Fe-bearing Minerals Research Articles

Transformation of Schwertmannite to erdite nanorod via an alkaline dissolution–recrystallization process for the effective adsorption of oxytetracycline

Schwertmannite (schw) is a common Fe-bearing mineral in the precipitation of mine wastewater and/or steel pickling wastewater. It could be easily converted to goethite and hematite via heating or hydrothermal treatment and could be used as adsorbent to remove contaminants from wastewater. Herein, the spherical schw was converted into erdite nanorod by a simple hydrothermal method with the addition of Na2S. Schw was spherical particle with a size of 0.4–1.5 [Formula: see text]m. After treatment, it was converted to erdite nanorod particles with 100 nm diameter and 200 nm length. By adding MnO2 at the [Formula: see text] ratio of 1, erdite nanorod grew radially to 1–1.5 [Formula: see text]m, whereas MnO2 was reductively dissolved and recrystallized to rambergite. In the absence of Fe, MnO2 was directly transformed to octahedral alabandite. The product EN-0, prepared without MnO2, showed the optimal [Formula: see text] of oxytetracycline (OTC, 7479.6 mg/g), which was 12 times that of schw. In OTC-bearing solution, erdite was unstable and automatically hydrolyzed to generate Fe–SH/Fe–OH-bearing flocs, and it exhibited abundant surface functional groups for OTC adsorption. Subsequently, the hydroxyl and amino groups on the side chain of OTC would also be complexed with the Fe–SH group to generate an OTC–Fe–S ligand, in the form of flake-like particles with a smooth surface. The formed Mn-bearing minerals, for example, rambergite and alabandite, also complexed with OTC as OTC–Mn–S ligands to form quadrangular prism with shoulder and length of 10 [Formula: see text]m and 20–100 [Formula: see text]m, respectively. Spherical schw was converted into a well-crystallized erdite nanorod with the addition of MnO2, and the product showed potential applications in OTC-bearing wastewater treatment.

Redox transformation of structural iron in nontronite induced by quinones under anoxic conditions

In natural anoxic subsurface environments, the geochemical cycles of iron are largely associated with the migration and transformation of organic matter. Intensive attention has been paid to the redox interaction of organic matter with aqueous Fe and iron (hydr)oxides. Whereas, the abiotic redox cycling of structural Fe in clay minerals induced by quinones has not been well understood. In this study, we selected nontronite (NAu-2) as a model Fe-bearing phyllosilicate clay mineral and 1,4-hydroquinone (H2Q)/1,4-benquinone (BQ) as a model quinone couple. Our results show that the structural Fe(III) in NAu-2, with tetrahedral Fe(III) priority, can oxidize H2Q into BQ, and octahedral Fe(II) in NAu-2 can reduce BQ to H2Q, with semiquinone radicals (SQ−) as intermediate. The extent of the redox reactions depends on the reduction potential difference between NAu-2 and H2Q/BQ. However, a fraction of Fe(II)-Fe(III)-OH and Fe(II)-Fe(II)-OH groups in the octahedral sheet are difficult to be oxidized by BQ, because the reduction potential gradient decreases to a low level as the reaction proceeds. And the structure of NAu-2 can only partially restored upon re-oxidation with tetrahedral Fe(III) irreversibility. Output of this study replenishes the understanding regarding redox cycling of structural Fe in clay minerals induced by quinones.

Transformation of Fe-bearing minerals from Dongsheng sandstone-type uranium deposit, Ordos Basin, north-central China: Implications for ore genesis

