Study On Kinetics And Mechanism Of 4-Chlorophenol Degradation By Potassium Ferrate(Ⅵ)

4-chlorophenols（4-CPs）are persistent environmental pollutants which are used in the manufacture of dyes,pesticides,textiles.However,4-chlorophenols are highly toxic to living beings bencause they are carcinogenic and teratogenic substabces.Thus several physico-chemical and biological methods have been used for removal of 4-CPs from the environment.In this paper,the ferrate solution was used for the treatment of 4-CPs as an oxidant.Due to the slow reaction of 2,2’-azino-bis（3-ethylbenzthiazoline-6-sulphoic acid）（ABTS）with low concentrations of ferrate,ABTS method has been used to determinate the rate of In（c/c₀）with respect to time under different conditions,and the kinetics and mechanism have been studied.The absorbance at 415 nm for ABTS（10）generation was linear with respect to Fe（VI）in buffer solutions.And the molar absorbance coefficient has been measured as 28000 L/mol·cm.The intermediate was studied by high performance liquid chromatography（HPLC）method,ion selective electrode（ISE）method,and ultraviolet（UV）Spectrophotometry.And the concentration was linear with respect to the peak area of the HPLC.While the contents measured b y ISE had good linearization with the voltages,and the linear range was 7×10^-5-4×10^-4 mol/L,where the regress coefficient was 0.9945.Meanwhile,the relative standard deviation of this method is less than 2.0%;the standard addition recovery was 102.09%.The main conclusions of the paper are as follows:（1）Environmental conditions were researched systematically,and the removal efficiency of ferrate was tested at different conditions,such as molar ratio and pH.When the molar ratio was 3,the degradation rate was 90%.And the optimal pH was 9.20.（2）The rate law for the oxidation of 4-CPs by ferrate was first order with respect to each reactant.The second-order rate constant of the total reaction was determined as a function of pH at room temperature.And the rate constant k was 48 L/mol·s,the activation energy was 19.93 kJ/mol.There were 4 parallel reactions,and 4HFeO^-and R O^--did not react in basic environment.Thus,k₁ =292 L/mol·s,k₃ =108 L/mol·s,k₄=17 L/mol·s.（3）According to the results determinated by chloride ion selective electrode and HPLC,it is obviously that when the molar ratio of potassium ferrate to 4-CPs was 3,the concentration of chloride ion was 76% of the initial concentration of 4-CPs;While the degradation rate of 4-CPs was 90%.Those results indicate that the intermediates of 4-CPs were chloride ion and chlorinated organic compounds.According to the results determinated by UV absorption spectra,the 4-CPs were gradually degraded by ferrate.And the intermediate substance may be chlorinated organic compounds with double bonds or benzene ring.Through the ring opening reaction,4-CPs become chlorinated organic compounds with simple structure.