Metal-bearing Phases Research Articles

Monitoring For Elemental Composition Of Particulate Matter Deposited In Snow Cover Around Coal-Fired Thermal Power Plant (Karaganda, Central Kazakhstan).

Studies on thermal power plant areas with respect to chemical composition of particulate matter deposited in snow cover are limited. This study aims to monitor (2014–2022) particulate load and trace elements associated with the particulate matter distributed around (0.5-4.5 km) the coal-fired thermal power plant in Karaganda. In this study, snow cover was used as an effective scavenger of atmospheric pollutants. Using instrumental neutron activation analysis and atomic absorption spectrometry, the content of 26 elements and Hg, respectively, was determined in the particulate phase of snow. The results showed that particulate load varied from 26 to 1751, with mean of 427 and a background of 47 mg m-2 d-1. Anthropogenic impact caused a significant increase in content of U, Hg, Ta, Zn, Na, Cr, Co, Sr, Rb, Cs, Sc, Ca, Fe, Nd, Ba (2–30 times) in the samples compared to the background. Metal-bearing phases of Zn, Ba, As, U-Ta-Nb were detected through scanning electron microscope. The highest levels of particulate load (169–1032 mg m-2 d-1) and element contents in the samples were localized up to 0.7 km from the thermal power plant. The changes of particulate load and element composition of snow deposits during the monitoring period were connected with temperature, modernization of dust-collecting equipment, composition of coal and fly ash, long-range transport of emissions from other industries. The element content and metal-bearing phases in the particulate phase of snow can be used as markers for identifying emission sources from coal combustion.

A novel method for extracting metals from asteroids using non-aqueous deep eutectic solvents

Extra-terrestrial mining and metal processing are vital for access to strategic metals for space exploration. This study demonstrates for the first time the catalytic dissolution of metals from meteorite proxies of metal-rich asteroids using a deep eutectic solvent (DES). DESs are of particular interest for extra-terrestrial mining as they can be designed to have relatively low vapour pressures and could potentially be made from organic waste products created in extra-terrestrial settlements. Three types of meteorites were investigated: two chondrites (H3, H5) and one iron (IAB-MG) meteorite. Chondrite samples were composed of silicates (olivine, pyroxene) with metal-rich phases occurring as native metal alloys, sulphides and oxides. Metallic Fe–Ni and troilite (FeS) are the most abundant metal-bearing phases in all three samples, particularly in the iron-rich meteorite. The samples were subjected to chemical micro-etching experiments with iodine and iron(III) chloride as oxidising agents in a DES formed from the mixture of choline chloride and ethylene glycol. Micro-etching experiments demonstrated that Fe–Ni rich phases are effectively leached out in this system, while other mineral phases remain unreactive.

Grain size and mineralogical constraints on leaching in the bottom ashes from municipal solid waste incineration: a comparison of five plants in northern Italy

Introduction: Bottom ashes (BA) from municipal solid waste incinerators (MSWIs) are currently classified by the European Waste Catalogue as industrial non-hazardous waste. To promote their reuse, identification and characterization of the heavy metal-bearing phases (both glass and minerals), as well as their weathering behavior, must be addressed for what concern the chemical composition, mineralogical phases, and in high concentrations and pollutants’ mobility. An important point to be noted is whether the results from a given plant can be generalized.Materials and methods: In this work, BA from five waste-to-energy (WtE) plants in northern Italy were sorted based on different grain sizes. The area showed similar MSW production, collected from a culturally homogeneous area, and similar collection management. For each grain size, a mineralogical, chemical, and physical characterization was carried out using XRF, XRD, TGA, and the leaching test.Results and discussion: We found that for major elements, the average chemical composition of the incinerators is similar, with some differences in minor elements. Ferrara (FE) and Forlì-Cesena (FC) BA show portlandite, higher ettringite, and less amorphous than the Torino (TO), Parma (PR), and Piacenza (PC) BA. This affects the pH, the release, and toxicity of the leachates. In FE and FC ashes, ettringite is insoluble, and we not only have low sulfate but also Ni and Ba beyond reglementary limits, suggesting that Ni and Ba are present as hydroxides with portlandite, which are soluble. In TO, PR, and PC, Cr and sulfates are beyond limits, suggesting that Cr comes from dissolution in ettringite. Cu and Cl are always beyond limits; the dissolution of chlorides accounts for only 30%–35% of the global Cl leachate. We observe that in the assessment of the potential toxicity of the ashes, mineralogy has a higher effect than the bulk chemical composition. Grain size sorting, although useful together with other techniques, is not by itself able to comply with the PTE risk level.Conclusion: The findings contribute to the development of efficient treatment strategies for BA, highlighting the need for a more thorough investigation to understand composition and properties and to find innovative ways to reuse, promoting the circular economy and sustainable waste management practices.

