水泥固化铅污染土的碳化机理及碳化度评价

Carbonation mechanism and carbonation degree evaluation on cement-stabilized lead-contaminated clay

为了探究水泥固化处理重金属污染场地在碳化作用下的微观结构演变规律及碳化度表征指标,选取典型加速碳化7 d后的铅污染土试样进行分析.采用X射线衍射、电镜扫描和热重分析等测试方法,分析了碳化作用对矿物成分、铅的赋存形态、孔隙分布特征及孔隙溶液pH值的影响规律.结果表明:固化重金属污染土中Pb主要以硅酸盐、氢氧化物等化学沉淀的形式被固定;碳化作用下水泥水化产物氢氧化钙和水化硅酸钙逐渐转化为摩尔体积更大的CaCO3和含硅凝胶,导致固化土总孔隙体积减小;固化污染土碳化度随试样深度的增大而减小,碳化部分的碳化度介于24%~28%之间,未碳化部分的碳化度介于0~3%之间;碳化度与孔隙溶液pH值成良好的线性关系.测量孔隙溶液pH值可间接评价水泥固化铅污染黏性土的碳化度.

To explore the microstructure evolution rule and the index of carbonation degree of heavy metal contaminated sites treated by cement solidification under the carbonation,the soil samples with lead contamination after typical accelerated carbonation for 7 d were selected for analysis.A series of X-ray diffraction,scanning electron microscopy and thermogravimetric were used to analyze the effects of carbonation on the mineral composition,the mineral forms of lead,the pore distribution density,and the pH value of pore solution.The results show that Pb in the solidified heavy metal contaminated soil is mainly fixed in the form of silicate,hydroxide and other chemical precipitation.Under the carbonization,the cement hydration products calcium hydroxide and hydrated calcium silicate are gradually converted into CaCO3 and silicon-containing gel with larger molar volume,resulting in a decrease in the total pore volume of the solidified soil.The carbonization degree of solidified contaminated soil decreases with the increase of the sample depth.The carbonization degree of the carbonized part is between 24%and 28%,and the carbonization degree of the uncarbonized part is between 0 and 3%.There is a linear relationship between the carbonation degree and the pH value of pore solution.The carbonation degree of cement solidified lead-contaminated clay can be indirectly evaluated by measuring the pH value of the pore solution.