High Pyrite Content Research Articles

A multi-step kinetics study on Chang-7 shale pyrolysis: Impact of shale inherent minerals

Pyrolysis is a significant process for the in-situ conversion and aboveground retorting of oil shale. However, the impact of inherent minerals on shale pyrolysis is still unclear. This study analyzed the effect of different inherent minerals on pyrolysis of Chang-7 oil shale, which is noted for its low carbonate, high silicate, and high pyrite content, through an integrated evaluation of kinetic and thermodynamic parameters. The pyrolysis process, arranged from 350℃ to 600℃, was deconvoluted into three distinct processes—bitumen, kerogen, and pyrite pyrolysis—using the bi-Gaussian method. Thermodynamic results showed that pyrolysis was endothermic and non-spontaneous. Minerals significantly reduced the pyrolysis activation energy. The ratio of pyrolysis activation energies for shale to kerogen increased with the carbonate-to-silicate content ratio. Master plot analysis indicated that, mineral removal shifted the reaction model from the contraction geometry model (Rn) to the diffusion model (Dn). This transition in reaction model was due to the formation of pores from demineralization and organic decomposition, facilitating the diffusion of heat and activated molecules into the interior of particles, which has been confirmed by porosity determination. This work provides an in-depth understanding of the impact of inherent minerals on shale pyrolysis, which is conducive to the efficient development and utilization of oil shale resources.

Pore Characteristics of Hydrate-Bearing Sediments from Krishna-Godavari Basin, Offshore India

Pore-filling hydrates are the main occurrence forms of marine gas hydrates. Pore characteristics are a vital factor affecting the thermodynamic properties of hydrates and their distribution in sediments. Currently, the characterization of the pore system for hydrate-bearing reservoirs are little reported. Therefore, this paper focuses on the Krishna-Godavari Basin, via various methods to characterize the hydrate-bearing sediments in the region. The results showed that X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) and cast thin section (CTS) can better characterize the mineral composition in the reservoir, high-pressure mercury injection (HPMI) focused on the contribution of pore size to permeability, constant-rate mercury injection (CRMI) had the advantage of distinguishing between the pore space and pore throat, and nuclear magnetic resonance cryoporometry (NMRC) technique can not only obtain the pore size distribution of nanopores with a characterization range greater than nitrogen gas adsorption (N2GA), but also quantitatively describe the trend of fluids in the pore system with temperature. In terms of the pore system, the KG Basin hydrate reservoir develops nanopores, with a relatively dispersed mineral distribution and high content of pyrite. Rich pyrite debris and foraminifera-rich paleontological shells are observed, which leads to the development of intergranular pores and provides more nanopores. The pore throat concentration and connectivity of the reservoir are high, and the permeability of sediments in the same layer varies greatly. The reason for this phenomenon is the significant difference in average pore radius and pore size contribution to pore permeability. This article provides a reference and guidance for exploring the thermodynamic stability of hydrates in sediments and the exploration and development of hydrates by characterizing the pores of hydrate reservoirs.

Influence of carbonate-inducing bacteria on desulfurization effect of medium and high sulfur coal gangue under spraying and preparation of desulfurized coal gangue mortar

Medium and high sulfur coal gangue (MHSCG) presents challenges for safe application on civil engineering building materials due to the high content of unstable pyrite, of which the acidic oxidation products are against alkali cementitious materials. For better utilization of MHSCG, in this research, the carbonate-inducing bacterium Sporosarcina Pasteurii with its nutrient (urea) and mineralization source (calcium) was firstly explored in MHSCG desulfurization leaching tests, revealing the mechanism of desulfurization. On this basis, the desulfurizing modification on MHSCG sand by the bacteria under different factors of OD600, urea and calcium was conducted. Moreover, the gangue sand was used to prepare the desulfurized coal gangue mortar (DCGM) and the relevant mechanical properties and influence mechanisms were discussed. The results of total sulfur and XRD analysis show that Sporosarcina Pasteurii can accelerate the desulfurization in the 7-days-spraying modification. When the optimum dosages of OD600 (0.84) and urea solution concentration (1.41 mol/L) are adopted, the total sulfur can be reduced by 33.66∼36.32 %. The total sulfur has been further reduced by 7.69 % compared with group without calcium as calcium concentration is 1.56 mol/L. The introduction of calcium can enhance the mechanical properties of MHSCG and DCGM although the desulfurization treatment has a negative impact on them. The crushing index of MHSCG sand at most decreases 10.44 % from it without calcium. When OD600 is about 0.90, urea concentration is about 1.50 mol/L and calcium concentration is about 1.49 mol/L, the 28-d compressive strength of DCGM increases to 32.01 MPa, 76.85 % higher than group without calcium, and 23.54 % higher than raw-material preparing mortar.

