High Resolution Scanning Auger Microscopy of Mineral Surfaces

There are a number of cases where scanning Auger microscopy can be used to determine the near-surface composition of minerals with extremely high lateral resolution. This involves collecting Auger spectra with reasonable signal to noise ratios without encountering significant beam induced charging or surface degradation, even if the beam is impinging on a grain less than 1μm in diameter. We typically use a 3 keV beam with less than 10 nA beam current on a sample surface that is tilted (to increase backscattered and secondary electron emission efficiency) and relatively flat. To further minimize surface degradation, vacuum levels are kept high and the beam is rastered or defocused whenever possible. The Auger spectra of minerals can be used to study modification of surfaces due to geochemical influences or to identify submicron grains if the near-surface composition is representative of the bulk composition. Also, high lateral resolution step scans can be performed across sharp interfaces between two grains, allowing for short-range studies of solid-solid interactions in rocks at grain boundaries. We also report on preliminary attempts to chemically quantify Auger peak intensities for silicate minerals. Measurements of peak-to-peak heights for oxygen and silicon lines for eight silicate minerals of well-known composition indicate that Auger sensitivity factors can vary significantly with O/Si ratio

A review on Pb-bearing nanoparticles, particulate matter and colloids released from mining and smelting activities

Lead (Pb) is one of the most paradoxical elements, both having diverse practical uses, as well as being extremely toxic to humans, and especially to children. The use of Pb records a steady growth with annual production currently exceeding 10 million metric tons. In spite of the environmental awareness of modern society, humans are still exposed to Pb through its emission by smelting and mining activities, and also by Pb-bearing mine wastes and soils. Here, we review the chemical and mineralogical forms of Pb generated from smelting and mining processes and subsequently altered in tailings, slag piles, and soils. In smelter plumes, Pb is emitted to the atmosphere either in the form of smaller nano-size particulate matter (PM) often associated with S, or larger micrometer Pb-bearing PM matter accompanied by oxide-silicate matrices. Pb-bearing phases in mine tailings and impacted soils depict a greater mineralogical and chemical complexity than those emitted from smelters and the larger particle size of this PM also leads to a lower Pb bioavailability. High resolution observations in aquatic system, soils and rock coatings impacted by smelting and mining activities show the presence of Pb-bearing phosphates, sulfides, sulfates, carbonates, and oxide nanoparticles. Larger micrometer size particles of Pb-bearing minerals form often through the aggregation of Pb-bearing nanoparticles, a process commonly referred to as crystallization through particle attachment. Mobilization of Pb within soil columns is strongly affected by the transport of colloids, especially those composed of organic matter and Fe-hydroxides because Pb is taken up efficiently by these two soil components. The extraordinary variability and complexities of all of these processes suggest that future reduction of Pb contamination in the environment and its impact on human health mainly depends on eliminating or greatly reducing Pb-release from smelting operations and tailings impoundments

Nanoscale Processes in the Environment: Nanobiogeochemistry of Microbe/Mineral Interactions

This project involves the application of nanoscience to the fields of fundamental and applied environmental geochemistry and biogeochemistry [1] Probing ligand-mineral interactions at the nanoscale: We have developed a chemical force microscopy (CFM) technique that probes the forces of interaction in aqueous solution between complex organic molecules and mineral surfaces in both distance and force nanospace. Using this method, previously unknown interactions between microbially produced siderophores and iron oxide mineral surfaces have been revealed Iron is a required nutrient for all organisms including bacteria, fungi and plants. The insoluble nature of iron in oxidizing, circumneutral aqueous environments, however, limits concentrations to levels well below the 10 -7 -10 -8 M required for bacterial growth. A response to this limitation is the extracellular release of low molecular weight biomolecules known as siderophores. With formation constants (K f ) on the order of 10 20-10 5 0 , the siderophore-Fe(III) complex is highly stable and thermodynamically favorable under environmental conditions. Indeed, much is known about siderophore interaction with soluble sources of iron; however, the largest source of iron in soils are solid forms, specifically, oxide minerals. Siderophores are known to release ferric iron from minerals, but the nature of the interaction of siderophores with the surface and the associated dissolution mechanism has been unknown. The CFM techniques used in this study have allowed us to directly measure the forces of interaction between siderophores and mineral surfaces for the first time A protein coupling technique was employed to covalently attach the siderophore azotobactin to a hydrazide terminated AFM tip. The activated tip was probed against two minerals: goethite (aFeOOH) and its isostructural Al-equivalent diaspore (a-AlOOH). Upon contact with each mineral surface, the adhesion force between azotobactin and the iron containing goethite was two to three times the value observed for the isostructural Al-equivalent diaspore. The relative force affinity for the iron containing mineral (versus aluminum) correlates with the difference between the aqueous complex formation constants estimated for azotobactin and Fe(III) (aq) (K f =10 2 8 ) and Al(III) (aq) (K f~1 0 1 6 ). Further, the adhesion force between azotobactin and goethite significantly decreases (4 nN to 2 nN) when small amounts of soluble iron (0.1 mM FeCl 3 ·6H 2 O) are added to the system at pH 3.5 suggesting a significant specific interaction between azotobactin's chelating groups and the mineral surface. Specifically, plateau features in the force data generated upon tip retraction fro

