Effects of Soil Buffering Capacity and Citric Acid in Electrolyte on Electrokinetic Remediation of Mine Tailing Soils

Effects of Soil Buffering Capacity and Citric Acid in Electrolyte on Electrokinetic Remediation of Mine Tailing Soils

Electrokinetic remediation was applied to the removal of heavy metals from mine tailing soils sampled from the piles at two abandoned mines (K and O) in which major contaminants were Cu, Pb, Cd, As and Zn. Experimental results on metal removal characteristics, tendency of electroosmosis, established soil pH profile and the role of citric acid as an electrolyte component were presented and discussed concerning to the buffering capacity and zeta potential of the soils. Since both tailing soils had positive zeta potential, electroosmotic flow formed toward anode and thus about 15-34% of removed metals were found in anode chamber, implying that the mechanisms of metal removal were by electromigration mostly and by electroosmosis in minor. The use of citric acid as an electrolyte component enabled us to maintain an acidic pH for the soil with a low buffering capacity (K soil), resulting in increased electroosmotic flow rate and 35-40% higher metal removal efficiency. Without the addition of citric acid, a steep pH gradient was developed in K soil and the electroosmotic flow rate was greatly diminished. For the soil with a high buffering capacity (O soil), there were no significant differences in pH gradient, eletroosmotic flow rate and metal removal, regardless the use of citric acid. Overall 37-41% of metals were removed for 2 weeks under the 2 conditions of 0.25 mA/cm(2) of current density and using electrolytes with 2.5 mS/cm conductivity.

Electrokinetic remediation was applied to the removal of heavy metals from mine tailing soils sampled from the piles at two abandoned mines (K and O) in which major contaminants were Cu, Pb, Cd, As and Zn. Experimental results on metal removal characteristics, tendency of electroosmosis, established soil pH profile and the role of citric acid as an electrolyte component were presented and discussed concerning to the buffering capacity and zeta potential of the soils. Since both tailing soils had positive zeta potential, electroosmotic flow formed toward anode and thus about 15-34% of removed metals were found in anode chamber, implying that the mechanisms of metal removal were by electromigration mostly and by electroosmosis in minor. The use of citric acid as an electrolyte component enabled us to maintain an acidic pH for the soil with a low buffering capacity (K soil), resulting in increased electroosmotic flow rate and 35-40% higher metal removal efficiency. Without the addition of citric acid, a steep pH gradient was developed in K soil and the electroosmotic flow rate was greatly diminished. For the soil with a high buffering capacity (O soil), there were no significant differences in pH gradient, eletroosmotic flow rate and metal removal, regardless the use of citric acid. Overall 37-41% of metals were removed for 2 weeks under the 2 conditions of 0.25 mA/cm(2) of current density and using electrolytes with 2.5 mS/cm conductivity.