Christopher S. Kim

Investigation of the light-enhanced emission of mercury from naturally enriched substrates

Incident radiation has been reported to facilitate mercury release from soils. In this study the influence of light on mercury emissions from substrates amended with pure synthetic mercury species, and from naturally and anthropogenically mercury-enriched substrates were investigated using laboratory experiments and in situ flux measurements. Light-enhanced emissions were found to occur from substrates amended with HgS, and from elemental mercury (Hg 0 ) and HgCl2 amended iron oxide and organic containing substrates. The magnitude of light-enhanced emissions for natural substrates ranged from 1.5 to 116 times that occurring in the dark at the same substrate temperature. Substrates containing corderoite, metacinnabar and ‘‘matrix bound mercury’’ (that bound to organic or inorganic phases) exhibited a higher degree of light-enhanced emissions relative to that containing predominantly cinnabar. Calculated activation energies for both laboratory and field data indicate that photo-reduction is a process associated with the light-enhanced emissions. Activation energies, derived using in situ mercury fluxes and soil temperatures, indicated that photo-reduction was a dominant process facilitating release of Hg from substrates with sunrise. Activation energies, calculated using daytime data, were less than those calculated for sunrise. This is hypothesized to be due to a pool of Hg 0 being developed with photo-reduction at first light that is released as soil temperatures and convective heat transfer increase during the day. This study demonstrated that light energy is the more dominant process controlling mercury emissions from naturally enriched substrates than soil temperature. r 2002 Elsevier Science Ltd. All rights reserved.

EXAFS study of mercury(II) sorption to Fe- and Al-(hydr)oxides: I. Effects of pH☆

The study of mercury sorption products in model systems using appropriate in situ molecular-scale probes can provide detailed information on the modes of sorption at mineral/water interfaces. Such studies are essential for assessing the influence of sorption processes on the transport of Hg in contaminated natural systems. Macroscopic uptake of Hg(II) on goethite (alpha-FeOOH), gamma-alumina (gamma-Al(2)O(3)), and bayerite (beta-Al(OH)(3)) as a function of pH has been combined with Hg L(III)-edge EXAFS spectroscopy, FTIR spectroscopy, and bond valence analysis of possible sorption products to provide this type of information. Macroscopic uptake measurements show that Hg(II) sorbs strongly to fine-grained powders of synthetic goethite (Hg sorption density Gamma=0.39-0.42 micromol/m(2)) and bayerite (Gamma=0.39-0.44 micromol/m(2)), while sorbing more weakly to gamma-alumina (Gamma=0.04-0.13 micromol/m(2)). EXAFS spectroscopy on the sorption samples shows that the dominant mode of Hg sorption on these phases is as monodentate and bidentate inner-sphere complexes. The mode of Hg(II) sorption to goethite was similar over the pH range 4.3-7.4, as were those of Hg(II) sorption to bayerite over the pH range 5.1-7.9. Conversion of the gamma-Al(2)O(3) sorbent to a bayerite-like phase in addition to the apparent reduction of Hg(II) to Hg(I), possibly by photoreduction during EXAFS data collection, resulted in enhanced Hg uptake from pH 5.2-7.8 and changes in the modes of sorption that correlate with the formation of the bayerite-like phase. Bond valence calculations are consistent with the sorption modes proposed from EXAFS analysis. EXAFS analysis of Hg(II) sorption products on a natural Fe oxyhydroxide precipitate and Al/Si-bearing flocculent material showed sorption products and modes of surface attachment similar to those for the model substrates, indicating that the model substrates are useful surrogates for the natural sediments.

Characterization and speciation of mercury-bearing mine wastes using X-ray absorption spectroscopy

Mining of mercury deposits located in the California Coast Range has resulted in the release of mercury to the local environment and water supplies. The solubility, transport, and potential bioavailability of mercury are controlled by its chemical speciation, which can be directly determined for samples with total mercury concentrations greater than 100 mg kg(-1) (ppm) using X-ray absorption spectroscopy (XAS). This technique has the additional benefits of being non-destructive to the sample, element-specific, relatively sensitive at low concentrations, and requiring minimal sample preparation. In this study, Hg L(III)-edge extended X-ray absorption fine structure (EXAFS) spectra were collected for several mercury mine tailings (calcines) in the California Coast Range. Total mercury concentrations of samples analyzed ranged from 230 to 1060 ppm. Speciation data (mercury phases present and relative abundances) were obtained by comparing the spectra from heterogeneous, roasted (calcined) mine tailings samples with a spectral database of mercury minerals and sorbed mercury complexes. Speciation analyses were also conducted on known mixtures of pure mercury minerals in order to assess the quantitative accuracy of the technique. While some calcine samples were found to consist exclusively of mercuric sulfide, others contain additional, more soluble mercury phases, indicating a greater potential for the release of mercury into solution. Also, a correlation was observed between samples from hot-spring mercury deposits, in which chloride levels are elevated, and the presence of mercury-chloride species as detected by the speciation analysis. The speciation results demonstrate the ability of XAS to identify multiple mercury phases in a heterogeneous sample, with a quantitative accuracy of +/-25% for the mercury-containing phases considered. Use of this technique, in conjunction with standard microanalytical techniques such as X-ray diffraction and electron probe microanalysis, is beneficial in the prioritization and remediation of mercury-contaminated mine sites.

