Search Results (49)

The Carboniferous coal seams in Northeast Kazakhstan remain insufficiently investigated, with a lack of comprehensive mineralogical and geochemical assessments necessary to understand the geological processes controlling coal quality. This study examines 15 coal samples from the Karagandy Coal Formation (KCF) at the Saradyr and Bogatyr mines using proximate and ultimate analyses, FTIR, XRD, SEM–EDS, ED-XRF, and ICP-OES, providing the first detailed comparison of mineralogical and geochemical characteristics—including depositional signals and inorganic constituent distribution—between these mines within the KCF. The coals exhibit an average ash yield of 24.1% on a dry basis, volatile matter of 21.6% on a dry and ash-free basis, and low moisture content of 1.1% (air-dry), with low sulfur levels of 0.7% in whole coal across both mines. Mineralogical composition is dominated by quartz and clay minerals, with minor pyrite, apatite, chalcopyrite, and rutile. Major oxides in the coal ash average 68.2% SiO₂ and 19.5% Al₂O₃, followed by Fe₂O₃, K₂O, and TiO₂ (3–12.1%). Among the 24 identified trace elements, Sm is the most abundant at 6.3 ppm with slight enrichment (CC = 2.8), Lu remains at normal levels (CC < 1), and most other elements are depleted (CC < 0.5). The Al₂O₃/TiO₂ ratios (3.8–10.8) indicate contributions from intermediate to mafic parent materials. The detrital mineralogy, parting compositions, and elevated ash content indicate significant accommodation space development during or shortly after peat accumulation, likely within a vegetated alluvial plain depression. These findings provide new insights into the depositional environment and coal-forming processes of the KCF and contribute to regional assessments of coal quality and resource potential. Full article

L. ferrooxidans and their metabolic products have been explored as viable flotation reagents of pyrite and chalcopyrite for froth flotation. Scanning electron microscopy (SEM), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS) and captive bubble contact angle measurements have been used to examine the surface physicochemical properties of pyrite upon exposure to L. ferrooxidans grown in HH medium at pH 1.8. C K-edge NEXAFS spectra, collected using scanning transmission X-ray microscopy (STXM), indicate hydrophilic lipids, fatty acids, and biopolymers are formed at the mineral–bacterium interface within hours of exposure. The Fe L-edge NEXAFS show oxidation of the mineral surface from Fe (II) sulfide to Fe (III) oxyhydroxides. The leaching of the iron species at the pyrite surface is accelerated in the presence of L. ferrooxidans and extracellular polymeric substances (EPS) as compared to HH medium controls, as shown by ToF-SIMS. The surface chemical changes induced by the interaction with L. ferrooxidans show a significant decrease in surface hydrophobicity within the first 2 h of exposure. The implications of these findings are the potential use of EPS, produced during early attachment of L. ferrooxidans, as a depressant for bioflotation or to enhance bioleaching. Full article

The evolution of the sedimentary environment in the Early Carboniferous Dawuba Formation of the Qiannan Depression significantly controlled the distribution of low-total organic carbon (TOC) sediments. In this study, the core samples were analyzed by thin section microscopy, field emission-scanning electron microscopy, pyrite morphology, X-ray diffraction, and geochemical analysis (TOC, sulfur, organic petrography, and major and trace elements). The formation is vertically divided into two members from bottom to top: Member 1 (average TOC = 1.15%) and Member 2 (average TOC = 0.88%). Depositional environment parameters indicate that Member 1 was in a suboxic-oxic transition environment, with weak detrital influx, and moderate paleoproductivity (more developed algae). Member 2 evolved into a stable oxic environment, with significantly enhanced detrital influx and reduced paleoproductivity. The correlations between multiple geochemical proxies (paleoredox, paleoproductivity, and terrestrial detrital influx) and TOC content indicate that high productivity in Member 1 was the main driver of organic matter accumulation, but the suboxic-oxic environment limited preservation efficiency (1.00% < TOC < 2.00%). Member 2, deposited during sea-level fall, experienced long-term oxic conditions and low productivity due to shallower water. Nevertheless, the partial reduction in the exposure time of organic matter within the oxic water column-driven by rapid detrital accumulation-represents a critical mechanism favoring organic-poor sediments (TOC < 1.00%). In conclusion, the development of low-TOC sediments in the Dawuba Formation reflects a transition from a relatively deep to shallow water column, where the synergistic effects of redox conditions, paleoproductivity, and terrigenous detrital influx controlled the distribution and enrichment of organic matter. Full article