Metal deportment in Pb-Zn mine wastes from a historic tailings pond, Plombières, East Belgium

The exploitation of mine waste materials as secondary resources requires in-depth mineralogical analyses, with metal deportment being of particular relevance for metal recovery. Using a combination of the Scanning Electron Microscope (SEM)-based Mineral Liberation Analyser (MLA) and Electron Probe Micro-Analyser (EPMA) methods, the deportment of lead and zinc in the historic Plombières mine site (East Belgium) was investigated. The mine site comprises four different materials: soil, metallurgical waste, brown and yellow tailings. The integration of the MLA and EPMA data allowed the identification and quantification of Pb- and Zn-bearing phases, including minerals present in low abundances as well as slag phases. Different slag types and Pb oxides phases are the main sources of lead in Plombières mine waste samples. These phases host 65 to 99 % of the Pb, the rest is distributed between cerussite (0 to 37 %), and/or anglesite (0 to 17 %). Approximately 95 % of Zn is hosted by different types of slags or by fraipontite, with minor amounts contributed by sphalerite (0.1 to 3 %), gahnite (1.0 to 2.4 %), willemite (0.1 to 2.9 %), and bannisterite (0 to 3 %). The MLA/EPMA measurements were validated by comparing calculated Pb and Zn grades with bulk grades measured by X-ray fluorescence spectroscopy. The coefficients of correlation between the measured and calculated values were found to be 0.89 for lead and 0.80 for zinc. Uncertainties on the metal deportments were estimated by bootstrap resampling and are typically low. The highest uncertainties are observed when the metal-bearing phases are present in low abundances, which is particularly noticeable in the yellow tailings. Considering the promising results, the integrated approach applied in this study should be applicable to other metals and waste deposits across the globe.

Vegetation and Environmental Changes on Contaminated Soil Formed on Waste from an Historic Zn-Pb Ore-Washing Plant.

Simple SummaryRemnants of former Zn-Pb mining in southern Poland are an important element of geographical space. Some of the post-mining areas have found new economic and residential functions. Many of them are undergoing ecological succession and constitute valuable natural habitats enriching biodiversity of the surrounding landscapes. There are places where we can observe and document various ecological and geochemical transformations in its historical and contemporary aspects. These changes provide a basis for observing and functioning of ecosystems developing in an area transformed under the influence of Zn-Pb mining.Post-mining waste from Zn-Pb ore exploitation undergoes processes of spontaneous succession and changes in soil chemical composition. The Zakawie area was industrially transformed by historical mining activity, ore enrichment, and the metallurgical processing of Zn-Pb ore. The subject of the study was to analyse the rate of vegetation succession (from 1999 to 2019), soil chemistry, and the relationships between them in an anthropogenic habitat with high concentrations of potentially toxic metals. Ecological and geochemical studies were carried out in an area contaminated with waste from a disused Zn-Pb ore-washing plant. Between 1999 and 2019, the transformation of grassland and meadow vegetation into scrub and forest–grassland communities was observed. This transformation led to a decrease in the area of Molinietum caeruleae meadow (from 25.8% in 1999 to 10.7% in 2019), whose place was taken by Prunus spinosa and Rhamnus cathartica. The community of xerothermic limestone grasslands completely disappeared, being replaced in favour of the Diantho-Armerietum and Prunus spinosa community. In this period, the share of lifeforms of plants and species composition (46 and 60, respectively) also changed. The Shannon and Simpson biodiversity index reached high values in the second investigation period, and it was 0.893 and 0.86, respectively. The anthrosols had a high content of Zn—85,360 mg kg−1, Pb—28,300 mg kg−1, Cd—340 mg kg−1, and As—1200 mg kg−1. Carbonates, clay minerals, and fe-oxides are predominant in the mineral composition of the rhizosphere; the metal-bearing phases are stable; and hardly soluble minerals include smithsonite, cerussite, monheimite, hemimorphite, and oxides of Fe and Fe-Mn. Mineralisation/crust processes formed on the epidermis, and their influences on root development were found. Scanning electron microscopy and energy-dispersive X-ray spectroscopy studies on rhizosphere soil components provide information on the type of minerals and their susceptibility to heavy metals release. The identification of some biotic and mineral structures in rhizospheres can be an interesting source of information on pedogenic processes identified in back-scattered electron images.