Pyrolytic hydrocarbon generation characteristics of the Chang 7 shale based on different experimental methods: Implications for shale oil and gas in the Ordos Basin

Shale oil and gas resources are abundant in the Chang 7 shale of the Yanchang Formation in Ordos Basin. To determine the characteristics and influencing factors of hydrocarbon generation evolution of the Chang 7 shale, a series of thermal simulation experiments were conducted on low‐maturity shale and kerogen samples. The results indicate that the maximum yield of shale oil are 294.5 and 304.3 mg/g TOC for kerogen sample at heating rates of 20 and 2°C/h, and the corresponding experimental temperatures are 360.2°C and 408.0°C, respectively. The utilization of lower heating rates is favourable for shale oil generation and it is recommended to employ a lower heating rate during in situ heating processes to maximize the economic benefits. The formation of crude oil cracking gas begins when simulating temperature exceeds 528.0°C (Easy Ro 2.6%) at a heating rate of 20°C/h and 480.0°C (Easy Ro 2.5%) at a heating rate of 2°C/h, as indicated by the carbon isotopic composition of gaseous hydrocarbons. The maximum oil production rate of the rock powder sample is 159.8 mg/g TOC, which is lower than that of the kerogen sample. It suggests that certain minerals in the Chang 7 shale may impede hydrocarbon generation. After the addition of pyrite, the highest yield of shale oil is 213.96 mg/g TOC, 33.9% higher than the yield of the original rock powder sample, reflecting the positive catalytic effect of pyrite on hydrocarbon generation of Chang 7 shale. Under geologic conditions, pyrite catalytic hydrocarbon generation may act primarily on the migration of organic matter by macromolecules, which considerably increases the probability of direct contact between pyrite and organic matter. Therefore, the organic‐rich shale with high pyrite content in Chang 7 member is the preferred target for in situ conversion of shale oil and gas in the Ordos Basin.

Modified approach to calculate brittleness index in shale reservoirs

The successful production of unconventional reservoirs through hydraulic fracturing is heavily dependent on the brittleness of the shale's. To precisely evaluate rock brittleness the mineral-based brittleness indices are considered reliable. Initially, only the weight fraction of quartz accounted for mineralogical brittleness, later dolomite was included in the group, further, it was divided into the silicate and carbonate groups. Due to its heterogeneous nature, shales contain some other minerals, however, the impact of these minerals on rock brittleness has yet to be analyzed. The mineral pyrite is commonly found in shales but its impact on rock brittleness is still undefined. In this research, we proposed a modified mineral-based brittleness index including mineral pyrite, and investigated its impact on rock brittleness. The modified index was evaluated using the data from three different shale reservoirs in China. In the next step, the Fracability Index (FI) model of rocks including pyrite mineral is calculated, and finally, the rock physics modeling is performed to evaluate the elastic response of the rock to this mineral. The modified brittleness index was found to be more accurate in predicting rock brittleness than other mineral-based brittleness indices. The correlation between the modified brittleness index and the FI model was higher than the correlation with other mineral-based brittleness indices. Further, rock physics modeling also proved that the rock with high pyrite content has low Poisson's ratio and high Young's modulus.. These properties are associated with brittle rocks, which further supports the inclusion of pyrite as a brittle mineral in the modified brittleness index. Hence, the findings of this research indicate that the modified brittleness index based on minerals is a reliable approach for predicting rock brittleness in shale reservoirs that contain pyrite. This study has an important application for the development and management of shale reservoirs. The modified brittleness index can be used to identify rocks that are more likely to be successfully fractured during hydraulic fracking process. Keywords: shale reservoirs; hydraulic fracturing; mineral brittleness; fracability index.