This study evaluates four physicochemical pretreatments—ultra-fine grinding, roasting, alkaline pressure oxidation (POX), and oxidative ammoniacal pre-leaching—for improving gold extraction from a refractory sulfide concentrate produced trough flotation. The gold extraction by direct cyanidation is only ~48.6%, mainly due to the encapsulation of gold by associated minerals. Ultra-fine grinding increased the BET surface area eight-fold but depressed gold dissolution from 74% to 18% due to accelerated thiosulfate decomposition and copper (I) passivation in the presence of a bigger surface area. Oxidative roasting at 750 °C converted pyrite–pyrrhotite to hematite without liberating additional gold, indicating limited benefit from thermal treatment. POX was conducted at 190 °C and 10 bar O₂ dissolved 33% of the solids and yielded only 26% of gold in a thiosulfate leaching step with 50% of the thiosulfate consumption. In contrast, a two-step oxidative ammoniacal conditioning (0.4 M NH₃ + 10 mM Cu²⁺ for 42 h) followed by thiosulfate leaching boosted gold extraction from 71% to 85% while cutting thiosulfate consumption from 48.4 to 29.0 kg t⁻¹. The results demonstrate that among the pretreatments investigated, oxidative ammoniacal pre-leaching provides the most effective and environmentally benign route to unlock encapsulated gold and enhance reagent efficiency for thiosulfate processing of refractory gold ore. Full article

Copper sulfide ores often contain significant amounts of silica and sulfur-bearing gangue minerals, complicating flotation efficiency. However, these challenges can be mitigated through collectorless flotation, which exploits the natural floatability of chalcopyrite and the hydrophilicity of silica minerals. Pyrite, the main sulfur gangue mineral, is also depressed under these conditions, improving concentrate quality by reducing the sulfur and iron content. Air exposure and pulp pre-aeration techniques can enhance chalcopyrite floatability, resulting in high recovery and grade. However, further processing of chalcopyrite concentrate using direct leaching remains challenging due to sulfur passivating layers. To overcome this, additive roasting is used as a pretreatment to improve the leachability of chalcopyrite. This study explored a combined collectorless flotation and additive roasting-leaching method using copper sulfide ore with chalcopyrite, quartz, and pyrite as the main minerals. Collectorless flotation achieved 94.5% recovery and a concentrate of 7.12% Cu from an initial 0.94%. Roasting this concentrate with additives like KCl and NaOH at 600 °C for 1 h, followed by leaching in 0.1 M H₂SO₄ at 25 °C with a hydrogen peroxide (H₂O₂) addition, resulted in copper dissolutions of 97% and 96.5%, respectively, with low iron dissolution. The proposed process achieved an overall copper recovery of 92%, demonstrating the effectiveness of combining collectorless flotation with additive roasting and atmospheric leaching. Full article

The aim of this study is to explore the feasibility of using flotation wastewater from copper–porphyry ore processing to synthesize a gel that serves as a precursor for a polymer nanocomposite used in supercapacitor electrode fabrication. These wastewaters—characterized by high acidity and elevated concentrations of metal cations (Cu, Ni, Zn, Fe), sulfates, and organic reagents such as xanthates, oil (20 g/t ore), flotation frother (methyl isobutyl carbinol), and pyrite depressant (CaO, 500–1000 g/t), along with residues from molybdenum flotation (sulfuric acid, sodium hydrosulfide, and kerosene)—are byproducts of copper–porphyry gold-bearing ore beneficiation. The reduction of Ni powder in the wastewater induces the degradation and formation of a gel that captures both residual metal ions and organic compounds—particularly xanthates—which play a crucial role in the subsequent steps. The resulting gel is incorporated during the oxidative polymerization of aniline, forming a nanocomposite with a polyaniline matrix and embedded xanthate-based compounds. An asymmetric supercapacitor was assembled using the synthesized material as the cathodic electrode. Electrochemical tests revealed remarkable capacitance and cycling stability, demonstrating the potential of this novel approach both for the valorization of industrial waste streams and for enhancing the performance of energy storage devices. Full article