Abstract Iron-bearing mineral assemblages and their distribution patterns directly reflect the redox environment in sediments, which plays a decisive role in the migration and precipitation of U. The Dongsheng sandstone-type U deposit hosted in fluvial and/or deltaic sandstones of the lower member of the Middle Jurassic Zhiluo Formation in the northeastern Ordos Basin has experienced multiple fluid events that impacted the redox conditions. Highly enriched in barren gray sandstones, pre-ore U (Umean = 12.05 ppm) associated with Fe-Ti oxides, clay minerals, and organic matter is likely one of the key sources of U for the mineralization. Different contents of Fe-bearing minerals, including biotite, Fe-Ti oxides, pyrite, hematite, goethite, and chlorite that were formed or altered under different redox conditions, resulted in sandstone units with distinct colors. The red sandstone is hematite-rich, indicating a highly oxidizing environment. The green sandstone is chlorite-rich and formed because of reducing hydrocarbon-rich fluids that overprinted the hematite-rich sandstone. The barren and mineralized gray sandstones consist of pyrite (with a higher content in mineralized sandstones), Fe-Ti oxides, and carbonaceous debris, which are indicators of a reducing environment. Based on the paragenetic relationship and sulfur isotopic compositions of ore-stage pyrite, bacterial sulfate reduction was responsible for the formation of framboidal pyrite (δ34S = –31.2 to –3.8‰), and the sulfur of this pyrite mainly came from the oxidation of pre-ore pyrite (δ34S = –19.1 to +20.3‰). Euhedral and cement pyrite overprinting framboids were produced via Ostwald ripening with δ34S values ranging from –56.9 to –34.3‰, lower than any values of framboidal pyrite. Therefore, these mineralogical and geochemical characteristics of the Dongsheng deposit suggest U mineralization involves both biogenic and abiogenic redox processes.

Oxalate-extractable aluminum alongside carbon inputs may be a major determinant for organic carbon content in agricultural topsoils in humid continental climate

The relative importance of various soil mineral constituents (e.g. clay-sized particles, aluminum- and iron-bearing mineral reactive phases) in protecting soil organic carbon (SOC) from decomposition is not yet fully understood in arable soils formed from quaternary deposits in humid continental climates. In this study, we investigated the relationships between soil physico-chemical properties (i.e. contents of oxalate-extractable aluminum (Alox) and iron (Feox) and clay size particle < 2 µm), grain yield (as a proxy for carbon input) and total SOC as well as SOC in different soil fractions for samples taken from the topsoil of an arable field at Bjertorp in south-west Sweden. We found a positive correlation between Alox and total SOC content, where Alox explained ca. 48% of the spatial variation in SOC. We also found that ca. 80% of SOC was stored in silt- and clay-sized (SC) fractions, where Al-bearing reactive mineral phases (estimated by Alox) may be important for organic-mineral associations and clay aggregation. Our results were supported by data collated from the literature for arable topsoil in similar climates, which also showed positive correlations between SOC and Alox contents (R2 = 23.1 – 74.5%). Multiple linear regression showed that including spatially-variable crop yields as a proxy for carbon inputs improved the prediction of SOC variation across the Bjertorp field. Other unquantified soil properties such as exchangeable calcium may account for the remaining unexplained variation in topsoil SOC. We conclude that Al-bearing reactive mineral phases are more important than clay content and Fe-bearing reactive mineral phases for SOC stabilization in arable topsoil in humid continental climates.

Coal and coal ash characteristics to understand mineral transformation : A case study from Senakin coal field Indonesia

Coal ash is a material from coal combustion and recently is an economical source for the extraction of valuable elements such as rare earth elements and Yttrium (REY) and base metals. Eight coal samples from Senakin coal field were collected to identify their mineralogy composition in raw coal and coal ash. The ashing was carried out on coal samples at temperature 1000°C for 1 hour. The coal and coal ash samples were made polish section to identify the organic and inorganic constituents. In addition, the minerals in coal sampel were identified by X-ray diffraction analysis. From this study, organic constituent consist of vitrinite (60 – 71%), liptinite (22 – 33%) and inertinite (5 – 9%). Minerals found in coal are kaolinite (25,78 – 46,90), pyrite (24,16 – 38,38%), quartz (6,07 – 12,80%), gypsum (4,81 – 10,34%), chlorite (2,56 – 8,40%), jarosite (0,72 – 4,63%), hematite (0,96 – 3,81%), calcite (0,37 – 5,07%), Mg-calcite (0,11 – 3,20%), dolomite (1,35 – 3,55%), and siderite (1,22%). Coal ash is composed of organic and inorganic components. Organic components found is unburned coal (3,09 – 8,55%) derived from maceral which does not burn out, mainly inertinite group. While inorganic components found are fe-oxide mineral (40,36 – 54,55%), quartz (24,55 – 33,64%), mullite (5,09 – 7,82%), cenosphere (7,45 – 10,91%), pleiosphere (1,64 – 2,36%), pyrite (0,18 – 1,27%), and spinel (0,18 – 1,09%). Fe-oxide minerals are interpreted derived from Fe-bearing minerals in coal samples such as pyrite, hematite, and siderite. Kaolinite which is the dominant mineral in coal is transformed to cenosphere, pleiosphere, and mullite. Quartz in coal ash derived from quartz in the coal sample because ashing temperature does not exceed the melting temperature of quartz. Characterization of the coal ash component can be used as a reference for the extraction method of valuable elements.

