An evaluation of hydroxyapatite-based filters for removal of heavy metal ions from aqueous solutions

Three hydroxyapatite(HA)-based materials have been investigated with respect to their potential for removing heavy metal ions from aqueous solutions. The materials have been evaluated as both loose powders and in the form of ceramic foams. The results have shown that all three grades of HA were found to be capable of removing a number of different ionic species although the more impure grades generally yielded the best performance. It is believed that the increased impurity levels resulted in increased numbers of lattice defects which were ideal adsorption/exchange sites. 100% removal could be achieved for some ions under the correct experimental conditions. For the ceramic foam filters, the optimum filtration parameters were found to be a high surface area, long filtration times, a low pH and a high filtrate temperature. Ion adsorption was positively detected as a mechanism of ion removal. Ion exchange was not observed but could not be completely ruled out.