The Group 12 elements mainly occur in sulfide ores, however, as with their Group 2 analogs, carbonate are known, but not as economically viable. The major zinc containing ore is zinc blende (also known as sphalerite), which is zinc sulfide (ZnS). Other important ores include, wurtzite (ZnS), smithsonite (zinc carbonate, ZnCO₃), and hemimorphite (calamine, Zn₂SiO₄). The basic form of zinc carbonate (hydrozincite, Zn₅(CO₃)₂(OH)₆) is also mined where economically viable. The main source of cadmium is as an impurity in zinc blende; however, there are several other ores known, e.g., cadmoselite (cadmium selenide, CdSe) and otavite (CdCO₃). Mercury sulfide (cinnabar, HgS) is the major source of mercury, and in fact metallic liquid mercury droplets are often found in the ore. The terrestrial abundance of the Group 12 elements is given in Table 2.

The naturally abundant isotopes of the Group 12 metals are listed in Table 3.

Many radioisotopes of zinc have been characterized. Zinc-65 that has a half-life of 244 days, is the most long-lived isotope, followed by ⁷²Zn with a half-life of 46.5 hours. The most common decay mode of an isotope of zinc with a mass number lower than 64 is electron capture, producing an isotope of copper, Equation 1.

(1)

The most common decay mode of an isotope of zinc with mass number higher than 64 is beta decay (β–), which produces an isotope of gallium, Equation 2.

(2)

Naturally occurring cadmium is composed of 8 isotopes. For two of them, natural radioactivity was observed, and three others are predicted to be radioactive but their decay is not observed, due to extremely long half-life times. The two natural radioactive isotopes are ¹¹³Cd (half-life = 7.7 x 10¹⁵ years) and ¹¹⁶Cd (half-life = 2.9 x 10¹⁹ years).

There are seven stable isotopes of mercury with the longest-lived radioisotopes being ¹⁹⁴Hg (half-life = 444 years) and ²⁰³Hg (half-life = 47 days). ¹⁹⁹Hg and ²⁰¹Hg are the most often studied NMR-active nuclei, having spins of ¹/₂ and ³/₂ respectively.

A summary of the physical properties of the Group 12 metals is given in Table 4. Because of the ns electron in the Group 12 metals are tightly bound, and hence relatively unavailable for metallic bonding, the metals are volatile with low boiling points, as compared to the Group 2 metals.

The most notable anomaly in the Group 12 metals is the low melting point of mercury compared to zinc and cadmium. In order to completely understand the reasons for mercury’s low melting point quantum physics is required; however, the key point is that mercury has a unique electronic configuration, i.e., [Xe] 5d 6s. The stability of the 6s shell is due to the presence of a filled 4f shell, because an f shell poorly screens the nuclear charge that increases the attractive coulomb interaction of the 6s shell and the nucleus. Such a configuration strongly resists removal of an electron and as such mercury behaves similarly to noble gas elements, which form weakly bonded and thus easily melting solids (Figure 3).

Figure 3: Liquid mercury.

The vast majority (95%) of zinc is mined from of the zinc sulfide ores. The zinc is most often mixed with copper, lead, and iron. Zinc metal is produced by extraction, in which the ore is ground and then the minerals are separated from the gangue (commercially worthless mineral matter) by froth flotation (a process for selectively separating hydrophobic materials from hydrophilic). Roasting converts the zinc sulfide concentrate produced to zinc oxide, Equation 3. Reduction of the zinc oxide with carbon, Equation 4, or carbon monoxide, Equation 5, at 950 °C into the metal is followed by distillation of the metal. Since cadmium is a common impurity in zinc ores, it is most often isolated during the production of zinc. Cadmium is isolated from the zinc metal by vacuum distillation if the zinc is smelted, or cadmium sulfate is precipitated out of the electrolysis solution.

(3)

(4)

(5)

Mercury is extracted by heating cinnabar (HgS) in a current of air, Equation 6, and condensing the vapor.

(6)