Tailings dust characterization and impacts on surface water chemistry at an abandoned Zn-Pb-Cu-Au-Ag deposit

The increased potential for dust mobilization as a result of climate change indicates a need to better understand interactions between dust and water. This research investigates the geochemical effects of tailings dust on surface waters near Stirling mine, Nova Scotia. Tailings were sieved to <63 μm as a proxy for dust and analyzed geochemically and mineralogically for the identification of primary and secondary metal-bearing phases using a scanning electron microscope with automated mineralogy, electron microprobe analysis and synchrotron-based microanalysis. Metal-hosting phases identified include in order of abundance; sphalerite (ZnS), cerussite (PbCO3), chalcopyrite (CuFeS2), Pb–Mn phases (possibly cesàrolite (PbMn3O6(OH)2)), smithsonite (ZnCO3), goethite (FeO(OH), aurichalcite ((Zn,Cu)5(CO3)2(OH)6), hydrohetaerolite (ZnMn2O4·H2O), tennantite (Cu6(Cu4Zn2)As4S12S), and galena (PbS). Shake flask tests were conducted in simulated stream waters (pH = 7) using sieved tailings and passive dry deposition collector filters to investigate the solubility of metal-hosting mineral phases within dust. Results indicate metal leaching at near neutral pH conditions. Sphalerite, cerussite and chalcopyrite are likely the main sources of Zn, Pb, and Cu in the shake flask leachate, based on calculated saturated indices and mass balance. Analyses of stream waters indicate similar conditions (pH, ORP, saturation indices, etc.) compared to the results of the shake flask tests, suggesting they provide reasonable insight about processes occurring in the field. Tailings dust generated at the site is therefore a potential source of metals to surface waters.

The Haidbach deposit in the Central Tauern Window, Eastern Alps, Austria: a metamorphosed orthomagmatic Ni-Cu-Co-PGE mineralization in the Polymetallic Ore District Venediger Nappe System – Hollersbach Complex

Abstract Cu-Ni-Co-PGE mineralization occurs at Haidbachgraben in the Early Palaeozoic, Subpenninic Hollersbach Complex of the Central Tauern Window, Austria. Massive sulfide ore formed from sulfide melt segregated from silicate melt during intrusion of pyroxenite into magmatic rocks formed in an MORB-type environment. Relics of magmatic minerals include chromian spinel and polyphase sulfide droplets composed of pyrrhotite, chalcopyrite and pentlandite preserved in recrystallized pyrite. Both ore and host rocks were multiply deformed and metamorphosed, leading to hornblendite carrying the ore, enveloped by chlorite-epidote schist. Conditions of – likely Variscan – amphibolite facies metamorphism are documented by relict pargasitic cores in hornblende and actinolite-tremolite, and by ternary sulfarsenide compositions in the Co-Ni-Fe solid solution series that are the most common accessory minerals found in the sulfide ore. Pyrrhotite, pentlandite, chalcopyrite and pyrite are the major sulfide minerals. Chalcopyrite is Cd-rich and retains a high-temperature magmatic signature. High Co/Sb and moderate Se/As ratios in pyrite also point to a magmatic environment of mineralization. The accessory mineral assemblage of small grain size (mostly &lt;10 µm) comprises native Au-Ag alloy and petzite as Au-Ag minerals, sperrylite, a variety of Pd tellurides and bismuthotellurides with elevated Sb, irarsite, and Re sulfides such as tarkianite and a Pb-Re sulfide. In addition, minor molybdenite, bournonite, scheelite and selenides have been identified. Two precious metal assemblages are present in individual samples: (1) hessite associated with Pd tellurides, often accompanied by sphalerite and chalcopyrite; (2) tarkianite forming euhedral inclusions in pyrite. Sperrylite and Au-Ag native alloys are present throughout and were also detected in silicate matrix. Most of the precious metal-bearing phases must have formed during recrystallization of base metal sulfides after the magmatic, and probably during later metamorphic events terminating in the Neoalpine Tauern crystallization.

