A New Electrokinetic Technique And Its Application In Remediation Of Heavy Metal Contaminated Soils

With the rapid development of China’s economy, the growing soil pollution fromheavy metal has become more serious and that should be resolved.As a new in-situ remediation technique, Electrokinetic remediation has been wideconcerned in contaminated soil remediation due to its advantages, such as low cost, highefficiency, and possible removal various pollutants. However, the "polarizationphenomenon" and “focusing effect” resulted from lower pH near anode and higher pHnear cathode due to electrolysis of water limited its wide application.In order to overcome the disadvantages of electrokinetic technique, an new ideawas put forwarded, that is, chelating nano-fibers were introduced to classicalelectrokinetic equipment to short the migration distance of heavy metal ions due toadsorption, and circulation of electrolytes was adopted to stable the pH of soil throughneutralization electrolyte of anode and cathode. The effects of experimental conditions,such as the type of chelating nano-fibers, location of fibers, and valtage, time, as well ascirculation model on pH and lead ion distribution in soil and lead ion removal efficiencywere investigated, and the performances of the electrokinetic technique werecharacterized in detail. The main conclusions of this thesis are as follows:(1) The pH value of soil and electrolytes is a key factor affecting the electrokineticremediation. In classical electrokinetic remediation, pH was lower near anode andhigher near cathode, and focus effect was obvious. It was impossible to improveremediation effectively only by simply extend remediation time or increase voltage. Inthe new electrokinetic remediation technology, the use of buffer solution andintermittent circulation of electrolytes kept the pH under control, that is, the pH of bothsoil and electrolytes did not changed much resulting in improving removal efficiency oflead from soil.(2) In the new electrokinetic remediation technology, fiber type affected adsorptioncapacity of lead. In comparasion, lead ion imprinted membrane was better foradsorption lead in the new electrokinetic remediation system at pH4.60.(3) In the new electrokinetic remediation technology, lead ion imprinted membranesignificantly improved remediation efficiency. However, the adsorption capacity wasrelated to the location of fibers in electrokinetic equipment, and the adsorption capacitywas very high if the fibers were located at cathode chamber or in the circulation pool. (4) Replacement of fibers located in circulation pool, at central of soil and cathodechamber will help to improve remediation efficiency and reduce energy consumption.(5) Compare with the classical electrokinetic remediation, the new electrokineticremediation technology achieved a reasonable remediation effect by extending the time.When the voltage was30V, the time was96h, the removal rate reached upto40.83%.In conclusion, in the classical electrokinetic remediation, remediation efficiencydecreases with the time, and the pH of soil altered significantly. In contrast, the newelectrokinetic remediation technique surmounted those shortcomings. However, thefibers played a pivitol role in this technique. Furthermore, the remediation efficiencyremained to be improved. It is necessary to study in detail.