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[3301-10-08] Suppression of sulfide oxidation by carrier microencapsulation: electrochemical study on the decomposition of Ti-catechol complex

^○Ilhwan Park¹, Kagehiro Magaribuchi¹, Carlito Baltazar Tabelin¹, Mayumi Ito¹, Naoki Hiroyoshi¹ (1. Hokkaido University)

司会: 飯塚淳（東北大学）

Keywords:acid mine drainage, carrier microencapsulation, Ti-catechol complex, electrochemical study

The oxidation of sulfide minerals (e.g., pyrite and arsenopyrite) by exposure to oxygen and water causes the generation of acid mine drainage (AMD), which leads to serious environmental problem because it is very acidic and contains high concentrations of heavy metals (e.g., Fe, Cu, Zn and Pb). To mitigate the generation of AMD, carrier microencapsulation (CME) using TiO₂ and catechol was developed and works by forming protective coating on the mineral surface. In our previous study, TiO₂ and catechol were used to form Ti-catechol complex but the amount of Ti extracted by catechol to from the complex was limited. In addition, the decomposition mechanism of Ti-catechol complex was not well understood. Thus, the present study investigated the formation of Ti-catechol complex and its electrochemical properties under various conditions.
Ti⁴⁺ ion dissolved in sulfuric acid and catechol were used to synthesize Ti-catechol complex, and the results showed that Ti (IV) tris-catecholate complex (i.e., Ti(Cat)₃^2-) was formed in the pH range of 5-12. Cyclic voltammogram of Ti-catechol complex at various scan rates showed only one anodic peak at 700 mV (vs. SHE), which was assigned to the oxidation of Ti-catechol complex. Among three catechol molecules coordinated with Ti⁴⁺, two of them have distorted oxygen-Ti⁴⁺ bonds because of unpaired electrons. This suggests that these sites are the most reactive part of the Ti-catechol complex and should react first oxidatively. Based on our results, the mechanism of decomposition is divided into two stages: (1) two catechol molecules that have high reactivity are oxidized to quinone, and (2) the remaining catechol molecule is dissociated because Ti (IV) monocatecholate complex is unstable.