An Evaluation of Lead Leachability from Monolithic Solids under Modified Semi-Dynamic Leaching Conditions

Modified semi-dynamic leaching tests (ANS 16.1) were conducted for artificial soils contaminated with lead oxide (PbO) in order to assess the long-term leaching behavior of lead (Pb). In order to simulate “worst case” leaching conditions, the ANS 16.1 test was modified by using 0.014 N acetic acid (pH = 3.25) instead of distilled water. Artificial soils were prepared by mixing amounts of kaolinite or montmorillonite with fine quartz sand. Stabilization/solidification (S/S) treatment using quicklime was then performed. Fly ash was also added, in some cases, to the artificial soils as a stabilizing agent. The effectiveness of quicklime treatment was evaluated by determining diffusion coefficients (De) and leachability indices (LX). A model developed by de Groot and van der Sloot (1992) was used in order to elucidate the controlling leaching mechanisms. Slurry tests were also performed by mixing PbO with quicklime and fly ash, in order to study the immobilization mechanisms of Pb. The resulting reaction products were identified using x-ray diffraction (XRD) analyses. Overall, the test results indicate that quicklime treatment was effective in immobilizing Pb and that the treated soils were acceptable for “controlled utilization” based on LX values. The controlling leaching mechanism was found to be diffusion, in most quicklime treated samples. Precipitation was identified as the most likely Pb immobilization mechanism in quicklime-fly ash treated slurries. Lead silicate, Pb2SiO4 (which is highly insoluble) is the most probable precipitate that can be associated with the decrease in Pb leachability. No evidence of pozzolanic reaction products such as calcium silicate hydrates (CSH) and calcium aluminate hydrates (CAH) was identified.

• 1. INTRODUCTION

• 2. REVIEW OF DIFFUSION MODEL

• 3. EXPERIMENTAL METHODOLOGY

• 4. RESULTS AND DISCUSSION

• 5. CONCLUSIONS

• 6. ACKNOWLEDGMENTS

• 7. REFERENCES