Ultrafine Mineral Associations in Superhigh-Organic-Sulfur Kentucky Coals

Two high-organic-sulfur Kentucky coals, the eastern Kentucky River Gem coal and the western Kentucky Davis coal, are examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), both including elemental analysis by energy-dispersive spectroscopy (EDS). From the SEM–EDS analysis, it is observed that the western Kentucky coal had areas with Pb and Cd in addition to the expected Fe and S and the eastern Kentucky coal had individual Fe–S-rich areas with La and Ni and with Si, Al, Cr, Ni, and Ti. TEM and selected area electron diffraction (SAED) analyses demonstrate that anglesite with a rim of Pb-bearing amorphous Fe-oxide occurs in the western Kentucky coal. Melanterite, an Fe-sulfate, with minor Al, Si, and K EDS peaks, suggests that clay minerals may be in close association with the sulfate, is also detected in the coal. A polycrystalline metal in the eastern Kentucky sample with a composition similar to stainless steel is adjacent to an Al-rich shard. Euhedral pyrite grains surrounded by kaolinite and gibbsite are detected. Overall, it is noted that element associations should not be assumed to be organic just because minerals cannot be seen with optical microscopy or with standard bulk analytical techniques, such as X-ray diffraction (XRD)

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

Shining Light on Black Rock Coatings in Smelter-Impacted Areas

Earth scientists have long known of the existence of black coatings on exposed rocks in smelter-impacted areas such as Sudbury, Ontario or Rouyn-Noranda, Québec. Black rock coatings in the Greater Sudbury area are remarkable geological records of atmospheric conditions, including mixing, scavenging, and oxidation processes, deposition rates, and the nature and source of anthropogenic releases to the atmosphere. The coatings are composed of an amorphous silica matrix that has trapped atmosphere-borne nanoparticles and has preserved their chemical and isotopic signature. These coatings are the product of high emissions of SO2 and subsequent non-stoichiometric dissolution of exposed siliceous rocks. The coatings contain spherical smelter-derived Cu–Ni-oxide particulate matter (micrometre and nanometre-sized) and metal-sulphate rich layers composed of nanometer aggregates of Fe–Cu sulphates. Lead, As, and Se-bearing nanoparticles emitted from smelters are incorporated in metal-sulphate-rich layers along the atmosphere-coating interface, presumably during coating formation. On a regional scale, ratios between different metal(loid)s in the coatings indicate that small diameter primary Pb, As and Se-bearing sulphate aerosols have been deposited at higher rates compared to larger, Ni-bearing particulate matter. High sulphur isotope values in coatings closer to smelting centres and their decrease with distance from the smelters is attributed to an increase in mixing of primary and secondary sulphates. SOMMAIRELes géoscientifiques connaissent depuis longtemps l’existence d’une couche noire sur les roches exposées aux abords des fonderies comme celles de Sudbury en Ontario ou Rouyn-Noranda au Québec.   Les couches noires des roches de la grande région de Sudbury constituent de remarquables enregistrements géologiques des phénomènes atmosphériques, notamment des processus de mélange, de piégeage, et d'oxydation, ainsi que des taux de sédimentation et de la nature et de l’origine des rejets anthropiques dans l'atmosphère.   Ces couches noires sont constituées d'une matrice de silice amorphe qui a piégé des nanoparticules atmosphériques et conservé leur signature chimique et isotopique.  Ces couches noires sont le produit de fortes émissions atmosphériques de SO2 et d’une dissolution non-stœchiométrique subséquente des roches siliceuses exposées.  Ces couches noires contiennent des sphérules de particules atmosphériques d’oxydes de Cu-Ni (de taille micrométrique et nanométrique) issues de la fonderie, et des couches riches en sulfate de métaux constituées d’agrégats nanométriques de sulfates de Fe-Cu.   Les nanoparticules de plomb, d’As et de Se émises par les fonderies sont incorporées dans les couches riches en sulfate de métal à l'interface de l’atmosphère et de cette couche, probablement lors de la formation de cette couche.  À l’échelle régionale, les rapports de concentration des différents métaux ou métalloïdes dans les couches noires indiquent que les aérosols de faible diamètre de sulfate de Pb, d’As et de Se primaires ont été déposés à des taux plus élevés que les particules nickélifères de plus grande dimension.  Les valeurs plus élevées des isotopes du soufre observées dans les couches à proximité des fonderies et leur diminution en fonction de l’éloignement des fonderies sont attribuées à une augmentation du mélange entre sulfates à l’émission et post-émission