Dissolution of Fe from Fe-bearing minerals during the brown-carbonization processes in atmosphere

Previous studies found Fe dissolution in atmosphere correlates to biomass burning, while the underlying mechanisms need to be further investigated. In this study, we reported a laboratory investigation about Fe dissolution behavior of two model Fe-bearing clay minerals of montmorillonite (SWy-2) and illite (IMt-2), and one standard mineral dust of Arizona test dust (AZTD) in atmospheric condition (pH = 2), after the minerals engaging into the brown-carbonization reaction with guaiacol, which is a commonly detected volatile phenol substance in biomass burning. The results show that the pre-brown-carbonization reaction promoted Fe dissolution from all the three minerals, attributing to the reduction of Fe(III) by gaseous guaiacol. The Fe dissolution from SWy-2, IMt-2 and AZTD were also compared under both light and dark conditions to simulate the daytime and nighttime atmospheric processes. As a result, model solar irradiation further promoted Fe dissolution from IMt-2 and AZTD, since both minerals contain moderate photo-reducible Fe(III) oxide or/and Fe(III) oxyhydroxide. The promotive effect of solar irradiation on Fe dissolution from AZTD would be gradually diminished because the photo-reactive Fe(III) is also guaiacol-reducible. Whereas, it was on the contrary for SWy-2 which does not contain the Fe(III) (oxyhydr-)oxide phase. And more dependently, the photo-induced hydroxyl radical (OH) on SWy-2 would re-oxidize the formed Fe(II), unless sufficient amount of guaiacol or brown-carbonization products on SWy-2 consumed the OH and complexed with surface coordinated Fe(III) forming photo-reducible Fe(III). The results of this study suggested the brown carbonization process on minerals would greatly mediate the Fe dissolution behavior from the Fe-bearing mineral dusts in atmosphere. Similar processes might need to be taken into consideration to accurately evaluate the input of Fe from atmosphere to open oceans.

Acidophilic Iron- and Sulfur-Oxidizing Bacteria, Acidithiobacillus ferrooxidans, Drives Alkaline pH Neutralization and Mineral Weathering in Fe Ore Tailings.

The neutralization of strongly alkaline pH conditions and acceleration of mineral weathering in alkaline Fe ore tailings have been identified as key prerequisites for eco-engineering tailings-soil formation for sustainable mine site rehabilitation. Acidithiobacillus ferrooxidans has great potential in neutralizing alkaline pH and accelerating primary mineral weathering in the tailings but little information is available. This study aimed to investigate the colonization of A. ferrooxidans in alkaline Fe ore tailings and its role in elemental sulfur (S0) oxidation, tailings neutralization, and Fe-bearing mineral weathering through a microcosm experiment. The effects of biological S0 oxidation on the weathering of alkaline Fe ore tailings were examined via various microspectroscopic analyses. It is found that (1) the A. ferrooxidans inoculum combined with the S0 amendment rapidly neutralized the alkaline Fe ore tailings; (2) A. ferrooxidans activities induced Fe-bearing primary mineral (e.g., biotite) weathering and secondary mineral (e.g., ferrihydrite and jarosite) formation; and (3) the association between bacterial cells and tailings minerals were likely facilitated by extracellular polymeric substances (EPS). The behavior and biogeochemical functionality of A. ferrooxidans in the tailings provide a fundamental basis for developing microbial-based technologies toward eco-engineering soil formation in Fe ore tailings.

