Development and application of carbon nanotubes reinforced hydroxyapatite composite in separation of Co(II) and Eu(III) ions from aqueous solutions

Multi-walled carbon nanotubes/strontium hydroxyapatite (MWCNT/SH) composite was synthesized, where CNTs were applied to improve the properties of HAP and increase the reinforcement of the composite. The composite CNTs/Sr-HAP and its precursor Sr-HAP were successfully applied in removal of Co(II) and Eu(III) ions from aqueous solutions. Sorption of Co(II) and Eu(III) onto the synthesized sorbents was investigated as a function of contact time and pH. The synthesized sorbents highly removed the studied radionuclides from their aqueous solutions with necessary time of 6 h to reach equilibrium. The maximum sorption capacity was 33.31 and 48.93 mg g^-1 for Co(II) sorption onto Sr-HAP and CNTs/Sr-HAP composite at pH 4.5, while it was 115.74 and 127.11 mg g^-1 for sorption of Eu(III) onto Sr-HAP and CNTs/Sr-HAP composite 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 FeCl₃ and HCl solutions. Co(II) was completely separated from Eu(III) by a ratio of 85.1 % using Cd(NO₃)₂ as an eluent in CNTs/Sr-HAP composite packed column.