Electrochemical Analyses of Metal Ions in HF and H2SiF6 Aqueous Solution for Recycling Silicate Glasses of Cathode-Ray Tube by Liquid-Phase Deposition

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We have proposed a new technique for recycling silicate glasses, removing metallic elements from them. This technique utilizes a liquid-phase deposition (LPD) method at lower temperatures than 40°C. In this LPD method, cathode ray tube (CRT) glasses are dissolved in hydrofluoric (HF) acid aqueous solution. An LPD-SiOF thin-film with thickness 1 μm was formed on a silicon (Si) substrate. The recycled LPD-SiOF film properties were compared with those for the high quality LPD-SiOF thin-film deposited using semiconductor grade hydrofluorosilicic acid (H2SiF6) aqueous solution. In the FTIR analysis, the chemical bonding structure for the recycled LPD-SiOF film is quite similar to high quality LPD-SiOF film. The refractive index at 632.8 nm for the recycled LPD-SiOF film is 1.43 and is the same as that for the high quality LPD-SiOF film. In order to separate metal oxides and metal ions from the H2SiF6 aqueous solution, we examined electrochemical analyses. The reactivity of various metal oxides with HF and H2SiF6 aqueous solutions was also evaluated. Undissolved metal oxides and precipitated metal fluorides can be separated by filtering. Some residual metal ions, such as Sb3+ and Fe3+, can be reduced to metals by electrolysis.
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