Study On The Electro-kinetic Remediation Of Heavy Metals Contaminated Soil

Electrokinetic remediation is a new green technology which has the advantages of ultimate disposal, high efficiency and low cost. It is particularly suited for the emergency treatment of heavy metal contaminated soil in the form of ion fraction. Research at home and aboard on electrokinetic remediation is still in the laboratory or the pilot stage.The result from field application is not stable and the success rate is not high.owning to the unsettlement of impacts from the influence factors. Orthogonal tests are designed to study electrokinetic remediation of nickel contaminated soil and chromium contaminated soil. In order to find a better heavy metal remediation technology, a combined process of soil washing and electrokinetic remediation is proposed.The main conclusions are as follows:(1) Electrokinetic remediation test of nickel: nickel removal rate in different types of soil varies as follow: sand soil, sandy loam, clay soil(fastest to lowest). The influence factors in the same type of soil decrease by importance: catholyte pH, anolyte pH, voltage gradient(highest to lowest). The distribution of nickel in the electric field shows a rising trend from anode to cathode.Most of nickel migrate to the cathode and near cathode. The removal rate of nickel reaches 99.9% in sandy soil on the following condition: catholyte p H 5, anolyte pH 7, and voltage gradient 1v/cm. there is a great impact on the removal rate of nickel from catholyte pH.(2) Electrokinetic remediation test of chromium: In the condition of micro current, the factors that influence chromium removal rate decrease by importance voltage gradient, anolyte pH, catholyte pH, electrode shape(highest to lowest). Total Cr and Cr6+ distribute similarly, diminishing from anode to cathode. The distribution of Cr3+ is not abvious.The removal rate of chromium reaches 80.9% after 144 hours with deionized as electrolyte on the following condition: catholyte pH 11, anolyte pH 3, and voltage gradient 1.5v/cm. In micro current, increasing the voltage gradient can improve the removal rate of chromium.Contrasting the test with KCl solution and water as electrolyte, water is more suitable as electrolyte in electrokinetic remediation.(3) Discussion on the new technology: according to research on soil washing, the optimum residence time is 24 h and the optimum water to soil ratio(mass ratio) is 0.5:1. So a combined technology is proposed: single-pass soil washing + electrokinetic remediation. After washing, The electric migration rate of Cr is improved to 91.6% while the total removal rate is improved to 93.6%, showing a very high applicability of the combined technology to the remediation of heavy metal contaminated soil. In the artificial soil, Cr is mainly in exchangeable fraction and carbonate-bound fraction. After electrokinetic remediation exchangeable fraction Cr decreases, while organio-bound fraction and residual fraction Cr incease.