Stability of alumina suspensions in the presence of Tiron

The stability of alumina suspensions in the presence of Tiron was studied and discussed in the light of surface properties of alumina powder used, ionization chemistry of Tiron, and sedimentation behavior of the suspensions. The point of zero charge of alumina with and without addition of Tiron was determined using a batch equilibration method. The sedimentation of the suspensions was evaluated via screen sedimentation tests as a function of pH and Tiron concentration. The dissociation constant, pKa1, of the hydroxyl groups of the Tiron molecule was determined by potentiometric titration carried out in water and KNO3 as a background electrolyte. Tiron was shown to adsorb specifically onto the alumina surface in the examined pH range 4-10, but impart stability to the suspensions only at pH ≥ 6.