Effects of natural and calcined oyster shells on Cd and Pb immobilization in contaminated soils

In Korea, soils adjacent to abandoned mines are commonly contaminated by heavy metals present in mine tailings. Further, the disposal of oyster shell waste by oyster farm industries has been associated with serious environmental problems. In this study, we attempted to remediate cadmium (Cd)- and lead (Pb)-contaminated soils typical of those commonly found adjacent to abandoned mines using oyster shell waste as a soil stabilizer. Natural oyster shell powder (NOSP) and calcined oyster shell powder (COSP) were applied as soil amendments to immobilize Cd and Pb. The primary components of NOSP and COSP are calcium carbonate (CaCO₃) and calcium oxide (CaO), respectively. X-ray diffraction, X-ray fluorescence and scanning electron microscope analyses conducted in this study revealed that the calcination of NOSP at 770°C converted the less reactive CaCO₃ to the more reactive CaO. The calcination process also decreased the sodium content in COSP, indicating that it was advantageous to use COSP as a liming material in agricultural soil. After 30 days of incubation, we found that the 0.1 N HCl-extractable Cd and Pb contents in soil decreased significantly as a result of an increase in the soil pH and the formation of metal hydroxides. COSP was more effective in immobilizing Cd and Pb in the contaminated soil than NOSP. Overall, the results of this study suggest that oyster shell waste can be recycled into an effective soil ameliorant.     

Adsorptive attenuation of ferrocyanide from seepage water in landfill clay liners

The spent potliner (SPL) landfill liner system provides the primary attenuation mechanism that blocks the leaching of ferrocyanide. If the seepage occurs, however, the off-site leaching potential of ferrocyanide will be enhanced, resulting in contaminant dispersion. In this study, the adsorptive attenuation of ferrocyanide by two common lining materials (kaolinite and montmorillonite) was investigated under various seepage settings, such as influent concentration, liner thickness, and seepage velocity. The attenuation of ferrocyanide through both lining materials was obvious by lowering the maximum concentration and retarding the peak arrival time and was greater than that expected from batch data, likely due to the high mass-volume ratio under seepage condition. In comparison, seepage of ferrocyanide through lining material layer was retarded when (1) influent concentration was halved, (2) liner thickness was 1.5-fold, and (3) seepage velocity was halved. These experimental results strongly support the concentration-specific and rate-limited adsorptive attenuation of ferrocyanide by lining materials during the seepage process. An extended desorption front was observed for all seepage conditions; it was particularly more apparent for montmorillonite with a slow seepage velocity, further supporting that the release of adsorbed ferrocyanide from adsorbent is energetically hysteretic. Among the factors investigated in this study, the greatest retardation of ferrocyanide movement from seepage water was achieved upon doubling liner thickness. Therefore, for the design of a SPL landfill liner to minimize the leaching potential and thus the environmental risk of ferrocyanide, optimization of the liner thickness should be considered foremost.