Lignin-enhanced reduction of structural Fe(III) in nontronite: Dual roles of lignin as electron shuttle and donor

Lignin is a major component of plant-derived soil organic matter (SOM) in soils and sediments. Fe-bearing clay minerals are widely distributed in these environments and often co-exist with lignin. While previous studies have reported the electron shuttling and donating roles of certain redox-active SOM in the dissimilatory reduction of structural Fe(III) in Fe-bearing clay minerals, the role of lignin in this process remains unknown. Here we studied this role by incubating an Fe-rich smectite (nontronite NAu-2) with two types of lignin (soluble and insoluble) in the absence and presence of an Fe(III)-reducing bacterium Shewanella putrefaciens CN32 under anaerobic condition. Lactate was added in some experiments as an extra electron donor. The results demonstrated that both soluble and insoluble lignins abiotically reduced structural Fe(III) in NAu-2. The reduction extent was proportional to lignin concentration. After abiotic reaction, lignin served as either electron shuttle or electron donor in the presence of CN32: (1) When lactate was present, lignin served as an electron shuttle to enhance the rate of Fe(III) reduction; (2) When lactate was absent, lignin served as an electron donor for Fe(III) reduction. Although the ultimate biotic Fe(III) reduction extents were similar in the presence of either soluble or insoluble lignin, the reduction rates with soluble lignin were higher than those with insoluble lignin, likely owing to their different electron transfer mechanisms. After interaction with NAu-2 and/or CN32, soluble lignin structure largely remained intact, but with some decreases of humic/fulvic acid-like and protein-like compounds, aromatic functional groups (e.g., CH, CO, COOH), and aliphatic/aromatic compounds. An increase of semiquinone-like organic radicals was observed after lignin interaction with NAu-2. These chemical changes of lignin were likely coupled with the reduction of structural Fe(III) in nontronite. Upon reduction, the nontronite did not display much dissolution and mineral transformation. The findings of this study provide insights into the role of lignin in promoting mineral-microbe interactions and have significant implications for coupled Fe and C biogeochemical cycles in soils and sediments.

Comparative study on ash characteristics of various high-alkali fuels using different ashing methods and temperatures

The comparative study on ash characteristics of various high-alkali fuel helps to solve the ash-related problems. In this paper, the ashes of wheat straw (WS) and three high-alkali coals (LA, ZJ, and TC) were prepared using the plasma ashing method (at <200 °C) and the traditional ashing method (at 575 °C, 815 °C, and 1000 °C). The mineral matters close to the initial state in raw fuel could be elucidated by the plasma ashing method because it could remove organic material without converting the primary minerals. The traditional method was employed to study the ash characteristics at the following stages of fuel conversion. The ash samples, including plasma ash (PA), low-temperature ash (LTA), medium-temperature ash (MTA), and high-temperature ash (HTA), were subjected to a variety of analysis techniques. The results show that wheat straw has a large amount of potassium, while sodium is the main alkali in coals. The PA samples of wheat straw and coals contain little less sodium or potassium than the LTA samples, and the alkali contents decrease further in the MTA and HTA samples. The ashing procedure affects the phases of K-bearing mineral in WS ashes, Na-bearing and Ca-bearing minerals in LA coal ashes, Na-bearing, Ca-bearing, and Fe-bearing minerals in ZJ and TC coal ashes. During the thermal analysis, all PA samples exhibit significant weight losses due to the decomposition, volatilization, and oxidization of minerals. The MTA and HTA samples of WS present severe fused surfaces, while those of ZJ coal are slightly melted.

Magnetic Mineralogy of Speleothems From Tropical-Subtropical Sites of South America

Fe-bearing minerals are a tiny fraction of the composition of speleothems. They have their origin in the karst system or are transported from the drainage basin into the cave. Recent studies on the magnetism of speleothems focused on the variations of their magnetic mineralogy in specific time intervals and are usually limited to a single sample. In this study, we describe a database of environmental magnetism parameters built from 22 stalagmites from different caves located in Brazil (South America) at different latitudes, comprising different climates and biomes. The magnetic signal observed in these stalagmites is dominated by low-coercivity minerals (∼20 mT) whose magnetic properties resemble those of the magnetite formed in pedogenic environments. Also, a comparison with few samples from soils and the carbonate from cave’s walls shows a good agreement of the magnetic properties of speleothems with those of soil samples, reinforcing previous suggestions that in (sub-)tropical regimes, the dominant magnetic phase in speleothems is associated with the soil above the cave. Spearman’s rank correlation points to a positive strong correlation between magnetic concentration parameters (mass-normalized magnetic susceptibility, natural remanent magnetization, anhysteretic remanent magnetization, and isothermal remanent magnetization). This implies that ultrafine ferrimagnetic minerals are the dominant phase in these (sub-)tropical karst systems, which extend across a diverse range of biomes. Although the samples are concentrated in the savannah biome (Cerrado) (∼70%), comparison with other biomes shows a higher concentration of magnetic minerals in speleothem underlying savannahs and lower concentration in those underlying moist broadleaf forests (Atlantic and Amazon biome) and dry forests (Caatinga). Thus, rainfall, biome, and epikarst dynamics play an important role in the concentration of magnetic minerals in speleothems in (sub-)tropical sites and indicate they can be an important target for paleoenvironmental research in cave systems.

