Point of zero charge and isoelectric point of alumina

The point of zero charge, pHpzc, and the isoelectric point, pHiep, of a commercial alumina sample was investigated in KNO3 solutions. The influence of the concentration and the initial pH value of KNO3 solution used for preparation and equilibration of the alumina suspension, as well as of the alumina/solution ratio on pHpzc and pHiep were investigated. The obtained results indicate that pHiep values are dependent on initial pH values of KNO3 solutions used for equilibration of alumina suspensions. Simultaneously with isoelectric point determination, the particle size of alumina was also measured. It was shown that the particle size of alumina increases with increasing suspension pH due to agglomeration, reaching the maximum value at pHiep.