Oxidation Of Chlorophenols By Supported MnO₂

Chlorophenol（CPs）are widely used in industrial,agricultural and pharmaceutical production.They are frequently detected in aquatic environment,and have a serious threat to water ecological environment.Therefore,it has great practical importance to study control technology of CPs in water.In this study,coated MnO₂ synthesized under optimized loading conditions on suitable carrier material was used as an oxidant to oxidize three kinds of CPs,4-chlorophenol（4-CP）,2,4-dichlorophenol（2,4-DCP）and 2,4,6-trichlorophenol（2,4,6-TCP）.The results are listed as follows:（1）By comparing the removal of 4-CP by the oxidation of MnO₂ coated on TiO₂,kaolinite,zeolite and quartz sand and also the source and the price of each material,kaolinite was selected as the suitable loading material.（2）Orthogonal experiments were used to optimize the loading conditions of kaolinite supported MnO₂,the optimal conditions are drying temperature 50℃,pH4.0,kaolinite dose 2g,loading twice,loading temperature 50℃ and loading time 60 min.The coated MnO₂ was characterized by XRD and SEM.Results showed that the surface of kaolinite is occupied by MnO₂ and the amount of loading MnO₂ is8.68±0.04mg/g.（3）All three CPs were efficiently degraded by supported MnO₂.The reaction of supported MnO₂ with three CPs is first order for each CP and the order is 0.82-1.05 for MnO₂.（4）The removals of all three CPs are increased with the increase of coated MnO₂ doses or the reaction temperature.However,their removals are decreased greatly with pH increasing.The removals of three CPs follow the sequence of2,4,6-TCP>2,4-DCP>4-CP under medium acidic conditions,whereas,the sequence is totally reversed under neutral and alkaline pH conditions.（5）The presence of Mg²⁺,Mn²⁺,Fe³⁺,Al³⁺,PO₄^3-and humic acid all perform an inhibitory effect on the oxidation of 4-CP by coated MnO₂,and the inhibition is strengthened with their increased concentration.（6）Continuous-flow oxidation experiments were conducted in a column packed with kaolinite supported MnO₂,4-CP solution was continuously flowed from the top to the bottom of the column.In the initial 0-6h,the concentration of 4-CP in the effluent is remained almost constant,and the concentration is increased linearly after6 h.Potassium permanganate solution was then used to regenerate the column,after which,second continuous experiment was carried out in the column.The two penetration curves are very similar,only with the effluent concentration of 4-CP in the second experiment is slightly higher than in the first experiment.Compared with the results of batch experiment,the continuous oxidation treatment is more effective,economical and practical for the control of CPs.