A magnetic approach to unravelling the paleoenvironmental significance of nanometer-sized Fe hydroxide in NW Pacific ferromanganese deposits

Ferromanganese nodules and crusts (Fe-Mn deposits) are being widely explored for their significant economic potential and paleoenvironmentally significant archives. Fe-Mn deposits contain abundant Fe-bearing minerals including detrital minerals, biogenic Fe-bearing components, but predominantly amorphous Fe hydroxides (AFH). Particularly, the hydrogenetic Fe that is formed in bottom water should be closely related with oceanic environmental and Fe-cycling processes. However, it remains challenging to characterize and quantify the x-ray amorphous AFH component in Fe-Mn deposits. To resolve this problem, we systematically investigated thermally treated hydrogenetic Fe-Mn deposits sampled from the northwestern Pacific Ocean to unravel the AFH component. Our results show that the nanometer-sized AFHs can be transformed into strongly magnetic nanometer-sized (approximately 10-20 nm) magnetite upon heating above 500°C, which can be feasibly quantified by systematic rock magnetic analyses. Using this novel approach, several Fe-Mn deposits at different water depths from the western Pacific Ocean are investigated. Our results indicate that the abundance of AFH increase at a water depth of ∼5000 m, which can be ascribed to bottom-current stratification. The magnetic approach to indirectly quantify the AFH component in Fe-Mn deposits has a great potential in exploring oceanic paleoenvironment significance.

Synthesis of novel erdite nanorods for the activation of peroxymonosulfate during p-nitrophenol wastewater treatment.

Fe-bearing salt and minerals are common reagents used in activating peroxymonosulfate (PMS) for Fenton-like oxidation in wastewater treatment. Fe-bearing reagents are used in mass production, which generate abundant Fe-bearing waste sludge in the absence of a reductant for Fe3+/Fe2+ cycling. Herein, a novel Fe/S-bearing mineral, erdite, was synthesized with a one-step hydrothermal route. The material exerted an Fe/S synergetic effect for p-nitrophenol degradation upon PMS activation and showed a one-dimensional structure similar to that of (FeS2)nn-. It contained short rods with diameters of 100 nm and lengths ranging from 200 to 400 nm. It grew radically to 0.8-2 μm in length upon the addition of MnO2. Ps-0.5, prepared by adding MnO2 in an Mn/Fe molar ratio of 0.5, showed optimal efficiency in removing approximately 99.4% of p-nitrophenol upon PMS activation. Only 3.3% of p-nitrophenol was removed without MnO2. The efficiency of p-nitrophenol removal through Ps-0.5 activation was higher than that through FeSO4, nanoscale zero-valent iron (nZVI), CuFeS2, and MnSO4 activation. The formed erdite rods were spontaneously hydrolyzed to Fe/S-bearing flocs, in which an electron was used by structural S to reduce Fe3+ to Fe2+ upon PMS activation. The reduction resulted in a high p-nitrophenol removal rate. This study provided new insight into the development of an effective PMS activator in wastewater treatment.

First-principles calculation of iron and silicon isotope fractionation between Fe-bearing minerals at magmatic temperatures: The importance of second atomic neighbors

