Johnnie N. Moore

High-Resolution Particle Size Analysis of Naturally Occurring Very Fine-Grained Sediment Through Laser Diffractometry

ABSTRACT In this paper, we present results from a large number of experiments aimed at quantifying method and instrument uncertainty associated with laser diffraction analysis. We analyzed the size distribution of fine-grained sediment ( 24 hours prior to analysis and using 60 seconds of ultrasonication during analysis. (2) Obscuration--a measure of the concentration of the suspension during analysis--produced the most reproducible results at about 20%. (3) Variations in refractive-index settings can significantly alter estimated grain-size distributions. (4) Assumed values for absorption (the degree to which sediment grains absorb the light) can have a profound effect on grain-size results. Absorption settings near 0 resulted in unexpected bimodal grain size distributions for sediments in the < 10 µm size fraction and significantly skewed the fine-grained tail of coarser samples, probably because of sub-optimal diffraction by particles with a diameter similar in size to the laser wavelength. Absorption settings closer to 1 produced very reproducible results and unimodal grain-size distributions over a wide range of refractive indexes. Our study has shown that laser diffraction can measure very fine-grained sediments (< 10 µm) quickly, with high precision ( 5% at 2 standard deviations), and without the need for extensive mineralogical determinations. These results make possible a new generation of studies in which high-resolution time-series data sets of sediment grain size can be used to infer subtle changes in paleohydrology.

A TEM study of samples from acid mine drainage systems: metal-mineral association with implications for transport

Transmission electron microscopy (TEM), with energy dispersive X-ray (EDX) analysis and energy filtered transmission electron microscopy/electron energy loss spectroscopy (EFTEM/EELS), as well as powder X-ray diffraction (XRD) and scanning electron microscopy (SEM), have been used to study bed sediments from two acid mine drainage (AMD) sites in western Montana, USA. TEM and associated techniques, including sample preparation via epoxy impregnation and ultramicrotome sectioning, afford the opportunity to better interpret and understand complex water-rock interactions in these types of samples. For the sample taken from the first site (Mike Horse mine), ferrihydrite is the dominant phase, Si and Zn are the most abundant elements sorbed to ferrihydrite surfaces, and Pb is notably absent from ferrihydrite association. Three additional important metal-containing phases (gahnite, hydrohetaerolite, and plumbojarosite), that were not apparent in the powder XRD pattern because of their relatively low concentration, were identified in the TEM. The presence of these phases is important, because, for example, gahnite and plumbojarosite act as sinks for Zn and Pb, respectively. Therefore, the mobility of Pb from this part of the drainage system depends on the stability of plumbojarosite and the ability of ferrihydrite to sorb the released Pb. From thermodynamic data in the literature, we predict that Pb will be released by the dissolution of plumbojarosite above a pH of 4 to 5, but it will then be recaptured by ferrihydrite if the pH continues to rise to 5.5 and higher, irrespective of competition effects from other metals. Therefore, only a relatively narrow pH window exists in which Pb can escape this portion of the system as an aqueous species. For the sample taken from the other site included in this study (the Carbonate mine), jarosite and quartz are the dominant phases. Interestingly, however, the jarosites are both Pb-poor and Pb-enriched. In addition, TEM reveals the presence of microcrystalline hematite with Si, S, and P sorbed to its surfaces, a nearly pure amorphous Si, Al oxyhydroxide, and an amorphous silica phase containing minor amounts of Al, Ca, and Fe. Pb will probably be released from these mixed K-Pb jarosites above pH 4 to 5, but the Pb may be retarded by the strongly adsorbing microcrystalline hematite in this pH range. The sink for Al in this system is the amorphous Si, Al oxyhydroxide, not Al(OH)3 which is typically used in AMD modeling schemes.

Differences in Hyporheic-Zone Microbial Community Structure along a Heavy-Metal Contamination Gradient

ABSTRACT The hyporheic zone of a river is nonphotic, has steep chemical and redox gradients, and has a heterotrophic food web based on the consumption of organic carbon entrained from downwelling surface water or from upwelling groundwater. The microbial communities in the hyporheic zone are an important component of these heterotrophic food webs and perform essential functions in lotic ecosystems. Using a suite of methods (denaturing gradient gel electrophoresis, 16S rRNA phylogeny, phospholipid fatty acid analysis, direct microscopic enumeration, and quantitative PCR), we compared the microbial communities inhabiting the hyporheic zone of six different river sites that encompass a wide range of sediment metal loads resulting from large base-metal mining activity in the region. There was no correlation between sediment metal content and the total hyporheic microbial biomass present within each site. However, microbial community structure showed a significant linear relationship with the sediment metal loads. The abundances of four phylogenetic groups (groups I, II, III, and IV) most closely related to α-, β-, and γ-proteobacteria and the cyanobacteria, respectively, were determined. The sediment metal content gradient was positively correlated with group III abundance and negatively correlated with group II abundance. No correlation was apparent with regard to group I or IV abundance. This is the first documentation of a relationship between fluvially deposited heavy-metal contamination and hyporheic microbial community structure. The information presented here may be useful in predicting long-term effects of heavy-metal contamination in streams and provides a basis for further studies of metal effects on hyporheic microbial communities.

