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.