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The OH-stretching infrared absorption spectrum of a tourmaline sample close to the foitite end-member is interpreted in the light of the density functional theory (DFT) modeling of iron-bearing Y3Z6 clusters in tourmaline. The iron-bearing clusters reflect the Al-rich and Na-deficient character of foitite and contain either two Fe2+ and one Al3+ or one Fe2+ and two Al3+ ions at the Y sites. The clusters are embedded in a tourmaline host structure with dravite composition. For the iron dimer models, the structural and vibrational properties corresponding to the ferromagnetic (FM) or anti-ferromagnetic (AFM) arrangement of the iron spins and the effect of vacancy ordering along the [001] axis are considered. A significant difference in the relaxed structure of the FM and AFM clusters is observed, stemming from the electron delocalization and Fe–Fe bonding interactions in the FM cluster. These bonding interactions are not allowed in the AFM cluster. In this case, the valence electrons with opposite spins remain separately localized on the two Fe atoms. The AFM configuration is more stable than the FM one in the theoretical models, provided that the description of the on-site Coulomb repulsion in Fe(3d) orbitals is improved within the DFT + U framework. Based on the theoretical results, the two bands at 3630 and 3644 cm−1 in the vibrational spectra of iron-rich and Na-deficient tourmalines are assigned to WOH groups associated with YFe22+YAl3+ environments with an AFM coupling of Fe ions and surrounded by one and two vacant X sites, respectively. The two major VOH bands of the experimental spectrum are interpreted on the same basis, and these interpretations are extrapolated to Mn-bearing tourmalines.

International audience; U-Th-Pb geochronology of REE-bearing minerals such as monazite and other phosphates has become a precise tool to date mineralization events through geological time. In the E-Colombian Guainía department, from 3 colluvial sites over western Guiana Shield Mesoproterozoic rocks Nb-Ta, U-Th and REE bearing minerals probably of pegmatitic origin were sampled including up-to-0.5 cm long monazite crystals. The monazite pan concentrate samples from sites near to the indigenous communities of Barranquilla, San Jose and Chorro Bocón (Espina hills) along the Cuyari, Guainía, and Inírida rivers respectively, were analyzed geochemically and geochronologically using LA-ICP-MS and EPMA. The monazites obtained from the 3 sites are rather similar among each another and of approximate composition Ce0.44La0.16Nd0.16Sm004Y0.03Gd0.02Dy0.01Pr0.05Th0.08Pb0.01Ca0.05Si0.05P0.91O3.94. Their EPMA and LA-ICP-MS ages suggest at least two mineralization events, a first one between 1528 and 1523 Ma in the Barranquilla and San Jose sites, related to rapakivi granites outcropping along the Cuyarí River and the Tabaquen rapakivi granite near the Guainía River, both emplaced ~1545 Ma ago. The second mineralization event from 1390-1343 Ma recorded in the Espina-hills is in the age range of the Matraca and Danta rapakivi granites that crystalized between 1400 and 1340 Ma ago. These different anorogenic rapakivi granites were emplaced between 1550 and 1300 Ma into Mesoproterozoic basement rocks and were probably caused by intra-plate processes associated with mantle plume activity within the Columbia (Nuna) supercontinent.

BACKGROUND Gradual depletion of high-grade ores for heavy metals has encouraged industries to search for alternative methods to recover metals. Wastes generated from metallurgical industries can be used as a secondary resource as it contains high concentrations of metals. RESULTS The bioleaching kinetics and biorecovery of zinc from Zn-plant leach residues (ZLR), collected from a currently operating Zn-plant in Tres Marias (Minas Gerais, Brazil) were investigated using sulfuric acid producing Acidithiobacillus thiooxidans (A. thiooxidans). Response surface methodology (RSM) with full factorial central composite design (CCD) was applied to optimize Zn bioleaching by A. thiooxidans. The experiments were performed by varying the initial elemental sulfur concentration (5–30 g L−1), pulp density (5–50 g L−1) and initial pH (3.0–4.0 pH units). More than 75% of Zn was extracted from ZLR by A. thiooxidans under optimized conditions (sulfur concentration 25.1 g L−1, pulp density 21.5 g L−1 and initial pH 3.3). The leaching efficiencies of culture supernatant (biogenic sulfuric acid) and chemical sulfuric acid were compared to understand the leaching kinetics. The Zn leaching kinetics of ZLR followed the shrinking core diffusion model. Zn was selectively recovered from the Fe-rich acidic bioleachate by biogenic sulfide precipitation. Fe was first removed (more than 85% of total Fe in the leachate) by adjusting the initial pH to 5.0, followed by selective Zn biorecovery. CONCLUSIONS Zn (>95%) was selectively recovered from Fe-depleted ZLR by biogenic sulfides (with 1:1, Zn:biogenic sulfide mass ratio). Biohydrometallurgy can be a potential alternative resource recovery strategy for the selective recovery of Zn from ZLR. © 2016 Society of Chemical Industry