Airborne particles in city bus: concentrations, sources and simulated pulmonary solubility.

PM10 and PM2.5 concentrations in Ljubljana city bus were monitored during entire shift, and individual particles were morphologically and chemically characterised in order to determine PM concentration variability, particle sources, solubility in simulated pulmonary environment and effects on human health. PM measurements revealed high mean PM10 (82.8μg/m3) and PM2.5 (47μg/m3), which were highest and most variable during rush hours with fluid traffic and lowest during traffic jams with standing vehicles. Individual particle analysis showed that airborne particles were dominated by metal-bearing phases, particularly small-sized (Cr,Mn,Zn)-bearing Fe-oxyhydroxides and Al-/Fe-Al-oxides, large (Fe,Cr,Ni)- and (Cu,Zn,Ni)-alloys, and small-sized Sb-sulphide and Ba-sulphate. Non-metallic phases were represented by (Ca,Mg)-carbonates, Al-silicates, Na-chloride and Ca-sulphate. Comparison with possible source materials (vehicle exhaust emissions, brake disc dust and road sediment) showed that primary sources of these metal-bearing phases were wear of brake discs, brake pads and tyres, and also wear of engine components and catalytic converters. Most non-metallic phases originated from resuspension of road sediment, containing road sanding materials, but also from emissions of burned fuel and lubricating oil (Ca-sulphate). Assessment of effects on human health indicated that mean PM concentrations, which significantly exceeded daily limit values, increased mortality (by 2-3%) and morbidity (by 7-8%) risk for bus drivers. Simplified PHREEQC calculations of airborne metal-bearing phase solubility in aqueous solutions simulating pulmonary environment showed that metallic Fe, Ba-sulphate, Sb-sulphide and Al-oxide, partly also Cu-bearing metal alloys, were soluble under reducing and oxidising conditions, but released metals were removed from solution by precipitation of stable secondary metal-bearing phases.

Formation of secondary mineral coatings and the persistence of reduced metal-bearing phases in soils developing on historic coal mine spoil

Acid mine drainage (AMD) from historic and abandoned coal mine spoil represents a potential long-term source of contaminants to surface and groundwater. Determining the risk associated within AMD generation and metal(loid) transport from coal mine spoil is complicated by the heterogeneous natural of spoil heaps and mineralogical and hydro(bio)geochemical factors that may limit or promote metal(loid) transport. The current work aims to determine if primary, reduced phases such as pyrite continue to persist in abandoned and historic coal mine spoil. This objective was accomplished through characterization soils undergoing active weathering while developing on coal mine spoil in Appalachian Ohio to determine the factors that might limit oxidative dissolution. Soils in the Huff Run Watershed (Ohio, USA) were sampled at 0–10 cm, 30–40 cm, 70–80 cm, and 110–120 cm depth. X-ray Diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS), and synchrotron-based X-ray Microprobe (XMP) analyses were used to determine the speciation and distribution of metal(loid)s and the minerals they are associated with. The XMP analyses included micro-focused XRD (μ-XRD), X-ray Fluorescence (μ-XRF) element and redox state mapping, and X-ray absorption Near Edge Structure (μ-XANES) Spectroscopy. Soil mineralogy was dominated by quartz, muscovite, kaolinite, and feldspar, with minor amounts of chlorite and other phases including pyrite, arsenopyrite, realgar, orpiment, hematite, and goethite. Soils from all depths contained metal(loid)-sulfide particles with secondary mineral surface coatings, often in physically complex and heterogeneous aggregates that were composed of clay minerals and secondary Fe(III)-(oxy)hydroxides. These assemblages were typically 10–20 μm in diameter, with an individual pyrite particle core grain size ranging from 0.5 to 10 μm, and secondary mineral surface coatings ranging in thickness from undetectable to 1 μm. Within these aggregates, S and As were present as: (1) small (<20 μm) phases that were spatially correlated with Fe and other trace metal(loids) (Cu, Se, and Zn) and identified as metal(loid)-sulfide minerals; and (2) As(III), As(VI), and S(VI) associated with secondary Fe(III)-(oxy)hydroxides. Intermediate S oxidation state was also observed to be associated with remnant coal and organic matter. These results indicate that pyrite and other metal(loid) sulfides are present in soils developing on historic coal mine spoil after several decades since waste emplacement. The persistence of the μm-scale pyrite grains is likely the result of the formation of the secondary mineral surface coatings which can limit complete oxidative dissolution. These phases also play a role in re-sequestration of metal(loid)s release from sulfide mineral weathering. This work highlights the importance for considering AMD generation from non-point sources, and the potential for long-term ecosystem impairment.