Mineralogy and elemental geochemistry of pyrite coal-balls, Datong Coalfield, Shanxi Province, China: Implications for differentiation mechanism

The pyrite coal-balls found in No.9 coal of Taiyuan Formation in Dongzhouyao Mine of Datong Coalfield were selected to investigate its mineralogy and elemental geochemistry using optical microscope observation, scanning electron microscopy combined with an energy-dispersive X-ray spectrometer (SEM-EDX), inductively coupled plasma mass spectrometry analysis (ICP-MS), laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS), and electron probe micro-analysis (EPMA). Due to the high content of pyrite, the major-element oxides in the coal-ball samples were mainly Fe2O3, with an average of 62.68 %. LA-ICP-MS results showed that coal-balls were enriched in Tl (CC = 32.79), Pb (CC = 9.22), and Mo (CC = 2.07), while the coals in the same layer were enriched in Ga (CC = 5.31), Tl (CC = 3.66), and Li (CC = 2.27). Affinities to S or Fe and the variation of elemental concentration in the environment during the formation of coal-balls were the primary factor of the elemental differentiation between coals and coal-balls, as well as within coal-balls. The coal-balls formed in four stages in a marine-continental transition environment, with Fe from terrestrial sources and S from marine phases, and its physical origin is basically consistent with that of some Carboniferous-Permian coals in the Datong Coalfield. According to the formation sequence and geochemical characteristics, four periods of pyrite coal-balls evolution have been proposed.

Static tests to assess acid mine drainage potential of copper sulfide flotation tailings

Most copper flotation tailings contain a significant amount of sulfide minerals that can generate effluent resulting from the oxidation of sulfides when they are exposed to oxygen and water. This study aimed to characterize and evaluate the acid drainage potential of five different copper flotation tailings, named samples I, II, III, IV, and V. Sample I was taken from an industrial operation, while Samples II, III, IV, and V were produced in pilot plant tests. All samples were characterized and submitted to static acid drainage tests, such as paste pH, Net Acid Generation (NAG) pH, and Modified Acid-Base Accounting (MABA). The sulfur as sulfide/total sulfur mass ratios varies from 0.40 up to 0.89 showing the presence of a high amount of minerals rich in pyrite and alunite, being higher than 13 wt% of pyrite in samples IV and V and around 19 wt% of alunite in sample III. Samples I and II presented a high number of alkaline elements, totalizing more than 8 wt% of K2 O+CaO+MgO, while samples III, IV, and V show the lowest amount of these elements (<4 wt%). Only samples III, IV, and V show Paste pH results lower than 5.0, indicating superficial oxidation on their surfaces and/or the presence of water-soluble acidity minerals. Due to the high pyrite content in samples III and IV, it was not possible to measure their NAG pH due to the high heat released with the addition of hydrogen peroxide. The low NAG pH obtained with sample III (5.30) was due to its high pyrite content (0.30 wt%) in comparison with the results obtained with sample I (NAG pH of 8.15 and 0.10 wt% of pyrite), and sample II (NAG pH of 8.18 and 0.10 wt% of pyrite). The MABA results show that samples III, IV and V presented acid drainage potential due to the neutralization potential (NP)/acidity potential (AP) ratio being lower than 1. On the other hand, samples I and II presented NP/AP ratio higher than 4, not showing potential to generate acid drainage. Due to these results, it is recommended to carry out acid drainage kinetic tests with samples III, IV, and V to determine the long-term weathering rates, evaluate lag time to acid generation and provide reaction rates for geochemical modeling.

