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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.