RETENTION OF CU(II) IONS BY AMORPHOUS AND APATITIC TRICALCIUM PHOSPHATES: AN UNDEMANDING ROUTE TO PRODUCE LIBETHENITE

Abstract

The retention of copper ions by amorphous and apatitic tricalcium phosphates was studied using X-ray photoelectron spectroscopy, X-ray diffraction, infrared spectroscopy, and induction-coupled plasma atomic emission spectroscopy. The experimental results of this study show that the amorphous tricalcium phosphate exposed for 48 hours to a 2.10-2 M copper ion solution with the initial molar ratio Cu(solution)/Ca(phosphate) = 1 retains 96% of the initial amount of copper. It also completely converts to copper hydroxyphosphate, the mineral known as libethenite. The research revealed that apatitic tricalcium phosphate subjected to a similar treatment removed only 38% of the initial amount of copper and was only partially transformed into libethenite. In this case, it turned out that by extending the exposure time of the phosphate or by increasing the initial molar ratio Cu(solution)/Ca(phosphate), the conversion of the apatitic phosphate becomes complete and leads to a retention capacity of 595 mg/g. X-ray photoelectron spectroscopy analysis of libethenite produced by the conversion of tricalcium phosphates confirms the chemical purity of this mineral. It reveals that the Cu2p core level exhibits a multiple structure that can be deconvoluted into five peaks at binding energies of 934.5 eV, 954.5 eV, 940.6 eV, 943.1, and 961.5 eV. The first two peaks were attributed to the Cu2p3/2 and Cu2p1/2 photoelectrons and are consistent with the divalent state of copper, while the other peaks, not all previously reported, were assigned to shake-up satellites arising from Cu+2 with d9 configuration in the ground state.