The adsorption of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) on Al(2)O(3) powder has been studied as a function of pH and concentration. The adsorption density of PBTCA is found to decrease with an increase of pH. Zeta potential measurements show that the addition of PBTCA results in a dramatic increase in the absolute zeta potential, as well as a shift of the isoelectric point to the more acidic region. PBTCA considerably enhances the stability of the alumina suspension via an electrostatic mechanism. The surface properties of alumina suspensions are examined by using Auger electron microscopy and FTIR analysis. Chemical interactions take place at the solid/water interface by forming complexes between Al(3+) ions and PBTCA. The dispersing ability of PBTCA is believed to be related to its high adsorption ability and the high number of dissociable protons. The morphology of the sediments is observed with scanning electron microscopy. It is found that the sediment surfaces exhibit fractal characteristics. The fractal dimension values of sediments are correlated with PBTCA concentration in the experimental range. Copyright 2000 Academic Press.