Mercury Speciation by X-ray Absorption Fine Structure Spectroscopy and Sequential Chemical Extractions:  A Comparison of Speciation Methods

Abstract

Determining the chemical speciation of mercury in contaminated mining and industrial environments is essential for predicting its solubility, transport behavior, and potential bioavailability as well as for designing effective remediation strategies. In this study, two techniques for determining Hg speciation--X-ray absorption fine structure (XAFS) spectroscopy and sequential chemical extractions (SCE)--are independently applied to a set of samples with Hg concentrations ranging from 132 to 7539 mg/kg to determine if the two techniques provide comparable Hg speciation results. Generally, the proportions of insoluble HgS (cinnabar, metacinnabar) and HgSe identified by XAFS correlate well with the proportion of Hg removed in the aqua regia extraction demonstrated to remove HgS and HgSe. Statistically significant (>10%) differences are observed however in samples containing more soluble Hg-containing phases (HgCl2, HgO, Hg3S2O4). Such differences may be related to matrix, particle size, or crystallinity effects, which could affect the apparent solubility of Hg phases present. In more highly concentrated samples, microscopy techniques can help characterize the Hg-bearing species in complex multiphase natural samples.

Geological and anthropogenic factors influencing mercury speciation in mine wastes: an EXAFS spectroscopy study

“…This identification of the relevant Hg species present and the proportions at which they are present in the sample represents the formal, EXAFS-determined Hg speciation of the sample. Application of the EXAFS technique to determine Hg speciation in calibrated mixtures of model Hg compounds (8) and a separate comparison of results from EXAFS spectroscopy and sequential chemical extractions on a selected suite of Hgbearing samples (9) further validated the use of EXAFS spectroscopy for determining Hg speciation in complex samples and better defined its limitations, where fit components should be considered accurate to ±25% of their stated value and fit components comprising less than 10% of a fit should be viewed with caution.…”

Effects of the November 2012 Flood Event on the Mobilization of Hg from the Mount Amiata Mining District to the Sediments of the Paglia River Basin

“…As the retorting of Hg ore mineral (generally cinnabar) is an inefficient process, waste calcines found at most Hg mines contain unconverted cinnabar, Hg(0) and ionic Hg compounds formed during processing [10,11]. Leaching and erosion of mine-waste result in anomalously high Hg concentrations in stream sediment and water [12][13][14][15], even decades after the end of mining [13,[16][17][18][19].…”

A comparison of devices using thermal desorption for mercury speciation in solids

“…Moreover, accessibility to this equipment is usually limited [6][7][8]. The Sequential Chemical Extraction (SCE) procedure which uses sequentially arranged solvents to extract Hg species into different liquid fractions has low detection limits.…”