Photo-oxidation of p-arsanilic acid in acidic solutions: Kinetics and the identification of by-products and reaction pathways

• Pseudo-first order rate constants are determined for each processes.
• The degradation pathways are proposed for ozonation and photoozonation.
• The degradation pathways are proposed for oxidation and photooxidation by H2O2.
• Formation of solid phases are observed.
• Characterization of solid phases were done.

Arsenic compounds have been used extensively in agriculture for applications ranging from cotton herbicides to animal feed supplements. While studying the kinetics and mechanism of p-arsanilic acid degradation via oxidation, the photodegradation and photo-oxidation processes that occurred while using irradiation at 254 nm were assessed. Ozone and hydrogen peroxide were used as oxidants. The relationships among the process efficiency, the process conditions and the type of oxidiser were demonstrated. The rate constants for the decomposition based on pseudo first order kinetics were 0.76 × 10−3 min−1 during photodegradation, 27.85 × 10−3 min−1 during ozonation and 35.1 × 10−3 min−1 during photo-ozonation, 32.3 × 10−3 min−1 during oxidation with H2O2 and 36.4 × 10−3 min−1 during photo-oxidation with UV/H2O2.After identifying the major products, degradation mechanisms were proposed. During photodegradation, oxidation and photo-oxidation with H2O2, the generation of a solid phase composed primarily of As3O5(OH) was observed.

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