North China Craton (NCC) formed the world’s largest karstic bauxite belt in the Late Carboniferous, with significant variations in metallogenic sources and conditions, which affect the overall understanding of karstic bauxite genesis. The Xiangcaowa bauxite deposit in the southern NCC is a large deposit of uncertain provenance and genesis. This study employed geological, mineralogical, and chronology analysis to investigate the sources and genesis of Xiangcaowa bauxite, further contributing to a full understanding of the origin of bauxite throughout the NCC. Xiangcaowa ore-bearing rock series is composed of bauxite and claystone layers. The composition of bauxite ore encompasses diaspore, kaolinite, anatase, pyrite, zircon, and rutile. Widely developed mineral assemblages, such as diaspore–anatase–pyrite, indicate that bauxite is mainly formed in reducing and alkaline karstic depressions. Detrital zircons, aged ~450, ~520, ~950, and ~1100 Ma, predominantly originate from igneous rocks in the North Qinling Orogenic Belt (NQOB), and the ~1650 and ~2400 Ma zircon age populations are primarily from the southern margin of the NCC. Detrital rutiles, which are concentrated in 800–510 Ma, are primarily from the metamorphic rocks of the South Qinling Orogenic Belt (SQOB); rutiles aged ~1500–910 Ma are primarily from metamorphic rocks in the NQOB. These results confirm that the principal sources of the bauxite are the igneous and metamorphic rocks within the NQOB, along with the metamorphic rocks of the SQOB, while the basement rocks of the NCC contribute only minorly to its formation. A large karstic bauxite deposit was formed by the transport of large amounts of weathered material into extensive karstic depressions where reducing and alkaline conditions favoured diaspore deposition. Full article

The flotation separation of sphalerite (ZnS) and pyrite (FeS₂) in a copper sulfate (CuSO₄)–butyl xanthate (BX) system is challenging because the indiscriminate activation of Cu²⁺ gives them similar floatability. To this end, the suitability of a novel depressant, luteolin (LUT), on the flotation separation of ZnS from FeS₂ in this system was studied. Micro-flotation tests and contact angle measurement results showed that ZnS could be selectively separated from FeS₂ using LUT as a depressant. At pH 7.0 ± 0.1, a flotation concentrate with a recovery of 93.90% ZnS and 2.84% FeS₂ was obtained after adding LUT in artificial mixed minerals tests. Adsorption differences and characteristics results showed that the affinity of LUT to FeS₂ was considerably higher than that of ZnS, which effectively hindered the subsequent adsorption of xanthate on FeS₂ but had a relatively weak effect on ZnS. Thus, a large floatability difference between ZnS and FeS₂ was achieved. Further analyses revealed that the adsorption behavior of LUT on FeS₂ occurred mainly through the interaction between 4–5 sites and Fe(II) at the solid/liquid interface. These findings shed light for the first time on the suitability of LUT for the successful flotation separation of ZnS from FeS₂, which has important guiding significance for the development of a lime-free depressant of FeS₂. Full article

The disadvantages of using lime to depress the flotation of copper-activated pyrite and pyrrhotite are well known. In this study, oxidized starch, prepared by the ozone nanobubble technology, was employed as an eco-friendly depressant for copper-activated pyrite and pyrrhotite in the flotation of chalcopyrite. Single mineral flotation showed that oxidized starch inhibited the flotation of copper-activated pyrite and pyrrhotite at pH 5.5 while having no significant impact on chalcopyrite flotation. Zeta potential and adsorption measurements, together with XPS analysis and EDTA extraction, were conducted to understand the mechanism underpinning the selective depression behavior of oxidized starch. It was found that oxidized starch had a stronger affinity for copper-activated pyrite and pyrrhotite than for chalcopyrite. The depression of pyrite and pyrrhotite by oxidized starch was due to the combined effect of the formation of hydrophilic Cu-starch complex and the oxidation of Cu(I) on their surfaces. Further, oxidized starch was examined in the flotation of an actual bulk sulfur concentrate where a comparable depression performance to that of lime was shown. This investigation may contribute to the greening of the chalcopyrite flotation process by demonstrating the promising potential of oxidized starch for copper-activated pyrite and pyrrhotite depression. Full article

