Abstract: During the co-disposal of heavy metal-containing waste in cement kilns, the kiln environment contributes significantly to the solidification of heavy metal ions. Nevertheless, partial heavy metals can permeate cement matrices via clinker phases, posing a potential leaching risk of heavy metal ions during the service life of cement products. Carbonation can reduce the alkalinity of concrete materials, alter their phases and microstructures, and enhance the leaching risk of heavy metal ions. The clinker prepared from urban sludge co-disposal in a commercial cement plant contains manganese and chromium, whose contents approach or exceed regulatory thresholds. Accordingly, the carbonation resistance of cement concrete containing high heavy metal residues in cementitious systems is explored, and the effects of carbonation on the leaching characteristics of heavy metal ions in concrete are analyzed in this study. Furthermore, the environmental hazards induced by heavy metal leaching are systematically evaluated. The results indicate that the relatively high-content heavy metals exert a slight influence on the carbonation resistance of cement concrete, and the law of development of its carbonation depth over time is similar to that of ordinary concrete. Heavy metals such as Mn can be effectively solidified in cement concrete with low leaching susceptibility; by contrast, the solidification efficiencies of Cr and Cr6+ are relatively inferior. Carbonation increases the leaching amounts of Cr and Cr6+ in concrete. Although the Cr content in cement clinker complies with the production limit requirements, the long-term cumulative leaching amount of Cr6+ in cement products under carbonation may exceed the limits set by surface water quality standards.

Key words: co-processing in cement kiln, accelerated carbonation, concrete, heavy metal ion leaching, hexavalent chromium

摘要： 在水泥窑协同处置含重金属废弃物的生产过程中，窑内环境对重金属离子具有高效的固化作用，部分重金属经由熟料进入水泥，致使水泥制品使用过程中存在重金属离子浸出风险。碳化作用能降低混凝土材料的碱度、改变其物相和微结构，增加重金属离子的浸出风险。基于某水泥厂水泥窑协同处置城市污泥生产的熟料中含有锰、铬等元素超过或接近限值，本工作研究了水泥中重金属含量相对较高条件下混凝土的抗碳化性能及碳化作用对混凝土重金属离子浸出特性的影响，评价了重金属浸出量对环境安全的危害性。结果表明，较高重金属含量对水泥混凝土的抗碳化性能影响较小，其碳化深度随时间的发展规律类似于普通混凝土；Mn等重金属能被很好地固化于水泥混凝土内，不易浸出；而Cr元素及Cr6+的固化效果较差；碳化作用使混凝土碳化区域中Cr元素及Cr6+的浸出量增大；尽管水泥熟料内Cr含量符合生产限值要求，但碳化作用下水泥制品中Cr6+的长期累计浸出量可能超出地表水质量标准的限值。

关键词: 水泥窑协同处置, 加速碳化, 混凝土, 重金属离子浸出, 六价铬