Combining selective sequential extractions, X-Ray Absorption Spectroscopy, and X-Ray Powder Diffraction for Cu (II) speciation in soil and mineral phases

Abstract

Interaction of Cu (II) ions with the matrix of soil and mineral phases of layered silicateswas assessed by the Miller method of selective sequential fractionation and a set ofsynchrotron X-ray methods, including X-ray powder diffraction (XRD) and X-rayabsorption spectroscopy (XANES). It was shown that the input of Cu into CalcicChernozem in the form of monoxide (CuO) and salt (Cu(NO3)2) affected thetransformation of Cu compounds and their affinity for metal-bearing phases. It wasfound that the contamination of soil with a soluble Cu(II) salt increased thebioavailability of the metal and the role of organic matter and Fe oxides in the fixationand retention of Cu. During the incubation of soil with Cu monoxide, the content of themetal in the residual fractions increased, which was related to the possible entry of Cuin the form of isomorphic impurities into silicates, as well as to the incompletedissolution of exogenic compounds at the high level of their input into the soil. Amechanism for the structural transformation of minerals was revealed, which showedthat ion exchange processes result in the sorption of Cu (II) ions from the saturatedsolution by active sites on the internal surface of the lattice of dioctahedralaluminosilicates. Surface hydroxyls at the octahedral aluminum atom play the mainrole. X-ray diagnostics revealed that excess Cu(II) ions are removed from the systemdue to the formation and precipitation of coarsely crystalline Cu(NO3)(OH)3.