This work investigates coal desulfurization by using reverse flotation. In this method, pyrite (the only source of sulfur in the studied coal) was separated from the meta-bituminous coal by using three different coal depressants (starch, dextrin and humic acid). A novel variable elimination approach was used to determine the contribution of the depressant type and the depressant concentration on the desulfurization performance. The results showed that the pyrite recoveries are influenced by the depressant type while the highest pyrite recovery was achieved in the presence of humic acid. Therefore, humic acid should be used in flotation rougher and scavenger cells in which the aim is to achieve high pyrite recovery. By contrast, the pyrite grades are affected significantly by the depressant concentration. Considering that the aim in flotation cleaner cells is to achieve high pyrite grade, any of the studied coal depressants can be successfully used but at high concentrations. This work demonstrated that the selection of flotation depressants depends on the type of flotation cells used in coal desulfurization. Full article

Pyrite has natural floatability and thus readily enters valuable mineral flotation concentrates, diluting their quality and decreasing their economic value. Its separation is challenging, depending on process conditions, the presence of activating ions, and water quality, particularly in regions where seawater is used. This study examines the effect of various doses of sodium metabisulfite (SMBS) on pyrite depression in freshwater and seawater under weakly alkaline conditions and with different copper ion concentrations. Without the addition of activators or depressants, pyrite recovery is 40% in freshwater and 60% in seawater, whereas with 10 ppm of SMBS, recoveries drop to 28% and 38%, respectively. The addition of 10 ppm Cu²⁺ increases recovery by 10% in freshwater and by 20% in seawater. In the presence of 75 ppm of PAX, maximum recovery reached 50% in freshwater and 80% in seawater. These results suggest that cationic bridges formed by seawater ions, combined with CaOH⁺ activation, play a critical role in pyrite activation, even in the presence of depressants. Full article

The clean and efficient utilization of coal is a promising way to achieve carbon neutrality. Coking coal is a scarce resource and an important raw material in the steel industry. However, the presence of pyrite sulfur affects its clean utilization. Nonetheless, this pyrite could be removed using depressants during flotation. Commonly used organic depressants (sodium lignosulfonate (SL), calcium lignosulfonate (CL), and pyrogallol (PY)) and inorganic depressants (calcium oxide (CaO) and calcium hypochlorite (Ca(ClO)₂)) were chosen in this study. Their inhibition mechanism was discussed using FTIR, XPS, and molecular dynamics (MD) methods. The desulfurization ability of organic depressants was shown to be better than inorganic ones. Among the organic depressants, PY proved to be advantageous in terms of low dosage. Physical adsorption was identified as the main interaction form of SL, CL, and PY onto the surface of pyrite, as evidenced from FTIR and XPS analyses. Similarly, MD simulation results showed that hydrogen bonds played a proactive role in the interactions between PY and pyrite. The diffusion coefficient of water molecules on the pyrite surface was also observed to decrease when organic depressants were present, indicating an increase in the hydrophilicity of pyrite. This research is of great significance to utilize sulfur-containing coal and minerals. Full article

