ZETA POTENTIAL OF APATITE IN AQUEOUS SOLUTIONS AND ITS CHANGE DURING EQUILIBRATION

Streaming potential experiments showed that the isoelectric point of apatite, in aqueous solutions, is initially at pH 4 and shifts towards a final value of pH 6 with time. Measurements of solution pH changes gave a value of 7 for the point of zero charge of apatite. Hydrogen, hydroxyl, and phosphate species were found to have a major role as potential-determining species. Zeta potential changes due to the addition of calcium and fluoride also are significant. The major effect of calcium appears to be due to its specific adsorption characteristics. Mechanism of charge development at the apatite surface is discussed in terms of pH-dependent hydrolysis of the surface species. © 1968.