Response Surface Methodology for Copper Flotation Optimization in Saline Systems

Response surface methodology (RSM) is one of the most effective tools for optimizing processes, and it has been used in conjunction with the Analysis of Variance (ANOVA) test to establish the effect of input factors on output factors. However, when this methodology is used in mineral flotation, its polynomial model usually performs poorly. An alternative is to use artificial neural networks (ANNs) in such situations. Within this context, the ANOVA test is not the best option for these model types; moreover, it requires statistical assumptions that are difficult to satisfy in flotation. This work proposes replacing the polynomial model of the RSM with ANNs and the Sobol methods to determine the influential input factors instead of the ANOVA test. This proposal is applied to two porphyry copper ores with a high content of pyrite, clay, and dilution media. In addition, this study shows how other computational intelligence techniques, such as swarm intelligence, can be incorporated into this type of problem to improve the learning process of ANNs. The results gave an adjustment of over 0.98 for R2 using ANNs, in comparison to values of around 0.5 when the polynomial model of RSM was utilized. On the other hand, the application of Global Sensitivity Analysis (GSA) identified the aeration rate and P80 size as the most influential variables in copper recovery under the conditions studied. Additionally, we identified significant interactions that affect the recovery of copper, with the interactions between the aeration rate, frother concentration, and P80 size being the most important.

Constraints on the Genesis of the Shuangwang Gold Deposit in Qinling Orogen, Central China: Evidence from In Situ Trace Element and Sulfur Isotope

The Shuangwang gold deposit, with more than 70 tons of Au, is located in the Fengxian-Taibai ore concentration area in the Qinling Orogen of central China, hosted in a Northwest-trending breccia belt. Fragments of the breccia body are cemented by ankerite, albite, quartz, calcite, and pyrite. Four metallogenic stages are identified in mineral paragenesis: quartz-albite, ankerite-pyrite-albite, pyrite-quartz-calcite, and fluorite-anhydrite. Pyrite, as the main gold-bearing mineral, was formed in the syn-ore and post-ore stages, which are analyzed for trace elements. The experimental results show that Au (0.02 to 11.68 ppm), As (198.45 to 5502.86 ppm), Ag (0.00 to 1.56 ppm), Co (0.02 to 1002.75 ppm), Ni (0.15 to 646.30 ppm), Cu (0.00 to 64.76 ppm), Sb (0.00 to 4.67 ppm), Zn (0.23 to 260.59 ppm), Pb (0.00 to 10.42 ppm), Se (0.00 to 386.24 ppm), and Bi (0.00 to 47.72 ppm) are enriched in syn-ore pyrite much more than in post-ore pyrite, especially arsenic. The high arsenic content and rapid crystallization of pyrite may be the main reasons for precipitation of gold. δ34SV-CDT values of pyrite formed in stage II (PyII) vary from 11.1 to 15.2‰ (mean = 12.9‰), while those for pyrite formed in stage III (PyIII) vary from 11.1 to 13.5‰ (mean = 12.0‰). In situ sulfur isotope analysis indicates that sulfur of the Shuangwang deposit comes from the wallrock, mixed with sulfur from magma.

The thermal transformation behavior and products of pyrite during coal gangue combustion

Pyrite is a common and important mineral in coal and coal gangue, and its thermal transformation behavior and products during combustion have an essential impact on the environment, coal combustion technology, and recycling utilization of coal ash and coal gangue. Two samples of coal gangue containing high pyrite content were studied using XRD, TG-MS, SEM-EDS, and TEM to reveal pyrite's thermal transformation behavior and products during coal gangue combustion. The results showed that pyrite was transformed into hematite nanospheres during coal gangue combustion in air and released SO2 gas in the process. The transformation proceeds in the sequence of pyrite (0 ∼ 400 °C) – nano-microspheric magnetite and jarosite (400 ∼ 500 °C) – nano-microspheric hematite (500 ∼ 1000 °C). Nano-hematite possessed the morphology of a nanospheric pseudomorph of magnetite. Nano-magnetite and jarosite as intermediates were transitional and unstable and formed in a weakly reducing–weakly oxidizing environment. The formation and thermal decomposition of jarosite was associated with the release of structural water from kaolinite dehydroxylation. During the phase transition reaction, SO2 was released twice: the first release was related to the formation of magnetite and jarosite, while the second release was related to the thermal decomposition of jarosite. Temperature was the main factor affecting the nanocrystallization of hematite, whose crystallinity improved with an increase in temperature. This research portrays a new thermal phase transformation mechanism of pyrite in coal gangue, which can provide a theoretical basis for the recycling of coal gangue.

