Grantee Research Project Results
2002 Progress Report: Processes Controlling the Chemical/Isotopic Speciation and Distribution of Mercury from Contaminated Mine Sites
EPA Grant Number: R827634Title: Processes Controlling the Chemical/Isotopic Speciation and Distribution of Mercury from Contaminated Mine Sites
Investigators: Brown Jr., Gordon E. , Johnson, Stephen B. , Rytuba, James J. , Slowey, Aaron S. , Kim, Christopher S. , Gustin, Mae Sexauer
Current Investigators: Brown Jr., Gordon E. , Johnson, Stephen B. , Zehner, Richard E. , Slowey, Aaron J. , Rytuba, James J. , Nacht, David M. , Kim, Christopher S. , Gustin, Mae Sexauer , Lowry, Gregory V. , Vette, Alan , Giglini, Anthony , Fitzgerald, Brian , Sladek, Chris , Engle, Mark , Coolbaugh, Mark , Shaw, Samuel
Institution: Stanford University , University of Nevada - Reno , United States Geological Survey , University of California - Berkeley
Current Institution: Stanford University , United States Geological Survey
EPA Project Officer: Chung, Serena
Project Period: October 1, 1999 through September 30, 2002
Project Period Covered by this Report: October 1, 2001 through September 30, 2002
Project Amount: $708,634
RFA: Mercury: Transport and Fate through a Watershed (1999) RFA Text | Recipients Lists
Research Category: Watersheds , Heavy Metal Contamination of Soil/Water , Water , Safer Chemicals
Objective:
The objectives of this research project are to: (1) determine the chemical speciation and relative abundance of different forms of Hg in mine wastes; (2) investigate the role of colloidal transport as a mechanism for dispersal of Hg from waste sites; (3) identify the mode of Hg sorption in downstream sediments and fine-grained precipitates; (4) determine the effects of complexing ligands on the desorption and sorption inhibition of Hg; (5) measure and correlate the emission of Hg into the atmosphere with Hg speciation, climate, and geologic factors; and (6) examine Hg isotope fractionation as a potential means of identifying Hg from specific localities and correlate the information on chemical and isotopic speciation of Hg along the various pathways by which Hg may travel. Substantial progress has been made on the first five objectives of the research project. New results/progress on Objectives 1, 2, 3, 4, and 5 are summarized below.
Progress Summary:
Mercury Speciation. Drs. Johnson, Brown, and Rytuba and Stanford graduate student Aaron Slowey are continuing studies of the molecular-level speciation of Hg in mercury-bearing samples from a variety of localities in the California Coast Range mercury mineral belt and in Nevada. Different particle size fractions are generated by laboratory column experiments on Hg mine wastes and characterized by x-ray absorption fine structure spectroscopy (XAFS), scanning electron microscopy (SEM), and analytical transmission electron microscopy (TEM). As an example of our findings, the colloidal fraction from calcines collected at the Sulphur Bank mine were found to consist of cinnabar, metacinnabar, and corderoite. This study is part of the Ph.D. work of Aaron Slowey.
Colloidal Transport of Mercury. During Years 1 and 2 of the project, Drs. Johnson, Brown, and Rytuba and Aaron Slowey conducted laboratory column experiments designed to examine the transport of Hg by colloids. Starting materials were calcines from the New Idria Hg mine in central California, as well as raw mine wastes from other localities, including the Sulphur Bank Mine in Lake County, CA. Following colloid generation from the columns, which is described in our Year 1 Progress Report, the colloidal fraction was characterized by a combination of X-Ray diffraction (XRD), Hg LIII-XAFS spectroscopy, SEM, and analytical TEM. One key finding is that most of the colloids are cinnabar or metacinnabar, which is surprising in light of the widely held belief that most heavy metals attach to colloidal particles as sorption complexes. Two manuscripts describing our column experiments, Hg-colloid generation, and detailed characterization of the colloids, have been submitted to the journal Environmental Science and Technology.
