Adsorption properties of metallic ions not essential for human metabolism, such as cadmium, lead, and mercury, on silica chemically modified with zirconium(IV) phosphate, SiZrP, were investigated using batch systems. The immobilization procedure was efficient and the functionalization degree was 2.82% for zirconium (0.31 mol g(-1)) and 2.54% for PO43-(0.27 mol g(-1)). These results indicate that phosphate reacted with zirconium in a 1:1 ratio. The equilibrium is reached very quickly( 15 min), indicating that the adsortion sites are well exposed, The best adsorption parameters were evaluated using 50 mL of aqueous phase at pH 4.5, an adsorption time of 15 min, and 0.2000 g of adsorbent. From adsorption isotherms obtained for the metals ions and distribution coefficients the affinity of SiZrP for the metal ions studied increases in the order Cd(II) < Pb(II) < Hg(II). Twice as much lead was adsorbed by the SiZrP surface (Nf = 10.0 mu mol g(-1))as cadmium (Nf = 5.0 mu mol g(-1)). For mercury, the capacity was greater; nevertheless an adsorption plateau was not observed. (C) 1998 Academic Press.