Selective copper dissolution during bioleaching of molybdenite concentrate

This study evaluates bioleaching treatments to remove copper from the Sarcheshmeh (Iran) molybdenite concentrate using a native strain of Acidithiobacillus ferrooxidans. Copper content of the concentrate was 0.83 wt.% as chalcopyrite. The tests showed selective dissolution of copper (chalcopyrite) from molybdenite concentrate. Up to 65% of copper content of molybdenite concentrate was removed via bioleaching with a native strain of A. ferrooxidans in less than 15 days. Ferrous sulfate, sulfur or pyrite was added to culture medium to enhance the activity of bacteria. Sulfur was the preferred additional source of energy for removing copper from molybdenite via bioleaching with A. ferrooxidans. In addition, 9K or Norris medium was also used as the culture medium in the experiments. The experiments showed that application of Norris medium would be better than that of 9K medium in order to remove copper from molybdenite via bioleaching. These results were backed up due to the fact that the cost of Norris medium was also less than that of 9K medium.     

非饱和土干化过程微观结构演化规律研究

水-力耦合特性是非饱和土最基本的力学特性之一,含黏粒土体的孔隙结构对含水率变化非常敏感,相应的孔隙分布曲线也会随之变化。基于已有的试验研究成果,揭示了水力路径下土体微观结构的演化规律,建立了孔隙比与孔隙分布曲线之间的关系,由此提出了一个能模拟干化过程中孔隙分布曲线变化的理论模型。所建立模型中,吸力增加后的孔隙分布曲线可由初始曲线通过平移、缩放以及分散三步得到;其中孔隙分布的平移量和缩放量与孔隙比线性相关,而分散程度与孔隙比满足指数衰减关系。模型预测结果表明,所建立的模型不仅能预测集聚体间和集聚体内孔隙分布的变化,而且能较好地反映中间态孔隙分布曲线的变化。     

多次干湿循环后土-水特征曲线的模拟

目前对于土体的干湿循环过程中变形、强度变化规律研究较多,而对经过多次干湿循环后土-水特征曲线的试验研究较少。由于吸力平衡需要时间太长,对干湿循环过程中土-水特征曲线的研究也多限于单次的干湿循环试验。但考虑到实际岩土工程中气候条件的多变性和自然环境的复杂性,一般土体均要经历多次干湿循环,因此,对多次干湿循环后的土-水特性曲线研究显得非常重要。结合已有的试验数据总结脱湿曲线与吸湿曲线随着干湿循环次数的变化规律,通过引入一个与干湿循环次数有关的函数,提出能预测多次干湿循环后土-水特征曲线的方法。本方法仅需土-水特征曲线的首次干湿循环脱湿与吸湿曲线和塑性指数,就可以预测多次干湿循环后的土-水特征曲线。     

Reactive transport processes occurring during nuclear glass alteration in presence of magnetite

In this study, we have investigated and clarified the processes occurring during the alteration of SON68 glass – the reference nuclear glass for the waste arising from reprocessing of spent fuel from light water reactors – at 50 °C in Callovo-Oxfordian clay groundwater in presence of magnetite. Magnetite is known to be one of the iron corrosion products expected to be present in the vicinity of glass in geological disposal conditions. The effects of the amount of magnetite relative to the glass surface and the transport of aqueous species during glass alteration were studied. A first series of experiments was focused on the effect of various magnetite amounts by mixing and altering glass and magnetite powders. In a second series of experiments, magnetite was separated from the glass by a diffusive barrier in order to slow down the transport of aqueous species. Glass alteration kinetics were analyzed and solids were characterized by a multiscale approach using Raman Spectroscopy, Scanning and Transmission Electron Microscopy, Energy-Dispersive X-ray and Scanning Transmission X-ray Microscopy coupled with Fe L_2,3-edge and C K-edge NEXAFS.It appears that glass alteration increases with the amount of magnetite and that the transport of aqueous species is a key parameter. Several processes have been identified such as (i) the silica sorption on the magnetite surface, (ii) the precipitation of Fe-silicates in the vicinity of the glass (iii) the precipitation of SiO₂ on the magnetite surface, (iv) the incorporation of Fe within the alteration layer. Process (iv) was not frequently observed, suggesting local variations in geochemical conditions. Moreover, this process is strongly influenced by the transport of aqueous species as indicated by the morphology and composition of the alteration layers. Indeed, when glass and magnetite are homogeneously mixed, the glass alteration layer consists of a gel enriched in Fe having the same Fe(II)/Fe(III) ratio as in magnetite. When both materials are separated by a diffusive barrier, the glass alteration layer consists of a porous gel (not enriched in iron) in presence of a mixture of Fe-silicates with Fe having the same valence as in magnetite, rare-earth precipitates and phyllosilicates. These results suggest that Fe incorporation within the alteration layer changes depending on the distance and the time required for dissolved Fe originating from the magnetite to reach the glass.     

