TY - JOUR
T1 - Silica- and sulfate-bearing rock coatings in smelter areas
T2 - Products of chemical weathering and atmospheric pollution I. Formation and mineralogical composition
AU - Mantha, Nathalie M.
AU - Schindler, Michael
AU - Murayama, Mitsuhiro
AU - Hochella, Michael F.
N1 - Funding Information:
This work was supported by a NSERC Discovery Grant to M.S., and an Ontario Graduate Scholarship to N.M. M.H. acknowledges NSF and EPA under NSF Cooperative Agreement EF-0830093 . Any opinions, findings, conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NSF or the EPA. This work has not been subjected to EPA review and no official endorsement should be inferred. We would like to thank D. Crabtree, A. McDonald, W. Zhe, J. Gray-Munro, W. Desjardin and T. Ulrich for technical assistance, B. Kamber and D. Pearson for comments on an earlier version of the Manuscript and J. Durocher and K. Skeries for their assistance in sampling, sample preparation and sample measurements. We are also indebted to M. Freund for the use of his XPS lab at the University of Manitoba. Electron microscopy characterization was performed at the Nanoscale Characterization and Fabrication Laboratory, ICTAS, Virginia Tech. The authors thank associate editor Ed Ripley and three anonymous reviewers for their comments on an earlier version of the paper.
PY - 2012/5/15
Y1 - 2012/5/15
N2 - Black rock-coatings occur in proximity to smelters and roast yards of the Greater Sudbury area, Ontario, Canada and contain information about the past interactions between surface minerals, and gaseous and particulate atmospheric components, many of which were pollutants. Rock-coatings were collected from various locations within the Sudbury area and are characterized with scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electron microprobe analysis, infrared spectroscopy and X-ray photoelectron spectroscopy. Acidic fumigations and rain, the result of vast quantities of SO 2 released from smelting, increased the chemical weathering rate of exposed rocks in the Sudbury area. Non-stoichiometric dissolution of the silicate minerals under acidic conditions resulted in the accumulation of silicic acid and the subsequent formation of a silica-gel type coating. The silica gel transformed overtime into amorphous silica, opal (opal C and opal-CT) and cristobalite. Dissolution of the underlying rock and also of metal-bearing particles by sulfuric acid resulted in the in situ formation of metal-sulfate-rich layers on the interfaces between the atmosphere and the silica-rich coating (atmosphere-coating interface, ACI) and between the silica-rich coating and the underlying rock (rock-coating interface, RCI). These metal-sulfate-rich layers contain nanometer aggregates of Fe-Cu-sulfate-hydroxide, goldichite, mereiterite, guildite, butlerite and antlerite. The silica-rich matrix also contains a mix of detrital grains from adjacent rocks and soils (feldspar, quartz, hematite, chlorite, montmorillonite) and non-dissolved smelter-derived nano- to micro-size particulates (metal-silicates, metal-oxides, C-spheres). The apparent disequilibrium between the embedded particles and the Fe-Cu-sulfates suggests that trapped nanoparticles were encapsulated into pores which prevented their equilibration with acidic metal-sulfate-bearing fluids. An XPS depth profile indicates a gradual transition from lower to higher concentrations of metals from the coating surface towards the metal-sulfate-rich layer on the ACI, which suggests that the outer surface of the coatings is currently leached on an angstrom scale by surface waters.
AB - Black rock-coatings occur in proximity to smelters and roast yards of the Greater Sudbury area, Ontario, Canada and contain information about the past interactions between surface minerals, and gaseous and particulate atmospheric components, many of which were pollutants. Rock-coatings were collected from various locations within the Sudbury area and are characterized with scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electron microprobe analysis, infrared spectroscopy and X-ray photoelectron spectroscopy. Acidic fumigations and rain, the result of vast quantities of SO 2 released from smelting, increased the chemical weathering rate of exposed rocks in the Sudbury area. Non-stoichiometric dissolution of the silicate minerals under acidic conditions resulted in the accumulation of silicic acid and the subsequent formation of a silica-gel type coating. The silica gel transformed overtime into amorphous silica, opal (opal C and opal-CT) and cristobalite. Dissolution of the underlying rock and also of metal-bearing particles by sulfuric acid resulted in the in situ formation of metal-sulfate-rich layers on the interfaces between the atmosphere and the silica-rich coating (atmosphere-coating interface, ACI) and between the silica-rich coating and the underlying rock (rock-coating interface, RCI). These metal-sulfate-rich layers contain nanometer aggregates of Fe-Cu-sulfate-hydroxide, goldichite, mereiterite, guildite, butlerite and antlerite. The silica-rich matrix also contains a mix of detrital grains from adjacent rocks and soils (feldspar, quartz, hematite, chlorite, montmorillonite) and non-dissolved smelter-derived nano- to micro-size particulates (metal-silicates, metal-oxides, C-spheres). The apparent disequilibrium between the embedded particles and the Fe-Cu-sulfates suggests that trapped nanoparticles were encapsulated into pores which prevented their equilibration with acidic metal-sulfate-bearing fluids. An XPS depth profile indicates a gradual transition from lower to higher concentrations of metals from the coating surface towards the metal-sulfate-rich layer on the ACI, which suggests that the outer surface of the coatings is currently leached on an angstrom scale by surface waters.
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U2 - 10.1016/j.gca.2012.01.033
DO - 10.1016/j.gca.2012.01.033
M3 - Article
AN - SCOPUS:84859911604
VL - 85
SP - 254
EP - 274
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
SN - 0016-7037
ER -