A Review of H2, CH4, and Hydrocarbon Formation in Experimental Serpentinization Using Network Analysis

The origin of methane and light hydrocarbons (HC) in natural fluids from serpentinization has commonly been attributed to the abiotic reduction of oxidized carbon by H2 through Fischer-Tropsch Type (FTT) reactions. Multiple experimental serpentinization studies attempted to identify the parameters that control the abiotic production of H2, CH4, and light HC. H2 is systematically and significantly formed in experiments, indicating that its production during serpentinization is well established. However, the large variance in concentration (eight orders of magnitude) is difficult to address because of the large number of parameters that vary from one experiment to another. CH4 and light HC production is much lower and also highly variable, leading to a vivid debate on potential role of metal catalysts and organic contamination. We have built a dataset that includes experimental setups, conditions, reactants, and products from 30 peer-reviewed articles reporting on experimental serpentinization and performed dimensionality reduction and network analysis to achieve an unbiased reading of the literature and fuel the debate. Our analysis distinguishes four experimental communities that highlights usual experimental protocols and the conditions tested so far. As expected, H2 production is mainly controlled by T and P though a strong variability remains within a given P-T range. Accessory metal-bearing phases seem to favor H2 production, while their role as catalyst or reactant is hampered by the lack of mineralogical characterization. CH4 and light HC concentrations are highly variable, uncorrelated to each other, and much lower than concentrations of potential reactants (H2, initial carbon). Accessory phases proposed as FTT catalysts do not enhance CH4 production, confirming the inefficiency of this reaction. CH4 only displays a positive correlation with temperature suggesting a kinetic/thermal control on its forming reaction. The carbon budget of some experiments indicates contamination in agreement with available labeled 13C studies. Salts in initial solutions are possible sources of organic contaminants. Natural systems certainly exploit longer reaction time or other reactional paths to form the observed CH4 and HC. The reducing potential of serpentinization can also produce intermediate metastable carbon phases in liquid or solid as observed in natural samples that should be targeted in future experiments.

Chromium, manganese, nickel, and cobalt mobility and bioavailability from mafic-to-ultramafic mine spoil weathering in western Massachusetts, USA.

Fragmented ultramafic bodies in New England were important mineral resources until the early twentieth century, yet few studies have addressed their potential to release trace metals to terrestrial and aquatic environments. Here, we evaluate the release of four trace metals (Cr, Co, Mn, and Ni) from a historic serpentine-talc "soapstone" quarry in Blandford, MA, USA. Soil pits, sediment and rock samples, and stream water samples were collected from upslope undisturbed areas, within the mine spoils and mine face, and downslope of the mine. In order to provide a bottom-up approach for understanding metal release, careful petrographic analysis, electron-dispersive spectroscopy, and wavelength-dispersive spectroscopy were employed to provide first-order insight into the mineralogy of the deposit and a determination of potential metal-bearing phases. Trace metals were primarily observed in ultramafic sheet silicates, primary Fe-oxides, and interstitial weathering-related sulfates. Bulk rock concentrations were Cr (1550mgkg-1), Co (230mgkg-1), Mn (1100mgkg-1), and Ni (1960mg kg1); Cr, Co, and Ni were elevated relative to the surrounding country rock. However, soils and sediments total concentrations were comparable to background soil concentrations: Cr (119mgkg-1), Co (73mgkg-1), Mn (894mgkg-1), and Ni (65mgkg-1). Moreover, < 0.5% of the total concentrations were bioavailable (0.1M ammonium acetate extraction), implying that metals are present as insoluble forms. However, ~ 20% of the total Cr, Mn, Ni, and Co concentrations were strong acid extractable, suggesting mobilization over the coming decades. Stream water concentrations of Mn and Cr were < 50µg L-1, below concentrations outlined by USEPA drinking water standards, and WHO water guidelines for Ni. These results suggest that transport of Cr, Mn, Ni, and Co from the serpentine-talc as dissolved compounds or sediments is limited by retention within silicate and oxides.

