【作者】 王海荣；

【导师】 朱志铎；

【作者基本信息】 东南大学 ， 岩土工程， 2021， 硕士

【摘要】 重金属污染场地严重威胁生态环境、人体健康和食品安全,固化/稳定化技术被广泛应用于修复重金属污染场地,水泥是固化污染土中常用的固化剂,但水泥高耗能、环境不友好的弊端使得寻找能够替代水泥的固化剂成为近些年环境岩土工程领域的研究热点,而地聚合物作为一种绿色环保的胶凝材料,因具有高强度和优良的固定重金属能力受到人们的广泛关注。因此本文以铅镉污染土为研究对象,通过室内试验和微观分析,确定了碱激发粉煤灰+高炉矿渣（FA+GGBS）基地聚合物固化剂的组成及制备,研究了地聚合物和水泥对铅镉污染土的固化效果,探讨了冻融循环对固化污染土性能的影响,分析了地聚合物固化污染土的微观特征,取得的主要成果如下:（1）通过无侧限抗压强度、毒性浸出、固化污染土p H试验,查明了液固比、GGBS掺量对固化污染土强度、Cd²⁺浸出毒性和p H的影响规律,优化了地聚合物固化剂的原材料组成。地聚合物固化剂中的液固比对固化污染土强度和Cd²⁺浸出浓度的影响显著,GGBS掺量的影响略小。随液固比增加,固化污染土强度先剧烈下降后保持稳定,Cd²⁺的浸出浓度先下降后上升,并在液固比为0.3时达到最低值。以Cd²⁺的浸出浓度为筛选标准,得到的固化剂材料组成及制备方法为:FA与GGBS的质量比为7:3,液固比为0.3,碱激发剂由Na OH调节硅酸钠溶液模数至1.5制备。（2）通过无侧限抗压强度、毒性浸出、固化污染土p H、浸出液p H及电导率、p H-dependent试验,评价了地聚合物固化高浓度铅镉污染土的效果,研究了浸提液p H对Pb²⁺、Cd²⁺浸出浓度的影响规律。掺加地聚合物固化剂后,固化污染土的强度约是未固化污染土的1.35～1.50倍,Pb²⁺、Cd²⁺的浸出浓度明显下降。同等固化剂掺量下,水泥固化污染土的无侧限抗压强度是地聚合物的2～2.5倍,且Pb²⁺、Cd²⁺的浸出浓度更低,但水泥固化污染土的p H更高,容易造成碱污染。当浸提液p H小于4时,固化污染土中Pb²⁺、Cd²⁺的浸出浓度随p H的增加而增加,当p H在4～10之间,Pb²⁺、Cd²⁺的浸出浓度变化不明显,当p H大于10时,Pb²⁺的浸出浓度剧烈上升,Cd²⁺的浸出浓度先下降后轻微上升。（3）通过冻融循环试验研究了冻融条件下地聚合物固化污染土质量损失率、无侧限抗压强度、应力应变曲线和重金属浸出浓度的变化。随冻融循环次数增加,固化污染土的质量损失率曲线经过了缓慢增长阶段、快速上升阶段和平稳变化阶段。与未冻融试样相比,地聚合物固化污染土的强度在冻融结束后下降了19%～32%,变形模量E₅₀降低了8%～10%,Pb²⁺、Cd²⁺的浸出浓度明显增加。（4）通过微观试验研究了铅镉对地聚合物微观形貌与结构、矿物成分的影响,定量分析了固化污染土中的孔隙分布情况。碱激发FA与GGBS的产物是C（N）-A-S-H凝胶,地聚合物对镉的固定机理主要是形成Cd（OH）₂,铅可取代C（N）-A-S-H凝胶中的钙被固定在地聚合物中。Pb²⁺、Cd²⁺的加入会降低体系的碱度,使凝胶的生成量减少、地聚合物的微观结构变得疏松。提高液固比增加了固化污染土中1～10μm以及大于10μm的大孔隙体积,而随FA+GGBS掺量增加,0.01～1μm的团聚体间孔隙体积减小。更多还原

