Improved Experiment Of Auxiliary Liquid Chamber Enhanced Electrokinetic Remediation Of Chromium Contaminated Soil

The improper stacking of chromium slag has caused a large area of soil pollution.Although the chromium（Cr）slag had been treated in a harmless way,the Crcontaminated soil still needs to be further remediated.Electrokinetic remediation can achieve the removal of pollutants from contaminated soil.Due to the opposite migration directions of Cr（Ⅲ）and Cr（Ⅵ）in the electric field and the conversion of Cr（Ⅵ）to Cr（Ⅲ）,after electrokinetic remediation of chromium-contaminated soil,there exist higher residual Cr in the middle of the soil.The soil is heterogeneous medium with complex composition.Analyzing changes in soil Characters like p H and Cr content at different depths after remediation can help to evaluate the impact of electrokinetic remediation on the soil and the remediation effect more accurately.In this paper,citric acid,ammonium citrate-sodium thiosulfate,lactic acid and potassium oxalate-oxalic acid were used as electrolytes and an auxiliary liquid chamber was set to remediate Cr-contaminated soil.After the remediation,the soil is divided into upper and lower layers,and the differences of soil properties（soil p H,conductivity,and water content）at different depths and the influence of different electrolytes on the remediation effect are analyzed.From the results we can know that:（1）The setting of the auxiliary liquid chamber can adjust soil moisture content,accelerate the migration of electrolyte to soil,and promote the migration of Cr from soil chamber to liquid chamber.The Cr collected in the auxiliary liquid chamber is much higher than that in anode chamber if the electric current is low.（2）When using potassium oxalate-oxalic acid as electrolyte,total Cr（50%）and Cr（Ⅵ）（91%）have the highest removal efficiency,but corresponding the energy efficiency is also the lowest due to the high current and the specific energy consumption is 671 k J/ g.While when citric acid is used,the total Cr removal efficiency is lower,but the energy efficiency is greatly improved and the specific energy consumption is only121.49 k J/g.（3）For the removal efficiency,the upper soil tend to have higher removal efficiency for total Cr or Cr（Ⅵ）.When oxalic acid-potassium oxalate is used,the gap is as high as 10%.The p H,conductivity and water content of the upper and lower soil layers are also different,and for each indicator,the difference is unique and there exists no connection among them.（4）After the remediation,the Cr content in the soil solution decreased obviously.The decrease is particularly obvious under the conditions of high effective voltage or moving electrodes.The convertion of Cr from non-liquid phase to liquid phase occurred when oxalic acid-potassium oxalate was used.（5）For the exchangeable speciation of Cr,Cr（Ⅵ）accounts for the majority.And only part of the Cr（Ⅲ）reduced from Cr（Ⅵ）will be complexed with the complexing agent and still exist in soil solution.The generated complex is electrically neutral and cannot be removed by electromigration.So it would take more time to remove Cr（Ⅲ）from the soil.