Background: Red mud is the residual mass resultant from NaOH digestion of bauxite ore by following the Bayer process for aluminum extraction. The global stockpile of red mud is estimated to be about 3 billion tons that either sent to marine disposal or as the dry stack in open space. In both cases, it poses a great environmental threat due to the high alkalinity and the presence of several heavy metals. On contrary, red mud contains a significant amount of rare earth elements (REEs). The increasing demands of REEs with fast depleting mineral reserves are therefore presenting red mud a potential secondary reservoir for REEs’ exploitation. In recent times, numerous studies are conducted using the pyro- and hydro-metallurgical routes albeit the disadvantages like high energy consumption, low recovery, and generation of secondary wastes have found to be associated with the disclosed processes. Due to the inherent benefits of low environmental stress, the less energy-intensive process using the microbial activity, bioleaching is increasingly attractive to the metallurgical operations, especially from the secondary resources.

Results: Henceforth, a feasibility study on the bioleaching of red mud has been investigated using Penicillium chrysogenum strain KBS3 (accession number GQ228447) with glucose, sawdust, and molasses as the substrate material. Three different modes of bioleaching (one-step, two-step, and spent medium) were examined with different capacity of metabolic production of acids. One-step bioleaching involving 12 mM citric acid, 2.5 mM oxalic acid, 1.8 mM tartaric acid, and 1162 mM gluconic acid. Whereas, the respective biogenic acid production was observed to be 15 mM, 1 mM, 0.5 mM, and 152 mM in two-step bioleaching, which were 63 mM, 29 mM, 23 mM, and 3 mM in the spent medium bioleaching while using glucose as the substrate and pulp density at 3%. Concomitant bio-mobilization was analyzed to be 79% Y, 28% La, and 28% Ce in a single-step bioleaching system. In the spent medium bioleaching 63% Y, 28% La, and 28% Ce could be mobilized into biogenic lixiviant, which was 67% Y, 20% La, and 15% Ce in a two-step leaching mode. Using molasses as the substrate, citric acid (4.21 mM, 3.57 mM, and 4.85 mM), oxalic acid (1.55 mM, 1.0 mM, and 0.09 mM), tartaric acid (1.18 mM, 0.95 mM, and 2.17 mM), and gluconic acid (210.19 mM, 52.5 mM, and 0.09 mM) were involved in one-step, two-step, and spent-medium bioleaching, respectively at the same pulp density of 3%. The resultant bio-mobilization was analyzed to be 57% Y, 13.5% La, and 12.77% Ce in one-step; 57% Y, 14% La, and 12% Ce in a two-step, and 49% Y, 6.3% La, and 2.9% Ce in the spent-medium bioleaching system. The insignificant mobilization of REEs (1-5%) was observed in the case of abiotic controls.

Conclusions: One-step bioleaching has shown good potential for the bio-mobilization of REEs from red mud using Penicillium chrysogenum strain KBS3 and glucose substrate. Future studies in this context may result in a more efficient process in terms of higher-yielding along with its environmentally-friendly properties.

Nowadays scientific and technological advances have allowed to Mankind to improve the life-style, but in this way, other problems have appeared. Currently, environmental problems are one of the most important. Many countries have developed a large number of environmental laws with the purpose of reducing human and industrial effects in the environment. In this work, a valorization procedure is developed for one of the most important wastes generated during aluminum recycling, namely, saline slag, finding that the final solids can be used for environmental applications. The procedure is divided into two steps: 1) recovery of aluminum from various slag fractions, and b) the use of recovered aluminum in the synthesis of two zeolites, namely, analcime (NaAlSi₂O₆·H₂O) and pollucite (CsAlSi₂O₆·nH₂O). Saline slag was ground, sieved (1 mm), washed and separated into two fractions of different sizes, one larger than 0.4 mm and other lower than 0.4 mm. The fraction <0.4 mm was treated under reflux conditions with NaOH or CsOH solutions of different concentrations. The extraction liquor contained aluminum and alkali metal cations; thus after adding the necessary amount of Si, hydrothermal synthesis was carried out at 200 °C for 24 hours, obtaining the zeolitic materials. The solids were characterized by powder X-ray diffraction, thermal analysis, FT–IR spectroscopy, element chemical analysis and electron microscopy. The results of the first step showed that a high percentage of Al (~ 44 wt.%) in the fraction <0.4 mm, can be recovered. The results of the second step indicated that crystalline analcime and pollucite zeolites can be hydrothermally synthesized from extractions liquors and a source of Si, being the only phases detected by PXRD.

