基于半动态淋滤试验的水泥固化铅污染黏土溶出特性研究

通过半动态淋滤试验,研究淋滤液pH分别为2,4,7时水泥固化铅污染土的溶出特性,以定量评价水泥固化铅污染土的环境安全特性。结果表明,当淋滤液初始pH为2时,试样中累积铅溶出质量约为pH为4和7时的47～106倍；而pH为4和7时累积铅溶出质量差别不明显。试样水泥掺量由12%提高到18%时,试样累积铅溶出质量降低了28%～68%,表明增大水泥掺量有利于铅的固定。通过对试验结果的理论分析,求算得出了铅扩散系数D_e；淋滤液初始pH=4,7时D_e很接近；而淋滤液初始pH=2时,D_e比pH=4或7时的D_e高约3,4个数量级；当水泥掺量由12%提高到18%时,试样D_e降低了约17%～99%。上述研究结果表明,强酸性淋滤液和水泥掺量明显影响固化污染土中铅溶出量和扩散系数。

Leaching properties of cement-solidified lead-contaminated clay via semi-dynamic leaching tests

The leaching characteristics of cement solidified/stabilized Pb-contaminated kaolin under different pH of leachant are investigated via a series of semi-dynamic leaching tests as well as quantitative evaluation of the effectiveness of solidification/stabilization treatment in remediating Pb-contaminated kaolin. The designed initial pH of leachant is 2, 4, and 7. The results show that the accumulated leached Pb mass at leachant pH of 2 is 47 to 106 times that at leachant pH of 4 and 7. Nevertheless, the difference of the accumulated leached Pb mass between leachant pH of 4 and 7 is marginal. When cement content increases from 12% to 18%, accumulated leached Pb mass decreases by 28% to 68%, indicating that the increasing cement content will enhance the immobilization of Pb. The diffusion coefficient (D_e) of Pb is back-calculated by conducting a theoretical analysis of the relationship between the leaching time and the leached mass ratio. It is found that the values of D_e of Pb at leachant pH of 4 and 7 are very close; and those of Pb at leachant pH of 2 are 3 or 4 orders of magnitude greater than those at the leachant pH of 4 or 7. In addition, an increase of the cement content from 12% to 18% results in a decrease of D_e by 17% to 99%. The present results indicate that the strong acidic leachant (pH<4) and the increase in cement content have significant influence on the leached mass as well as diffusion coefficient of Pb for the cement-stabilized soils.