This study investigated changes in the chemical properties of carbonated waste cement, including the phase transformation, gel polymerization, and specific surface area, as well as cation exchange capacity (CEC) and the adsorption ability of heavy metal ions (Cr⁶⁺ and Cu²⁺). Highly crystalline calcite and highly polymerized silica gel with a three-dimensional network were found to form in carbonated waste cement. The specific surface area and the CEC of waste cement increased with an increase in the carbonation percentage. In addition was a linear relationship between the specific surface area and the carbonation percentage of the waste cement. When the carbonation percentage of waste cement was 35%, the CEC of the carbonated waste cement reached approximately 22 meq/100 g (The unit of [meq/100 g] is milliequivalent per 100 gram. The unit indicates the concentrations of electrolytes.). The increase of the CEC confirmed that carbonated waste cement could adsorb heavy metals.