Abstract
When dissolved calcium salts are reacted in aqueous medium in the presence of phosphate anions, a gelatinous precipitate forms. Maturation of this precipitate eventually leads to the formation of hydroxyapatites (HA). HA is a stable solid with high specific surface area, and interesting adsorption properties. Thermal treatment at 800°C eliminates adsorbed organic matter and generates crystalline HA. Such HA can be recovered and reused by dissolution in acidic water. We have experimented with recycled HA the co-precipitation of textile dyes, and found that HA can be reused many times without loss of activity. However, in the case of blue dyes containing cupric ions, the metal ions remain in the solid phase following calcinations and the reactivity decreases slightly. In most cases, a very high level of dye removal was observed (above 98%), with little loss of recycled HA (12%). This makes the dye remediation process by HA co-precipitation economical and durable. Laboratory tests with a real industrial effluent showed a linear relationship between absorbance abatement and introduced calcium concentration, indicating the feasibility of the process.
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