Novel substituted Hydroxyapatite nanoparticles as a solid phase for removal of Co(II) and Eu(III) ions from aqueous solutions

Abstract Ionic substitution is a tool to improve the sorptive properties of hydroxyapatite (HAP). Based on this concept, strontium and magnesium/cadmium substituted HAP nanoparticles were synthesized, by a co-precipitation method, and applied in removal of Co(II) and Eu(III) ions from aqueous solutions. The influence of different sorption parameters such as equilibration time and solution pH on sorbed amount of Co(II) and Eu(III) was studied and discussed. The sorption process followed the pseudo-second-order kinetic with necessary time of 24 h to reach equilibrium. The maximum sorption capacity of Co(II) was 33.31 mg g −1 for Sr-HAP at pH 4.5 and 28.93 mg g −1 for (Mg-Cd)HAP at pH 1.1, while it was 115.74 and 137.31 mg g −1 for sorption of Eu(III) onto Sr-HAP and (Mg-Cd)HAP at pH 2.5, respectively. Desorption of Co(II) and Eu(III) from loaded samples was studied using various eluents and maximum recovery was obtained using FeCl 3 and HCl solutions.