During Year 3 of the project, we continued column experiments to develop our understanding of mechanisms underlying particle-associated transport of Hg. Samples from calcine piles at the Sulphur Bank Mine, Lake County, CA, were sequentially exposed to electrolyte solutions and then to low levels of both oxalic and citric acids. This methodology represents a significant refinement over our previous experiments (which used relatively high levels of malonic acid), as oxalic and citric acids are very common in nature, and the concentrations utilized were selected to closely mimic the concentrations of organic acids typically found in vegetated environments. The conditions, therefore, represent a simple model for newly revegetated mine tailings environments. Although the time required to generate particles from mine tailings increased markedly with decreasing organic acid concentrations, even the lowest organic acid concentrations were found to lead to colloid generation (primarily cinnabar, metacinnabar, and corderoite) rather than sorbed Hg complexes. In contrast, measurements of dissolved Hg in the solutions eluted from the columns showed very low concentrations ( 30 ppb beyond the first 10-15 pore volumes for a 1mM organic acid solution), indicating that the vast majority of Hg is transported in the colloidal phase.
Further work has focused on the role played by the organic acids in promoting colloid generation. Results indicate that exposure to oxalic and citric acids promotes dissolution of significant quantities of metal cations, including silicon, iron, aluminum, and calcium from the mine tailings examined. Furthermore, although organic acids such as oxalic acid were found to very weakly interact with negatively charged particle surfaces, they are strongly sorbed to positively charged surfaces, where they can lead to both enhanced surface dissolution and reversal of surface charge.
Sorption of Mercury on Particle Surfaces. Drs. Brown and Rytuba and Chris Kim have assessed the types of Hg(II) sorption complexes that form on common mineral particles (goethite, boehmite, and -alumina) in Hg-mine waste environments using XAFS spectroscopy. This work is now complete and the results are reported in a paper that is now in press in the Journal of Colloid and Interface Science (Kim, et al., in press).
Effects of Complexing Ligands on Hg(II) Sorption and Transport. During Years 1 and 2 of the project, Drs. Johnson, Brown, and Rytuba and Aaron Slowey conducted uptake experiments in which the sorption of Hg(II) on goethite (-FeOOH), boehmite (-AlOOH), and -alumina (-Al2O3) was examined in the presence of chloride and sulfate ions as a function of pH to determine how these common inorganic ligands interfere with or enhance Hg(II) uptake on these particle surfaces. The reaction products were characterized at the molecular level using XAFS spectroscopy.
In Year 3 of the project, we have begun examining the effects of common organic ligands, including oxalate and citrate, on Hg speciation, sorption, and transport.
Atmospheric Emissions of Mercury. In this component of the project, Drs. Gustin, Rytuba, and Brown and Chris Kim have focused on assessing parameters that control Hg emissions from mine waste and surrounding Hg-enriched terrains, developing a database of emissions, and scaling up emissions for select sites. Other important tasks include linking Hg emissions with substrate Hg speciation and assessment of the speciation of Hg in the air associated with mining sites. Hg fluxes have been measured from representative geologic units for 18 areas of mining activity. These include areas exploited for Hg, Au, Ag, Cu, Pb, and Zn, and energy resources, including geothermal, oil and gas, as well as those where Hg was added to extract Au and Ag from ores. Hg fluxes from areas of hydrothermally altered rocks not associated with ore deposits and of rocks with background Hg concentrations also were collected. These data were used to model natural source Hg emissions for Nevada (Zehner and Gustin, 2002). Reactive gaseous Hg concentrations were measured in the air above two naturally enriched areas; one that has been significantly impacted by mining (Sulphur Bank Superfund Site-CA) and the other that is fairly undisturbed (Steamboat Springs Geothermal Area-NV). In addition, Hg emissions from one area of anthropogenic Hg contamination (Carson River Superfund Site-NV) also were measured. Reactive gaseous Hg data also were collected for a pristine area within the same region for comparison. Hg emissions were measured from mine waste in the New Idria mining district (CA) pre- and post-remediation. Detailed laboratory experiments were done in collaboration with the Stanford group, which involved measuring Hg emissions as a function of the chemical form of Hg identified in the substrate by extended XAFS (EXAFS) spectroscopy.
In Year 3 of the project, we also have explored potential connections between Hg speciation and the extent of gaseous Hg emissions from mine wastes employing the spectral databases we have generated using XAFS spectroscopy (Stanford Group) and controlled flux measurements at a number of localities (University of Nevada-Reno Group). Hg emissions then were measured on the same samples on which we performed XAFS measurements at constant temperature under both light and dark conditions based on the known ability of light to increase Hg flux rates. This degree of enhancement can be expressed as the ratio of emissions under light to emissions under dark conditions ("light:dark"), which serves as a useful index because it is independent of total Hg concentration differences among individual samples.
