Removal of Coexisting Pb²⁺, Cu²⁺ and Cd²⁺ Ions from Water by Addition of Hydroxyapatite Powder

Abstract

Removal of single, binary and ternary divalent heavy metal ions, i.e., Pb²⁺, Cu²⁺ and Cd²⁺, respectively, from their chloride or nitrate aqueous solutions was studied by the addition of hydroxyapatite in an agitated tank adsorber.
The isotherms for each single component were of the rectangular type, i.e., the amounts removed from aqueous phase were constant irrespective of the concentration of solutions. For binary and ternary systems, equilibrium relations were expressed in terms of selectivity coefficient.
Concentration decay curves were prepared from experimental data for comparison with theoretical calculations.
Regarding mass transfer, it was found that Pb²⁺ was collected on the apatite structure very fast, while the two other ions showed some resistances other than film diffusion resistance.
Furthermore, the apatite structure was studied by X-ray difractometry.