Effect of addition of rice husk on the fate and speciation of heavy metals in the bottom ash during dyeing sludge incineration

Abstract Bottom ash obtained from the incinerated dyeing sludge is rich in heavy metals, leaching of which is harmful to the environment. In this investigation, an in-situ passivation technology based on co-firing of dyeing sludge and rice husk is proposed to inhibit the mobility of heavy metals from bottom ash. However, the fate of heavy metals under different dosages of rice husk and the passivation mechanism are still unclear. In this study, the effect of rice husk on the characteristics of heavy metals (Cr, Cu, Ni and Zn) in bottom ash was investigated, and the passivation mechanism of the in-situ technology has been revealed. After co-combustion using the addition of 30% rice husk, the leaching concentrations of Cu, Ni and Zn have been found to meet the threshold as prescribed by the integrated wastewater discharge standard (GB8978-1996), while the leaching of Cr remains at an undesirable level. Interaction within the constituents inhibited the leaching of heavy metals during the co-combustion process, especially under a high dosage of rice husk. The newly formed silicoaluminate mineral during co-combustion is the heavy metal-bearing phase, and the generation of which is significantly related to the passivation of heavy metals.

Assessment of contribution of metal pollution sources to attic and household dust in Pb-polluted area.

Attic and household dusts from Pb-polluted area were investigated using various analytical techniques for source apportionment and assessment of source contribution of metal-bearing phases. Mineralogically, attic dust consists of gypsum, anhydrite, and metal-bearing phases, while household dust comprises C-bearing particles and only minor metal-bearing phases. Sulfur isotope composition of sulfides and sulfates in attic dust shows that they result from past primary smelting of local sulfide ore, while those in household dust originate directly from local mine-waste material. Pb isotope ratios show that Pb-bearing phases in both dust types mostly originate from mining and primary smelting of local Pb-ore. Individual metal-bearing particles were apportioned by their composition, morphology, and mineralogy to phases from past Pb-smelting, present-day Pb-recycling, and past mining/mine-waste mechanical processing. Calculated source contribution of metal-bearing phases to indoor dust showed that primary Pb-smelting was important pollution source in the past, while active Pb-recycling has contributed only negligible amount of material so far. However, material from mining/mine-waste processing is an important currently active pollution source. Study demonstrated that simultaneous investigation of characteristics and isotopic composition of metal-bearing phases in different indoor dust types serves as tool for assessment of source contribution of past and recent airborne metal pollution.

Mineralogical, geochemical, and leaching study of historical Cu-slags issued from processing of the Zechstein formation (Old Copper Basin, southwestern Poland)

Historical Cu-Slags located at former industrial sites in Poland are exposed to weathering that may trigger release of metallic contaminants to the surrounding soils. However, the extent to which different metals are leached depends on the mineral composition of the slags and the conditions of their deposition. Historical slags are often crystalline and composed of phases with a variable response to weathering. Also, weathering of crystalline slags (CS) is different from that of amorphous slags (AS). To understand how the slag phase composition triggers weathering and the ultimate release of metallic elements, we studied the leaching of historical crystalline and amorphous slag. A combined geochemical and mineralogical approach determined the weathering sequence(s) of slag components subjected to different conditions of specific slag disposal. In detail, experiments under: i) various pH conditions in the range of 2–13 in a batch mode simulated slag deposition within a deep soil profile, whereas ii) exposure to solutions of artificial root exudates (ARE) in a dynamic experimental system simulated slag deposition within topsoil. The results demonstrated that crystalline phases in the order Leucite > Plagioclase > Pyroxene are preferentially dissolved in inorganic conditions of a pH ≤ 7, in contrast to glass, which is preferentially dissolved in alkaline conditions (pH > 7). Also, inorganic conditions better promote the dissolution of metal-bearing phases (sulphides and metals) when compared to silicates. In contrast, artificial root exudates do not show preferential dissolution of any phase and cause the strongest leaching in all of the analyzed conditions. We show that reconstructing the susceptibility of complex crystalline slags to weathering requires a specific approach including analyses and interpretation of all major components such as Ca, Mg and K, not merely a focus on Si and metals.