Low-maturity shale oil predominates in shale oil resources. China’s onshore shale oil, particularly the Cretaceous Nenjiang Formation in the Songliao Basin, holds significant potential for low-maturity shale oil, presenting promising exploration and development prospects. This study delves into the hydrocarbon generation conditions, reservoir characteristics, and oil-bearing property analysis of the mud shale from the Nen-1 and Nen-2 sub-formations of the Nenjiang Formation to pinpoint favorable intervals for shale oil exploration. Through the integration of lithology, pressure, and fracture distribution data in the study area, favorable zones were delineated. The Nen-1 sub-formation is widely distributed in the Changling Depression, with mud shale thickness ranging from 30 to 100 m and a total organic content exceeding 2.0%. Type I kerogen predominated as the source rock, while some samples contained type II kerogen. Organic microcomponents primarily comprised algal bodies, with vitrinite reflectance (R_o) ranging from 0.5% to 0.8%. Compared to Nen-1 shale, Nen-2 shale exhibited less total organic content, kerogen type, and thermal evolution degree, albeit both are conducive to low-maturity shale oil generation. The Nen-1 and Nen-2 sub-formations predominantly consist of clay, quartz, feldspar, calcite, and pyrite minerals, with minor dolomite, siderite, and anhydrite. Hydrocarbons primarily reside in microfractures and micropores, including interlayer micropores, organic matter micropores, intra-cuticle micropores, and intercrystalline microporosity, with interlayer and intra-cuticle micropores being dominant. The free oil content (S₁) in Nen-1 shale ranged from 0.01 mg/g to 5.04 mg/g (average: 1.13 mg/g), while in Nen-2 shale, it ranged from 0.01 mg/g to 3.28 mg/g (average: 0.75 mg/g). The Nen-1 and Nen-2 sub-formations are identified as potential intervals for shale oil exploration. Considering total organic content, oil saturation, vitrinite reflectance, and shale formation thickness in the study area, the favorable zone for low-maturity shale oil generation is primarily situated in the Heidimiao Sub-Depression and its vicinity. The Nen-2 shale-oil-enriched zone is concentrated in the northwest part of the Heidimiao Sub-Depression, while the Nen-1 shale-oil-enriched zone lies in the northeast part. Full article

Gold grains are observed in a variety of forms, such as coarse-liberated native gold grains, and ultra-fine grains associated with sulfide or non-sulfide mineral particles, in the form of solid solution in sulfide minerals, mainly pyrite. In the flotation of gold ores, bulk sulfide mineral flotation is generally applied to maximize gold recovery. This approach gives high gold recoveries, but it also causes the recovery of barren sulfide minerals (i.e., sulfide mineral particles with no gold content), which increases concentrate tonnage and transportation costs and reduces the grade sometimes to below the saleable limit (approx. 10 g/t Au). This study addresses the differences between gold-bearing and barren pyrite particles taken from various ore deposits and utilizes these differences for the selective flotation of gold-bearing pyrite. The laboratory scale flotation tests conducted on three pyrite samples having different cyanide soluble gold contents show that a selective separation between gold-bearing pyrite and barren pyrite particles could be achieved under specific flotation conditions. Gold recovery is correlated directly with the cyanide-soluble gold in the ore samples. Electrochemical experiments were conducted to elucidate the differences in surface properties of the two types of pyrite. The barren pyrite particles were more cathodic and prone to cathodic reduction of OH⁻ and depressant ions on the surface, and they could be depressed effectively without significantly affecting the gold-bearing particles. Full article

Pyrite is an important proxy used to reflect the redox state of a sedimentary environment. Currently available studies on pyrite focus on the process of sulfur cycles between an ocean and sediment. However, our understanding of the biogeochemical cycle of sulfur in terrestrial lake basins remains unclear, and the growth patterns of different types of pyrite are poorly understood. In this paper, we used samples from the 3⁴ section of the Qianjiang depression in the Jianghan Basin as direct research objects by combining pyrite and sulfur isotope determination. The one-dimensional diffusion–advection–reaction simulation (1D-DAR) model was applied to simulate the changes in the pyrite content and sulfur isotope values in the sediment. The results show that the sediments in the saline lake basin environment contain a high organic matter content, a high sedimentation rate, and a high H₂S diffusion oxidation rate, reflecting the strong reducing background and high productivity of this ancient lake. Sensitivity tests revealed that the organic matter content and H₂S diffusion oxidation rate at the sediment–water interface are sensitive to the pyrite content. The sedimentation rate, organic matter content, and sulfate concentration are sensitive to the pyrite’s sulfur isotope values. However, the variation in the active iron content had little effect on the pyrite content or sulfur isotope value. Full article