绿片岩-低角闪岩相变质条件下磁铁铁矿与黄铁矿间的Fe同位素分馏

对辽宁省鞍山一本溪地区经历了绿片岩一低角闪岩相变质的新太古代条带状铁建造中磁铁矿和黄铁矿矿物对的Fe同位素分析结果显示:相对于标准IRMM-014,所有样品的磁铁矿和黄铁矿均显示Fe的重同位素富集;且黄铁矿的Fe同位素比值均大于磁铁矿的Fe同位素比值(ε57Fe黄铁矿ε57Fe磁铁矿),两种矿物的Fe同位素比值之差为△57Fe黄铁矿-磁铁矿=2.23～5.13.黄铁矿富集铁的重同位素表明矿物的Fe同位素组成并不代表其原始沉积的特征,而是在区域变质作用过程中Fe同位素发生了交换的结果.由同位素平衡判别图解可知,在绿片岩一低角闪岩相变质作用中,磁铁矿-黄铁矿间的Fe同位素基本达到了平衡,且在平衡条件下黄铁矿比磁铁矿更富集Fe的重同位素,二者之间的Fe同位素平衡分馏系数α黄铁矿-磁铁矿≈1.000 4‰±0.06‰(2σ).这一研究成果是对变质作用过程中Fe同位素的地球化学行为认识的重要进展.     

干湿过程中花岗岩残积土抗拉强度变化研究

利用自制的土体直拉强度测试仪,研究了重塑花岗岩残积土在不同含水率下、增湿过程和干燥过程中抗拉强度的变化规律,并从胶结力和湿吸力的角度讨论了抗拉强度变化规律的微观机制。结果表明：不同含水率条件下抗拉强度随含水率增加呈现先增后减,峰值两侧呈较好的指数规律;增湿过程中抗拉强度随含水率增加呈先增后减趋势,峰值两侧为一次函数规律;干燥过程中抗拉强度随含水率降低出现指数增加阶段、平稳阶段和小幅降低阶段3个阶段,其抗拉强度峰值为不同含水率条件下抗拉强度的4倍。花岗岩残积土在不同含水率和增湿过程中的抗拉强度的变化主要受湿吸力控制,而干燥过程中抗拉强度变化的同时受湿吸力和胶结力的控制,且胶结力对抗拉强度的贡献超过70%。土体的干燥开裂过程对应干燥过程中抗拉强度变化的几个阶段,干燥时湿吸力是土体内部拉应力的来源,这说明湿吸力既是抗拉强度的贡献者,同时也是抗拉强度的破坏者。该研究结果从另一种角度解释了土体抗拉强度的形成来源及其变化的主控因素。     

粘土干湿循环中裂缝演变过程的数值模拟

在非饱和土简化固结理论基础上,对粘土在干湿过程中,表面裂缝从形成、发展到闭合的发展过程进行了数值模拟,模拟结果说明,本文采用的基于非饱和简化固结理论的计算方法是可行、实用的.     

