Removal of phosphate by adsorption onto oyster shell powder—kinetic studies

Kinetic studies on the removal of phosphate by adsorption onto oyster shell powder have been investigated at 24 °C. The results showed that the equilibrium occurred in 10 min and the equilibrium data followed the Freundlich isotherm. Freundlich constants were found to be kf, 1.4 × 10−2, and n, 0.71. The phosphate removal was not influenced by pH over the range 5.0–10.5. Continuous agitation studies at 24 °C and 530 rpm reached equilibrium after 7.7 days, when 24 g dm−3 of oyster shell powder reduced the phosphate concentration from 50 to 7.0 mg dm−3. The Lagergren rate constant for the slow adsorption process was observed to be 3.81 × 10−4 dm3 min−1. Comparison with calcium carbonate, GR grade, showed that oyster shell powder and CaCO3 behave more or less in the same way.