In order to elucidate the processes involved in iron and silicon isotopes partitioning during magmatic differentiation, it is essential to know the precise value of equilibrium fractionation factors between the main minerals present in the evolving silicic melts. In this study, we performed first-principles calculations based on the density functional theory to determine the equilibrium iron and silicon isotopes fractionation factors between eleven relevant silicate or oxide minerals in the context of magmatic differentiation, namely: aegirine, hedenbergite, augite, diopside, enstatite, fayalite, hortonolite, Fe-rich and Fe-free forsterites, magnetite and ulvospinel. Results show that Fe2+-bearing silicate minerals display significant differences in iron isotope fractionation factors that cannot be neglected, even at high temperature (1000 °C). Various physical and chemical parameters control the iron isotopic fractionation of silicate minerals. However, the main parameter, after temperature and the iron oxidation state, is the nature and number of iron second neighbors (i.e. the local chemical composition around Fe atoms). This conclusion is also valid for silicon isotopes. In the investigated nesosilicates and inosilicates, silicon isotope reduced partition function ratios (also called β-factors) show no correlation with the average Si-O bond length, which remains almost constant, but Si β-factors are correlated with the local chemical composition of the minerals. Fractional crystallization is one of the mechanisms, which could explain the evolution of iron isotopic compositions during magmatic differentiation. Using the present theoretical set of equilibrium fractionation factors allows us to assess the impact of inter-mineral isotopic fractionations, and shows that pyroxene appears to be the main mineral phase driving the isotopic evolution to a heavier signature in the most evolved lavas.

Conversion of Fe-bearing minerals in sludge to nanorod erdite for real electroplating wastewater treatment: Comparative study between ferrihydrite, hematite, magnetite, and troilite

Ferrihydrite, hematite, magnetite and troilite are typical Fe-bearing minerals, and served as major components of Fe-rich sludges generated in water treatment, refining, steel processing and mining industry, respectively. To recycle such Fe-rich sludges to prepare erdite-bearing flocculant, the phase transformation of the four Fe-bearing minerals to nanorod erdite should be clarified. In the study, the four minerals were hydrothermal treated to prepare nanorod erdite separately by simply adding Na2S and NaOH. Among the four minerals, ferrihydrite was weakly crystallized and easily converted to nanorod erdite with diameter of 200–500 nm and length of 2–5 μm, along with dotted distribution of hematite as byproduct. Only a small portion of hematite was involved in the formation of nanorod erdite with length of 2 μm, but the involvement of magnetite and troilite in erdite formation did not occur. The Fe dissolution from Fe-bearing minerals in alkaline solution was a key step for erdite crystallization, which apparently enhanced at high NaOH concentration. By increasing NaOH concentrations from 1 to 6 M, radial growth of nanorod erdite from both ferrihydrite and hematite steadily improved to 5–10 μm and 5 μm, separately. Fer-P, the product of ferrihydrite, contained plenty of nanorod erdite and exhibited remarkable removal efficiency of Cr, Cu and Zn from real electroplating wastewater. By adding 0.5 g Fer-P, the removal percentage of Cr, Cu and Zn were all more than 99.95%, which were higher than other conventional reagents such as polyaluminium chloride, polyferric sulfate, powder activated carbon, and diatomite. The total residual heavy metal concentrations were less than 0.1 mg/L, which met the standard of discharging electroplating-wastewater of China. Nanorod erdite was spontaneously hydrolyzed to generate Fe/S-bearing colloid, which contained abundant Fe–S–H groups for chelating heavy metals in comparison with ligands in electroplating wastewater, maintaining the residual heavy metals at low level. In summary, rather than magnetite/troilite-rich sludge, ferrihydrite/hematite-rich sludge can be served as desirable resources to prepare erdite-bearing flocculant for real electroplating wastewater treatment.

Mineralogical Characterization and Optimization of Fe and Mn Through Roast-Leaching of Ferromanganese Ore

Iron and manganese both are important ferrous metals, and they usually need to be extracted separately for better usage. Ferromanganese ore from the Yunnan Province of China was investigated by subjecting it to reduction roasting, leaching, magnetic separation, hydrometallurgical separation process, X-ray diffraction (XRD), electron probe micro-analysis (EPMA) and scanning electron microscopy/energy-dispersive spectroscopy (SEM-EDS). It is noted that the ferromanganese ore contains valuable components or elements of 21.41 wt% Fe2O3 and 19.88 wt% MnO, which are 14.99% and 15.40% of the total of Fe and Mn, respectively, with a large amount of impurities comprising 33.00 wt% SiO2, 9.81%wt% Al2O3, etc. After roasting, microscopic examination showed the presence of haematite, magnetite, pyrolusite, psilomelane, hollandite, marcasite, pyrite, limonite, braunite and manganite, while XRD analysis showed that the magnetite content increases with the increase in roasting temperature, reflecting the increase in conversion of haematite to magnetite. Based on EPMA and SEM-EDS analysis, it was shown that the haematite and magnetite interface were the main Fe-bearing minerals; however, the dissemination of the two minerals, that is, haematite and magnetite with the coexistence of Fe- and Mn-bearing minerals, will result in difficulty in effective separation of Fe and Mn. The effective roasting temperature and roasting time were 800 °C and 60 min, respectively, to avoid the formation of a composite oxide of MnxFe3-xO4 beyond 800 °C. The Fe recovery via roasting and magnetic separation only was 66.56%, whereas a combination of magnetic separation which ensued after the leaching process showed a recovery of 80.08% and 59.95% of Fe and Mn, respectively.

