Process And Mechanism Study On Mechanochemical Treatment Of Chlorinated POPs Using CaO-Al

Degradation of persistent organic pollutants （POPs） induced by intense ball milling is defined as mechanochemistry （MC）, and become an attractive non-combustion technology, due to its benign reaction condition and feasibility to industrial application. Concerning the problems of lower dechlorination effect of conversional additives, uncertainty of degradation mechanism of POPs by MC, complex influence of processing parameters on degradation efficiency, and complicated composition of fly ash （FA）, our thesis will try to develop a more effective dechlorination reagent, and to investigate the degradation mechanism of MC process, and to establish and verify a reaction kinetic model including a variety of operating parameters, and to explore the application of mechanochemical process of municipal solid waste incineration （MSWI） FA.The MC degradation of three chlorinated pesticides （HCBz, P.P’-DDD and y-HCH） under different reagents proved that CaO-Al （containing calcium oxide and aluminum powder） is the best reagents with fastest rate, saving 30% of milling time compared with sole CaO. According to the chemical analysis by GC-ECD, IC and XRD, etc., as well as the characterization methods of Raman spectrum, EPR and SEM, etc., it was inferred that CaO-Al and HCBz was milled and Mechanochemically decomposed to amorphous chlorides and carbon after MC reaction, from activated aromatic radicals, through gradually dechlorination to lower CBz, destruction of benzene rings to alkanes, and polymerization of benzene rings to graphite. MC reaction was induced by local ’tribomicroplasma phenomenon’ caused by high energy ball milling, observed by melted micro-spheres with diameter uniformly below 1μm （after 8 h） observed by SEM.Considering the influences of different processing parameters （milling time, rotate speed, ratio of balls to materials, ratio of reagent to pollutant） to the mechanochemical degradation of POPs, a more accurate "Sigmoid" model （χ=1-（1+R K Do） exp（-R K D₀）） of reaction kinetics, assuring the conversion as a function of the specific energy dose （D₀=C_R Pe0 t）, was set up, by substituting the relative velocity in radical direction of milling ball and vial （vn=vτ-Vvτ） for complete velocity of ball, and replacing the total kinetic energy of ball with effective collision power per unit mass of ball （P0e） by relating t, Ω and C_R. Then the simulation was carried out on the HCBz degradation by CaO-Al reagents by applying modified’Sigmoid function’, fitting with an average rate constant of Ka=1.065E-05 under 44 milling cases, the residual sum of squares was 1.214E-02 under 12 milling cases of R=20, by applying the average Ka in the reaction kinetic model. The conversion efficiency can be predicted in case the milling conditions and rate constant were given, by applying the "S" kinetic model. The MC degradation efficiency of POPs was defined by the specific energy dose and additive process, but independent of milling form, guiding the application of MC reactions on other ball-milling equipments.Concerning the dioxin and heavy metals contained in municipal solid waste incineration fly ash, firstly it was discovered that the inorganic chlorides （about 10% of NaCl and KCl） contained in raw FA would block the mechanochemical degradation of PCDD/Fs, by comparing with the MC treatment of water-washed FA （WFA）, and confirmed by chlorinated WFA （CWFA）. The highest degradation efficiency of PCDD/Fs （93.2%） in WFA was obtained by applying CaO-Al reagents, and the TEQ value with 0.58 ng/g after milled was much lower than the criteria of landfill with 3 ng/g. Then a part of heavy metals （Cr、Cu、Pb） were solidified by MC in direct milling of FA and WFA samples, through chemisorption of crystals and physical inclusion, the solidification efficiencies of heavy metals were higher after water washing of FA. Finally the solidification effects of heavy metals contained in fly ash by applying CaO-Al and CaO were compared, as well as different contents of sole CaO were designed. The results turned out that all heavy metals were effectively solidified below the landfill criteria by congrinding with only 5% CaO for 10h or 10% CaO for 6h without the assistant of Al, through the adsorption of heavy metals by calcium silicate gel synthetised from CaO and SiO2 contained in FA, as well as the sediment of heavy metal hydroxides by substituting the calcium ion in Ca（OH）2. On the premise of water washing, the pollutants of dioxins and heavy metals could be resolved by MC treatment of CaO-Al or CaO process, particularly, much higher degradation efficiency of PCDD/Fs would be received by CaO-Al, and the solidification effects of heavy metals of CaO-Al and CaO were similar..