CaO对钙矾石固化/稳定化重金属铅污染土的影响

为研究CaO的赋存形态及含量对钙矾石固化/稳定化重金属铅污染土效果的影响，采用高铝水泥提供AlO2-，纯石膏或磷石膏提供SO42-，高铝水泥、石膏、普通硅酸盐水泥或生石灰提供CaO，制备不同组分固化剂配比的固化土，测试试样强度和孔隙溶液pH值等宏观物理力学指标，通过醋酸缓冲溶液法测试试样的铅溶出量，对比分析不同固化剂固化土的矿物成分与微观结构特征。结果表明，钙矾石固化/稳定化重金属铅污染土效果显著；钙矾石对孔隙的填充作用带来的增强效果不能代替水化硅酸钙胶结土颗粒的胶结作用，普通硅酸盐水泥对试样的强度更有利，但其后期强度增幅不大，而生石灰有利于固化土强度的持续增长；生石灰较普通硅酸盐水泥对钙矾石的形成、稳定和重金属Pb2+的固化/稳定化更有利；磷石膏和纯石膏对试样的pH值、无侧限抗压强度及钙矾石固化/稳定化重金属Pb2+的效果影响较小；固化土体微观结构特征表明，CaO含量对钙矾石生成形态及作用效果影响显著。当CaO含量较低时，早期生成的钙矾石将向单硫型硫铝酸钙转化。研究成果可丰富重金属污染场地原位处理技术，具有重要的理论意义和工程应用价值。

Effect of CaO on ettringite stabilization/solidification of lead-contaminated soil

In order to investigate the effect of CaO in different modes of occurrence and content on ettringite stabilization/solidification of lead-contaminated soil, artificial contaminated soils were solidified using high-alumina cement for AlO2- and gypsum and phosphogypsum for SO42-. All of the additives used include Portland cement or lime, which provide CaO. The pH value, strength of solidified samples and leaching concentration were investigated to understand the influence of different binders on physical-mechanical and leaching properties of ettringite-solidified soils with contamination. The micro-structural characteristics of solidified soils with contamination were also explored. The results show that the ettringite is able to stabilize/solidify heavy metal-contaminated soil. The cementation of calcium silicate hydrate cementing soil particles cannot be replaced by the filling effect of ettringite. Lime with higher CaO content is more beneficial not only due to the formation and stability of ettringite, but also due to the effect of stabilization/solidification of Pb2+-contaminated soil. Solidified samples with cement-contaminated curing agent have higher unconfined compressive strength but slow strength growth in later stage. Gypsum and phosphogypsum have little impact on pH value, unconfined compressive strength and the solidification result of solidified samples. The results of SEM test from microstructure features also indicate that the content of CaO affects the shape and effectiveness of ettringite. Ettringite can be transformed into calcium sulphoaluminate in case of insufficient CaO content. This research advances the on-site treatment technology of heavy metal contaminated sites, and is important in theoretical research and engineering application for remediation of heavy metal contaminated sites.