2001 Progress Report: Processes Controlling the Chemical/Isotopic Speciation and Distribution of Mercury from Contaminated Mine Sites

EPA Grant Number: R827634
Title: Processes Controlling the Chemical/Isotopic Speciation and Distribution of Mercury from Contaminated Mine Sites
Investigators: Brown Jr., Gordon E. , Gustin, Mae Sexauer , Kim, Christopher S. , Lowry, Greg , Rytuba, James J. , Shaw, Samuel
Current Investigators: Brown Jr., Gordon E. , Coolbaugh, Mark , Engle, Mark , Fitzgerald, Brian , Giglini, Anthony , Gustin, Mae Sexauer , Johnson, Stephen B. , Kim, Christopher S. , Lowry, Gregory V. , Nacht, David M. , Rytuba, James J. , Shaw, Samuel , Sladek, Chris , Slowey, Aaron J. , Vette, Alan , Zehner, Richard E.
Institution: Stanford University , United States Geological Survey [USGS] , University of Nevada - Reno
Current Institution: Stanford University , United States Geological Survey [USGS]
EPA Project Officer: Hiscock, Michael
Project Period: October 1, 1999 through September 30, 2002
Project Period Covered by this Report: October 1, 2000 through September 30, 2001
Project Amount: $708,634
RFA: Mercury: Transport and Fate through a Watershed (1999) RFA Text |  Recipients Lists
Research Category: Water and Watersheds , Mercury , Water , Safer Chemicals


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 in the presence of common complexing ligands; (4) determine the effects of aqueous complexing ligands on the desorption and sorption inhibition of Hg; (5) measure and correlate Hg emission 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 mercury may travel. Substantial progress has been made in the first five objectives of the project. Less progress than expected has been made toward Objective 6, which was considered to be exploratory in the original proposal, with some chance for success, but with some big unknowns, such as the extent to which different Hg isotopes fractionate during natural and anthropogenic (e.g., calcining or Hg-ores) processes. Results from Objective 6 are summarized in our 2000 Progress Report. Results/progress toward each of the other five objectives are summarized below.

Progress Summary:

Mercury Speciation. Drs. Brown and Rytuba and Chris Kim (doctoral student) have continued x-ray absorption fine structure spectroscopic (XAFS) studies of Hg in Hg-bearing samples from a variety of localities in the California Coast Range Hg mineral belt and in Nevada. We continue to find that cinnabar (HgS, hex) or metacinnabar (HgS, cub) are dominant Hg species in most samples, which is consistent with the fact that cinnabar is the primary ore mineral in Hg deposits and is very thermodynamically stable. Mercuric chloride species have been identified only in calcines from hot-spring Hg deposits, consistent with high levels of Cl in these local hydrothermal systems. In contrast, samples from silica-carbonate Hg deposits, where high Cl levels are absent, are lacking in Hg-Cl phases as determined by XAFS analysis. These results show a dependence of Hg speciation on geological origin of the initial Hg ore and on the sensitivity of XAFS in distinguishing between samples from the different ore types. Two published papers and two papers submitted for publication have resulted from this work (Kim, et al., 1999; Kim, et al., 2000).

Although some calcine samples were found to consist exclusively of mercuric sulfide, others contain additional, more soluble Hg phases, indicating a greater potential for the release of Hg into solution. Also, a correlation was observed between samples from hot-spring Hg deposits, in which Cl levels are elevated, and the presence of Hg-Cl species. Speciation results demonstrate that XAFS can identify multiple Hg phases in heterogeneous samples with a quantitative accuracy of ±15 percent for the Hg-containing phases considered. XAFS, in conjunction with x-ray diffraction (XRD) and electron probe microanalysis, is beneficial in prioritizing and remediating Hg-contaminated mine wastes.