The fate of geothermal arsenic in the Madison and Missouri Rivers, Montana and Wyoming

Geothermal As from Yellowstone National Park causes high As concentrations (10–370 μg/L) in the Madison and Missouri Rivers in Montana and Wyoming. Arsenic transport is largely conservative in the upper basin as demonstrated by the near equivalence of dissolved and total-recoverable As concentrations, the constancy of As loads, and consistent ratios of concentrations of As to conservative geothermal tracers. Diurnal cycling of As between aqueous and solid phases in response to pH-induced changes in sorption equilibria causes small variations of about 10–20% in dissolved As concentrations. HCl-extractable As concentrations in river and lake sediment in the upper basin are variable depending on position relative to the As-rich headwaters and geochemical and physical processes associated with lakes. In the lower Missouri River, large quantities of suspended sediment from tributaries provide sufficient sorption sites for substantial conversion of As from the aqueous phase to the solid phase.

Grain size partitioning of metals in contaminated, coarse-grained river floodplain sediment: Clark Fork River, Montana, U.S.A.

The traditional concept of the relationship between metal content and grain size assumes that the fine fraction carries most of the metals in natural sediments. This concept is supported in many cases by strong, significant linear relationships between total-sediment metal concentrations and percentages of various fine-size fractions. Such observations have led to development of methods to correct for the effects of grain size in order to accurately document geographical and temporal variations and identify trends in metal concentrations away from a particular source. Samples from the floodplain sediment of a large, coarse-grained river system indicates that these concepts do not hold for sediments contaminated by mining and milling wastes. In this particular system, the application of methods to correct for grain-size effects would lead to erroneous conclusions about trends of metals in the drainage. This indicates that the a priori application of grain-size correction factors limits interpretation of actual metal distributions and should not be used unless data indicate that correlations exist between metals and particular size fractions.

Mineralogy and trace element association in an acid mine drainage iron oxide precipitate; comparison of selective extractions

Abstract Mineral and trace element characterization of an Fe-rich precipitate from an acid mine system was accomplished by X-ray diffraction (XRD), differential X-ray diffraction, and ICP chemical analysis. A primary objective was to evaluate the effectiveness of common selective dissolution treatments in determining the association of minerals with potentially toxic trace elements. The precipitate consisted primarily of goethite, a poorly crystalline phase resembling synthetic ferrihydrite, dolomite and gypsum in clay-size fractions. The ammonium oxalate and EDTA treatments, which are thought by some workers to dissolve only poorly crystalline phases, were found to dissolve a significant amount of crystalline goethite. However, the oxalate extraction did dissolve more ferrihydrite than the other treatments tested. A solution of 0.1 M hydroxylamine hydrochloride in 0.1 M HNO 3 , which is thought by some to dissolve mostly the highly soluble Mn-oxides was found to also dissolve goethite, as did 0.25 M hydroxylamine hydrochloride in 25% (v/v) acetic acid, 0.25 M hydroxylamine hydrochloride in 0.25 M HCI, 0.5 M HCI, and Na-dithionite buffered with Na-citrate and 1.0 M NaHCO 3 . Both trace and major elements that were extracted with the various treatments were found to vary significantly and non-systematically when compared to the proportion of total extractable Fe. These selective extractions cannot be used to make reliable conclusions about trace metal and mineral associations. Gypsum was identified by XRD in claysize separations from the sample, but this phase was not detected in diffraction scans of the bulk sample. This finding indicates that individual phases can be segregated by particle size.