Past, present and future global influence and technological applications of iron-bearing metastable nanominerals

Iron-bearing nanominerals such as ferrihydrite, schwertmannite, and green rust behave as metastable precursors leading to the formation of more thermodynamically stable iron mineral phases (e.g., jarosite, goethite, hematite, and magnetite). However, this transformation may last from days to tens or even hundreds of years, making them the most predominant iron-bearing minerals at environmental conditions and at the human time scale. The present review characterizes ferrihydrite, schwertmannite, and green rust nanominerals according to their main physical and chemical properties, and at both nano- and meso-scales. It also presents a comprehensive review of the multiple past and present Earth environments where these nanominerals have played, and still play, a pivotal role in the geochemistry, mineralogy and environmental nanogeosciences of these environments. Finally, the present and future technological applications of these nanominerals as well as their role in the generation of a more sustainable human-Earth relationship is discussed, with a special emphasis on their use in new circular economies and green based technologies

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

Fall 2007 American Geophysical Union Meeting Student Travel Support for Environmental Nanomaterials Session (#B35) (December 10-14, 2007)

The purpose of award no. DE-FG02-08ER15925 was to fund travel for students to present at the Fall 2007 American Geophysical Meeting. This was done successfully, and five students (Bin Xie, Qiaona Hu, Katie Schreiner, Daria Kibanova, and Frank-Andreas Weber) gave excellent oral and poster presentations at the meeting. Provided are the conference abstracts for their presentations

One hundred mineralogical questions impacting the Future of the earth, planetary and environmental sciences

We aim to identify 100 mineralogical questions that, if answered, would have the greatest impact on resolving current and future challenges in the Earth, planetary, environmental and material sciences

Discovering Environmentally-Critical Nanomineralogy: Highly Reactive Mn-Oxyhydroxide Nanofiber Nucleation and Growth Catalyzed by Nanohematite

Manganese oxides typically form by the oxidation of aqueous Mn(II) catalyzed by mineral surfaces and are nonspecific but potent redox-active mineral components commonly found in the environment. They therefore participate in a wide array of reactions with organic and inorganic compounds. They often exhibit high sorptive reactivities and capacities exceeding those exhibited by iron oxides. When present, they can play a key role in the mobility and bioavailability of important aqueous ions. The present study investigates abiotic Mn(II) oxidation catalyzed by nanoparticulate hematite in the presence of molecular oxygen in batch reactors. The kinetics of the reaction is studied as a function of the hematite particle size and the presence of organic ligands. The effect of organic ligands on the morphology of Mn-oxides is also studied. Surface-area normalized rate constants suggest differences in reactivity of hematite depending on its particle size. The end product of Mn(II) oxidation, a higher valent manganese oxyhydroxide identified as the mineral hausmannite, has been characterized by employing a suite of analytical techniques including high-resolution TEM, EELS mapping, SAED and SEM. The resultant Mn-oxyhydroxides have a unique nanosized, fiber-like morphology. SEM analyses were used to describe the formation and growth of Mn-oxyhydroxides fibers over time. Mössbauer analysis on nanoparticulate hematite after complete Mn(II) oxidation indicate small detectable amounts of Fe(II) suggesting hematite reduction and resorption of ferrous iron. These findings suggest that the formation of Mn-oxides can be influenced by the bulk mineralogical and geochemical composition of the surrounding environment, as well as by the interfacial solute–solid nanochemistry of the solid-phase oxidant. This study further signifies the relevance of lowtemperature interfacial geochemistry in the formation and the transformation of environmentally pertinent nanominerals

Discovering Environmentally-Critical Nanomineralogy: Highly Reactive Mn-Oxyhydroxide Nanofiber Nucleation and Growth Catalyzed by Nanohematite