Metals and radionuclides (MaR) in the Alum Shale of Denmark: Identification of MaR-bearing phases for the better management of hydraulic fracturing waters

Hydraulic fracking is used to enhance the production of tight gas reservoirs. Because shale reservoirs can contain toxic elements (metals and radionuclides), the release rates of these elements must be quantified in order to determine the possible environmental impact of fracking. This paper is devoted to the complete and precise determination of the mineralogy of the Alum Shale in Denmark, which is known for its high content of gaseous hydrocarbons. Its metal-bearing phases are identified and quantified using complementary analytical techniques (i.e., X-ray diffraction, electron microscopy and electron probe analysis, and X-ray tomography). A detailed quantitative mineralogical composition is calculated using three different approaches (i.e., matrix inversion, quantitative X-ray diffraction, and the MQ program), which is then used to determine the quantity of polluting elements in each phase. Pyrite (FeS2) is the major metal-bearing phase (e.g., As, Cu, Co, Ni, Pb, Zn, V, U). Elements such as V, Ra, Cs, Be, Cr, Ba are trapped in clay minerals, whereas U, Cd, Mo, and Hg are present in organic matter. It is essential to better identify toxic element-bearing phases to formulate fracking fluids with the lowest possible chemical reactivity in order to avoid the release of pollution by flowback waters.

Follow-up geochemical studies and mineralogical investigations by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) of soil samples from the industrial zone of Sisak, Croatia

Geochemical investigation of topsoil from a mixed industrial and residential area in the southern part of the city of Sisak was carried out in order to determine the concentration, spatial distribution, metal-bearing phases and sources of Ba, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V, W and Zn by applying inductively coupled plasma mass spectrometry (ICP-MS) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). The uncontrolled industrial development in a very short period of only 50years, beginning in the 1930s and ending in the 1980s, has left a legacy of serious contamination of topsoil. The concentrations of studied elements in topsoil in the industrial zone were generally elevated and at some locations much higher compared to the rest of the Sisak area.Morphologies and chemical composition of metal-bearing particles in the heavy mineral fraction of three selected soil samples were studied using SEM/EDS. According to the results of the SEM/EDS analysis, the sources of studied elements could be ascribed predominantly to anthropogenic input from steelworks, recycling of steel scrap, ferroalloys production and to a lesser extent to the pedological processes in the soil and parent material. It is concluded that the SEM/EDS results provide significant information about the sources and apportionment of anthropogenic induced contamination in soil, and assist in the interpretation of conventional analytical results.

Characterisation of secondary metal-bearing phases in used dental amalgam and assessment of gastric solubility.

Detailed SEM/EDS investigation of used dental amalgams was carried out in order to characterise morphology and chemical composition of secondary metal-bearing phases resulting from long-term exposure of dental amalgam to oral environment, and assess their solubility in gastric environment. The investigation revealed numerous secondary phases, represented by compositionally and morphologically complex Hg-, Cu-, Sn-, Ag-, Zn-bearing sulphides and oxides/hydroxides, while sulphates and phosphates are scarce. Secondary metal-bearing phases mostly occur at the amalgam/tooth interface; however, some phases were found only on the occlusal surfaces of amalgam. Secondary phases mostly form porous aggregates of minute crystallites and micro- or nanocrystalline crusts. In oral environment, these phases are mostly stable and represent trapping media for dissolved potentially toxic metals released during amalgam corrosion. Simplified PHREEQC calculations of solubility of secondary metal-bearing phases in aqueous environment under conditions similar to those in gastric environment showed that secondary phases are more soluble in gastric environment than in oral solutions, which is mostly due to their forms of occurrence. Secondary phases in gastric environment thus act as secondary sources of potentially toxic metals, particularly Sn, Zn and also Cu, which are released both under reducing and oxidising conditions especially in acidic environment. Only very small amounts of Hg are potentially released and should not represent serious threat. Secondary phases that contribute the most to bioaccessibility of these metals are Sn hydroxychlorides, Sn oxides/hydroxides, Sn sulphates/hydroxysulphates, Sn oxides, Zn sulphides and Cu sulphides (Cu2S).