Some significant results from the comparisons of Hg speciation and Hg emissions include the finding that the light:dark ratio is greater among samples containing metacinnabar (HgS, cubic) relative to samples containing just cinnabar (HgS, hexagonal) (i.e., light enhancement is more pronounced in samples containing metacinnabar). This finding has implications for the atmospheric release and cycling of Hg from specific types of mine wastes, particularly because our previous XAFS studies have shown that calcines (roasted ore) typically contain high proportions of metacinnabar, which is generated by the ore roasting process.
Flux measurements paired with XAFS speciation analyses of a mine calcine from New Idria (CA) show that with decreasing particle size, the light:dark ratio increases, which is consistent with the higher available surface areas in the smaller size fractions. However, this trend is due more to declining Hg flux rates under dark conditions than enhanced Hg flux rates under light conditions once normalized for total Hg concentration. Because XAFS analysis has shown in this and other cases that the proportion of HgS in a sample increases with decreasing particle size (likely because of its low hardness combined with its low solubility), the flux measurements indicate that non-HgS phases, such as HgO and Hg3Cl3O2H, may be significantly larger contributors of gaseous Hg than HgS phases. Therefore, regions with appreciable Hg-oxides and Hg-chlorides, such as hot-spring type Hg deposits, may be of more concern regarding atmospheric Hg emissions than areas where HgS dominates. These findings currently are being summarized in a manuscript to be published in Environmental Science and Technology.
Future Activities:
Future activities are continuing in the following focus areas: (1) Hg speciation in selected mine wastes in the California Coast Range using a combination of XAFS spectroscopy and TEM; (2) Hg-containing colloid generation and characterization from natural mine tailings and calcined ore; (3) the effects of common, low molecular weight organic acids on the speciation and transport of Hg(II) in mining wastes; (4) collaborative studies with Dr. Mae Gustin to correlate types of Hg speciation with Hg emissions to the atmosphere at selected mining sites, particularly those with large amounts of Hg-containing seasonal flocs; and (5) completion of manuscripts.
Journal Articles on this Report : 4 Displayed | Download in RIS Format
Other project views: | All 93 publications | 28 publications in selected types | All 27 journal articles |
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Type | Citation | ||
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Kim CS, Rytuba JJ, Brown GE Jr. EXAFS study of mercury(II) sorption to Fe- and Al-(hydr)oxides. I. Effects of pH. Journal of Colloid and Interface Science 2004;271(1):1-15. |
R827634 (2001) R827634 (2002) R827634 (Final) |
not available |
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Kima CS, Rytuba J, Brown GE. EXAFS study of mercury(II) sorption to Fe- and Al-(hydr)oxides - II. Effects of chloride and sulfate. Journal of Colloid and Interface Science 2004;270(1):9-20 |
R827634 (2001) R827634 (2002) R827634 (Final) |
not available |
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Lowry GV, Shaw S, Kim CS, Rytuba JJ, Brown Jr GE. Macroscopic and microscopic observations of particle-facilitated mercury transport from New Idria and Sulphur Bank mercury mine tailings. Environmental Science & Technology 2004;38(19):5101-5111. |
R827634 (2002) R827634 (Final) |
Exit Exit |
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Slowey AJ, Johnson SB, Rytuba JJ, Brown GE. Role of organic acids in promoting colloidal transport of mercury from mine tailings. Environmental Science & Technology 2005;39(20):7869-7874 |
R827634 (2001) R827634 (2002) |
not available |
Supplemental Keywords:
surface water, groundwater, dissolution, environmental geochemistry., RFA, Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, Bioavailability, Hydrology, Remediation, Contaminated Sediments, Environmental Chemistry, Chemistry, Arsenic, Fate & Transport, Water Pollutants, Groundwater remediation, Mercury, fate and transport, contaminated mines, colloidal particles, contaminated sediment, chemical speciation, emissions, biogeochemical cycling, methylmercury, mining, geochemistry, sulfide, atmospheric deposition, groundwater, mercury vaporRelevant Websites:
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.