Manganese oxides typically form by the oxidation of aqueous Mn(II) catalyzed by mineral surfaces and are nonspecific but potent redox-active mineral components commonly found in the environment. They therefore participate in a wide array of reactions with organic and inorganic compounds. They often exhibit high sorptive reactivities and capacities exceeding those exhibited by iron oxides. When present, they can play a key role in the mobility and bioavailability of important aqueous ions. The present study investigates abiotic Mn(II) oxidation catalyzed by nanoparticulate hematite in the presence of molecular oxygen in batch reactors. The kinetics of the reaction is studied as a function of the hematite particle size and the presence of organic ligands. The effect of organic ligands on the morphology of Mn-oxides is also studied. Surface-area normalized rate constants suggest differences in reactivity of hematite depending on its particle size. The end product of Mn(II) oxidation, a higher valent manganese oxyhydroxide identified as the mineral hausmannite, has been characterized by employing a suite of analytical techniques including high-resolution TEM, EELS mapping, SAED and SEM. The resultant Mn-oxyhydroxides have a unique nanosized, fiber-like morphology. SEM analyses were used to describe the formation and growth of Mn-oxyhydroxides fibers over time. Mössbauer analysis on nanoparticulate hematite after complete Mn(II) oxidation indicate small detectable amounts of Fe(II) suggesting hematite reduction and resorption of ferrous iron. These findings suggest that the formation of Mn-oxides can be influenced by the bulk mineralogical and geochemical composition of the surrounding environment, as well as by the interfacial solute–solid nanochemistry of the solid-phase oxidant. This study further signifies the relevance of lowtemperature interfacial geochemistry in the formation and the transformation of environmentally pertinent nanominerals

Abiotic U(VI) Reduction by Biogenic Mackinawite

Biostimulation of dissimilatory metal and/or sulfate reducing bacteria (DMRB and DSRB) has been extensively researched as a remediation strategy for mitigating subsurface uranium [U(VI)] contamination. These bacteria derive energy by reducing oxidized metals as terminal electron acceptors by utilizing organic substrates as electron donors. Iron [Fe(III)], an abundant subsurface element, represents a substantial sink for electrons from DMRB, and the reduction of Fe(III) leads to the presence of dissolved Fe(II) and/or reactive biogenic Fe(II)- and mixed Fe(II)/Fe(III)- mineral phases. Likewise, reduction of other electron acceptors such as sulfates by DSRB leads to the formation of sulfide-bearing minerals in subsurface environments. Thus, when evaluating the potential for insitu uranium remediation in heterogeneous subsurface media, it is important to understand how the presence of alternative electron acceptors such as Fe(III) and sulfate affect U(VI) remediation and the long term behavior and reactivity of reduced uranium. Consequently, abiotic U(VI) reduction by reactive forms of biogenic Fe(II) and sulfide-bearing minerals will be a potentially important process for uranium immobilization. In this study, amendment of Fe(III) and sulfate to a culture of Shewanella putrefaciens CN32 (DMRB) bacterium, resulted in the production of biogenic mackinawite, a Fe(II)-bearing sulfide mineral. This biogenic mineral was systematically characterized by X-ray powder diffraction (XRD), electron microscopy (SEM, TEM, HRTEM) and Mössbauer spectroscopy. Batch experiments involving biogenic mackinawite and U(VI) were carried out at room temperature under strict anoxic conditions. Following complete reduction of uranium (determined by ICP analysis), the biogenic mackinawite was analyzed by a suite of analytical techniques including X-ray absorption spectroscopy (XAS), SEM, HRTEM and Mössbauer spectroscopy to determine the speciation of uranium and concomitant phase transformation(s) with respect to mackinawite. SEM and selected area electon diffraction (SAED) analyses showed reduction of U(VI) to nanoparticulate UO2 on the surface of biogenic mackinawite. These findings are consistent with XANES analysis that indicate reduction of U(VI) to U(IV) and μXRF analysis that was used to map iron and uranium in the sample. Determining the speciation of uranium is critical to success of a remediation strategy. The present work elucidates abiotic molecular scale redox interactions between biogenic mackinawite and uranium