| Following the12first control POPs under the Stockholm convention, in May2009, ninekinds of chemicals, including four, five, six and seven bromine biphenyl ether, were added tothe list of controlled chemicals on the fourth conference of contracting party. Deca-BDEshad been developed since the early1980s in china, and more than20enterprises onceproduced Deca-BDEs. The production capacity had reached50,000ton per year but the actualannual production was about25,000ton in2006, accounting for1/5of the world’s totalproduction. It is very common that manufacturers induced site pollution Meanwhile, the useof Deca-BDEs and nonstandard recycling of electronic wastes using primitive technologiesalso caused contaminated sites. Soil pollution can reslut in the accumulation of pollutants inplants and animals and transfer in food chain, which will ultimately affect the health of plants,animals and humans. In this research, we firstly studied simultaneous determination ofPoly-Brominated Diphenyl Ethers (PBDEs) in the soil. Then we artificially contaminated thesoil with DecaBDE to carry out the study of thermal desorption, more specifically, to explorethe effects of equipment parameters, soil characteristics, and characteristics of the pollutantson thermal desorption. The main results are listed as follows:A method was developed for the simultaneous determination of17polybrominateddiphenyl ethers (PBDEs) in the soil by accelerated solvent extraction-gaschromatography-mass spectrometry (ASE-GC/MS). The n-hexane and dichloromethanemixture (V: V=1:1) was selected to extract the samples. The clean-up step was optimizedusing silica gel and alumina, then analyzed by gas chromatography-negative chemicalionization-mass spectrometry. The results showed that all the17components of PBDEs,including the high-brominated diphenyl ethers, could be well separated on a short capillarycolumn in32mins. And in this study, the results showed that the recovery of BDE209was80.80%, and the others ranged from86.39%to103.19%. The detection limit of BDE209was198.33pg/g, and those of the other16polybrominated diphenyl ethers was in the range of0.85~114.33pg/g. With the high sensitivity, good reproducibility and recovery, this methodcan be well used for the analysis of PBDEs in soils.The main studied equipment parameters were temperature, residue time, vacuum, carrier gas. Six levels temperatures(200,300,325,350,400and450℃) and six levels of residuetimes (10,20,30,40,50and90min) were set in the experiment. The removal rates andresidual concentrations of polybrominated diphenyl ethers (PBDEs, including BDE28,47,66,99,100,138,153,154,183,190,196,197,203,205,206,207,208and BDE209) werestudied. The total PBDEs concentration of brown soil sample was1136.69mg/kg. In thelow-temperature section,200℃and300℃, the remove rates of PBDEs was lower, the highestremoval rate was76.81%and the concentration of PBDEs in the soil was263.57mg/kg afterbeing heated with the temperature of300℃for90min. In the middle-temperature section,325℃and350℃, the PBDEs residues were much less than those in the low-temperaturesection, the concentration of PBDEs in the soil was114.01mg/kg after being heated with thetemperature of350℃for40min and the remove rate was about90%. In the high-temperaturesection,400℃and450℃, The PBDEs concentration was4.81mg/kg after a20-minuteheating with the temperature of450℃. The removal rate, more than99%, of PBDEs wasreceived. The results showed that the removal rates of PBDEs increased with the temperatureor residence time. According to the results of the experiment, the optimum temperature andresidue time to disposal the brown soil samples were400℃a nd20min, respectively.Comparaed with brown soil samples,the PBDEs removal rates of black soil were higher. ThePBDEs removal rates reached under94%the temperature of350℃for10min.The PBDEs removal rates was effected by pressure, and changed with temperature underatmospheric conditions and vacuum; The flow rate of carrier gas was also studied. The resultsshowed that the PBDEs removal rates decreased by pressure, and the difference betweenatmospheric conditions and vacuum was large. Under negative pressure, there was littledifference among removal rates. The optimum pressure to disposal the experiment soilsamples was76kpa under comprehensive consideration. Under60kpa, The PBDEs removalrates was higher than that of atmospheric conditions, and the gap first increased, thendecreases with temperature, and the largest at350℃. The PBDEs removal rates wereincreased after adding carrier gas at each temperature, when the temperature was lowerthan350℃, the change of PBDEs removal ratewas obvious.Under laboratory conditions, effects of soil particle size and organic matter content onremediation of soil contaminated by decabromodiphenyl ether with thermal desorptiontechnology were studied. Five different particle sizes (75,75-125,125-250,250-425and425-850μm) and two organic matter content of soils were setted.The results showed that theremoval rates of different particle sizes of soils(75,75-125,125-250,250-425and425-850μm) contaminated by PBDEs with the concentration of1000mg/kg were49.53%,73.88%,79.39%,83.56%,87.09%, respectively. The total removal rate of PBDEs increased with the particle size increasing, and BDE209was removed more easier than BDE206, BDE207andBDE208from soils. The removal rate of small particle size was improved with the rise oftime and the prolonging of time. In addition, the organic matter content in soil was also astrong influence factor on the thermal removal rates of PBDEs. The PBDEs removal rate fromthe soil after being oxidated with H2O2was higher than that of the original soil with the samePBDEs concentration below450℃.Pollutant concentration was also selected to study. Two kinds of soils (black soil andbrown soil) at six concentration levels (10,50,100,500,1000,2000mg/kg) were choosen astest materials. The experimental results showed thatthe PBDEs removal rate decreased withthe increase of concentration, when the concentration was low, the PBDEs removal rateschanged slightly under low concentration. The PBDEs removal rates of high concentrationwas higher than that of low concentration level, and the gap first increased, thendecreased,and the largest gap was at300℃. |
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