Study On The Photochemical Degradation Of Phenol In Wastewater By The Common Manganese Oxide Minerals

As essential source of Mn element, one of important adsorbents, redox agents, catalysts and carriers for environmental information in soils and aquatic system, Mn oxide minerals have been attracting more and more concerns of researchers on their resource and environmental properties. Investigations on the environmental and resource properties of them could shed light on geochemistry behaviors of Mn, soil progress, and relations between soil quality and soil environment. They are also of great significance to promote exploration and utilization of Mn oxide minerals. Mn oxide minerals in soils, a kind of semiconductor, may play a very important role on degradation of pollutants. In addition, Mn oxide minerals have much environmental properties, such as adsorption, redox, catalysis. Therefore it is supposed that phenol degradation by MnO₂-UV may exhibit three mechanisms: one is direct chemical oxidization on the surface of MnO₂; another is the degradation of phenol by UV irradiation; the last one is the photodegradation of phenol catalyzed by MnO₂, but the mechanism of degradation of phenol is still not very clear.In this paper, synthetic manganese oxides (birnessite, cryptomelane, todorokite) were used as materials, kinetics characteristics of photochemical degradation of phenol wastewater and influencing factors on itin the presence of manganese oxides were investigated. The results are as follows.1. Effects of UV irradiation and bubbling with gas on degradationrateof phenol and removal rate of COD. (1)Bubbling with air into the experimental system has no obvious effect on degradation of phenol. (2)When phenol solution was degraded in the presence of UV irradiation, the degradation rate of phenol is 39.34%, and the removal rate of COD is 7.48% after 4h of reaction. It means that UV irradiation is liable to degradate phenol, but the deep degradation of phenol is not greatly proceeded. (3) When Phenol solution was degraded on condition that UV irradiation and bubbling with air was used, the removal rate of phenol reaches 69.50%, and the removal rate of COD goes up to 14.39% after 4h of reaction. In comparison with the effect of degradation when only UV irradiation was used, the photodegradation rate of phenol is quite enhanced. Two possible mechanisms were assumed to account for that: 1) the stirring of air bubbling; 2) the indirect degradation of phenol by O₂ with UV irradiation.2. Degradation of phenol with different minerals without UV irradiation under the corresponding experimental conditions. The magnitude order of the degradation rate of phenol was: H-birnessite (91.70%) >cryptomelane (86.81%) >Na-birnessite (14.93%)...