Weak acid leaching of uranium ore from a high carbonate uranium deposit

Mineralogical study showed that the Yuejin uranium ore is from a low grade, high carbonate and high pyrite sandstone type uranium deposit. Uranium leaching rate, uranium speciation of leachate, leaching kinetics and precipitation analysis were investigated under the conditions of different acidity, liquid–solid ratio and H2O2 concentration. The test results showed that the weak acid leaching process can be used to develop high carbonate type uranium deposits, however, because of the high content of pyrite, other oxidants except high concentration H2O2 need to be considered.

Experimental investigation on the effects of different fracturing fluids on shale surface morphology

With the widely use of hydraulic fracturing technique, large volumes of fracturing fluids are injected into shale reservoirs. The physical and chemical reactions between fracturing fluids and shale will change the surface roughness of shale fractures, which further impacts the production efficiency of hydrocarbons. To quantify the impacts of fracturing fluids on shale fracture roughness, a series of imbibition tests were conducted on shale samples soaked in different fracturing fluids (acid (pH = 6), neutral (pH = 7) and alkaline (pH = 8)) with different time (short-term (0–3 months) and long-term (3–12 months)). The surface morphology, microstructure, mineral composition, and element changes of shale samples before and after imbibition were determined. The results showed that: (1) pyrite and kaolinite were the main minerals that dissolved in the short-term of imbibition. The dissolution of pyrite caused the rapid decreasing of pH values for all fracturing fluids (decreased by 43%–51%). In the long-term of imbibition, clay minerals (illite-montmorillonite) and feldspar were the major dissolved minerals, resulting in the rise of pH values (increased by 10%–19%). (2) the dissolution, hydrolysis, and hydration process during imbibition resulted in the increase of fractal dimension (increased by 9%–30%). Alkaline fracturing fluid had higher effect on the roughness of shale than that of acid and neutral fracturing fluids. (3) the joint homogeneity on the shale fracture surface which obtained from the joint rose diagram revealed that acidic and neutral fracturing fluids enhanced the joint homogeneity (increased by 64% and 74.6%), whereas alkaline fracturing fluid weakened the joint homogeneity, which decreased by 43.8%. In this study, the impact of fluid-rock interaction on shale fracture surface roughness is explored for the first time, a variety of methods are used to evaluate, and the differences of different methods are compared. The results show that different pH fracturing fluids have significant changes in the surface roughness of shale fractures. For shale formation with high pyrite content, alkaline fracturing fluid has stronger reconstruction ability. Above conclusions may have significant impact on the efficiency of hydraulic fracturing.

The accumulation model of organic matters for the Niutitang Formation shale and its control on the pore structure: a case study from Northern Guizhou

Shale gas reservoir is a fine-grained sedimentary rock with component of clastic particles and organic matters, and the accumulation of the organic matters would determine the effective development of shale gas. The paleoclimate, detrital influx, redox of the water and paleoproductivity are effective geochemical indicators that could help to find the favorable shale gas reservoir stratum. In this study, the shale samples collected from Niutitang Formation (Northern Guizhou, China) were launched the measurements of the content of major elements and trace elements, and the characteristics of geochemical indicators were analyzed, which can be used to discuss the accumulation model of organic matters. Besides, the pore structure of shale sample controlled by the enrichment of organic matters is also discussed. The paleoclimate is dominant cold and dry, and it changes to warm and humid at the later Niutitang period, and the detrital influx also increased at the later Niutitang period; the water environment of Niutitang Formation shale presents as reductive, and the paleoproductivity of the Niutitang Formation shale is commonly high. The enrichment of organic matters in the Niutitang Formation is dominantly controlled by the redox of the water, while the hydrothermal activity and the paleoproductivity lead to the difference enrichment of organic matters in the Niutitang Formation shale. The accumulation model of organic matters also influences the characteristics of pore structure from the Niutitang Formation shale, and the pore structure could be divided into two types. The shale with high content of organic matters also features high content of quartz and pyrite, and these minerals contribute to the preservation of pore space in the shale, while that of the clay minerals is contrary. The high content of organic matters and preferable pore characteristics indicate the Niutitang Formation favors the development of shale gas, especially that for the lower Niutitang Formation.

