Laboratory studies on the removal of phosphates from sewage by the coagulation process (Part 2)

Summary

This paper preeents a comparison of the capacities of Al⁺³, Fe⁺³, Ca⁺² and Mg⁺² to remove phosphates from solution. The results indicate that in pure orthophosphate solutions, calcium, aluminium, and iron (III) are the most efficient coagulants. In sewage, however, calcium is the poorest removing agent. Consideration of the reaction mechanisms involved in the process of phosphate removal leads us to propose precipitation and complex formation mechanisms using di- and trivalent cations respectively. Adsorption of phosphates on the hydroxide floc of the coagulants is believed to play a minor part in the process.