removal by hydrothermally modified fumed silica and pulverized oyster shell

A calcined and hydrothermally annealed material for phosphate removal was prepared in a hollow cylindrical shape from fumed silica generated by a ferroalloy factory, and pulverized oyster shell. Phosphorus removal from wastewater by this material calcined at a range of temperatures (700–900 °C) and hydrothermally annealed at temperatures from 130 to 180 °C, for 8–16 h, was investigated and the most suitable physicochemical conditions were determined. XRD, SEM, EDS, and XRF techniques were used to characterize the microstructures and compositions of the materials produced, and UV–Vis spectrophotometry using the ammonium phosphomolybdate blue method was used to determine the phosphate concentration in the wastewater. The results indicate that calcium carbonate in oyster shell reacted with SiO2 in fumed silica and formed hydrated calcium silicate after hydrothermal treatment, and the hydrated calcium silicate reacted with phosphate ions in wastewaters to form hydroxyapatite precipitate. The optimal conditions for material production were calcination at 800 °C, and hydrothermal annealing at 150 °C for 12 h. Materials made under these conditions showed 74% or 92% phosphate removal after 2 or 4 h, respectively.

Hydrated calcium silicates formed during sintering and hydrothermal annealing processes and then reacted with phosphate in wastewater and precipitated a calcium phosphate (Ca5(OH)(PO4)3).Figure optionsDownload high-quality image (72 K)Download as PowerPoint slideResearch highlights
► This material has high sorption capacity, is readily collectable and also possess a sustained phosphate removing capacity.