Geological and anthropogenic factors influencing mercury speciation in mine wastes: an EXAFS spectroscopy study

Abstract The speciation of Hg is a critical determinant of its mobility, reactivity, and potential bioavailability in mine-impacted regions. Furthermore, Hg speciation in these complex natural systems is influenced by a number of physical, geological, and anthropogenic variables. In order to investigate the degree to which several of these variables may affect Hg speciation, extended X-ray absorption fine structure (EXAFS) spectroscopy was used to determine the Hg phases and relative proportions of these phases present in Hg-bearing wastes from selected mine-impacted regions in California and Nevada. The geological origin of Hg ore has a significant effect on Hg speciation in mine wastes. Specifically, samples collected from hot-spring Hg deposits were found to contain soluble Hg-chloride phases, while such phases were largely absent in samples from silica-carbonate Hg deposits; in both deposit types, however, Hg-sulfides in the form of cinnabar (HgS, hex.) and metacinnabar (HgS, cub.) dominate. Calcined wastes in which Hg ore was crushed and roasted in excess of 600xa0°C, contain high proportions of metacinnabar while the main Hg-containing phase in unroasted waste rock samples from the same mines is cinnabar. The calcining process is thought to promote the reconstructive phase transformation of cinnabar to metacinnabar, which typically occurs at 345xa0°C. The total Hg concentration in calcines is strongly correlated with particle size, with increases of nearly an order of magnitude in total Hg concentration between the 500–2000 μm and III -EXAFS analysis of samples from Au mining regions, where elemental Hg(0) was introduced to aid in the Au recovery process, identified the presence of Hg-sulfides and schuetteite (Hg 3 O 2 SO 4 ), which may have formed as a result of long-term Hg(0) burial in reducing high-sulfide sediments.

The layered sodium silicate magadiite; an analog to smectite for benzene sorption from water

Smectites have long been recognized as useful adsorbents for environmental pollutants due to their ability to exchange interlayer cations for charged organic or metal cations in solution. In natural smectite, the negative charge within the interlayer is partially compensated by alkali and alkaline earth cations, particularly K, Ca and Na. In the presence of water, these cations become strongly hydrated and create a highly hydrophilic environment. Such an environment allows the adsorption of charged organic cations through ion exchange. Because non-ionic organic compounds (NOCs), such as benzene, cannot compete with the highly polar water molecules, they are not effectively adsorbed. A number of investigators have remedied this problem by intercalating large organic cations within the interlayer sites of smectite (reviewed by Sheng et al. 1996). These organic cations typically include a charged terminal group (such as -NH3) attached to a long, nonpolar hydrocarbon chain. Through the substitution of large organic cations into the smectite interlayer, the formerly hydrophilic interlayer site is made increasingly hydrophobic as the hydrated metal cations are replaced with organic cations. As a result, the interlayer sites are more effective sorbents for NOCs. Like smectite, the layered Na-silicate magadiite (Na2Si14029.9H20) is easily intercalated with large organic cations, such as hexadecyltrimethylammonium (HDTMA) or hexadecylpyridinium (HPD) (Lagaly et al. 1975a). Magadiite was first identified by Eugster (1967) in Lake Magadi, Kenya, but it has since been found in Alkali Lake, Oregon (Rooney et al. 1969), and Trinity County, California (McAtee et al. 1968). Although the structure of magadiite is not known, studies of the basal spacing of magadiite in air and vacuo (Brindley 1969) and after intercalation with various organic cations (Lagaly et al. 1975a, 1975b) strongly suggest that magadiite consists of layered silicate sheets that are loosely bonded by hydrated sodium cations. The high propensity for cation exchange of magadiite suggests that it may serve as an analog to smectites for the sorption of NOCs. One possible advantage of magadiite-like sorbents is their ease of synthesis. Whereas the formation of smectite in the laboratory at low temperatures (--<150 ~ requires complex procedures and often results in poorly crystalline material (Guven 1988), magadiite readily precipitates from Naand silica-rich solutions at temperatures from 100 to 175 ~ (Beneke and Lagaly 1983; Fletcher and Bibby 1987; Muraishi 1989; Yates and Heaney 1995). In light of these observations, the present study was initiated to compare the sorption behavior of magadiite with that of bentonite in aqueous solutions containing a range of benzene concentrations.

