A 2(4-1) fractional factorial design is employed to study Cu(II) desorption on organofunctionalized silicas. Two types of silicas, at amounts of 100 and 200 mg and two acidic levels, and contact times were employed. Our study indicates that the effects of HCl and contact time on the percentage number of moles of copper are 13.23 and 18.53, respectively. However, the binary interaction of these factors is very small. Three important antagonistic and synergistic binary effects involving the silica type, acidic quantity, and contact time factors are found. The silica mass showed an insignificant principal effect. The desorption data are compared with those previously published concerning adsorption processes on both functionalized silicas. (C) 2000 Academic Press.22716670