Effect And Kinetics Of Oxidation Of Perfluorooctanoic Acid In Water By Persulfate

Perfluorooctanoic acid?PFOA?is a sort of emerging pollutants and also is a sort of persistent organic pollutants that has caused widespread concern.The oxidation treatment of PFOA has become a research topic at present.Persulfate has attracted much attention because it can oxidize PFOA effectively.The effect and the kinetic characteristics of oxidation of PFOA in water by persulfate was analyzed in this study,in order to provide the technical support and the theoretical basis for the practical applications in the future.In this study,oxidation of PFOA in water by persulfate oxidation was analyzed.The main research contents were as follows:?1?The effect of the initial pH?from 1 to 12?,the initial concentration of persulfate(from 0 to 400 mmol·L^-1)and the temperature?from 25 to 60??on the defluorination rate of PFOA(200?mol·L^-1)for 24 h were investigated.?2?The characteristics of the decay kinetics of persulfate,the transformation behavior of persulfate,the formation kinetics of sulfate and the defluorination kinetics of PFOA were analyzed under the condition of initial pH 2.?3?The effect of alkaline or H₂O₂ which are both persulfate activator on oxidation of PFOA by persulfate was analyzed at 25?.The main conclusions were shown as follows,respectively.?1?The initial pH,the initial concentration of persulfate and the temperature had significant effects on the defluorination rate of PFOA.Lower the initial pH?from 12 to 1.5?was,higher the initial concentration of persulfate(from 0 to 400 mmol·L^-1)was and higher the temperature?from 25 to 60??was,higher the defluorination rate was.And the highest defluorination rate was up to 87%.The initial pH 1 was not conducive to the defluorination of PFOA and made the defluorination rate reducing.?2?The decay of persulfate follows pseudo first order dynamic model,and the relationship between the apparent rate constant(k_PS)and the temperature obeys the Arrhenius equation and the Eyring equation.The values of apparent activation energy,apparent activation entropy and apparent activation enthalpy are 137.6 k J·mol^-1,63.88 J·mol^-1·K^-1 and 134.8 k J·mol^-1respectively.Persulfate is reacted with PFOA and water at the same time,and mainly consumed by reaction with water.And persulfate is mainly converted into SO₄^2-or HSO₄^-.The defluorination kinetic model,ln?1-??=-k_Ft,could approximately describe the relationship between the defluorination rate???and the reaction time?t?.The apparent rate constant?k_F?is proportional to the square root of the initial concentration of persulfate,and the relationship between k_F and the temperature obeys the Arrhenius equation and the Eyring equation.The values of apparent activation energy,apparent activation entropy and apparent activation enthalpy are 93.13 k J·mol^-1,-57.44 J·mol^-1·K^-1 and 90.50 k J·mol^-1 respectively.The values of apparent activation free energy at 25?calculated based on k_F and k _PS were similar,they were107.5 k J·mol^-1 and 115.8 k J·mol^-1 respectively.?3?At 25?,The presence of H₂O₂(20,200 or 2000 mmol·L^-1)is not conducive to the oxidation of PFOA(0.2 mmol·L^-1)by S₂O₈^2-(20 mmol·L^-1)and would reduce the effect of oxidation of PFOA.At 25?,OH^-(from 1 to 3 mol·L^-1)plays a significant role in inhibiting the oxidation of PFOA(0.5 or 2 mmol·L^-1)by S₂O₈^2-(500 mmol·L^-1).There is no significant difference in the degree of inhibition at different initial concentrations of OH^-.There is no obvious feasibility for treatment of PFOA by alkaline-activated persulfate.