Genesis of a Ag-Pb-Zn-F system: Insights from in situ sulfur isotope and trace elements of pyrite, and rare earth elements of fluorite in the Baiyine'lebu deposit, Inner Mongolia, China

The recently discovered Baiyine’lebu Ag-Pb-Zn-F deposit in the southern Great Xing’an Range is hosted by NNE-trending transgressional fractures within Late Permian granodiorite. The fluorite ore veins in the periphery of the mining area show close spatial association with the Ag-Pb-Zn ore bodies. A total of four mineralization stages are recognized based on the cross-cutting relationships and mineral assemblages, among which three types of pyrite are identified, including: i) coarse-grained pyrite (Py1) from stage I quartz-pyrite vein, ii) fine-grained cubic pyrite (Py2) from stage II quartz sulfide-rich vein, showing association with metallic sulfide minerals, and iii) anhedral, irregular pyrite (Py3) disseminated in Ag-bearing sulfide ore vein from stage III. The stage IV is quartz-fluorite-calcite vein with very rare distribution of pyrite. Here we investigate the texture, trace element and sulfur isotopic composition of pyrite and rare earth elements (REEs) of fluorite to gain insights into the genesis and mineralization process of the Baiyine’lebu Ag-Pb-Zn-F deposit. Systematic trace element analyses indicate that the compatible and some other elements (Co, Ni, Cr and As) were incorporated in the pyrite structure via isomorphism in all pyrite types, whereas ore metals such as Cu, Pb, Zn, and Sn entered pyrite as structurally bound elements or micro/nanosized mineral inclusions. The Ag concentrations significantly increase from Py1 to Py3 in the form of invisible nanoparticles of sulfides or micro- to nano-sized mineral inclusions during the decrease of temperature. The narrow range of sulfur isotopic compositions from −0.80 to 3.88 ‰ (average in 1.17‰) indicates a relatively homogeneous sulfur source. In combination with REE patterns of fluorite, we propose that the ore-forming fluids originated mainly from post-magmatic hydrothermal fluid mixed with meteoric water in stage IV. The hydrothermal fluorite veins in the periphery of the Baiyine’lebu deposit could be genetically linked to the Ag-Pb-Zn veins. The purple fluorites with enriched REEs and positive Eu anomaly can be used as a proxy for prospecting Ag-Pb-Zn deposits. In addition, the high Sn content of pyrite in hydrothermal Ag-Pb-Zn deposit indicates the potential of Sn mineralization in the surrounding area or deeper level of the ore field in the South Great Xing’an Range.

An Alternative Method for the Obtention of Ceramic Foams from Gold and Silver Tailings with High Pyrite Content

Mining extraction operations generate a large number of tailings that contain different mineral phases such as quartz (principally), complex silicates, metallic elements, etc. Tailings impose a serious concern as it is possible to have acid mine drainage potential, leaching, and percolation events of heavy metals into the environment under certain conditions. The objective of this work was to evaluate the technical feasibility of producing ceramic foams from gold and silver tailings with high sulfide gangue through a previous flotation process to eliminate impurities associated to this gangue, as it can produce SO2 in the foaming process, and to analyze the effect of the sintering time and the temperature on the characteristics of foams obtained with this type of waste. The results showed that the inverse flotation reduced the presence of impurities associated to sulfides. In addition, it was possible to observe that in the absence of a foaming agent, it was possible to obtain ceramic foams with an apparent density and a mechanical strength near to 1.0 g/cm3 and 0.5 MPa, respectively, when a higher sintering temperature and time were used. On the other hand, the presence of the foaming agent reduced the apparent density to 0.5 g/cm3 without decreasing to a great extent the mechanical strength of ceramic foams at lower sintering temperatures.