Ore processing generates a large amount of sterile and waste from purification and concentration processes. This material, in contact with the environment, can cause major environmental impacts. CMM-Votorantim at Tres Marias benefits silicate and sulphide Zn ores. The tailings from one stage of the process are deposited in an area called PH9 on the banks of the Sao Francisco River and subsequently removed and placed in a waterproofed settling basin. The area of the old deposit presented problems in the process of environmental recovery and, therefore, it became opportune to investigate chemically the level of contamination there. The area has 14.4 ha and is located in the municipality of Tres Marias / MG with a slope towards the bed of the Sao Francisco River. The soil samples were collected in two cross profiles, one North - South and the other East - West, totaling 29 georeferenced points with a distance of 20 m. A soil sample was collected at each point. After preparation at the Soil Laboratory of Unimontes, Campus Janauba - MG, the samples were analyzed in the ICP OES laboratory of the NGqA of the CPMTC of UFMG - Campus Belo Horizonte. Total and available concentrations of calcium, magnesium, aluminum, iron, manganese, copper, zinc and organic matter, together with pH were determined. For the graphical representation, we opted for a grouping the results in pH ranges versus concentrations. The results show that the area has magnesium contamination, thus causing severe structural degradation of the soil. The concentrations of the other elements in the PH9 area are within the limits allowed for land use in agricultural activity, but approaching the upper limit allowed.

Various mineral processing operations to produce pure metals from mineral ores generate sludges, residues, and other unwanted by-products/wastes. As a general practice, these wastes are either stored in a reservoir or disposed in the surrounding of mining/smelting areas, which might cause adverse environmental impacts. Therefore, it is important to understand the various characteristics like heavy metal leaching features and potential toxicity of these metallurgical wastes. In this study, zinc plant leach residues (ZLRs) were collected from a currently operating Zn metallurgical industry located in Minas Gerais (Brazil) and investigated for their potential toxicity, fractionation, and leachability. Three different ZLR samples (ZLR1, ZLR2, and ZLR3) were collected, based on their age of production and deposition. They mainly consisted of Fe (6-11.5 %), Zn (2.5 to 5.0 %), and Pb (1.5 to 2.5 %) and minor concentrations of Al, Cd, Cu, and Mn, depending on the sample age. Toxicity Characteristic Leaching Procedure (TCLP) results revealed that these wastes are hazardous for the environment. Accelerated Community Bureau of Reference (BCR) sequential extraction clearly showed that potentially toxic heavy metals such as Cd, Cu, Pb, and Zn can be released into the environment in high quantities under mild acidic conditions. The results of the liquid-solid partitioning as a function of pH showed that pH plays an important role in the leachability of metals from these residues. At low pH (pH 2.5), high concentrations of metals can be leached: 67, 25, and 7 % of Zn can be leached from leach residues ZLR1, ZLR2, and ZLR3, respectively. The release of metals decreased with increasing pH. Geochemical modeling of the pH-dependent leaching was also performed to determine which geochemical process controls the leachability/solubility of the heavy metals. This study showed that the studied ZLRs contain significant concentrations of non-residual extractable fractions of Zn and can be seen as a potential secondary resource for Zn.

Sludges, dusts, residues and other wastes originating from ferrous and non-ferrous metallic industries pose a serious environmental threat, if not disposed properly. Disposal of these wastes is expensive and remediation is a necessary step to be implemented to control the adverse environmental effects if disposal is done improperly. Since the past couple of decades, the world’s high-grade metal reserves have been depleted considerably, but the demand for metals in day-to-day life in this electronic era is growing rapidly. The depletion of high-grade ores urges the mineral industry to look for alternative resources for metal extraction. Sludges, dusts, and other wastes generated by the metallurgical industries are interesting options as they still contain significant amounts of valuable base and heavy metals, sometimes even precious metals like gold and silver and also rare earth elements, depending on the nature of the mining site and composition of the primary ores used. This chapter overviews various hydrometallurgical and bio-hydrometallurgical leaching processes for the extraction of metals from these wastes. Different strategies of metal recovery such as solvent-extraction, electrowinning, bio/chemical sorption and bio/chemical precipitation from the wastes generated by various ferrous and non-ferrous metallic industries are overviewed.

