Simultaneous Removal Behavior of Phosphate and Fluoride Ions in the Presence of Scallop Shell

Abstract

Phosphate and fluoride ions were simultaneously removed from model industrial waste water, with the formation of fluorine-containing apatite. 70% of fluoride and 50% of phosphate ions were removed in the presence of calcium ion from calcium nitrate. Using scallop shell powder (calcite CaCO₃) instead of the calcium ion increased removal efficiency (%) of fluoride and phosphate ions to 92% and 97% at 48 h, respectively. This was ascribed to alkaline condition of pH higher than 8 due to the solution of CaCO₃, accelerating fluorine-containing apatite formation. With a mixture of calcium ion and scallop shell powder, high removal efficiency at the initial stage was obtained as opposed to the gradual increase with only scallop-shell, suggesting that an induction period of reaching sufficient concentration of calcium ion for apatite formation existed. These results showed that scallop shells were a promising material for simultaneous removal of phosphate and fluoride ions in waste water from e.g. electronic device plants.