Mobilization and immobilization of heavy metals in contaminated soils by carbon dioxide partial pressure manipulation
Heavy metal and radioactive isotope contamination is common in several sites across the nation, and its remediation is important due to actual and potential detrimental impacts on human health and the environment. This study proposes an alternative and innovative technique for metal mobilization by using carbon dioxide. CO2 in the presence of water forms carbonic acid, which releases the metals attached to the soil particles into the surrounding groundwater. Once in the water (aqueous phase), it is easier to remove and reutilize or dispose of the metals present with currently available technologies. To demonstrate the previous statement, three soil samples were characterized and tested. All soil samples were artificially contaminated. A solution containing Cd, Cr, Cu, Ni, Pb and Zn was added to the first two soils. In addition to the six metals previously mentioned, Sr and Ba were also added during contamination of the third soil sample. Heavy metals utilized in the experiment are those commonly found in contaminated sites across the world. The experiments were conducted in experimental cells of dimensions 76 x 33 x 33 centimeters, which simulate the interaction between the soil particles, sparged gasses, and groundwater in a real aquifer. CO2 gas was injected into the cell before the water had contact with the contaminated soil using horizontal sparging “wells” located at the bottom of the cell. Water samples were taken at three different places within the cell (after CO2 injection in the mobilization zone, in the air sparging zone, and in the immobilization zone) to analyze the ability of this technique to mobilize and immobilize dispersed metal contamination in soil. Manipulation of partial pressure of CO2 was very successful in mobilizing and immobilizing metals. A particularly good candidate for this approach is the radionuclide Sr-90 (half-life 29 years), which was mobilized in concentration as high as 9.7 mg/L in the experimental cell. Other good candidates for the implementation of this technique are cadmium and nickel, which were mobilized in concentrations as high as 0.10 and 0.33 mg/L in the experimental cell, respectively. Strontium, cadmium and nickel are of significant environmental concern at former nuclear weapons production sites and metal processing and refining facilities, correspondingly. Even though results for metals such as barium, copper, lead and zinc were not conclusive, it is believed that these metals could also be readily mobilized to facilitate their removal from contaminated soils at numerous sites. This innovative technique is of potential interest to environmental and consulting firms in charge of clean-up and remediation activities, institutions and organizations disposing of nuclear and mining wastes, scientists, the general public, and to federal agencies such as the Environmental Protection Agency and the Department of Energy.
Environmental science|Environmental engineering
Gomez Paez, Juan Daniel, "Mobilization and immobilization of heavy metals in contaminated soils by carbon dioxide partial pressure manipulation" (2003). ETD Collection for University of Texas, El Paso. AAI3128308.