Oligomerization in As (III) sulfide solutions: Theoretical constraints and spectroscopic evidence

Helz, George R.; Tossell, J. A.; Charnock, John; Pattrick, R. A. D.; Vaughan, David J.; Garner, C. David

doi:10.1016/0016-7037(95)00330-4

Cited by 132 publications

(161 citation statements)

References 41 publications

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“…We attribute this peak in our experiments to the formation of aqueous thioarsenite species; such species have previously been studied in the laboratory (25,26,41) and have recently been observed (42) in the field. However, as previously noted, this second arsenic peak may be due to a metastable species or transient process not adequately modeled with a thermodynamic model such as Geochemists' Workbench.…”

Section: Aqueous Thioarsenite Chemistrymentioning

confidence: 77%

Laboratory Investigations of Enhanced Sulfate Reduction as a Groundwater Arsenic Remediation Strategy

Keimowitz

Mailloux

Cole

et al. 2007

Environ. Sci. Technol.

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Landfills have the potential to mobilize arsenic via induction of reducing conditions in groundwater and subsequent desorption from or dissolution of arsenic-bearing iron phases. Laboratory incubation experiments were conducted with materials from a landfill where such processes are occurring. These experiments explored the potential for induced sulfate reduction to immobilize dissolved arsenic in situ. The native microbial community at this site reduced sulfate in the presence of added acetate. Acetate respiration and sulfate reduction were observed concurrent with dissolved iron concentrations initially increasing from 0.6 μM (0.03 mg L −1 ) to a maximum of 111 μM (6.1 mg L −1 ) and subsequently decreasing to 0.74 μM (0.04 mg L −1 ). Dissolved arsenic concentrations initially covaried with iron but subsequently increased again as sulfide accumulated, consistent with the formation of soluble thioarsenite complexes. Dissolved arsenic concentrations subsequently decreased again from a maximum of 2 μM (148 μg L −1 ) to 0.3 μM (22 μg L −1 ), consistent with formation of sulfide mineral phases or increased arsenic sorption at higher pH values. Disequilibrium processes may also explain this second arsenic peak. The maximum iron and arsenic concentrations observed in the lab represent conditions most equivalent to the in situ conditions. These findings indicate that enhanced sulfate reduction merits further study as a potential in situ groundwater arsenic remediation strategy at landfills and other sites with elevated arsenic in reducing groundwater.

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Section: Aqueous Thioarsenite Chemistrymentioning

confidence: 77%

Laboratory Investigations of Enhanced Sulfate Reduction as a Groundwater Arsenic Remediation Strategy

Keimowitz

Mailloux

Cole

et al. 2007

Environ. Sci. Technol.

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“…Finally, Helz et al (1995) suggested the experiments of Mironova et al (1991) with the highest m H2S suffered from experimental contamination or colloid formation because if As 2 S 3 •H 2 O were an important species then the solubility of amorphous orpiment would have been significantly greater than that reported by Eary (1992).…”

Section: H 3 As 3 S 6mentioning

confidence: 88%

“…Because evidence exists for the species H 2 As 3 S 6 -1 and HAs 3 S 6 -2 , and because Helz et al (1995) used ab initio quantum mechanical predictions and spectroscopic data to confirm the stability of As-S trimers relative to the dimers, it was assumed in this study that H 3 As 3 S 6 0 also exists. To reconcile this tentative assumption with the results of Mironova et al (1991), only those data points that conformed to a predicted slope of +1.5 on a plot of log m H2S versus log m As were included in regression calculations.…”

Section: H 3 As 3 S 6mentioning

confidence: 99%

“…Also, for the case of arsenic sulfide complexes, Akinfiev et al (1992) developed parameters assuming that the stable complexes are dimers, although many lines of evidence now support the existence of trimeric species (Eary, 1992;Helz, et al, 1995). Systematic correlations between standard partial molal thermodynamic properties have not been developed for some species, even though trends for other ions and complexes have been identified (Shock and Helgeson, 1988;Shock et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Hydrothermal Chemistry of Gold, Arsenic, Antimony, Mercury and Silver

Bessinger¹,

Apps²

2003

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A comprehensive thermodynamic database based on the Helgeson-Kirkham-Flowers (HKF) equation of state was developed for metal complexes in hydrothermal systems. Because this equation of state has been shown to accurately predict standard partial molal thermodynamic properties of aqueous species at elevated temperatures and pressures, this study provides the necessary foundation for future exploration into transport and depositional processes in polymetallic ore deposits. The HKF equation of state parameters for gold, arsenic, antimony, mercury, and silver sulfide and hydroxide complexes were derived from experimental equilibrium constants using nonlinear regression calculations. In order to ensure that the resulting parameters were internally consistent, those experiments utilizing incompatible thermodynamic data were re-speciated prior to regression.Because new experimental studies were used to revise the HKF parameters for H 2 S 0 and HS -1 , those metal complexes for which HKF parameters had been previously derived were also updated. It was found that predicted thermodynamic properties of metal complexes are consistent with linear correlations between standard partial molal thermodynamic properties. This result allowed assessment of several complexes for which experimental data necessary to perform regression calculations was limited.Oxygen fugacity-temperature diagrams were constructed from predicted thermodynamic properties to illustrate how thermodynamic data can be used to understand the transport and deposition of metals in hydrothermal systems such as the Carlin-type gold deposits. Assuming a linear relationship between temperature and pressure, metals are predicted to predominantly be transported as sulfide complexes at a total aqueous sulfur concentration of 0.05 m. Also, the presence of arsenic and antimony mineral phases in the deposits are shown to restrict mineralization within a limited range of chemical conditions. Finally, at a lesser aqueous sulfur concentration of 0.01 m, host rock sulfidation can explain the origin of arsenic and antimony minerals within the paragenetic sequence.2

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“…Using XAS to determine As speciation in sulfidic solution, Helz et al (2005) demonstrated the presence of As-S oligomers in solutions of As(III) and S 2- (Helz et al, 1995).…”

Section: Advancements Through Synchrotron Sciencementioning

confidence: 99%