Nanoscale Processes in the Environment: Nanobiogeochemistry of Microbe/Mineral Interactions

This project involves the application of nanoscience to the fields of fundamental and applied environmental geochemistry and biogeochemistry [1] Probing ligand-mineral interactions at the nanoscale: We have developed a chemical force microscopy (CFM) technique that probes the forces of interaction in aqueous solution between complex organic molecules and mineral surfaces in both distance and force nanospace. Using this method, previously unknown interactions between microbially produced siderophores and iron oxide mineral surfaces have been revealed Iron is a required nutrient for all organisms including bacteria, fungi and plants. The insoluble nature of iron in oxidizing, circumneutral aqueous environments, however, limits concentrations to levels well below the 10 -7 -10 -8 M required for bacterial growth. A response to this limitation is the extracellular release of low molecular weight biomolecules known as siderophores. With formation constants (K f ) on the order of 10 20-10 5 0 , the siderophore-Fe(III) complex is highly stable and thermodynamically favorable under environmental conditions. Indeed, much is known about siderophore interaction with soluble sources of iron; however, the largest source of iron in soils are solid forms, specifically, oxide minerals. Siderophores are known to release ferric iron from minerals, but the nature of the interaction of siderophores with the surface and the associated dissolution mechanism has been unknown. The CFM techniques used in this study have allowed us to directly measure the forces of interaction between siderophores and mineral surfaces for the first time A protein coupling technique was employed to covalently attach the siderophore azotobactin to a hydrazide terminated AFM tip. The activated tip was probed against two minerals: goethite (aFeOOH) and its isostructural Al-equivalent diaspore (a-AlOOH). Upon contact with each mineral surface, the adhesion force between azotobactin and the iron containing goethite was two to three times the value observed for the isostructural Al-equivalent diaspore. The relative force affinity for the iron containing mineral (versus aluminum) correlates with the difference between the aqueous complex formation constants estimated for azotobactin and Fe(III) (aq) (K f =10 2 8 ) and Al(III) (aq) (K f~1 0 1 6 ). Further, the adhesion force between azotobactin and goethite significantly decreases (4 nN to 2 nN) when small amounts of soluble iron (0.1 mM FeCl 3 ·6H 2 O) are added to the system at pH 3.5 suggesting a significant specific interaction between azotobactin's chelating groups and the mineral surface. Specifically, plateau features in the force data generated upon tip retraction fro

Potential use of engineered nanoparticles in ocean fertilization for large-scale atmospheric carbon dioxide removal

Artificial ocean fertilization (AOF) aims to safely stimulate phytoplankton growth in the ocean and enhance carbon sequestration. AOF carbon sequestration efficiency appears lower than natural ocean fertilization processes due mainly to the low bioavailability of added nutrients, along with low export rates of AOF-produced biomass to the deep ocean. Here we explore the potential application of engineered nanoparticles (ENPs) to overcome these issues. Data from 123 studies show that some ENPs may enhance phytoplankton growth at concentrations below those likely to be toxic in marine ecosystems. ENPs may also increase bloom lifetime, boost phytoplankton aggregation and carbon export, and address secondary limiting factors in AOF. Life-cycle assessment and cost analyses suggest that net CO2 capture is possible for iron, SiO2 and Al2O3 ENPs with costs of 2–5 times that of conventional AOF, whereas boosting AOF efficiency by ENPs should substantially enhance net CO2 capture and reduce these costs. Therefore, ENP-based AOF can be an important component of the mitigation strategy to limit global warming

Nanoparticles in fossil and mineral fuel sectors and their impact on environment and human health: A review and perspective