Environmentally important, poorly crystalline Fe/Mn hydrous oxides: Ferrihydrite and a possibly new vernadite-like mineral from the Clark Fork River Superfund Complex

Abstract Ferrihydrite and a vernadite-like mineral, in samples collected from the riverbeds and floodplains of the river draining the largest mining-contaminated site in the United States (the Clark Fork River Superfund Complex), have been studied with transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis. These poorly crystalline minerals are environmentally important in this system because contaminant heavy metals (As, Cu, Pb, and/or Zn) are always associated with them. Both two- and six-line ferrihydrite have been identified with selected-area electron diffraction. For the vernadite-like mineral, the two d values observed are approximately between 0.1 and 0.2 Å larger than those reported for vernadite, the Mn hydrous oxide that is thought to have a birnessitelike structure, but which is disordered in the layer stacking direction. In several field specimens, the ferrihydrite and vernadite-like minerals are intimately mixed on the nanoscale, but they also occur separately. It is suggested that the vernadite-like mineral, found separately, is produced biogenically by Mn-oxidizing bacteria, whereas the same mineral associated with ferrihydrite is produced abiotically via the heterogeneous oxidation of Mn2+aq initially on ferrihydrite surfaces. Evidence from this study demonstrates that the vernadite-like mineral sorbs considerably more toxic metals than does ferrihydrite, demonstrating that it may be a good candidate for application to heavy-metal sorption in permeable reactive barriers.

Particle-size and chemical control of As, Cd, Cu, Fe, Mn, Ni, Pb, and Zn in bed sediment from the Clark Fork River, Montana (U.S.A.)

Mining and smelting in the headwaters of the Clark Fork River have significantly enriched Clark Fork River bed sediment in As, Cd, Cu, Mn, Pb, and Zn. These enriched elements are present predominantly in (operationally defined) “reducible” and “oxidizable” chemical phases, with small contributions from “residual” phases. In size fractionated samples (300, 63–300, 38–63, 17–38, and < 17 μm) metals and arsenic concentrations generally increase with decreasing particle size, with the greatest contribution to this increase from the “reducible” phase. Copper is an exception, with the strongest contribution to this increase from the “oxidizable” phase. Anomalously high concentrations in the coarsest (300 μm) fraction of some of the samples described in this study are due to preferential concentration of iron and manganese oxides on coarse particles, and entrapment of coarse organic material on 300 μm sieves. Clark Fork bed sediment is, in general, quite coarse; the relatively high concentrations of metals in the coarse fractions of these sediments are therefore important to the bulk metal and As content of this system.

Using FlFFF and aTEM to determine trace metal–nanoparticle associations in riverbed sediment

Environmental context. Determining associations between trace metals and nanoparticles in contaminated systems is important in order to make decisions regarding remediation. This study analysed contaminated sediment from the Clark Fork River Superfund Site and discovered that in the <1-μm fraction the trace metals were almost exclusively associated with nanoparticulate Fe and Ti oxides. This information is relevant because nanoparticles are often more reactive and show altered properties compared with their bulk equivalents, therefore affecting metal toxicity and bioavailability. Abstract. Analytical transmission electron microscopy (aTEM) and flow field flow fractionation (FlFFF) coupled to multi-angle laser light scattering (MALLS) and high-resolution inductively coupled plasma mass spectroscopy (HR-ICPMS) were utilised to elucidate relationships between trace metals and nanoparticles in contaminated sediment. Samples were obtained from the Clark Fork River (Montana, USA), where a large-scale dam removal project has released reservoir sediment contaminated with toxic trace metals (namely Pb, Zn, Cu and As) which had accumulated from a century of mining activities upstream. An aqueous extraction method was used to recover nanoparticles from the sediment for examination; FlFFF results indicate that the toxic metals are held in the nano-size fraction of the sediment and their peak shapes and size distributions correlate best with those for Fe and Ti. TEM data confirms this on a single nanoparticle scale; the toxic metals were found almost exclusively associated with nano-size oxide minerals, most commonly brookite, goethite and lepidocrocite.

Prediction of water-soluble metal concentrations in fluvially deposited tailings sediments, upper Clark Fork Valley, Montana, U.S.A.

Abstract Mine tailings deposited by historic floods contaminate large areas of the upper Clark Fork floodplain. Metal sulfates precipitate on the floodplain surface as byproducts of sulfide weathering and are concentrated by evaporation of soil moisture. These salts dissolve readily releasing high concentrations of Al, As, Cd, Cu, Fe, Mn, Zn and H + to rainwater and cause periodic fish kills when contaminated runoff reaches the river. A pollution index is proposed to quantify the average enrichment of water-soluble metals over aquatic hazard levels which occur in floodplain surface sediments. A strong correlation between pH and the pollution index was observed. Because the pollution index can be predicted from pH, reconnaissance mapping of metal contamination in surface sediments on the Clark Fork floodplain and in other contaminated river systems can be conducted simply with a pH meter.