Acknowledgements. MINECO and ERDF (financing, MAT2016-78863-C2-R). Junta de Castilla y León (formation programs, AJ and AM). Santander Bank (AG).

The report describes slurry and drainage water's characteristics and shows the conditions of their formation in the technogenic system of the Komsomolsky Tin-ore District, Russian Far East. The investigation was conducted using environmental monitoring, and physico-chemical modeling method in the Selektor software complex. In a wide ambient temperature range (from minus 25 to 45 °С) the Eh-pH parameters of micropore solutions, which form technogenic (anthropogenic) waters at various host-rock – sulfide ratios (95:5, 50:50, 5:95), were determined. Depends on the primary ores and host rocks composition ionic and molecular composition of technogenic waters, as well as association of crystallized hypergene (supergene) minerals were established.

The negative impact of slurry and drainage water on the hydrosphere and the health of the region's population is shown. Following to environmental monitoring, the content of dissolved metals exceeds background concentrations (times): slurry waters, Zn – up to 385000, Fe – 24253, Cu – 26230, Pb – 1703, Al – 915, Ca – 44766, Mg – 100285; drainage waters, Zn – up to 38200, Fe – 921, Cu – 768, Pb – 1470, Al – 253, Ca – 78133, Mg – 60557. Modeling reveals, that from saturated technogenic waters, Fe, Cu, Zn, Pb, Al, Ca, Mg, K, and Na minerals of the following classes precipitate: oxides and hydroxides, sulfates, carbonates, arsenates, phosphates, and silicates. The tendency of double growth for 24 types of digestive, respiratory, and nervous system diseases during the period from 1991 to 2001 has been noted, moreover, the morbidity rate of children significantly exceeds that of adults.

Ecandrewsite (ZnTiO₃), the zincian end-member of the ilmenite group minerals (IGM) has been found as an accessory relic phase in amphibolites from the Upper Proterozoic-Lower Cambrian metamorphic basement of the Pampa de Olaen region, in the eastern hillside of the Sierra Grande, Córdoba, Argentina. IGM grains occur as anhedral to subhedral inclusions as centers of coronitic titanite, as a result of retrograde metamorphic reactions. Electron microprobe analyses of IGM reveal compositions between Ec₅₆Pph₂₃Ilm₂₁ and Ilm₉₅Pph₅ along a solid solution trend ranging from manganoan ferroan ecandrewsite toward ilmenite s.s., passing through intermediate members such as ferroan manganoan ecandrewsite, zincian manganoan ilmenite and manganoan ilmenite. Ecandrewsite and other members of the IGM are considered refractory accessory minerals of a basic igneous rock (likely basalt) later on affected by medium grade regional metamorphism. The inclusions of IGM in titanite would represent non-consumed remnants of the protholithic IGM after coupled reactions with plagioclase that led to the formation of titanite during a retrograde metamorphic event. Even considering that Zn is a relatively widespread element in the metasedimentary associated sequence, we believe that the chemical trend between near end-members ecandrewsite and ilmenite reflects the magmatic composition of IGM in the protholith, where the variations of the Zn contents were controlled by the substitution of Fe by Zn+Mn in the absence any type of regular zonation. However, it is not discarded that chemical adjustments among members of the IGM could have been introduced during prograde regional metamorphism. This would be the first worldwide record of ecandrewsite in amphibolites.

Two manganese prospects were studied. The Kanif prospect is hosted within an ophiolitic complex located 110 km southeast of Birjand, Southern Khorasan province (eastern Iran). The ophiolitic sequence in this region hosts manganese ore occurring as small discrete patches associated with radiolarian cherts. Ore minerals identified by XRD methods and petrographic studies are pyrolusite, hematite, and goethite showing replacement, colloidal and brecciated textures. Carbonate and silica are the gangue minerals. Based on the ICP-ES-MS methods, the average grade of Kanif is 33.92% Mn. Fluid inclusions hosted by calcite from Kanif demonstrate that the ore-forming solutions had salinities within the range of 0.5-4.5 wt% NaCl eq., homogenization temperatures within the range 100-220˚C and densities of about 0.8-1 g/cm³. Pressure is estimated to be about 50 bars, corresponding to a depth of ~150 meters at the time of formation. The Basiran prospect features veins/veinlets and is located 212 km SW of Birjand, Southern Khorasan province (eastern Iran). These veins/veinlets are hosted by andesitic rocks of Eocene to Oligocene age. Ore minerals identified by XRD methods and petrographic studies are pyrolusite, psilomelane, hematite, goethite and limonite, displaying colloform and open-space filling textures. Gypsum, carbonate and silica are the gangue minerals. Alteration zones, specifically argillic alteration zone, are developed along the veins/veinlets within the andesitic wall rocks. Based on the mineralogical and geochemical data, the primary manganese minerals were Mn oxides and hydroxides, which have gradually been converted to psilomelane and finally pyrolusite. The average Mn grade within the veins/veinlets is 25.95%. Fluid inclusion data show that the ore-forming solutions had salinities within the range of 0.5-5.5 wt% NaCl eq., TH range of 120-220˚C and density about 0.8-1 g/cm³. The pressure was estimated to be less than 50 bars, corresponding to a depth of ~150 meters and a hydrothermal origin. This study focused on investigation of fluid inclusions based on petrography, variety, morphologies, salinity and homogenization temperature for different styles of manganese prospects. Kanif is located in Sistan zone and Basiran is located in lut block. Results and Interpretation of microthermometric data suggest hydrothermal origins for both the Kanif and Basiran Mn prospects.