Nanogeochemistry of hydrothermal magnetite

Magnetite from hydrothermal ore deposits can contain up to tens of thousands of parts per million (ppm) of elements such as Ti, Si, V, Al, Ca, Mg, Na, which tend to either structurally incorporate into growth and sector zones or form mineral micro- to nano-sized particles. Here, we report micro- to nano-structural and chemical data of hydrothermal magnetite from the Los Colorados iron oxide–apatite deposit in Chile, where magnetite displays both types of trace element incorporation. Three generations of magnetites (X–Z) were identified with concentrations of minor and trace elements that vary significantly: SiO₂, from below detection limit (bdl) to 3.1 wt%; Al₂O₃, 0.3–2.3 wt%; CaO, bdl–0.9 wt%; MgO, 0.02–2.5 wt%; TiO₂, 0.1–0.4 wt%; MnO, 0.04–0.2 wt%; Na₂O, bdl–0.4 wt%; and K₂O, bdl–0.4 wt%. An exception is V₂O₃, which is remarkably constant, ranging from 0.3 to 0.4 wt%. Six types of crystalline nanoparticles (NPs) were identified by means of transmission electron microscopy in the trace element-rich zones, which are each a few micrometres wide: (1) diopside, (2) clinoenstatite; (3) amphibole, (4) mica, (5) ulvöspinel, and (6) Ti-rich magnetite. In addition, Al-rich nanodomains, which contain 2–3 wt% of Al, occur within a single crystal of magnetite. The accumulation of NPs in the trace element-rich zones suggest that they form owing to supersaturation from a hydrothermal fluid, followed by entrapment during continuous growth of the magnetite surface. It is also concluded that mineral NPs promote exsolution of new phases from the mineral host, otherwise preserved as structurally bound trace elements. The presence of abundant mineral NPs in magnetite points to a complex incorporation of trace elements during growth, and provides a cautionary note on the interpretation of micron-scale chemical data of magnetite.     

Numerical simulation of crack formation process in clays during drying and wetting

Clays generally crack upon drying and the cracks gradually close up because of expansion of the clays induced by rainfall infiltration. Based on the concept of air drainage ratio, we introduce an improved simplified consolidation theory for unsaturated soils and apply it to solve the crack formation problem. We present initial conditions, special consideration, and finite-element (FEM) formulations for simulation of cracks under axisymmetric conditions. Similar to finding solutions for sand-well consolidation problems, a prism of clays surrounded by polygonal distributed cracks is simplified as a cylinder. Numerical simulations using the FEM formulations are performed on the processes of crack occurrence, propagation, and closure during drying and wetting. To investigate the influence of air drainage ratio distribution, three different schemes are adopted for computation. It is found that the behaviour of cracks in clays during drying and wetting can be well represented using the approach proposed in the paper. The simplified consolidation theory used in the paper for unsaturated soils is more suitable for crack analysis than the general consolidation theory currently applied.     

Oxidation of pyrite during extraction of carbonate associated sulfate

The sulfur isotopic composition of carbonate associated sulfate (CAS) has been used to investigate the geochemistry of ancient seawater sulfate. However, few studies have quantified the reliability of δ³⁴S of CAS as a seawater sulfate proxy, especially with respect to later diagenetic overprinting. Pyrite, which typically has depleted δ³⁴S values due to authigenic fractionation associated with bacterial sulfate reduction, is a common constituent of marine sedimentary rocks. The oxidation of pyrite, whether during diagenesis or sample preparation, could thus adversely influence the sulfur isotopic composition of CAS. Here, we report the results of CAS extractions using HCl and acetic acid with samples spiked with varying amounts of pyrite. The results show a very strong linear relationship between the abundance of fine-grained pyrite added to the sample and the resultant abundance and δ³⁴S value of CAS. This data represents the first unequivocal evidence that pyrite is oxidized during the CAS extraction process. Our mixing models indicate that in samples with much less than 1 wt.% pyrite and relatively high δ³⁴S_pyrite values, the isotopic offset imparted by oxidation of pyrite should be much less than ? 4‰. A wealth of literature exists on the oxidation of pyrite by Fe³⁺ and we believe this mechanism drives the oxidation of pyrite during CAS extraction, during which the oxygen used to form sulfate is taken from H₂O, not O₂. Consequently, extracting CAS under anaerobic conditions would only slow, but not halt, the oxidation of pyrite. Future studies of CAS should attempt to quantify pyrite abundance and isotopic composition.     

