The nature of arsenic in uranium mill tailings by X-ray absorption spectroscopy

In order to understand the evolving world of environmental issues, the ability to characterize and predict the stability and bioavailability of heavy métal contaminants in mine waste is becoming increasingly more important. X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopies were used to characterize a series of synthetic and natural samples associated with mine tailings processing. XANES was shown to be excellent as a tool to rapidly differentiate oxidation states of arsenic within the samples. The EXAFS spectra provided information on the mineralogy of the precipitated raffinate and tailings and showed that these samples are composed of a mixture of amorphous ferric arsenates, adsorbed arsenates and a mixture of other poorly ordered arsenates.

XAFS Study of Arsenical Nickel Hydroxide

International audienceTo Investigate the role played by nickel co-ions in contributing to the stability of arsenic, fluorescence XAFS measurements at both arsenic K-edge and nickel K-edge, respectively, on amorphous arsenical nickel hydroxide, crystalline arsenical nickel hydroxide, and annabergite reference compounds have been carried out. The XAFS results indicate that the arsenic-bearing nickel hydroxides have a well-defined arsenic local structure with multiple coordination shells, suggesting a compound formation mechanism instead of surface adsorption. The degradation of the arsenic local structure in the crystalline arsenical nickel hydroxide is observed. The XAFS of annabergites are compared to that of the arsenical nickel hydroxide and possible structural models are discussed