Abstract:

In this study, a method based on flotation assistance of homogeneous liquid-liquid microextraction (FA-HLLME) combined with inductively coupled plasma-mass spectroscopy (ICP-MS) was proposed for the measurement of trace Samarium in Mineral concentrate samples. As one of the miniaturized separation and extraction techniques, homogenous liquid-liquid microextraction (HLLME) has been widely applied in the field of Mineral processing. PAN (1-(2-Pyridylazo)-2-naphthol) was used as the complexing agent and 1-Dodecanol and Acetone were selected as extraction and homogeneous solvents, respectively. The factors that influenced the extraction efficiency for Samarium measurement (including pH, extraction, and homogeneous solvents, the concentration of PAN and NaCl, extraction time) were studied statistically. Under the optimum conditions (pH=8.0, 140µL 1-Dodecanol, 1.2 mL Tetrahydrofuran, 3.045×10^-4 mol L^-1PAN, 2.5mol L^-1 NaCl, and 120 sec of extraction time), the linear dynamic range for Samarium determination was 10.0 - 220.0 ng L^-1 (R²=0.9862) with a limit of detection (LOD) for Samarium was 2.91 ng L^-1. The relative standard deviation (R.S.D.) (C=40 ng L^-1, n=7) was 2.1% and the enrichment factor of 250 for Samarium extraction. The proposed method was successfully applied to the measurement of Samarium in different Mineral concentrate samples.

Monohydrocalcite (CaCO₃·H₂O) is a mineral rarely found in natural environments. Here we report finding of this mineral in the composition of the microbialites in Laguna de los Cisnes (Isla Grande, Chile), a saline alkaline lake with high Mg/Ca ratio. We have made a detailed structural and mineralogical description of these microbialites with the use of light and scanning electron microscopy, infrared spectroscopy and X-ray analysis. The predominantly carbonate composition of microbialites was revealed. Carbonates were represented mainly by high-magnesium calcites and monohydrocalcite. Calcite and aragonite were found in minor quantities. In addition, a small amount of silicates and amorphous hydromagnesite were found.

The yellowish-brown surface layer of microbialites consists of numerous crystals within a mineralized exopolysaccharide (EPS) matrix. A large number of unicellular and filamentous algae, as well as areas of released EPS, are also seen here. Below is a slimy green layer. This layer is not mineralized, it represents an "algal-bacterial mat" consisting of algae, cyanobacteria, and diatoms developed in EPS. Chisel-shaped crystals of monohydrocalcite and its amorphous spherical precursors are numerous in these upper layers. The deeper layers are mineralized, they consist predominantly of Mg-carbonates with varying degrees of Mg. Algae and cyanobacteria are decomposed or fossilized there.

Thus, monohydrocalcite occurs in the composition of the microbialites being one of the main mineral components. As in other lacustrine localities it is formed in the presence of algae and cyanobacteria. To our knowledge this is the first report on the discovery of monohydrocalcite in South America.