Magnetic characterization and iron oxide transformations in Technosols developed from thermal power station ash

Fly and bottom ash originating in thermal power stations (TPSs) are industrial wastes containing magnetic minerals, primarily Fe-bearing phases, which are formed during coal combustion. Ash deposited on disposal sites becomes the parent material for technogenic soils (Technosols), in which the transformations of Fe-bearing magnetic minerals accompany the soil-forming processes. This study presents the application of magnetic methods together with mineralogical techniques for the determination of the magnetic properties and mineral composition of (1) fresh (unweathered) fly and bottom ash resulting from bituminous coal and lignite combustion, and (2) two Technosols developed on dry ash disposal site and former ash settling pond. Magnetite with a mean coercivity (B1/2) of 36–47 mT and hematite (B1/2 of 200–900 mT) were found to be the major magnetic minerals of fresh fly and bottom ash. The size of magnetic grains of ash ranged from 1 to 20 µm, which corresponds to the typical pseudo-single-domain grains. The heterogeneity of the parent material (i.e. TPS ash) along the soil profiles significantly affected the magnetic parameters and composition of magnetic minerals. In the soil developed from bituminous coal ash, the magnetic susceptibility ranged from 771 to 2538 × 10-8 m3 kg−1, whereas in the soil developed from lignite ash it was 622–7657 × 10-8 m3 kg−1. The most abundant Fe oxides in Technosols were (i) magnetite with (ii) a few percent of hematite admixture (both minerals mainly inherited from fresh ash and partly neoformed), and (iii) low-coercivity maghemite (B1/2 ~ 15–20 mT) which most likely formed by the surface oxidation of fine magnetite grains inherited from the parent material. Magnetic methods were found to be a valuable research technique in the case of TPS ash-derived Technosols, for the identification of Fe-bearing magnetic minerals that are hardly recognizable by mineralogical methods, and for tracking the transformations of magnetic minerals resulting from soil-forming processes.

Iron and magnesium isotope systematics from the Shuangwang gold deposit in the Qinling Orogen, central China

Iron and Magnesium isotopes have been increasingly widely applied to trace mineralization processes of hydrothermal ore systems. In this study, Fe and Mg isotope compositions of whole-rocks, Fe-bearing minerals (pyrite and ankerite) and Mg-bearing mineral (ankerite) from the Shuangwang gold deposits are investigated to evaluate Fe and Mg isotope behaviors in a gold deposit hydrothermal system and provide new constraints on ore-forming processes. The results showed that the magmatic rocks in the Shuangwang gold deposit (mainly granodiorite, monzonitic granite and lamprophyre) yielded δ56Fe values of 0.05–0.10‰ and δ26Mg values concentrated in a narrow range from −0.23‰ to −0.21‰. The gold orebodies are hosted by a NW-trending breccia belt. The wall rock samples (mainly argillaceous limestone, carbonaceous slate and albitite) have higher δ56Fe values of 0.12–0.29‰ and a wide δ26Mg range from −2.54‰ to −0.35‰. Pyrite mineral separates show larger δ56Fe variation from −0.44‰ to 0.16‰, whereas ankerite has a small δ56Fe range from −0.15‰ to −0.06 and a δ26Mg range from −0.66‰ to −0.35‰.