Zinc plant purification residue (ZPR), a typical Zn-hydrometallurgical waste, was collected from the Três Marias Zn plant (MG, Brazil). ZPR was characterized for its metal content and fractionation, mineralogy, toxicity and leachability. Toxicity characteristics leaching procedure (TCLP) and European Community Bureau of Reference (BCR) sequential extraction results revealed that this ZPR displays high percentages of metals (Cd, Cu, Zn and Pb) in the highly mobilizable fractions, increasing its hazardous potential. Bulk chemical analysis, pH dependent leaching and acid (H2SO4) leaching studies confirm that the ZPR is polymetallic, rich in Cd, Cu and Zn. The sulfuric acid concentration (1 M), agitation speed (450 rpm), temperature (40 °C) and pulp density (20 g L(-1)) were optimized to leach the maximum amount of heavy metals (Cd, Cu and Zn). Under optimum conditions, more than 50%, 70% and 60% of the total Cd, Cu and Zn present in the ZPR can be leached, respectively. The metals in the acid leachates were investigated for metal sulfide precipitation with an emphasis on selective Cu recovery. Metal sulfide precipitation process parameters such as initial pH and Cu to sulfide ratio were optimized as pH 1.5 and 1:0.5 (Cu:sulfide) mass ratio, respectively. Under optimum conditions, more than 95% of Cu can be selectively recovered from the polymetallic ZPR leachates. The Cu precipitates characterization studies reveal that they are approximately 0.1 μm in diameter and mainly consist of Cu and S. XRD analysis showed covellite (CuS), chalcanthite (CuSO4·5H2O) and natrochalcite (NaCu2(SO4)2(OH)·H2O) as the mineral phases. ZPRs can thus be considered as an alternative resource for copper production.

Esta pesquisa teve como proposta principal a análise geoquímica de superfície para os solos do sitio arqueológico cemitério Caixa d'agua, localizado no Município de Buritizeiro - Norte do Estado de Minas Gerais - além, de uma caracterização dos aspectos do meio físico e paleoecológicos. Os elementos químicos selecionados Al, Fe, P, Ca, Cu e Zn foram analisados a partir de amostras de solos amostradas em áreas de sepultamento pré-histórico, a leitura foi feita através de Florescência de Raios X. Os elementos analisados representam uma assinatura geoquímica típica associada à atividade antrópica pré-histórica.

Objetivou-se neste trabalho determinar os teores de metais pesados em amostras de solos de uma topolitoseqüência coletada no Triângulo Mineiro, Estado de Minas Gerais, para testar a hipótese de que tais elementos podem ser utilizados na identificação e separação da influência do material de origem. Os teores de Cd, Cr, Cu, Fe, Mn, Ni, Pb e Zn foram determinados por dois procedimentos de ataque ácido: HNO3/HClO4 (4:1) e HF/HNO3/HClO4 (20:6:3), e dosados por espectrofotometria de absorção atômica. Técnicas de análise multivariada foram utilizadas. Os resultados permitem estabelecer que os metais pesados são indicativos do material de origem, podendo ser usados na separação e delimitação de sua área de influência. As técnicas multivariadas adotadas mostraram-se viáveis nesse modelo de estudo quando analisadas conjuntamente. The present study had the purpose to determine the contents of heavy metals in soil samples of a topolithosequence collected in the Triângulo Mineiro, State of Minas Gerais, in order to test the hypothesis that these elements could be used in the identification and separation of the influence of the parent material. The contents of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn were determined through two types of concentrated acid attack: HNO3/HClO4 (4:1) and HF/HNO3/HClO4 (20:6:3), and dosed by espectrophotometry of atomic absortion. Procedures of multivariated analysis were used for the statistical data evaluation. The results confirm the hypothesis and permitted to conclude that the heavy metals are indicator of the parent material, being able to be used for the separation and delimitation of the area of their influence. The adopted multivariated techniques proved to be viable for this kind of study only when analysed as a whole.