The geological origin of Hg ores has a significant influence on Hg speciation in mine wastes, as samples collected from hot-spring Hg deposits were found to contain soluble Hg-Cl phases, while such phases were largely absent in samples from silica-carbonate Hg deposits. Calcining, which involves roasting ore in excess of 600°C, caused transformation of cinnabar to metacinnabar, possibly resulting in higher atmospheric and aqueous release rates from calcines compared to ores. Hg(0) introduced into Au mining regions also appears to have transformed to Hg-sulfides and Hg-sulfate through burial in high-sulfide sediments. Particle size strongly influenced total Hg in waste samples, with increases of an order of magnitude between the 500-2000 mm and less than 45 mm size fractions. The proportion of Hg-sulfides also increases by 7 to 15 percent as particle size decreases, suggesting that more soluble Hg phases are leached through weathering. Distribution from mine wastes does not have much impact on Hg speciation, perhaps because of the stable Hg-sulfides comprising a high proportion of Hg released, largely as fine-grained particulates, into aquatic systems.

Colloidal Transport of Mercury. During Year 2 of the project, Drs. Lowry, Shaw, Brown, and Rytuba and Chris Kim continued column experiments designed to examine Hg transport by colloids. Starting materials were calcines from the New Idria Mine (CA) and mine wastes from other localities, including the Sulfur Bank Mine, Lake County, CA. Following colloid generation from the columns, the colloidal fraction was characterized by a combination of XRD, Hg LIII-XAFS spectroscopy, scanning electron microscopy (SEM), and analytical transmission electron microscopy (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 this work are in preparation for submission to the journal, Environmental Science and Technology.

Sorption of Mercury on Particle Surfaces. Hg(II) sorption onto mineral particles may sequester Hg in mine tailing and aquatic systems if sorption complexes are strongly bonded. To assess the types of Hg(II) sorption complexes that may form in Hg mine wastes, Drs. Brown and Rytuba and Chris Kim have conducted uptake studies of Hg(II) on goethite and alumina particles and have characterized reaction products using XAFS. Macroscopic uptake studies of Hg(II) onto goethite show that Hg(II) sorbs strongly over the pH range 4.3-7.4; XAFS analysis of these samples indicates that Hg(II) forms inner-sphere, bidentate corner-sharing complexes on goethite. In comparison, Hg(II) was found to sorb relatively weakly onto gamma-alumina from pH 5.2-7.8. XAFS spectra show a distinct change in sorption mode at pH = 6.2. Experiments devised to test the possibility of alumina dissolution and reprecipitation indicate two distinct sorption modes in this system: (1) sorption of Hg(II) directly onto gamma-alumina; and (2) sorption of Hg(II) onto an Al-hydroxide precipitate such as bayerite, a phase known to form at the thermodynamically unstable surface of gamma-alumina. A paper describing Hg(II) sorption on these solids as a function of pH has been submitted to the Journal of Colloid and Interface Science.

Effects of Complexing Ligands on Hg(II) Sorption. In a companion study, Drs. Kim, Brown, and Rytuba conducted uptake experiments in which the sorption of Hg(II) on goethite and g-alumina was examined in the presence of chloride and sulfate ions as a function of pH. One or both ligands are common in environments where Hg is deposited and they have the potential for complexing Hg in solution and for forming ternary Hg surface complexes on these and other solids. Hg(II) uptake studies on these phases were conducted in the presence of Cl- and SO42- to determine how these ligands interfere with or enhance Hg(II) sorption. Reaction products were characterized using XAFS spectroscopy. A paper describing this work has been submitted to the Journal of Colloid and Interface Science.

Atmospheric Emissions of Mercury. Dr. Gustin and several students focused on assessing parameters controlling Hg emissions from mine waste and surrounding Hg-enriched terrains, developing a database of emissions and scaling up of emissions for select sites. Other important tasks include linking Hg emissions with substrate Hg speciation and assessment of the speciation of mercury in the air associated with mining sites. This work has built on a previous STAR Grant No. R822529: "Investigation of the light enhanced emissions of Hg from substrate." The collaboration with Stanford has allowed us to compare Hg speciation in substrates determined by XAFS spectroscopy with speciation from the sequential extraction method. This collaboration has improved understanding of the influence of speciation on light-enhanced Hg emissions and has generated a significant database of Hg emissions from mining-disturbed areas (primarily areas of Hg and Au extraction). Through monitoring of parameters while sampling and conducting laboratory studies, environmental parameters most significant in controlling emissions and the influence of Hg speciation and concentration on emissions are being investigated. This information is being integrated into geographic information system models for scaling up point source emission data to large areas. Our inventory of Hg emissions has been expanded to include placer Au deposits, oil and gas fields, vein mineralization, and stream precipitate deposits. These studies are being supported by information on the speciation of Hg associated with these deposits provided by the Stanford group.

