Correspondence/Rebuttal pubs.acs.org/est
Comment on “Predominance of Aqueous Tl(I) Species in the River System Downstream from the Abandoned Carnoules Mine (Southern France)” TlFe3(SO4 )2 (OH)6(s) + 6H+(aq)
C
asiot et al.1 published a very interesting study on the speciation of Tl(I) in a river system downstream from an abandoned Pb−Zn mine. We agree that this is one of the best and most comprehensive papers to examine Tl speciation in a mining environment. It is of particular importance because Tl is highly toxic and is studied to a lesser degree than other prominent toxic metals such as Pb, Cd, and Hg.2,3 However, we recently discovered errors in the calculation of the theoretical solubility equilibrium constants (Log K) calculated by Casiot et al.1 (see Table 1) for the following thallium minerals: dorallcharite (TlFe3(SO4)2(OH)6), lanmuchangite (TlAl(SO 4) 2·12H 2O) and lorandite (TlAsS2 ). The incorrect proposed stability field for dorallcharite within the circumneutral-alkaline pH region in the Eh-pH diagram of Tl (see Figure 2) raised some queries and prompted us to investigate the authors’ thermodynamic calculations and modelling. While it is a lesser studied member of the isostructural jarosite-alunite group of minerals, dorallcharite (TlFe3(SO4)2(OH)6), is expected to form under typical jarosite formation conditions which encompass oxidizing, ferric rich and acidic (pH < 3) environments.4−6 In fact, the authors previously demonstrated long-term abiotic and biotic K-jarosite precipitation at low pH values (1−3) in batch experiments containing Carnoules AMD water.7 At higher pH values, jarosites are unstable and will dissolve to form goethite or metastable phases such as schwertmannite or ferrihydrite.8,9 The dissolution and instability of various jarosite group minerals under circumneutral pH conditions has been extensively documented and it is highly unlikely that dorallcharite would form at the Amous DC station under the high pH values (∼8) shown in the Eh-pH diagram for Tl.10−15 It was unclear on how the authors calculated the Log K values, we recalculated the theoretical equilibrium solubility product constants and suggest the Log K values for dorallcharite (TlFe3(SO4)2(OH)6), lanmuchangite (TlAl(SO4)2·12H2O) and lorandite (TlAsS2) should be changed from 2.245, 16.551, and 38.256 to −9.90, −16.3 and −28.9, respectively. We calculated the new solubility product constants (Log Ksp) by combining the Gibbs free energy of reaction at 25 °C at equilibrium:
= Tl+(aq) + 2SO4 2 −(aq) + 3Fe3 +(aq) + 6H2O(l)
By combining eqs 1 and 2 and inputting the Gibbs free energy of formation of the anions and cations and the predicted Gibbs free energy for formation for Dorallcharite:16−19
ΔG° f ,298,dorallcharite = ΔG° f ,298(Tl+) + 3ΔG° f ,298(Fe3 +) + 2ΔG° f ,298(SO4 2 −) + 6ΔG° f ,298(H2O) + RT ln K sp
(4)
where Log K= −9.90 Moreover, for the calculation of the Log K of Lorandite (TlAsS2), the aqueous As species in the dissolution reaction was changed from H2AsO3−(aq) to H3AsO3°(aq) to reflect the aqueous As species most likely to form during arsenic sulfide dissolution17 thereby changing the dissolution reaction to
TlAsS2(s) + 3H2O(l) = Tl+(aq) + H3AsO3°(aq) + 2HS−(aq) + H+(aq)
(5)
Based on the data presented by the authors, we anticipate the new Log K values will not have a significant impact on the interpretation of their results because the particulate matter in their system generally comprises less than 10% of total Tl. However, based on the limited thermodynamic data for Tl minerals cited in the literature,1,18,19 we feel it is important for the authors to recalculate and change the current Log Ks and to reconstruct their Eh-pH diagram to better reflect Tl-jarosite stability so as to ensure that other researchers do not use the incorrect values in future modeling efforts.
Christina M. Smeaton,* Christopher G. Weisener Brian J. Fryer
Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario, Canada, N9B 3P4.