Analyzing the Origin of Low Resistivity in Gas-Bearing Tight Sandstone Reservoir

Complex characteristics exist in the resistivity response of Gs reservoirs in the central inversion belt of the Xihu Sag, East China Sea Basin. Some drilling wells have confirmed the existence of abnormally low resistivity in gas reservoirs of the area; and the electrical logging response was unable to reflect fluid properties of the reservoir accurately. Therefore, it is necessary to analyze the origin of the low resistivity and determine its controlling factors. Based on experimental data of core analysis and numerical simulations of mud invasion, this study thoroughly explores the origin of low resistivity in the subject gas-bearing reservoir considering both internal and external factors. The results indicated that when there is no or a low degree of mud invasion, the fine lithology, complex pore structure, additional clay mineral conductivity, and high content of pyrite are the main internal factors driving the conditions present in the studied gas reservoir. When mud invasion occurs, the invasion of highly saline mud is the main external cause of low resistivity. The numerical simulation results indicated that a formation with good permeability and high overbalance pressure has a deep invasion depth. The resistivity around the well is obviously reduced after the invasion, and low resistivity would form easily. Combined with actual data of several wells, the main influencing factors of the reservoir’s electrical characteristics were analyzed, and the main controlling factors of low resistivity in the gas reservoirs are given. This study provides valuable support for studying the low-contrast complex reservoir conductivity mechanism. The study also offers novel ideas for accurate calculation of saturation and the meticulous evaluation of reservoir for subsequent studies.

Study of the Electrooxidation of a Zinc Concentrate.

Zinc has wide industrial applications; consequently, its extraction procedures have been extensively studied. Hydrometallurgy is one of the most common methods employed for zinc recovery. However, the electrooxidation of sphalerite and the effect of the pyrite content in the concentrate have not been investigated; thus, in this work, zinc recovery from low-iron sphalerite mineral with a relatively high pyrite content (EBHSS), in a sulfate medium was further explored. The reaction mechanism of the anodic dissolution of the EBHSS mineral was established by microelectrolysis using mineral carbon paste electrodes; these results were used to determine adequate conditions for the macroelectrolysis of the sample. The macroelectrolysis indicated that EBHSS has a low electrodissolution rate; additionally, different analyses of the species produced in the macroelectrolysis showed that the ohmic drop registered in the collector had no influence in the passivation of the EBHSS surface. It was also determined that the dissolution of EBHSS was driven by the charge transfer of the sphalerite particles, which are not very efficient for electronic conductivity. Experiments using doped EBHSS led to an increase of the electrodissolution rate, which consequently increased the recovered zinc.

ЛЕЖАЛЫЕ ХВОСТЫ ФЛОТАЦИИ МЕДНО-КОЛЧЕДАННЫХ РУД ИЗВЛЕЧЕНИЯ ЗОЛОТА И СЕРЕБРА: АНАЛИЗ РЕСУРСНОГО ПОТЕНЦИАЛА

The article analyzes the possibility and efficiency of processing stale tailings of flotation plants of the copper pyrite complex. The resource potential, material composition and technological capabilities of processing a number of technogenic objects are considered. The interrelation and influence of mineralogical and technological factors on the choice of tailings processing technology are analyzed. The results of chemical, mineral and phase analysis of stale flotation tailings of the studied pyrite ores are presented. According to the complex studies’ results, it is established that the stale flotation tailings of copper pyrite ores belong to a refractory type of geo-resources due to the high content of pyrite and low, at the level of ppm, gold and silver content, which are present mainly in the “resistant” minerals - chalcogenides, sulphides, their intergrowths. The article presents a factor analysis and conditions for the elemental composition of tailings formation: mineralogical, technological and environmental. The territorial accessibility and technological capability of the investigated technogenic formations are analyzed. In the course of experimental studies, the elemental composition of stale tailings has been revealed - the main components of which are: iron, sulfur, silicon and aluminum. According to the results of X-ray phase analysis, it has been found that the main ore mineral of the tailings is pyrite. At the same time, it is noted that the main share of gold in the stale flotation tailings is presented in the form of sulphides in the form of finely dispersed and isomorphic inclusions. The heterogeneous morphometric and mineral composition of sulphide aggregates, their difficult opening and high dispersion characterize stale tailings as a raw material that is difficult to float. The revealed features of the material composition of stale tails indicate the impossibility of extracting valuable components (gold and silver) from this resource using existing traditional technologies. It has been proved that it is possible to effectively extract precious metals from this category of raw materials only after their deep opening by chemical processing. The relevance of the research lies in the need to process gold-containing man-made waste in order to significantly expand the raw material base of mining enterprises, as well as to improve the ecological situation of the city-forming mining enterprises of the South Urals. The aim of the research is to study the material composition of stale tailings and develop a technology for selective extraction of gold and silver. The object of research is the stale flotation tailings of copper-pyrite enterprises of the Southern Urals. The subject is the mineral composition, the content of useful components of lying tailings and the technology of gold and silver selective extraction from them. Material and research methods. During the experiments, a set of physicochemical and chemical methods of analysis has been used: thermodynamic analysis, synchronous thermal analysis using a combined thermal analyzer of the Netzsch STA 449 F3 Jupiter brand, UV spectroscopy with an automated data processing system), qualitative chemical and assay analyzes

