Oxidation Of Organic Compounds In The Transition Metal Ions-activated Sulfite Systems

In recent years,more and more refractory and toxic organic compounds have been detected in wastewater which can hardly be degraded by conventional water treatments.Sulfate radical based advanced oxidation process(SR-AOPs),have emerged as a promising method in the field of oxidative decontamination of polluted water.Past studies manily focused on this SR-AOPs with peroxydisulfate(PS)or peroxymonosulfate(PMS)as oxidants,especially the systems involving transition metals and oxidants(i.e.Fe(?)-PS system,Ni(?)-PMS system and Co(?)-PMS system).In this dissertation,oxysulfur radicals including sulfite radical SO3'-,sulfate radical SO4'-,peroxymonosulfate radical SO5'-produced by transition metal ions such as Cr(?),Co(?),Fe(?)activated sulfite were used to oxidize organic compounds.The removal efficiency,the oxidation mechanism were examined,and the role of sulfur species were elucidated.The main content and results consist of:In the first part of the work,Cr(?)-S(?)system containing sulfite ions that rapidly and simultaneously reduces Cr(?)and oxidize organic pollutants in the presence of oxygen in aqueous solutions was investigated,using azo dye A07 to be the main model contaminant.The effects of initial pH,Cr(?)/S(?)molar ratio,dissolved oxygen were examined in batch experiments,and radical-scavenging experiments were also conducted to identify the activity of the radicals.The results showed that acidic conditions(pH 3.0)facilitated degradation of organic compounds and reduction of Cr(?)as well;and oxygen played an important role in A07 decolorization in the system.Quenching experiments comfirmed the main active species in the Cr(VI)-S(IV)system was oxysulfur radicals(mainly SO4'-and SO5'-)(72.5%),and hydroxyl radicals(OH')accounted for 21.7%in the experiments.In addition,experiments of rapid degradation of several kinds of organic pollutants were also conducted.Preliminary results showed that the removal rates of the analogs of phenols or aromatic amines in this Cr(?)-S(?)system have a relationship with the electronic parameters(Hammett constant,?)of the substituted groups.Thus,the Cr(?)-S(?)system,provides an excellent strategy of"waste control by waste" for removing multiple industrial contaminants.In the second part of the work,the efficiency Cobalt(?)(Co(?))for the activation of sulfite ions following the oxidation of paracetamol(PARA)used as model contaminants was inverstigated.Physico-chemical parameters that can impact the paracetamol oxidation(pH,initial PARA concentration,Co(?)/S(?)molar ratio,oxygen concentration)and contribution of various radicals were investigated in order to elucidate the chemical mechanism.Main results showed that the pH is a key factor controlling the efficiency in the Co(?)-Sulfite system.Higher efficiency is observed at pH between 9.0 and 10.0.Increasing S(?)concentrations slightly promoted the oxidation of PARA.In fact,an excess of sulfite ions(2 mM)inhibits the reaction through the scavenging of SO4'-and SO5'-.Moreover,oxidation efficiency drastically decreases from?85%to less than 5%in absence of oxygen.SO4'-was confirmed to be the main oxidant responsible for the PARA oxidation,and radical-scavenging experiments also suggested the possible implication of SO5'-.For the first time the second order rate constant between SO4'-and PARA(1.33 ± 0.79 × 109 M-1 s-1(at pH 5)and 6.14 ?0.99×108 M-1 s-1(at pH 11.0))was detemined.The third part of the work mainly investigated the PARA oxidation in Cu(?)-S(?)system,and the character of low concentration of Cu(?)was emphasized.The effects of initial pH,the dosage of Cu(?)/Sulfite,dissolved oxygen on PARA degradation were examined in batch experiments.The results showed that the optimum pH for the reaction was 10.0,and low concentration of Cu(II)(10 ?M)could achieve a good performance on PARA oxidation.A comparative study for PARA decontamination by Cu(?)-S(?)system and Cu(?)-PMS system was also presented in this section,and Cu(?)-S(?)system proved to be much more efficient than Cu(?)-PMS system when other conditions remained the same.Several kinds of free radical quenchers were used for mechanism study,and results comfirmed that the main reactive oxygen species was the SO5'-,which accounted for 51.7%in the experiments on PARA oxidation.The fourth part of the research mainly inverstigated the efficiency of Fe(?)-S(?)system using aniline as pollutant model compound in water.Chemical kinetics,influencing factors,and mechanism of aniline oxidation were examined with emphasizing the contribution of different oxysulfur radicals(mainly SO4'-and SO5'-).Our results showed a significant enhancement of aniline oxidation efficiency is observed at pH 4.0 with 1.0 mM S(IV)concentration and 0.1mM Fe(III)concentration.Moreover,oxidation efficiency drastically decreased to 10%in absence of oxygen which indicated the importance of oxygen.Through competition kinetic experiments and radical scavengers experiments we concluded that SO5'-was responsible for about 60%of the aniline oxidation in Fe(III)-S(IV)system under typical conditions investigated in this work.We also determined the second order rate constants between SO5'-and aniline(5.8±0.6×106 M-1 s-1(at pH 3))and SO4'-and aniline 7.7 ± 0.5 × 109 M-1 s-1(at pH 3.0)).