Ethyl lactate enhances ethylenediaminedisuccinic acid solution removal of copper from contaminated soils

A new approach using aqueous ethyl lactate-modified [S,S]-ethylenediaminedisuccinic acid (EDDS) washing solutions for the removal of Cu from field-contaminated soils was examined in the laboratory. At pH 7 the maximum extraction efficiencies of Cu were about 41% by EDDS solution (EDDS:Cu molar ratio=8), and <2% by ethyl lactate solution. However, greater extraction efficiencies of up to 50% were achieved by amending the EDDS solution with ethyl lactate (EDDS:Cu molar ratio=2, ethyl lactate:Cu molar ratio=25). The pH of the extraction solution did not have a significant effect on the extraction of Cu. The washing agent could also be regenerated quite effectively for economy of use. Sequential extraction results showed that the two most bioavailable Cu fractions, i.e., the acid extractable and reducible fractions, were significantly reduced. The mechanism responsible for the enhanced extraction efficiency in the presence of ethyl lactate is the increased the stability constant of Cu-EDDS complexes in the presence of ethyl lactate, which enhanced desorption of Cu from soil.