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Electrochemical processes are used to recover elemental arsenic from NaH2AsO3 solutions, oxidize As2O3 suspensions to arsenic acid, and reduce arsenic acid to arsine. The electrolysis conditions are optimized for obtaining elemental arsenic: 0.8–0.9 M NaH2AsO3, 0.03–0.05 A/cm2, 20–25°C. The introduction of tetraalkylammonium salts containing C9–C12 substituents, e.g., trimethylcetylammonium bromide, is shown to stabilize the current efficiency in terms of As at a level of 45–50%. The current efficiency of copper cathodes attains 89% in 1–2 M H3AsO4 solutions at a current density of 0.2 A/cm2. In the electrosynthesis of arsenic acid, quantitative substance and current yields are achieved in 2–3 M HCl solutions. Low-waste processes are proposed for preparing arsenic, H3AsO4, and As2O5 from As2O3. The resulting arsenic is suitable for producing high-purity (99.9999%) material. The physicochemical processes underlying arsine generation are examined, and a bench-scale electrochemical arsine generator is described which can be used in the manufacturing of semiconductor materials. |
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