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

Three hydroxyapatite (HA)-based materials were investigated with respect to their potential for removing heavy metal ions from aqueous solutions. The materials were evaluated as both loose powders and as ceramic foams. Initial experiments assessed which ions could be removed. A matrix of experiments was then performed to evaluate the influence of various filter and filtrate characteristics on filter effectiveness. Selectivity measurements and regeneration trials were also carried out. The ion-removal mechanism was determined by examining the heavy metal ion uptake to Ca2+ ion release rate and by characterising the filters before and after use by EDX, XRD and zeta potential measurements. Results showed that all three grades of HA were capable of removing a number of different ionic species although the more impure grades generally yielded the best performance. Ion adsorption was positively detected as a mechanism of ion removal. Ion exchange was not observed but could not be completely ruled out. 27 refs.