Long-term leaching characteristic study of coal processing waste streams

A study of the mobility of major and potentially hazardous trace elements from coal processing waste materials was conducted using two types of leaching tests. The baseline leaching test simulates stable waste storage under water, whereas the kinetic test models the storage of waste under more variable conditions including intermittent exposure to air and variations in humidity. Coarse and fine refuse materials were obtained from three commercial coal preparation plants that were being used to upgrade US bituminous run-of-mine coal containing low-to-high amounts of pyritic sulfur. X-ray diffraction analyses revealed a large variation in mineralogy between the coarse and fine refuse streams due to the mineral fractionation that occurs in the processing units and plant. The coarse refuse samples contained higher pyrite contents while the fine refuse samples had high clay content and a minor amount of calcite. This variation in mineralogy resulted in relatively large difference in the leaching characteristics of the waste streams. The most acidic pH and highest release of trace elements were observed in the leachate of coarse refuse containing medium-to-high amounts of coal pyrite, while the fine refuse samples released lower amounts of trace elements in their circumneutral leachate. The least amount of trace elements was observed in the leachate of low pyritic refuse streams. The test data suggested that the most effective disposal practice for coal waste material is segregation and isolation of the coal pyrite and co-disposal of the coarse and fine refuse streams.

Semiconductor-Microbial Mechanism of Selective Dissolution of Chalcocite in Bioleaching.

Chalcocite-dominant secondary copper ore with a high pyrite content had a rapidly increased iron concentration in the middle and later periods of bioleaching, which increased the difficulty of separating copper and iron ions in the leaching solution. In the two aspects of microbial community succession and energy band theory, the selective dissolution mechanism of chalcocite in this type of copper ore was analyzed and illustrated using experiments and first-principles calculations. The results showed that controlling the solution potential at a lower level was beneficial to the selective leaching of chalcocite, while bacteria promoted the leaching of pyrite and chalcocite simultaneously by oxidizing Fe2+ to Fe3+ in the solution. Below 700 mV of solution potential, the bacterial community, mainly consisting of Acidithiobacillus and Sulfobacillus, had a stronger promotion on the selective dissolution of chalcocite. The solution energy level of bioleaching was higher than ideal pyrite but lower than ideal chalcocite, which resulted in the accumulation of electrons on the surface of pyrite and the formation of holes at the top of the chalcocite valence band. When bacteria assisted the oxidation of Fe2+ to Fe3+ and caused the raise of the solution potential, the difference between the solution energy level and the top of the pyrite valence band would be smaller than the width of the pyrite energy gap. Below 700 mV, the assistance of Acidithiobacillus and Sulfobacillus on the oxidation of Fe2+ was weak. Chalcocite would be selectively dissolved by oxygen and a small amount of Fe3+ in the solution. Because of the existence of Fe, Cu, and S vacancies in real minerals, the atomic activity in the Cu–S bond and the Fe–S bond enhanced, and the reaction difficulty between chalcocite, pyrite, and electron acceptors in the solution reduced. The solution potential should be controlled at 600 mV or less to ensure the selective dissolution of chalcocite.