酸雨环境下磷酸镁水泥固化锌污染土溶出特性研究

Semi-dynamic leaching tests on leaching properties of MPC-solidified zinc-contaminated soil under acid rain environment

通过对磷酸镁水泥(简称MPC)固化锌污染土进行半动态淋滤试验,以研究酸雨作用下重金属的溶出特性,通过更新淋滤液试验组的浸出液电导率和pH的测试来再次印证Zn^(2+)在半动态淋滤试验中的淋滤特性,并添加普通硅酸盐水泥(简称CEMI)固化土试验组进行对比。通过对MPC固化锌污染土半动态淋滤后浸出液中锌离子浓度的测试,分析淋滤液初始pH值、固化剂类型对MPC固化污染土累积锌溶出特性的影响规律。试验结果表明,CEMI组试样累积锌溶出质量大于MPC组试样;初始淋滤液pH=2时的试样表面溶出锌总量普遍高于pH为4和7,而pH=4和7时的试样表面溶出锌总量比较接近;采用更新淋滤液方式的3组试样溶出的Zn^(2+)量均大于不更新淋滤组;氧化镁与磷酸盐的比值(M/P)为6∶1的试样固化效果优于M/P为3∶1的试样。通过试验数据计算分析,得到了有效扩散系数De;锌的De会随酸雨初始pH的下降而增大,淋滤液初始pH=2时的锌的De普遍大于pH=4,7时的De几个数量级。研究结果表明,酸雨作用下影响磷酸镁水泥固化锌污染土溶出特性的主要因素为水泥固化剂的种类以及酸雨的pH值。

The semi-dynamic leaching tests are conducted to investigate the leaching characteristics of MPCsolidified/stabilized Zn-contaminated soil under the effect of acid rain, and the CEMI groups are added to compare with the MPC ones. The concentrations of Zn^2＋ in leachant and pH of leachant are measured. Thus the effects of the initial pH of leachant and the type of curing agent on the cumulative mass of leached Zn are determined. The results show that the effects of acid rain on the CEMI groups are much greater than on the MPC groups. The accumulated leached Zn mass at leachant pH of 2 is much larger than that at leachant pH of 4 and 7. Nevertheless, the difference of the accumulated leached Zn mass between leachant pH of 4 and 7 is marginal. The amount of Zn^2＋ release by samples updating the leachant is greater than that of the samples that have no updating leachant. The sample with M/P of 6∶1 is better than that of 3∶1 in the curing effect. The diffusion coefficient（De） of Zn is back-calculated by conducting theoretical analysis of the relationship between the leaching time and the leached mass ratio. The De at leachant pH of 2 is larger than that at leachant pH of 4 and 7. It is found that the values of De of Zn at leachant pH of 4 and 7 are very close. According to the above data, it can be known that the types of cement and pH values of acid rain have significant influence on the leaching properties of MPC-solidified zinc-contaminated soil under acid rain environment.