Comparative study on the stabilizing effect of 2-phosphonobutane-1,2,4-tricarboxylic acid and citric acid for alumina suspensions

The influences of two multivalent anionic electrolytes: citric acid and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) on the properties of alumina aqueous suspensions were investigated in this paper. The adsorption amount was determined as a function of the pH and the dispersant concentration via UV-vis method based on the decolorization reaction of ferric 5-nitrosalicylate complex. The suspension stability was characterized by measuring ζ potential, sedimentation height and the viscosity. The optimal concentration for PBTCA and citric acid was ≈1.0 and 0.6 wt%, respectively. The dispersing ability of PBTCA was found to be higher than that of citric acid. This phenomenon was interpreted by comparing the dissociation and adsorption characteristics of the two dispersants. The high affinity of PBTCA for Al3+ promotes a ligand exchange process at the alumina surface and enables a high adsorption of PBTCA on alumina under alkaline conditions. The effect of milling on the deagglomeration of the powders, with the addition of PBTCA, was characterized by measuring the effective particle size of the suspension and the specific surface area of the freeze-dried sediments.