Effects of Some Multivalent Ions on Coagulation and Electrokinetic Behaviours of Colemanite Particles

Abstract

The effects of magnesium, barium, aluminium, and ferric cations as multivalent ions on the coagulation and electrokinetic behaviours of colemanite have been investigated in relation to pH and cation concentration. The zero point of charge for colemanite was determined to be at pH 10.2. The positive surface charge of colemanite increased in the presence of multivalent ions at pH values below the zero point of charge. Also, these ions changed the zeta potential of colemanite from negative to positive within the pH range 10.2 to 12. In the experiments, the coagulation of colemanite with ferric ions was more efficient than with the other ions and the effect of ferric ions varied considerably depending on the concentration and pH. The coagulation recovery values of colemanite suspension increased quickly up to 2.5 × 10–3 M concentration of ferric ions and the maximum value (~93 %) was obtained at a pH of 11.5. It was also found that the coagulation behaviour of the colemanite suspension in the presence of multivalent cations was in good agreement with the electrokinetic characteristics.