Removal of Cadmium from Dilute Solutions by Hydroxyapatite. III. Flocculation Studies

Abstract

Synthetic hydroxyapatite in a fine particulate dispersion has been used previously for the removal of Cd²⁺ cations from dilute aqueous solutions. In the present work the flocculation of these hydroxyapatite particulates was examined with and without the presence of Cd²⁺ ions by applying the conventional inorganic flocculents ferric chloride and aluminum sulfate. An optical technique was applied in order to monitor the flocculation dynamics of the dispersed particles, complemented by electrophoretic and turbidity measurements. The relative size of aggregates formed during flocculation, expressed as a “flocculation index,” could be continuously measured by this technique. Results indicated that the flocculation index provided important information about flocculation mechanisms. The main parameters examined included flocculent dose, solution pH, and mixing intensity. The optimum conditions for efficient flocculation were determined.

Key Words:

• Hydroxyapatite sorbent
• Cadmium
• Flocculation
• Zeta potential