Use of dicalcium phosphate dihydrate to remove nickel ions from aqueous solutions

Abstract

The removal of nickel ions from aqueous solutions by dicalcium phosphate dihydrate (CaHPO₄.2H₂O) was investigated by X-ray photoelectron spectroscopy, X-ray diffraction, infrared spectroscopy, thermal analysis and inductively coupled plasma - atomic emission spectrometry. The results of this investigation demonstrate the ability of dicalcium phosphate to remove nickel ions and help identify the mechanism responsible for the transfer of these metal ions from solution to solid phosphate. The results  show that, on the one hand, when the phosphate was exposed to the nickel solution for less than 1200 minutes, the nickel retention mechanism was dominated by a substitution process, as evidenced by the equimolar exchanges between the nickel extracted from the solution and the calcium released by phosphate, as well as the preservation of the initial phosphate structure. On the other hand, for exposure times greater than 1200 minutes, the transfer of nickel occurs by the dissolution of the dicalcium phosphate and the precipitation of a new phase of isomorphic structure with Ni₃(PO₄)₂.8H₂O.