Modified silica for the extraction of cadmium(II), copper(II) and zinc(II) ions from their aqueous solutions

Increasing concentrations of heavy metal ions in aquatic systems have led to a search for very efficient matrices for their removal, Zirconium(IV) phosphate has been used for many years as a cation-exchanger and dispersion of this phosphate on a high surface area silica might be expected to improve the extraction properties of the material. Modified silica matrices (SiZrP) were prepared by refluxing high surface area silica with zirconium tetrachloride dissolved in ethanol, followed by stirring the dried product in an appropriate volume of 0.1 M H3PO4. The dried SiZrP samples thus obtained were used to extract Cd2+, Cu2+ and Zn2+ ions from their aqueous solutions under varying conditions. The most efficient SiZrP sample was obtained when ZrCl4, was allowed to react with the silica in a 1:1 ratio. High extraction of all the ions studied at an initial concentration of 150 ppm was achieved over the pH range 3.5-6.0, with the order of metal ion extraction being Cd2+ > Cu2+ > Zn2+.