The effects of pressure, temperature, time, and ligand to metal ratio (50:1–200:1) on the extraction efficiency of metal ions with 4,4′-dimethyl-2,2′-bipyridyl (DMBP) as a chelating ligand were systematically investigated in supercritical carbon dioxide (sc-CO2). Eight metal ions (Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+) were tested, respectively, to be extracted from solid matrix into sc-CO2. The best extraction efficiency for Co2+ (83.68%) was obtained in the optimized condition (DMBP and perfluoro-1-octanesulfonic acid tetraethylammonium salt as a co-ligand used, 25 MPa, 323 K, 20 min, ligand to metal ratio of 200). Extraction from mixed metal ions with DMBP was also achieved and the results showed that selectivity for Co2+ ion was notable (98.17%) in the above-mentioned conditions. Finally, the detailed calculation results exhibited that the extraction constants (Kex) of the metal ions increased with the increase of the extraction efficiency in the same extraction system.