| The effectiveness of quicklime-based stabilization/solidification (S/S) to immobilize arsenic (As) in soil environments was evaluated by performing semi-dynamic leaching tests. Based on these tests the long term As leaching mechanisms were also determined. Based on X Ray diffraction (XRD) mineralogical analyses and batch geochemical testing the controlling As immobilization mechanisms were also elucidated. Artificial soil samples as well as field soil samples contaminated with As were tested. The S/S effectiveness was evaluated by measuring As cumulative fraction release, effective diffusion coefficients (De ) and leachability indices (LX) for the tested soils. Upon treatment As release was significantly reduced. Arsenic cumulative fraction release levels varied between 0.15% to 3.73% as a function of soil composition and type of treatment. Treatment was more effective in the presence of kaolinite and quicklime for the artificial soils, whereas it was more effective in the presence of quicklime-fly ash for the field contaminated soils. Upon treatment, De values were lowered while LX values were always higher than 9, suggesting that the S/S treatment was effective since treated soils were acceptable for “controlled utilization”. Moreover, based on a model developed by De Groot and Van Der Sloot (1992), the leaching mechanism for all treated soils was determined to be diffusion. The controlling mechanism of As immobilization whether sorption, precipitation, or inclusion in pozzolanic reaction products was also considered. Upon quicklime treatment, the amount of clay present in the soil did not influence As leachability, indicating that sorption was not the controlling immobilization mechanism. Also, samples, which would be expected to form pozzolanic reaction products at higher rates and amounts, showed elevated As leachability levels. In order to further elucidate the immobilization mechanisms, an in-depth mineralogical study was designed and undertaken. Overall, the effectiveness of both As (III) and As (V) immobilization appeared to increase with increasing Ca/As molar ratios for all slurries tested. (Abstract shortened by UMI.)... |