Combining selective sequential extractions, X-Ray Absorption Spectroscopy, and X-Ray Powder Diffraction for Cu (II) speciation in soil and mineral phases

Interaction of Cu (II) ions with the matrix of soil and mineral phases of layered silicates was assessed by the Miller method of selective sequential fractionation and a set of synchrotron X-ray methods, including X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (XANES). It was shown that the input of Cu into Calcic Chernozem in the form of monoxide (CuO) and salt (Cu(NO3)2) affected the transformation of Cu compounds and their affinity for metal-bearing phases. It was found that the contamination of soil with a soluble Cu(II) salt increased the bioavailability of the metal and the role of organic matter and Fe oxides in the fixation and retention of Cu. During the incubation of soil with Cu monoxide, the content of the metal in the residual fractions increased, which was related to the possible entry of Cu in the form of isomorphic impurities into silicates, as well as to the incomplete dissolution of exogenic compounds at the high level of their input into the soil. A mechanism for the structural transformation of minerals was revealed, which showed that ion exchange processes result in the sorption of Cu (II) ions from the saturated solution by active sites on the internal surface of the lattice of dioctahedral aluminosilicates. Surface hydroxyls at the octahedral aluminum atom play the main role. X-ray diagnostics revealed that excess Cu(II) ions are removed from the system due to the formation and precipitation of coarsely crystalline Cu(NO3)(OH)3.

Geochemical modeling-based rehabilitation proposal for abandoned sulfidic flotation mill tailings, Kirki, Thrace, NE Greece

A total number of eight (8) tailings dams are found at the Kirki flotation plant and are either built on impermeable Neogene formations or permeable alluvial deposits of the Kirkalon and Eirini streams. The tailings dams were originally constructed without any environmental concerns, nowadays their embankments are highly eroded, and toxic material is readily transported to the nearby streams, resulting in degradation of the quality of both stream waters and sediments. Stream water sampling revealed that concentrations of dissolved Pb, Mn, Cd and SO4 increase rapidly in the vicinity of the Kirki flotation plant. Four case-specific PHREEQC scenarios were employed including “Direct Precipitation,” “Evaporation,” “Mixing with Rain water” and “Mixing with Stream water” in order to investigate the effect of interaction between water accumulated on the surface of the tailings dams and the precipitation or dissolution of heavy metal-bearing phases that may control heavy metal solubility. All tests performed concluded that such interaction plays a very important role in the environmental behavior of the toxic tailings material of the Kirki flotation plant. Based on the results of the PHREEQC tests, the proposed rehabilitation plan includes the construction of a sealing system in order to eliminate tailings dam wall erosion and infiltration effects. The suggested plan is limited to dams 2, 3, 4, 5, 6, 7 and 8, whereas dam 1 is empty and requires no remediation. Additionally, and only for dams 5, 7 and 8, built on top of permeable alluvial formations a few meters above the ground water head, chemical improvement of the tailings material is suggested to limit toxic pollutants dissolution. In particular, installation of lime piles is proposed in order to further improve the quality of possible small-scale, low-quality percolating solutions that might migrate to underground aquifers.

Studying the transformation of Cu2 + ions in soils and mineral phases by the XRD, XANES, and sequential fractionation methods

Interaction of Cu2+ ions with the matrix of Calcic Chernozem and mineral phases of layered silicates was assessed by the Miller method of sequential fractionation and a set of synchrotron X-ray methods, including X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (XANES). A model laboratory experiment was carried out to study the effect of organomineral matrix on the sorption of Cu2+ ions. The time of soil incubation with Cu compounds was 3years. It was shown that the input of Cu into Calcic Chernozem in the form of monoxide (CuO) and salt (Cu(NO3)2) affected the transformation of Cu compounds and their affinity for metal-bearing phases. It was found that the contamination of soil with a soluble Cu2+ salt increased the bioavailability of the metal and the role of organic matter and Fe oxides in the fixation and retention of Cu. During the incubation of soil with Cu monoxide, the content of the metal in the residual fractions increased, which was related to the possible entry of Cu in the form of isomorphic impurities into silicates, as well as to the incomplete dissolution of exogenic compounds at the high level of their input into the soil. A mechanism for the structural transformation of minerals was revealed, which showed that ion exchange process result in the sorption of Cu2+ ions from the saturated solution by active sites on the internal surface of the lattice of dioctahedral aluminosilicates. Surface hydroxyls at the octahedral aluminum atom play the main role. X-ray diagnostics revealed that excess Cu2+ ions are removed from the system due to the formation and precipitation of coarsely crystalline Cu(NO3)(OH)3.