Mechanisms of Copper and Mercury Adsorption on Bentonite Clays from EXAFS Spectroscopy

Abstract

Copper(II) and Mercury(II) cations are classified as important heavy metal pollutants in industrial wastewaters. In this study, Extended X-Ray Absorption Fine Structure (EXAFS) spectroscopy was used to provide information about the coordination environment and nearest neighbouring atoms involved in the copper(II) and mercury(II) ions adsorption on raw and calcined bentonite clays from Northeast Brazil. EXAFS experiments were carried using a channet-cut Si (111) monochromator. All the spectra were performed in transmission mode and Cu (8987 eV) K and Hg (12284 eV) L edges were collected. Each spectrum corresponded to an average of 3 independent scans. Standard compounds (copper and mercury oxides) were used in order to distinguish the bond differences between the heavy metal and coordination spheres (O atoms). Based on EXAFS investigation, it is possible to conclude that the structure of heavy metal ions on clays does not depend primarily of the calcinations of the structure. The main metal interaction observed for copper and mercury ions occurred on hydroxyl groups.