Geochemistry of cadmium

Abstract

Cadmium, a transition metal, is a member of Group IIB of the periodic table, which also includes zinc and mercury. Pure cadmium is a bluish-white metal but does not occur as such in nature. It was first discovered in 1817 by a German chemist, F. Stromeyer, as a constituent of the zinc ore smithsonite (ZnCO3). Cadmium is mainly found in zinc, lead-zinc and lead-copper-zinc ores, and its concentration is usually related to their zinc content. It is also found in varying amounts as a natural component of the surface environment in rocks, overburden and soils, water, air, plant and animal tissues. Its geochemical behavior is similar to that of zinc because of the similar electron structures and ionization potentials of the two elements. In nature cadmium is nearly always present in the Cd2+ oxidation state and occurs as eight stable isotopes as shown in table 1. 112Cd and 114Cd are the most common. Radioactive isotopes with mass numbers 104, 105, 107, 109, 111, 113, 115, 117, 118 and 119 have been made artificially, of which 113 Cd has the longest half-life of 5.1 years27.