Use of calcium phosphates to remove nickel, copper and cobalt ions from aqueous solutions

Abstract

This work concerns the use of amorphous tricalcium phosphate and apatitictricalcium phosphate to remove nickel, copper and cobalt ions from aqueous solutions. The amorphous or apatitic calcium phosphates were first exposed to separate solutions of Ni(II), Cu(II) or Co(II) salts for 48 hours at room temperature, then residual solids and solutions were separated and analysed. X-ray photoelectron spectroscopy, X-ray diffraction and infrared spectroscopy were applied to observe chemical and structure modifications in the solid phosphates whereas inductively coupled plasmaatomic emission spectrometry measurements were performed to evaluate the metal ions content changes in both solids and solutions. These analyses and measurements demonstrate the ability of amorphous and apatitic phosphates to remove metal ions from aqueous solutions. They assist in identifying the mechanisms involved in the metal ions transfer from solutions to solid phosphates and clarifying differences with respect to the widely studied hydroxyapatite system. Finally, they reveal, for copper and cobalt ions, the conversion of these phosphates to Cu 2 (PO 4)(OH) and Co 3 (PO 4) 2 .8H 2 O.

Retention of Cu(ii) Ions by Amorphous and Apatitic Tricalcium Phosphates: An Undemanding Route to Produce Libethenite

“…The equivalence between the proportions of copper ions removed from the solution and those of calcium ions released by the phosphates leads to predict a copper retention mechanism involving a simple exchange between these two ions. The involvement of such a mechanism has been clearly identified in the retention of nickel ions by amorphous and apatitic phosphates [10]. In this case, it has been shown that the exchange of nickel with calcium ions occurs without causing any change in the structures of the two phosphates.…”

“…Subject to similar treatment, HA remains relatively intact. This contrast in reactivity between HA and tricalcium phosphates prompted interest in discovering how these phosphates might then be distinguished from HA when challenged for use in metal ion retention processes [10]. Experiments carried out with nickel, cobalt, and copper ions have unambiguously demonstrated the ability of amorphous and apatitic phosphates to remove variable but significant amounts of these metal ions from aqueous solutions [10].…”

“…This contrast in reactivity between HA and tricalcium phosphates prompted interest in discovering how these phosphates might then be distinguished from HA when challenged for use in metal ion retention processes [10]. Experiments carried out with nickel, cobalt, and copper ions have unambiguously demonstrated the ability of amorphous and apatitic phosphates to remove variable but significant amounts of these metal ions from aqueous solutions [10]. They also showed that when the transfer of metal ions from solutions to solid phosphates involves a dissolution-precipitation process, the residual solids produced do not identify with any HA derivative.…”

“…They also showed that when the transfer of metal ions from solutions to solid phosphates involves a dissolution-precipitation process, the residual solids produced do not identify with any HA derivative. For the experiment carried out with copper ions, the results obtained revealed the formation of copper hydroxyphosphate, Cu 2 (PO 4 )(OH) [10].…”