Nanoscience and technology have enabled better insights into the environmental and health impacts arising from the mining, production and use of fossil and mineral fuels. Here we provide an overview of the nanoscience-based applications and discoveries concerning coal and mineral fuel (i.e., uranium-containing minerals) mining, refining/production, use, and disposal of wastes. These processes result in massive nanoparticle release and secondary nanoparticle generation which have highly significant environmental implications and human health consequences on local, regional, and even global levels. Until recently, very little was known about nanoparticle fractions. Recent advancements and sophistications enable us to detect, collect and study these materials which are roughly 1 nm (0.001 μm) up to several tens of nanometers in size. These materials are known to behave differently (chemically, electrically, and mechanically), relative to their macroscopic equivalents. This is what makes nanoscience fascinating and difficult to predict, underscoring the importance of this emerging new field. For example, nanoparticles associated with coal and mineral fuel influence the release, uptake, and transportation of hazardous elements associated with mining, processing, and waste storage in the surrounding areas. This includes long distance transport down streams, rivers, and eventually to oceans such as from coal and uranium mine drainages. In terms of human health, in all phases of mining, production/refining, use, and waste disposal, the associated nanoparticles can be acquired through oral ingestion, inhalation, and dermal absorption. Inhalation has been shown to be particularly damaging, where lung, heart, kidney, and brain diseases are prevalent. Relative to all other fields of science and engineering associated with coal and mineral fuel mining, production, use, and clean-up efforts, nanoscience, although a much newer field then the rest by comparison, is still greatly under-represented and under-utilized. There is also a continuing gap between what we so far know about the behavior of nanoparticles, and what remains to be discovered

Low Concentrations of Silver Nanoparticles in Biosolids Cause Adverse Ecosystem Responses under Realistic Field Scenario

A large fraction of engineered nanomaterials in consumer and commercial products will reach natural ecosystems. To date, research on the biological impacts of environmental nanomaterial exposures has largely focused on high-concentration exposures in mechanistic lab studies with single strains of model organisms. These results are difficult to extrapolate to ecosystems, where exposures will likely be at low-concentrations and which are inhabited by a diversity of organisms. Here we show adverse responses of plants and microorganisms in a replicated long-term terrestrial mesocosm field experiment following a single low dose of silver nanoparticles (0.14 mg Ag kg−1 soil) applied via a likely route of exposure, sewage biosolid application. While total aboveground plant biomass did not differ between treatments receiving biosolids, one plant species, Microstegium vimeneum, had 32 % less biomass in the Slurry+AgNP treatment relative to the Slurry only treatment. Microorganisms were also affected by AgNP treatment, which gave a significantly different community composition of bacteria in the Slurry+AgNPs as opposed to the Slurry treatment one day after addition as analyzed by T-RFLP analysis of 16S-rRNA genes. After eight days, N2O flux was 4.5 fold higher in the Slurry+AgNPs treatment than the Slurry treatment. After fifty days, community composition and N2O flux of the Slurry+AgNPs treatment converged with the Slurry. However, the soil microbial extracellular enzymes leucine amino peptidase and phosphatase had 52 and 27% lower activities, respectively, while microbial biomass was 35% lower than the Slurry. We also show that the magnitude of these responses was in all cases as large as or larger than the positive control, AgNO3, added at 4-fold the Ag concentration of the silver nanoparticles

Adatom Fe(III) on the hematite surface: Observation of a key reactive surface species

The reactivity of a mineral surface is determined by the variety and population of different types of surface sites (e.g., step, kink, adatom, and defect sites). The concept of "adsorbed nutrient" has been built into crystal growth theories, and many other studies of mineral surface reactivity appeal to ill-defined "active sites." Despite their theoretical importance, there has been little direct experimental or analytical investigation of the structure and properties of such species. Here, we use ex-situ and in-situ scanning tunneling microcopy (STM) combined with calculated images based on a resonant tunneling model to show that observed nonperiodic protrusions and depressions on the hematite (001) surface can be explained as Fe in an adsorbed or adatom state occupying sites different from those that result from simple termination of the bulk mineral. The number of such sites varies with sample preparation history, consistent with their removal from the surface in low pH solutions

Physicochemical conditions and timing of rodingite formation: evidence from rodingite-hosted fluid inclusions in the JM Asbestos mine, Asbestos, Québec

Fluid inclusions and geological relationships indicate that rodingite formation in the Asbestos ophiolite, Québec, occurred in two, or possibly three, separate episodes during thrusting of the ophiolite onto the Laurentian margin, and that it involved three fluids. The first episode of rodingitization, which affected diorite, occurred at temperatures of between 290 and 360°C and pressures of 2.5 to 4.5 kbar, and the second episode, which affected granite and slate, occurred at temperatures of between 325 and 400°C and pressures less than 3 kbar. The fluids responsible for these episodes of alteration were moderately to strongly saline (~1.5 to 6.3 m eq. NaCl), rich in divalent cations and contained appreciable methane. A possible third episode of alteration is suggested by primary fluid inclusions in vesuvianite-rich bodies and secondary inclusions in other types of rodingite, with significantly lower trapping temperatures, salinity and methane content. The association of the aqueous fluids with hydrocarbon-rich fluids containing CH4 and higher order alkanes, but no CO2, suggests strongly that the former originated from the serpentinites. The similarities in the composition of the fluids in all rock types indicate that the ophiolite had already been thrust onto the slates when rodingitization occurred