In the present work we apply the so-called cBΩ thermodynamic model to study the diffusion of Si in stishovite crystal at high pressure and over a wide temperature range. According to this model [1,2], the point defect activation Gibbs free energy is expressed as a function of the bulk properties of the material, i.e. g^act=cBΩ, where B is the isothermal bulk modulus, Ω is the mean atomic volume and c is a dimensionless constant. In this way, other important point defect parameters, such as the activation volume V^act, the activation entropy S^act and the activation enthalpy h^act may be estimated, if the thermoelastic properties of the material are known over a wide temperature and pressure range. Our calculations are based on previously reported self-diffusion coefficients in stishovite single crystals measured at 14 GPa and at temperatures from 1400 to 1800 ^oC, in the [110] and [001] directions, by Shatskiy et al. [3]. Furthermore, the EoS of stishovite, proposed by Wang et al. [4] has been used for the accurate implementation of the cBΩ model. Our results suggest that the aforementioned point defect parameters exhibit considerable temperature dependence over the studied temperature range (1000-2000 ^oC). The estimated activation volumes (4.8-5.8 cm³/mol, in the range 1400-1800 ^oC) are in agreement with the experimental results reported by Xu et al. [5]. Our study confirms the potential of the cBΩ model for the theoretical investigation of diffusion processes in minerals, in order to overcome the experimental difficulties and the lack of experimental data in mantle conditions.

REFERENCES

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3. Shatskiy, A., Yamazaki, D., Borzdov, Y.M., Matsuzaki, T., Litasov, K.D., Cooray, T., Ferot, A., Ito, E., Katsura, T. Stishovite single-crystal growth and application to silicon self-diffusion measurements, Mineral. 2010, 95, 135–43, Doi: 10.2138/am.2010.3255.
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The Intra-Sudetic Basin, a Late-Paleozoic intramontane trough located on the NE flank of the Bohemian Massif, comprises numerous outcrops of continental (extension-related) Early-Permian volcanogenic rocks that are commonly altered to spilites. In this contribution, we provide insights into the formation of spilitized (albite- and chlorite-rich) trachyandesites from Głuszyca quarry (Lower Silesia, Poland) based on mineralogical and micro-textural investigations supported by apatite fission-track dating (AFT). Our results indicate that the trachyandesites, emplaced as a shallow-level laccolith-type body, have been strongly affected by chloritization of both aegirine and augite, combined with an occasional celadonitization of volcanic glass. Furthermore, chlortitization of sodic pyroxenes must have released notable amounts of Na⁺, which could be involved during later pervasive albitzation of primary andesine-labradorite. According to various chemical and semi-empirical thermometers, the replacive chlorites formed in the range of 124-170°C. Trachyandesites from Głuszyca contain abundant fluorapatites marked by the occurrence of swallow-type terminations, which are indicative of rapid-cooling formation conditions. Central AFT ages of the samples vary between 161-182 Ma and correspond to the Middle-Jurassic period. Meanwhile, these ages are significantly younger than the emplacement of igneous rocks during Middle Rotliegendes period (~299-271 Ma). The discrepancy between the stratigraphic age of the rocks and the AFT results cannot be, however, explained by, for example, slow cooling rates of magmatic body, compositional variations of apatite, or burial under Late-Mesozoic sediments. Hence, it may be assumed that the obtained AFT ages (161-182 Ma) reflect the timing of spilitization and associated partial reheating of volcanic rocks from the Intra-Sudetic Basin above the apatite partial annealing zone (70-110°C).

We examined the distribution of Fe, Mn, Cu, Zn, and Pb in one core of metalliferous, and one core of non-mineralised (background) carbonate sediments (located 69 km northwards), from the Pobeda hydrothermal field. Mechanisms of metal accumulation in sediments (12 samples) were evaluated based on sequential extraction of geochemical fractions, including mobile (exchangeable complex, authigenic Fe-Mn hydroxides, and sulfides), and lithogenic (fixed in crystalline lattices) forms. Maps of element distribution in sediment components were obtained using a scanning electron microscope equipped with an energy-dispersive spectrometry detector. In metalliferous sediments, according to X-Ray diffraction data, the main Fe mineral phase was goethite FeOOH (37–44% on a carbonate-free basis). Contents of Fe and Mn reached 31.6 and 0.18%, respectively, whereas concentrations of Cu, Zn and Pb were 0.98, 0.36, and 0.059%. The coefficient of metal enrichment relative to background values varied from 16 to 125 times. The exception was Mn, for which no increased accumulation was recorded. Main mass of Fe (up to 70% of total content) was represented by the lithogenic fraction; among geochemically mobile fractions, 90-97% of total Fe was found in the form of authigenic oxyhydroxides. The same fraction was the predominant host for Mn in both metalliferous and background sediments (55-85%). 40-96 % of Cd, Cu, Zn, and Pb were associated with these Fe and Mn fractions. The sulfide fraction amounted to roughly 10% of each metal. In metalliferous sediment core, the maximum concentrations of metals and their geochemically mobile fractions were recorded in deeper core intercepts, an observation that might be attributed to influence of hydrothermal diffused fluids. Our data suggested that metals are mostly accumulated in carbonate sediments in their contact zone with the underlying serpentinized basalts.