Application of three methods for determining mercury speciation in mine waste

Three methods, pyrolytic and chemical extractions (PCE), extended X-ray adsorption fine structure spectroscopy (EXAFS) and solid-phase-Hg-thermo-desorption (SPTD) were applied to determine mercury speciation in amended substrates and mine waste samples. Although these three methods determine Hg speciation by fundamentally different processes, comparison of the results are useful for validation of the three methods. PCE uses pyrolysis and weak leaches to determine relative percentages of volatile, ‘soluble’ and residual Hg in substrate. The results are operationally defined and specific species cannot be determined with this method. EXAFS is a nondestructive method which uses high energy synchrotron-sourced X-ray radiation to identify specific species based on scattering patterns. Least squares data analysis is done to link patterns to a database of model compounds. This method is most useful for identification of specific species, given that they are included in the model database. Identification of Hg0 is difficult using EXAFS. SPTD identifies Hg species by incremental heating and comparison of thermal release patterns to a database of compounds. SPTD allows the identification of a more limited number of specific species than EXAFS, but is the best of the three methods for the identification of Hg0. Overlapping release patterns make the identification of species, such as HgS and some forms of matrix-bound Hg, difficult. Results of PCE analyses indicate that volatile and leachable forms of Hg in mine waste are low relative to the total Hg concentration. This was supported by EXAFS and SPTD analysis which identified HgS as the primary component of mine waste. In contrast, analysis of tailings from mills that utilized Hg to amalgamate Au and Ag from ores yielded conflicting results. The results of this study illustrate the importance of using multiple analytical methods for the evaluation of Hg in the substrate.

Environmental Impact of the Helen, Research, and Chicago Mercury Mines on Water, Sediment, and Biota in the Upper Dry Creek Watershed, Lake County, California

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Figure 3. Silica-carbonate alteration developed along the mineralize fault zone in serpentinite (barren slopes) at Chicago mercury mine in the upper part of Dry Creek.. iv Figure 6. Helen mine drainage and FeOOH precipitate 100 feet from adit. Hg concentration in filtered surface water is 3 ng/L (sample HEL0703W3) and is much higher, 52-710 ng/L in filtered (<0.2m) pore waters (samples HEL0703SED1A and 1B) taken from a core in the FeOOH Figure 7. Mine drainage effluent channel in waste rock developed downstream from the Helen Mine. .35 Figure 8. Iron oxyhydroxide precipitate containing 550 ppm mercury precipitated from mine drainage effluent from the Helen Mine after waters have reacted with waste rock.. Figure 10. Helen tributary coated with FeOOH resulting from mine drainage from the Helen Mine area. The site is located just above the confluence with Dry Creek (sample sites 21HM3 and Figure 17. Chicago Mine remains of brick retort and pile of waste rock and calcines (sample sites for 21-CH-1C and 2C). The remains of the ore crib are located on the north bank of Dry Creek, which is shown in the lower right of the photo.. Figure 18. Calcines and condenser soot (sample sites 21-CH-4C, 450 ppm Hg,) below waste rock near ore crib (lower right in fig. Figure 24. Lower mine drainage seep at Helen Mine (as in fig. 8). The white, efflorescent salt along the margin was sampled in July during dry season (sample sites 23HM11and HEL0703W4). .....47 Figure 25. Log plot of Mg verses SO4 in mine drainage from the Helen and Research mines and in waters in Dry Creek and the Helen Mine tributary to Dry Creek. The Helen Mine tributary is dominantly mine drainage effluent that is diluted by surface water. Dry Creek water downstream, noted by D, from the confluence with the Helen Mine tributary has higher sulfate than water above the confluence, noted by A. The sample point noted by D has a higher sulfate concentration than does point A, which was sampled during a higher flow Figure 33. Speciation of Hg in Dry Creek sediment samples, collected 4 km downstream from the Helen Mine consisting of a clay-silt and a medium sand sample. Hg speciation determined by sequential chemical extraction indicates …