重金属作用下改性水泥系隔离墙化学相容性研究

Study on chemical compatibility of amended cement-soil vertical cutoff wall permeated with heavy metal solutions

水泥系隔离墙被广泛应用于工业污染场地修复工程,但其防渗性能有待改善,且在高浓度、毒理性重金属污染作用下的化学相容性有待研究。通过室内试验研究了不同粒化高炉矿渣(GGBS)掺量、膨润土掺量和固化剂总掺量对水泥系隔离墙的强度和渗透特性的影响;综合考虑成墙效果和成本,选出固化剂掺量为20%(水泥、粒化高炉矿渣和膨润土掺量分别为8%、8%和4%)作为改性水泥系竖向隔离墙的最优配比。通过柔性壁渗透试验研究了重金属锌、铅污染作用下改性水泥系隔离墙试样的化学相容性。结果表明,重金属溶液作用下试样防渗性能的下降由重金属种类、重金属浓度以及试样孔隙液pH值三者共同决定。重金属种类对防渗性能的不利影响为:硝酸锌-硝酸铅>硝酸锌>硝酸铅。锌、铅溶液作用下试样的渗透系数为自来水作用下渗透系数的1.49~10.10倍,且重金属溶液的浓度越高渗透系数越大。在满足防渗要求前提下,该配比墙体材料能阻挡50 mmol/L的硝酸锌污染液、100 mmol/L的硝酸铅污染液和10 mmol/L硝酸锌-硝酸铅污染液。

Cement-soil vertical cutoff wall is extensively applied to the remediation of industrial contaminated sites,but its impermeability needs to be improved and also the chemical compatibility under the effect of high concentration and toxic heavy metal contamination needs to be studied.Through laboratory tests,physical,strength and permeability properties of different cement-soil vertical cutoff wall samples based on different mixing ratios of GGBS(ground granulated blast furnace slag),bentonite,and curing agent were studied.Considering the quality of the vertical cutoff wall and economic cost,the curing agent dosage of 20%(the mixing ratios of PC,GGBS and bentonite are 8%,8%and 4%,respectively)was validated as the optimal ratio for the amended cement-soil vertical cutoff wall.The chemical compatibility of cement-soil vertical cutoff wall materials under the effects of heavy metal zinc and lead pollution,in terms of hydraulic conductivity,is examined by a flexible-wall permeability test.The result shows that the decrease in the impermeability of the cement-soil vertical cutoff wall under the action of heavy metal solutions is jointly dominated by three factors,i.e.,heavy metal species,the concentration of heavy metal,and the p H of pore solution.The adverse effect of the type of heavy metals on the impermeability of the samples is in this order:zinc nitrate-lead nitrate solution>zinc nitrate solution>lead nitrate solution.The hydraulic conductivities of the samples permeated with different heavy metal solutions are between 1.49 and 10.10 times that of sample permeated with tap water and increase with the increase of concentration of the heavy metal solution.Under the premise of meeting the requirement of hydraulic conductivity,the amended cement-soil vertical cutoff wall could barrier 50 mmol/L of zinc nitrate solution,100 mmol/L of lead nitrate solution and 10 mmol/L of zinc nitrate-lead nitrate solution.