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.