酸雨作用下含磷固化剂处理铅锌镉复合污染土的半动态浸出试验研究

Effect of acid rain on leaching characteristics of lead,zinc and cadmium-contaminated soils stabilized by phosphate-based binder: semi-dynamic leaching tests

酸雨pH可显著影响固化重金属污染土的浸出量。定量评价固化污染土在暴露条件下(例如酸雨)对周边水土体环境的影响,需要明确固化污染土的有效扩散系数和阻滞因子这两个关键参数。现有研究多集中在固化污染土的浸出特性和表观扩散系数,有关有效扩散系数和阻滞因子的研究很少。本次研究旨在研究改进的KMP固化剂固化重金属Pb、Zn、Cd复合污染土在酸雨作用下的有效扩散系数和阻滞因子。解吸附试验表明,随着污染土中重金属Pb、Zn、Cd浓度增加,固化污染土的解吸附量增大,且解吸附曲线满足Freundlich平衡吸附/解吸附方程。半动态浸出试验结果表明,污染土中重金属Pb、Zn、Cd浸出机制主要由扩散控制,且拟合曲线斜率分别为0.60,0.56和0.61,表观扩散系数Dobs为1.05×10^(-16),7.84×10^(-13)和2.11×10^(-12) m^2/s。结合解吸附试验和半动态浸出试验结果可知,Pb、Zn、Cd的阻滞因子Rd分别为17165.6,254.6和109.3,有效扩散系数De分别为1.82×10^(-12),1.96×10^(-10),2.34×10^(-10) m^2/s。与其他学者结果相比,固化污染土中Pb的有效扩散系数低于其他学者的两个数量级,而Zn和Cd的求算结果与其他学者一致。

The previous studies show that acid rain pH significantly affects the leachability of stabilized heavy metals-contaminated soils. The parameters of diffusion coefficient （De） and retardation factor （Rd） are critical for quantitative assessment of impact of stabilized contaminated soils on the surrounding environment. However, the effective diffusion coefficient and the retardation factor of the stabilized soils have not been well addressed in the previous studies. This study investigates the diffusion of heavy metals leached from a new binder, namely modified KMP, stabilized Pb, Zn and Cd-contaminated soils. A series of tests including desorption tests and semi-dynamic leaching tests are conducted to determine the obvious diffusion coefficient （D^obs） and the retardation factor （Rd）, respectively. The desorption test results show that the leached concentrations of Pb, Zn and Cd increase with the increase in their initial concentrations. It is also found that the desorption curves can be fitted using the Freundlich desorption/adsorption model. The semi-dynamic leaching test results show that the leaching of heavy metals released from the stabilized soils is controlled by diffusion process. The obvious diffusion coefficients （D^obs） of Pb, Zn and Cd are estimated as 1.05×10^-16,7.84×10^-13 and 2.11×10^-12 m^2/s. Combined with the desorption and semi-dynamic leaching tests, the retardant factors ofPb, Zn and Cd are estimated as 17155.6, 251.6, and 109.7. The effective diffusion coefficients are therefore determined as 1.82×10^-12,1.96×10^-10 and 2.34×10^-10 m^2/s for Pb, Zn and Cd, respectively. Compared with those of the previous studies, the effective diffusion coefficients of Pb presented in this study is 2 orders of magnitude lower, whereas the effective diffusion coefficients of Zn and Cd are consistent with those reported in the previous studies.