Oxidative Degradation Of Organic Pollutants In The Interface Of Iron Oxides/Water And Interface Of Manganese Oxides/Water

In order to understand the environmental chemistry behavior of organic pollutants in natural environment, especially in surface water environment, iron oxides and manganese oxide, two metal oxides existed in natural environment with high content, were used to degrade 2-Mercaptobenzothiazole (MBT) under oxidative degradation processes. Based on the thorough investigation of the MBT oxidative degradation by iron oxide-oxalic acid system and manganese oxides, it was wished that the process of environmental geochemistry of organic pollutants in natural environmental with the presence of iron oxides and/or manganese oxides could be fully understood, and furthermore, the basic data and new technology for repairing environment which contaminated by organic pollutants were wished to be referenced in this investigation.The heterogeneous photochemical systems of iron oxides-polycarboxylic acid can be used to model the photochemical degradation process of organic pollutants in the interface of natural soil mineral/water. In natural environment, iron oxides can be reduced by dissolved organic maters (DOM) to generate dissolved and adsorbed Fe-polycarboxylic acid photo active species, among which the Fe-oxalate has the most high photo reactive activities. There are high concentrations of polycarboxylic acid, such as oxalic acid, citric acid, et al., in the secretion of plant root. In this study, iron oxide-oxalic acid heterogeneous photo chemical systems were investigated to degrade MBT, and the main affecting factors, including the dosage iron oxide, the initial concentration of organic acid, pH, intensity of illumination, and additional transient metal ions et al., were studied to understand the photochemical reaction process. It was observed that the state of [≡Fe(C₂O₄)_n]^(2n-3)- which existed in the surface of iron oxide, was the most important factor which affect the reaction efficiency of the system. In this paper, the variations of pH, concentration of oxalic acid, and the concentrations of Fe(II) and Fe(III) during the reaction process of iron oxide-oxalic acid system were also studied. This research disclosed the coupling processes of oxidize-reduce circulation of Fe species, the generation and transformation of active oxygen species (H₂O₂ O₂^-· , HO^·, C₂O₄^·), and the photochemical degradation of organic pollutants. And the results of this study can provide new clews for thoroughly understand the transformation of hazardous organic maters in the interface of iron oxides, and also for disclosing the chemical process of Fe species in soil.The oxidative reaction of DOM and the reductive dissolve of manganese oxides in the interface of manganese oxides have received widely attention in the field of environmental chemistry and soil chemistry. The manganese oxides have high oxidative activities and the degradation processes of organic pollutants in natural environment are related with manganese oxides. In this paper, the reaction kinetics and thermodynamics of MBT degradation in the interface of manganese oxides under different pH, dosage of manganese oxides, initial concentration of MBT, and temperature were studied. During the degradation and mineralization of MBT by manganese oxides, Mn(TV) or Mn(III) in manganese oxides were reduced to Mn²⁺. In the study, the degradation kinetics model, which can describe the relations of the degradation ratio of organic pollutants in the interface of manganese oxides with the initial concentration of organic pollutants, with the dosage of manganese oxides, and with the pH values, was set up. This research also investigated the relations between the structures and characters of manganese oxides with the degradation parameters, and with the apparent activation energies, and it was found that the activation energy was negatively related with the oxidative activities of manganese oxides. The main factors which affect the oxidative reaction in the interface of manganese oxides were also studied, and the results showed that the presences of organic acids and reductive metal ions can inhibit the degradation of organic pollutants. In the later part of this study, the relations between transformation of organic pollutants and the soil chemical process of manganese oxides were further investigated.