Study Of The Flushing Technique On PCBs Heavily Contaminated Soils

With the the gradual improvement of national corresponding laws, regulations andpolicies, a large number of e-waste dismantling workshops will be upgraded or relocated.Thus, there will be a lot of e-waste contaminated soils sites need repair. At present, moststudies of e-waste contaminated soils focused on pollutants’ survey, exposure levels and riskassessment. There were few researches on the remediation of contaminated sites’soils, so it iscrucial to do some related researches on remediation technologies to repair the soilscontaminated by PCBs in e-waste dismantling sites. Chemical leaching remediationtechnology has the advantages of easy operation, good controllability, fast repairation speedand mild repair conditions. So it is suitable for the remediation of soils which are heavilycontaminated by PCBs as well as need quick repairation in e-waste dismantling sites,Particularly.So first of all, we studied the washing efficiencies of different eluents on PCBs (Aroclor1254) contaminated soils and discussed the influences of flushing time, elution times and thepH of eluents on the elution efficiencies; Then in order to simulate flushing process of actualsoil contaminated by PCBs more realistically, we studied the elution efficiency of soil columnleaching method on the PCBs polluted soil and discussed the leaching rate, leaching way andthe influences of different eluents on longitudinal residual distribution of PCBs in the soilcolumn; Finally, based on B3LYP/6-31G (d) methods and PLS regression analysis, we builtPCBs’ n-octanol/water partition coefficient (logKow) and micelle/water partition coefficient(logKmw) QSAR models and discussed the mechanism of Aroclor1254solubilized by TX-100from the aspect of PCBs’molecular structure preliminarily. The main conclusions werediscussed as follows:The results showed that the overall washing efficiencies of seven eluents on PCBscontaminated soil followed the sequence of TX-100≈TW-80＞SDBS＞β-CD＞Saponin＞RL＞CTMAB. When the mass concentration of eluents was10g/L, the elution rate of TX-100,TW-80, SDBS, β-CD, Saponin, RL, CTMAB could reach up to54.99%,53.12%,46.99%,25.35%,14.76%,13.70%,0%, respectively. Taking the flushing efficiency, soil adsorptionamount, the cost of eluents and whether friendly to the environment into consideration,TX-100and β-CD were chosen as the two preferable flushing agents for PCBs contaminatedsoil. Soil column leaching experienment showed that good leaching efficiency could beachieved under the condition of2mL/min’s leaching rate and continuous leaching way. Afterwashing, the longitudinal residual distribution of PCBs in soil column varied with the type ofeluents. The flushing rates on laboratory simulation soil and actual contaminated soil byTX-100solution could reach to74.49%and89.24%, respectively.We built the QSAR models of logKowand logKmw. In model of logKow, the values ofsquared correlation coefficient (R2) and cross-validation test (Q2cum) was0.992and0.988, itshowed this optimal model was stable as well as had high fitting precision and goodpredicting ability. In model of logKmw, the values of R2and Q2cumwas0.852and0.746. ThelogKmwvalues of PCBs predicted by the model were very close to those observed. The studyindicated that PCBs with smaller dihedral angle of the two benzene ring plans(DA), higherelectronic spatial extent(Re) and lower molecular total energy(ET) tend to be more inclined tomicelle.