六价铬污染模拟含水层的注入型黄原胶凝胶阻截屏障试验研究

Experimental research on the injectable xanthan gum gel intercepting barrier of simulated Cr(Ⅵ) contaminated aquifer

由于工业废物的不合理排放,大量的重金属污染物Cr(Ⅵ)进入地下环境,严重威胁着人类健康和生态环境。Cr(Ⅵ)在地下水环境中高度易迁移的特性,造成其污染修复上的困难,亟待一种绿色、经济、有效的阻截方式提高地下水对Cr(Ⅵ)的阻控能力。研究利用焦亚硫酸钠原位还原地下水中的Cr(Ⅵ),产生Cr^(3+)作为黄原胶交联剂,形成凝胶阻截屏障,探究了各类成分对凝胶时间、黏度变化的影响及凝胶屏障对含水层的阻截效果,得到如下结论:(1)在Cr(Ⅵ)质量浓度达到200 mg/L的体系中,质量分数0.4%的黄原胶溶液在1.5 h内即可形成具有一定机械强度的凝胶;(2)凝胶具有耐盐性,适用于常见含水层,2.5~5 g/L的Na+和K+对凝胶起促进作用;(3)注入型凝胶阻截屏障能够大幅降低中砂介质的渗透系数至1×10^(-7)cm/s,满足地下水阻截需求。注入型凝胶屏障的形成无需引入有害物质,阻截结束后注入型屏障可经生物作用自然降解,不会长期改变含水层水力条件。研究成果可为Cr(Ⅵ)污染地下水中凝胶阻截屏障的构筑提供理论基础。

Due to the unreasonable discharge of industrial waste, a large amount of heavy metal pollutant Cr(Ⅵ)enters the underground environment, which seriously threatens human health and ecological environment. The high mobility of Cr(Ⅵ) in groundwater environment makes it difficult to repair. A green, economic and effective interception method is urgently needed to improve the ability of groundwater Cr(Ⅵ) pollution control. In this paper, sodium metabisulfite is selected as a reducing agent, and Cr^(3+)generated from Cr(Ⅵ) in groundwater is used as an xanthan gum crosslinking agent to form a gel blocking barrier. The influences of various components on gel time and viscosity changes and the blocking effect of gel barrier on aquifer are studied. The results indicate that(1) in the system with Cr(Ⅵ) concentration up to 200 mg/L, xanthan gum solution with 0.4% mass concentration can form gel with certain mechanical strength within 1.5 h.(2) The gel has salt resistance and is suitable for common aquifers. Na+and K+of 2.5-5 g/L can promote the gel.(3) The injected gel blocking barrier can significantly reduce the coefficient of permeability of medium sand media to 1×10^(-7)cm/s, which can meet the demand of groundwater blocking. Injection-type gel barriers are formed without the introduction of harmful substances. After the interception, injection-type gel barriers can be naturally degraded by biological action without long-term changes under the aquifer hydraulic conditions. This study provides a theoretical basis for the construction of gel barrier in chromium contaminated groundwater.