THE ROLE OF ZETA-POTENTIAL IN THE COLLOID STABILITY OF CALCIUM-OXALATE DIHYDRATE DISPERSIONS

The electrophoretic behavior and colloid stability of dilute dispersions of calcium oxalate dihydrate (COD) in electrolyte solutions have been studied. The effects of pH and potential-determining ions (Ca2+ and C2O42-) on electrophoretic mobility of COD dispersions have been calculated. The change in mobility on addition of four monovalent anions was investigated. The addition of divalent cations caused an increase in mobility, which suggests that Co2+, Ba2+ and Mg2+ display an inhibitory effect on aggregation of COD particles. A divalent anion such as HPO42- induces a large decrease in mobility, which is confirmed by the very negative specific adsorption potential, phi(j), of that anion. This tendency is more pronounced with the addition of pyrophosphate anion. The colloid stability of a COD sol has been studied using the semiempirical relationship provided by Eilers and Korff. This EK index shows that the cobalt ion at relatively high concentration and the dibasic phosphate anion at low concentration can be used as an inhibitor of COD agglomeration.