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

抄録

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.