COMPLEXING AGENT USING BOTH CHEMICAL AND ELECTROCHEMICAL PROCESSES FOR THE REMOVAL OF HEAVY METALS FROM A CONTAMINATED SOIL

摘要

Some agricultural soil samples taken near an Algerian mine of a complex ore have shown an important contamination with zinc and lead. Laboratory studies were performed to remove these metals from the soil without decreasing its fertility, and it is the reason for which EDTA has been tested. In the first part of the research, static leaching was performed in the presence of various concentrations of EDTA Extraction of both zinc and lead were studied versus some parameters, such as pH and contact time. Removal yields were around 50% for the two metals. Using the optimal parameters, leaching with agitation was performed, and a better extraction was obtained, up to 4 h of mixing, for the more stable complexes (lead-EDTA), while it decreased for the less stable complexes (Zn, and Ca). In the second part of the work, in situ treatment was simulated using an electrochemical process where the soil was inserted between four compartments. The extreme contains graphite electrodes and between each compartment an ion exchange membrane allows the transport selectivity. The complexing agent was added inside the soil (central compartment) and it was shown that the current effect enhanced the removing of the metals. However, the kinetic energy diminished. It was as well observed that a good correlation with the conditional stability constants of the different complexes formed with the metals studied. According to the soil composition, the removal yields can be predicted. Moreover, the invariability of calcium amounts shows that the reagents used conserve the soil nature.