ΔG°reaction = ΣΔG° f ,298products − ΣΔG° f ,298reactants
(3)
(1)
with the free energy of reaction related to the Ksp by:
ΔG°reaction = − RT ln K sp
(2)
For example, in the case of dorallcharite, TlFe3(SO4)2(OH)6, the dissolution reaction proceeds via © 2012 American Chemical Society
Published: January 5, 2012 2473
dx.doi.org/10.1021/es203760h | Environ. Sci. Technol. 2012, 46, 2473−2474
Environmental Science & Technology
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AUTHOR INFORMATION
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REFERENCES
Correspondence/Rebuttal
Corresponding Author
*Phone: (519) 253-3000, x4246; fax: (519) 971-3616e-mail:
[email protected]. (1) Casiot, C.; Egal, M.; Bruneel, O.; Verma, N.; Parmentier, M.; Elbaz-Poulichet, F. Predominance of aqueous Tl(I) species in the river system downstream from the abandoned Carnoules Mine (Southern France). Environ. Sci. Technol. 2011, 45 (6), 2056−2064. (2) Cheam, V. Thallium contamination of water in Canada. Water Qual. Res. J. Canada 2001, 36 (4), 851−878. (3) Peter, A. L.; Viraraghavan, T. Thallium: a review of public health and environmental concerns. Environ. Int. 2005, 31 (4), 493−501. (4) Dutrizac, J. E. The behavior of thallium during jarosite precipitation. Metall. Mater. Trans., B 1997, 28 (5), 765−776. (5) Stoffregen, R.; Alpers, C.; Jambor, J. L. Alunite-jarosite crystallography, thermodynamics, and geochronology. Rev. Mineral. Geochem. 2000, 40 (1), 453. (6) Balic Zunic, T.; Moelo, Y.; Loncar, Z.; Micheelsen, H. Dorallcharite, Tl0.8K 0.2Fe3(SO4)2(OH)6, a new member of the jarosite-alunite family. Eur. J. Mineral. 1994, 6 (2), 255. (7) Egal, M.; Casiot, C.; Morin, G.; Parmentier, M.; Bruneel, O.; Lebrun, S.; Elbaz-Poulichet, F. Kinetic control on the formation of tooeleite, schwertmannite and jarosite by Acidithiobacillus ferrooxidans strains in an As (III)-rich acid mine water. Chem. Geol. 2009, 265 (3− 4), 432−441. (8) Bigham, J.; Nordstrom, D. K. Iron and aluminum hydroxysulfates from acid sulfate waters. Rev. Mineral. Geochem. 2000, 40 (1), 351. (9) Bigham, J.; Schwertmann, U.; Traina, S.; Winland, R.; Wolf, M. Schwertmannite and the chemical modeling of iron in acid sulfate waters. Geochim. Cosmochim. Acta 1996, 60 (12), 2111−2121. (10) Smeaton, C. M.; Fryer, B. J.; Weisener, C. G. Intracellular precipitation of Pb by Shewanella putrefaciens CN32 during the reductive dissolution of Pb-jarosite. Environ. Sci. Technol. 2009, 43 (21), 8091−8096. (11) Smith, A. M. L.; Dubbin, W. E.; Wright, K.; Hudson-Edwards, K. A. Dissolution of lead- and lead-arsenic-jarosites at pH 2 and 8 and 20 degrees C: Insights from batch experiments. Chem. Geol. 2006, 229 (4), 344−361. (12) Smith, A. M. L.; Hudson-Edwards, K. A.; Dubbin, W. E.; Wright, K. Dissolution of jarosite [KFe3(SO4)(2)(OH)(6)] at pH 2 and 8: Insights from batch experiments and computational modelling. Geochim. Cosmochim. Acta 2006, 70 (3), 608−621. (13) Weisener, C. G.; Babechuk, M. G.; Fryer, B. J.; Maunder, C. Microbial dissolution of silver jarosite: Examining its trace metal behaviour in reduced environments. Geomicrobiol. J. 2008, 25 (7−8), 415−424. (14) Welch, S. A.; Christy, A. G.; Kirste, D.; BeaviS, S. G.; Beavis, F. Jarosite dissolution ITrace cation flux in acid sulfate soils. Chem. Geol. 2007, 245 (3−4), 183−197. (15) Welch, S. A.; Kirste, D.; Christy, A. G.; Beavis, F. R.; Beavis, S. G. Jarosite dissolution II-Reaction kinetics, stoichiometry and acid flux. Chem. Geol. 2008, 254 (1−2), 73−86. (16) Gaboreau, S.; Vieillard, P. Prediction of Gibbs free energies of formation of minerals of the alunite supergroup. Geochim. Cosmochim. Acta 2004, 68 (16), 3307−3316. (17) Nordstrom, D.; Archer, D. Arsenic thermodynamic data and environmental geochemistry. Arsenic Ground Water 2003, 1−25. (18) Xiong, Y. L. Hydrothermal thallium mineralization up to 300 degrees C: A thermodynamic approach. Ore Geol. Rev. 2007, 32 (1− 2), 291−313. (19) Xiong, Y. L. The aqueous geochemistry of thallium: speciation and solubility of thallium in low temperature systems. Environ. Chem. 2009, 6 (5), 441−451.
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