The key roles of Fe-bearing minerals on arsenic capture and speciation transformation during high-As bituminous coal combustion: Experimental and theoretical investigations

The conversion of As vapor released from coal combustion to less hazardous solids is an important process to alleviate As pollution especially for high-As coal burning, but the roles of key ash components are still in debate. Here, we used multiple analytical methods across the micro to bulk scale and density functional theory to provide quantitative information on As speciation in fly ash and clarify the roles of ash components on As retention. Fly ash samples derived from the high-As bituminous coal-fired power plants showed a chemical composition of typical Class F fly ash. In-situ electron probe microanalysis (EPMA) was for the first time used to quantify and distinguish the inter-particle As distribution difference within coal fly ash. The spatial distribution of As was consistent with Fe, O, and sometimes with Ca. Grain-scale distribution of As in coal fly ash was quantified and As concentrations in single ash particles followed the order of Fe-oxides > aluminosilicates > unburned carbon > quartz. Sequential extraction and Wagner chemical plot of As confirmed that Fe minerals rather than Al-/Ca-bearing minerals played a vital role in capturing and oxidizing As3+ into solid phase (As5+). Magnetite content in fly ash well-correlated with the increase ratio of As before and after magnetic separation, suggesting magnetite enhanced As enrichment in fly ash. Density functional theory (DFT) indicated that the bridges O sites of octahedral structure on Fe3O4 (111) surface were likely strong active sites for As2O3 adsorption. This study highlights the importance of magnetite on As transformation during bituminous or high-rank coal combustion in power plants and has great implications for developing effective techniques for As removal.

Influencing Factors of the Mineral Carbonation Process of Iron Ore Mining Waste in Sequestering Atmospheric Carbon Dioxide

Mining waste may contain potential minerals that can act as essential feedstock for long-term carbon sequestration through a mineral carbonation process. This study attempts to identify the mineralogical and chemical composition of iron ore mining waste alongside the effects of particle size, temperature, and pH on carbonation efficiency. The samples were found to be alkaline in nature (pH of 6.9–7.5) and contained small-sized particles of clay and silt, thus indicating their suitability for mineral carbonation reactions. Samples were composed of important silicate minerals needed for the formation of carbonates such as wollastonite, anorthite, diopside, perovskite, johannsenite, and magnesium aluminum silicate, and the Fe-bearing mineral magnetite. The presence of Fe2O3 (39.6–62.9%) and CaO (7.2–15.2%) indicated the potential of the waste to sequester carbon dioxide because these oxides are important divalent cations for mineral carbonation. The use of small-sized mine-waste particles enables the enhancement of carbonation efficiency, i.e., particles of &lt;38 µm showed a greater extent of Fe and Ca carbonation efficiency (between 1.6–6.7%) compared to particles of &lt;63 µm (0.9–5.7%) and 75 µm (0.7–6.0%). Increasing the reaction temperature from 80 °C to 150–200 °C resulted in a higher Fe and Ca carbonation efficiency of some samples between 0.9–5.8% and 0.8–4.0%, respectively. The effect of increasing the pH from 8–12 was notably observed in Fe carbonation efficiency of between 0.7–5.9% (pH 12) compared to 0.6–3.3% (pH 8). Ca carbonation efficiency was moderately observed (0.7–5.5%) as with the increasing pH between 8–10. Therefore, it has been evidenced that mineralogical and chemical composition were of great importance for the mineral carbonation process, and that the effects of particle size, pH, and temperature of iron mining waste were influential in determining carbonation efficiency. Findings would be beneficial for sustaining the mining industry while taking into account the issue of waste production in tackling the global carbon emission concerns.

EXAFS Determination of Clay Minerals in Martian Meteorite Allan Hills 84001 and Its Implication for the Noachian Aqueous Environment

The aqueous environment of ancient Mars is of significant interest because of evidence suggesting the presence of a large body of liquid water on the surface at ~4 Ga, which differs significantly from the modern dry and oxic Martian environment. In this study, we examined the Fe-bearing minerals in the 4 Ga Martian meteorite, Alan Hills (ALH) 84001, to reveal the ancient aqueous environment present during the formation of this meteorite. Extended X-ray absorption fine structure (EXAFS) analysis was conducted to determine the Fe species in ALH carbonate and silica glass with a high spatial resolution (~1–2 μm). The μ-EXAFS analysis of ALH carbonate showed that the Fe species in the carbonate were dominated by a magnesite-siderite solid solution. Our analysis suggests the presence of smectite group clay in the carbonate, which is consistent with the results of previous thermochemical modeling. We also found serpentine in the silica glass, indicating the decrease of water after the formation of carbonate, at least locally. The possible allochthonous origin of the hematite in the carbonate suggests a patchy redox environment on the ancient Martian surface.