A method of removing metal ions from silicate glasses for recycling by liquid-phase deposition

A method of removing metal ions from silicate glasses for recycling was studied. This method utilizes a liquid-phase deposition (LPD) technique using a hydrofluosilicic acid (H2SiF6) aqueous solution supersaturated with silica. Silicate glass powder prepared from a glass bottle was dissolved in aqueous hydrofluoric acid (HF) solution. The fluorinated silicon oxide (SiOF) separated from the H2SiF6, and then an LPD-SiOF gel was formed in the supersaturated H2SiF6 aqueous solution. Almost all ratios of metals to silicon (Si) were reduced by at least one order of magnitude. The LPD-SiOF powder formed by drying the LPD-SiOF gel at 23 °C showed a different chemical bonding structure than that of the initial silicate glass powder. The LPD-SiOF powder showed a cluster structure of spheres 1–2 μm in diameter. A possible mechanism for removal of the non-Si primary component metal oxides and other impurity metal ions is proposed. The features of this method and a possible application for recycled silica are also discussed.