Characterization of a natural magnetite

Single crystals of a rock magnetite were separated from steatite cobbles collected in a geological site near the city of Serro (18° 36′ 47′′ S 43° 22′ 46′′ W), Minas Gerais, Brazil. A typically well-shaped magnetite single crystal was characterized by chemical analysis, ⁵⁷Fe Mössbauer spectrometry at 300, 77 and 4 K and under an applied magnetic field of 6 T at 10 K, magnetization measurements and electronic microprobe. From Mössbauer data, the sample is stoichiometric with a tetrahedral and octahedral site occupancy ratio of 1:2. Elemental chemical analysis and point-to-point electron microscope probing show some inclusions of lamellar ilmenite (≤ 1 mass%) randomly distributed throughout the magnetite matrix, and also that the magnetite matrix is constituted only by Fe²⁺ and Fe³⁺, with no isomorphic substitution. Results are discussed on the basis of the magnetization curve and of the temperature dependence of the AC magnetic susceptibility. The Verwey transition occurs in the temperature range of 100–115 K, observed by a sudden change in the temperature dependence of the magnetization.     

Response of Callovo-Oxfordian claystone during drying tests: unsaturated hydromechanical behavior

The French National Agency for Nuclear Waste Management is currently studying the Callovo-Oxfordian claystone as a potential repository for nuclear waste. This study focuses on the hydromechanical (HM) unsaturated response of the rock subjected to hydraulic loading. Static atmosphere drying tests highlighted the HM coupling and mechanical anisotropy of the samples. A coupled poroelastic model was proposed, involving highly nonlinear equations. Numerical simulations were performed using the finite element code Code_Aster. Through a sensitivity analysis, the most suitable parameters for estimation were found to be the Biot coefficient and 3 of the 4 independent parameters of the Van Genuchten?CMualem relations. The parameters were estimated according to an inverse procedure that minimizes a cost functional. The estimates could not outline any hysteretic behavior, but they appeared to be divided into two groups (depending on their fitted values). The convergence and stability of the inverse algorithm were studied, and the results showed that direct computations must be run prior to the inversion to ensure its convergence. No plasticity occurred in the samples (according to the model), whereas irreversible phenomena do take place in situ.     

Vanadium in magnetite gabbros and its behaviour during lateritic weathering,Windimurra Complex,Western Australia

Shephards Discordant Zone is a 500–600 m thick interlayered sequence of deformed, altered and metamorphosed magnetite metagabbro and about 50 layers or lenses of magnetitite (> 80–90% magnetite). The sequence shows progressive magmatic fractionation upwards: Ti and Ti/Fe increase, and V, V/Ti and Cr decrease upwards in magnetite and in whole‐rock compositions. The main magnetite‐rich sequence (about 400 m thick) is deeply weathered, with 40 m of saprolite showing vertical zonation of weathering minerals due to progressive weathering. Magnetitites (average 1% V₂O₃) are resistant to weathering and show little chemical change, but magnetite gabbros (average 0.27% V₂O₃) are extensively weathered and show progressive loss of Ca, Na, Mg and S. Plagioclase, magnetite (1.37% V₂O₃), chlorite (up to 0.35% V₂O₃), actinolite, epidote and minor sulfides in unweathered rocks weather to kaolinite, hematite, goethite and minor vermiculite, ilmenite remaining largely unaffected. Vanadium is essentially immobile during weathering and is unaffected during weathering of magnetitites (1% V₂O₃), but is slightly depleted during weathering of magnetite gabbros (0.23% V₂O₃).     

