Species fine structure of transition metal Cu(II) in aqueous chloride-bearing solutions: Insights from X-ray absorption spectroscopy and ab initio XANES calculations

Abstract

Knowledge of the structure and speciation of aqueous Cu(II)-chloride complexes is important for understanding Cu(II) behavior in the deep removal technology of Cu impurity from nickel electrolysis anolytes containing chloride. In this paper, X-ray absorption spectroscopic measurements are reported for dissolved copper in lithium chloride (up to ~ 16 mol kg−1) solutions at room temperature. The speciation and structure of corresponding solutions has been probed by performing a combined ab initio XANES theoretical and experimental analysis. The EXAFS spectrum was analyzed as well within this approach. Our XAS data and ab initio XANES calculations favored the five-coordinated [Cu(H2O)5]2+ with square pyramidal configuration over the four-(square planar and tetrahedron, [Cu(H2O)4]2+) and six-coordinated (octahedron, [Cu(H2O)6]2+) structure in dilute Cl− solution (~ 0.55 mol kg−1). This is also supported by the EXAFS refinement with the [CuO5] model having the lowest statistical error. In the highest Cl− concentration solution, the results of both methods show that tetrahedral [CuCl4]2– complexes are predominant. Upon manually adjusting its geometric parameter to the distortion degree α of ~ 18° and average CuCl bond distance of 2.25 Å of a squashed tetrahedral model, not only does the calculated XANES spectrum well reproduce the experimental spectrum, but also the statistical error in the EXAFS refinements is lowest.