【Abstract】 Cement is a common binder for remediation of lead and cadmium contaminated sites.However,due to its high energy consumption and unfriendly environment,it has become a research hotspot in the field of environmental geotechnical engineering to find a substitute for cement.Geopolymer,as a kind of green and environment-friendly cementitious material,has attracted wide attention because of its high strength and strong ability to solidify heavy metals.Therefore,in this paper,the artificially prepared high concentration lead and cadmium contaminated soil is taken as the research object.Based on laboratory test and micro analysis,the optimal ratio of fly ash+ground granulated blast-furnace slag（FA+GGBS）based geopolymer was determined,the solidification effect of geopolymer and cement on lead and cadmium contaminated soil was compared,and the influence of freeze-thaw cycle on the properties of solidified contaminated soil was discussed.The main results are as follows:（1）The effects of liquid-solid ratio and GGBS content on the strength,leached Cd²⁺concentration and p H of solidified contaminated soil were investigated,and the raw material composition of geopolymer was optimized.The influence of liquid-solid ratio on the strength and the leached Cd²⁺concentration was significant,while the influence of GGBS content was slight.With the increase of liquid-solid ratio,the strength of solidified contaminated soil decreased sharply at first and then remained stable.The leached Cd²⁺concentration decreased first and then increased,and reached the lowest value when the liquid-solid ratio was 0.3.Taking the leached Cd²⁺concentration as the screening standard,the optimal ratio of geopolymer was that the mass ratio of FA and GGBS was 7:3,and the liquid-solid ratio was0.3.（2）The effect of geopolymer on solidification of lead and cadmium contaminated soil was evaluated,and the effect of leachate p H on leached Pb²⁺and Cd²⁺concentration was studied.The strength of solidified contaminated soil was about 1.35～1.50 times of that of untreated contaminated soil.And the leached concentration of Pb²⁺and Cd²⁺decreased significantly.Under the same dosage of binder,the unconfined compressive strength of cement solidified contaminated soil was 2～2.5 times of geopolymer.The leached Pb²⁺and Cd²⁺concentration was lower,but the p H of cement solidified contaminated soil was higher,which was easy to cause alkaline pollution.When the p H of leaching solution was less than 4,the leached Pb²⁺and Cd²⁺concentration increased with the increase of p H.When the p H was between 4 and 10,the leached Pb²⁺and Cd²⁺concentration did not change significantly.However,when the p H was greater than 10,the leached Pb²⁺concentration increased sharply,while the leached Cd²⁺concentration first decreased and then increased slightly.（3）The mass loss rate,unconfined compressive strength,stress-strain curve and leached heavy metal concentration of geopolymer solidified contaminated soil under freeze-thaw cycles were studied.With the increase of freeze-thaw cycles,the mass loss rate curve went through slow growth stage,rapid rise stage and stable change stage.Compared with the samples without freeze-thaw cycle,the strength of geopolymer solidified contaminated soil decreased by 19%～32%after freeze-thaw cycle.The deformation modulus E₅₀ decreased by8%～10%.And the leached Pb²⁺and Cd²⁺concentration increased significantly.（4）The effects of lead and cadmium on the morphology,structure and mineral composition of geopolymer were studied by microscopic experiments,and the change of pore structure in solidified contaminated soil was quantitatively analyzed.The product of alkali activated FA and GGBS was C（N）-A-S-H gel.The main mechanism of Cd²⁺immobilization by geopolymer was the formation of Cd（OH）₂.Pb²⁺could be solidified in geopolymer by replacing Ca of C（N）-A-S-H gel.The addition of Pb²⁺and Cd²⁺would reduce the alkalinity of the system and reduce the gel production,making the microstructure of geopolymer looser.The increase of liquid-solid ratio mainly increased the volume of pores between1-10μm and more than 10μm.With the increase of FA+GGBS content,the volume of pores between0.01～1μm increased.更多还原