微晶石墨氧化-膨胀过程中微形貌与结构变化

为深度揭示微晶石墨氧化和膨胀过程中结构的变化规律,分别采用SEM-EDS、XRD、Raman和FTIR等测试分析手段对其产物结构进行表征研究.结果表明:微晶石墨经氧化后,层间域被撑大,结构层上接入大量的羟基、羧基和环氧基等亲水性含氧官能团.随氧化剂（KMnO₄）用量增加,产物层间距、结构缺陷和无序度逐渐增大.高温膨胀后,氧化微晶石墨被还原,结构中的部分吸附水和含氧官能团被除去,结构缺陷与无序度减小,部分sp2区域得到了恢复.膨胀微晶石墨颗粒含有丰富的网络型孔隙结构,孔径集中在2~5 nm.      

Crystallization and Oxidation of Kilauea Basalt Glass: Processes during Reheating Experiments

Crystallization and oxidation are usually considered as a consequenceof cooling and emplacement of a magma, whereas little is knownabout crystallization upon reheating. However, the common eruptionof basalt on the Earth and other rocky planetary bodies resultsin reheating at the interface. To explore the range of possibleprocesses of crystallization and oxidation, reheating experimentswere carried out on basalt glass from Kilauea in air and inargon atmosphere. In air, interface-controlled crystallizationstarts with the formation of pyroxene dendrites and Fe–Tioxides at their apices below 840°C. Above 920°C, crystallizationof the bulk glass occurs and includes in addition growth ofplagioclase. In argon, the growth of only pyroxene is observedbetween 850 and 936°C. Crystallization is interface controlledbelow 890°C, and occurs within the bulk above 890°C.On the basis of T-dependent studies of the formation of Fe³⁺(detected by Mössbauer spectroscopy),     

Nature and extent of carbonate precipitation during aquifer thermal energy storage

Heating of calcite-saturated groundwater induces no precipitation to thermodynamic equilibrium with respect to end-member Ca-carbonates. Column experiments, using native groundwater and aquifer sediment, were performed to study the controlling factors in the kinetics of carbonate precipitation for a natural system by injection of groundwater in a sediment core at 90°C. The temperature increase induced a fast precipitation of a CaFe-carbonate, containing Mn and phosphate, and a CaMgFe-carbonate, containing Mn, within at most 10 h. Both precipitates varied in composition and were partly amorphic, partly crystalline. Prolonged precipitation, after almost all Fe[II] had been removed, was extremely slow despite a twelve-fold supersaturation with respect to end-member calcite. The resulting supersaturation cannot be explained by either calcite precipitation kinetics, Mg-inhibition, Mg-calcite solubility control, or Ca-organic acid complexing, because these factors may explain a two-fold supersaturation at most. The maintenance of supersaturation is attributed to inhibition of precipitation by phosphate and/or organic acids. The influence of secondary reactions, as cation-exchange and silicate weathering, is of minor importance on the carbonate chemistry. Cation-exchange was observed in the initial stages of heated water injection. Potassium, NH₄ and Fe become desorbed upon temperature increase. Related Ca-adsorption is insufficient to avoid Ca-carbonate precipitation. Weathering of silicates occurs continuously and leads to the release of Na, Ca and Mg.     

Crystal structure of magnetite under pressure

The crystal structure and the unit-cell parameters of magnetite have been studied at room temperature up to a pressure of 4.5 GPa using a diamond anvil cell and a four-circle X-ray diffractometer. The isothermal bulk modulus (K _T ) and its pressure derivative (K' _T ) determined by fitting the pressure-volume data to the Murnaghan equation of state are 181(2) GPa and 5.5(15), respectively. The positional parameter u does not vary significantly over the pressure range of this study. The linear compressibilities of the interatomic distances and the bulk moduli of the polyhedra have been calculated from the pressure dependences of the unit-cell edge a and the u parameter. The Bloch equation has been modified to derive a relationship between the Néel temperature and the parameter u. The modified Bloch equation gives a closer agreement with the experimental results than the Weisz equation.     

膨胀土干湿循环胀缩裂隙演化的CT试验研究

对南阳重塑膨胀土在干湿循环过程中裂隙的演化进行了CT试验研究，试样的CT图像显示了原有裂隙开展，新裂隙产生，裂缝数量增加并连通，最后形成裂隙网络的过程。定义了基于CT数据的裂隙损伤变量，分析了裂隙损伤变量随累计干缩体变的变化规律。