ABSTRACT

The trace elements of group 4 are titanium (Ti), zirconium (Zr), and hafnium (Hf ). Ti is associated with silicate minerals and considered a trace element only because of its low concentrations in plant and animal tissues. The next two metals, Zr and Hf, are widely distributed in both the litho-and biosphere and are often included in the REE group. The geochemical properties and terrestrial abundance of these elements as well as the physical and chemical properties differ (Table 9.1). Their common characteristics are the weak solubility of their hydroxides and oxides in water, an af nity to bond with oxygen.