Significant results include our finding that Hg emissions from mine areas are significantly higher than from surrounding Hg-enriched terrains; this is attributed to the fact that in areas of mining, Hg concentrations in the substrate are higher and mining has increased the surface area from which emissions occur. In addition, disturbance exacerbates Hg emissions from the substrate. However, the majority of Hg emitted from mining areas is from surrounding mining-disturbed terrains with low levels of enrichment. This is due to the large surface area of low Hg concentration substrates relative to the mining area. Based on preliminary data, reactive gaseous Hg in air above these sites is influenced by substrate mineralogy and the atmosphere interacting with the site. Hg speciation in the substrate influences the magnitude of emissions with respect to incident light, thus influences total emissions.

Future Activities:

In the next year, we will continue our activities in the following focus areas: (1) studies of Hg speciation in selected mine wastes in the California Coast Range using a combination of XAFS and analytical TEM; (2) studies of Hg-containing colloid generation and characterization from natural mine tailings and calcined ore; and (3) collaborative studies with Dr. Mae Gustin to correlate types of Hg speciation with Hg emissions at selected mining sites, particularly those with large amounts of Hg-containing seasonal flocs. We also will complete manuscripts for publication in peer-reviewed journals associated with the Ph.D. thesis work of Chris Kim, and with several new studies initiated by Stanford graduate student Aaron Slowey and a new post-doc, Dr. Steven Johnson, a colloid chemist from the University of Melbourne who was recently hired to work on colloidal transport of mercury. A major effort will be made in Year 3 of the project to study the effects of different types of chemical perturbations on colloidal generation and to identify the types of colloidal particles with which Hg is primarily associated. Characterization of colloidal particles generated in our column experiments using analytical TEM at the National Center for Electron Microscopy at the Lawrence Berkeley National Laboratory are generating useful information on their identity, size, shape, and distribution. XAFS studies of Hg(II) speciation in mining wastes have yielded unique information on the types of Hg(II) species present. Dr. Gustin's group will continue studies of Hg emissions in several localities, including one additional field season and a number of additional field measurements. She also is collaborating with the Brown-Rytuba group to correlate Hg speciation, as determined by a combination of XAFS spectroscopy and TEM measurements, with airborne Hg emissions. This correlation could only be made after development of experimental protocols for determining Hg speciation in complex mine wastes by the Stanford group.

Journal Articles on this Report : 6 Displayed | Download in RIS Format

Other project views: All 93 publications 28 publications in selected types All 27 journal articles
Type Citation Project Document Sources
Journal Article Kim CS, Rytuba JJ, Brown Jr GE. Utility of EXAFS in characterization and speciation of mercury-bearing mine wastes. Journal of Synchrotron Radiation. 1999;6:648-650. R827634 (2001)
R827634 (Final)
not available
Journal Article Kim CS, Brown Jr GE, Rytuba JJ. Characterization and speciation of mercury-bearing mine wastes using X-ray absorption spectroscopy (XAS). Science of the Total Environment 2000;261(1-3):157-168. R827634 (2000)
R827634 (2001)
R827634 (Final)
not available
Journal Article 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
Journal Article Kim CS, Rytuba JJ, Brown Jr GE. Geological and anthropogenic factors influencing mercury speciation in mine wastes. Applied Geochemistry 2004a;19(3):379-393. R827634 (2001)
R827634 (Final)
not available
Journal Article 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
Journal Article 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:

surfacewater, groundwater, dissolution, environmental geochemistry., RFA, Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, Bioavailability, Hydrology, Contaminated Sediments, Remediation, Environmental Chemistry, Arsenic, Chemistry, 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 vapor

Relevant Websites:

Synthesis Report of Research from EPA’s Science to Achieve Results (STAR) Grant Program: Mercury Transport and Fate Through a Watershed (PDF) (42 pp, 760 K)

Progress and Final Reports:

Original Abstract
  • 2000 Progress Report
  • Final Report