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Dissolution, Adsorption, and Redox Reaction in Ternary Mixtures of Goethite, Aluminum Oxides, and Hydroquinone
- Zhang, Huichun, Rasamani, Kowsalya Devi, Zhong, Shifa, Taujale, Saru, Baratta, Laura R., Yang, Zijie
- Journal of physical chemistry 2019 v.123 no.7 pp. 4371-4379
- adsorption, aluminum, aluminum oxide, goethite, hydroquinone, ions, iron, iron oxides, oxidation, pH, quinones
- To better understand the oxidative reactivity of iron oxides in the fate of contaminants in acidic environments, we examined the reactivity of goethite in binary mixtures with Al₂O₃ by carrying out oxidation experiments of hydroquinone (HQ) in the presence of goethite and/or Al₂O₃ at pH 3. Kinetic results revealed inhibiting effects of 0.2–20 g/L of three different types of Al₂O₃ on the oxidative reactivity of goethite. Surprisingly, soluble Al ions of 0.18–18 mM had a negligible impact on the reactivity. It turned out that the Fe³⁺ dissolved from goethite partly contributed to the observed HQ oxidation and the Al₂O₃ adsorbed the Fe³⁺ to lead to the slower HQ oxidation. The observed pseudo-first-order rate constants in HQ oxidation had a strong linear correlation with Fe³⁺ concentration in various goethite and Al₂O₃ mixtures. Separate experiments confirmed the reactivity of Fe³⁺ toward HQ and the linear correlation between [Fe³⁺] and HQ oxidation reactivity. Finally, sedimentation experiments showed negligible heteroaggregation between goethite and AluC–Al₂O₃ or nAl₂O₃ but intensive heteroaggregation between goethite and Alu 65–Al₂O₃, which explained the observed highest inhibition effect of Alu 65. Overall, oxide mixtures are very complex whose reactivity is determined by many factors such as oxide dissolution.