Search Results (1,401)

The discharge of chromium-containing wastewater into natural aquatic systems poses a substantial risk to both ecosystem integrity and human health. In this study, a pyrite-amended Leersia hexandra Swartz (L. hexandra) constructed wetland was established to investigate the mechanisms underlying pyrite-mediated regulation of wetland processes. In normal conditions, the presence of L. hexandra enhanced the removal of NH₄⁺-N, NO₃⁻-N, TN, and TP, with the maximum removal efficiencies increased by up to 35.4%, 17.8%, 9.5%, and 25%, respectively, compared with the constructed wetland without L. hexandra. Although Cr(VI) led to a general decline in removal efficiencies, appreciable removal of NH₄⁺-N, TN, TP, and COD was still sustained. Notably, under Cr(VI) stress, pyrite amendment improved the removal of NH₄⁺-N and COD, with maximum removal efficiencies reaching 99% and 87.5%, respectively, and achieving optimal overall efficiency. Moreover, physiological and biochemical assessments indicated that L. hexandra exhibited superior performance in the pyrite-amended system compared with the unamended control following Cr(VI) exposure, with the peak SOD activity decreased by 27.6%, peak POD activity decreased by 21.9%, peak CAT activity increased by 29.6%, and peak MDA content decreased by 29.4%, suggesting that pyrite mitigated Cr(VI) stress. Given the pivotal role of microbial assemblages in nutrient transformation, shifts in microbial community structure were further analyzed after pyrite addition, revealing discernible alterations. Collectively, these findings demonstrate that pyrite incorporation into L. hexandra constructed wetlands enhances the removal of specific nitrogen species under Cr(VI) stress, while its promotive effect on phosphorus removal remains comparatively limited. Full article

The selective separation of chalcopyrite from pyritic ores represents a major industrial challenge due to inadvertent copper activation. This study systematically investigates the batch flotation kinetics of a complex sulfide ore (Draa Sfar North, Morocco) using a first-order kinetic model ($R^2>0.916$). The impacts of pulp pH, chemical depressants, and specialized collectors were evaluated to optimize the copper/iron selectivity index ($S{I}_{Cu/Fe}$). The results reveal a high-alkalinity paradox: At pH 11.0, chalcopyrite kinetics experience a severe passivation bottleneck ($K_{i,Cu}=0.1330 {\min }^{-1}$). At pH 11.5, selectivity collapses ($SI=2.64$) due to persistent iron sulfide floatability ($K_{i,Fe}=0.2066 {\min }^{-1}$). Conversely, natural pH ($\approx 6.0$) provides a superior baseline ($SI=3.32$), where 40 g/t sodium cyanide (NaCN) yielded a peak index of $S{I}_{Cu/Fe}=10.25$. As an eco-friendly substitute, sodium lignosulfonate (LSNa) achieved outstanding performance ($S{I}_{Cu/Fe}=5.30$), reducing iron kinetics to their lowest level ($K_{i,Fe}=0.0356 {\min }^{-1}$) via ferric–anionic complexation. Furthermore, Danafloat 271 secured the highest collector-driven selectivity ($S{I}_{Cu/Fe}=5.03$) by suppressing the iron matrix ($K_{i,Fe}=0.0306 {\min }^{-1}$) following Hard–Soft Acid–Base principles. This study clarifies specific aspects of selective copper–iron flotation, demonstrating that natural pH circuits with green depressants or selective collectors offer a sustainable alternative. Full article

Pyrite is one of the most common sulfide minerals in polymetallic sulfide ores, and its flotation behavior directly affects the selective separation efficiency of valuable minerals. This study investigated the effects of collector type, pulp pH, pH regulator, and combined collector ratio on pyrite flotation using sodium butyl xanthate (SBX), diethyl dithiocarbamate (DDTC), ammonium dibutyl dithiophosphate (ADDP), and Aerophine 3418A (3418A), together with cyclic voltammetry (CV) and DFTB analyses. The results showed that DDTC and SBX exhibited stronger collecting ability than 3418A and ADDP at natural pH. Increasing pH significantly depressed pyrite flotation, with CaO exerting stronger inhibition than NaOH. Combined collectors displayed pronounced component dependence and ratio sensitivity. CV results indicated that collector adsorption on pyrite is an irreversible electrochemical process, and that calcium-bearing species in the CaO system passivate surface active sites, thereby inhibiting collector adsorption. DFTB calculations revealed that collecting performance is governed by the coordination stability of double-bonded S atoms with surface Fe sites and resistance to hydration. The research results can provide a theoretical basis for regulating pyrite flotation behavior and optimizing reagent regimes in the flotation separation process of complex sulfide ores. Full article

This study investigates the occurrence characteristics of solid bitumen and its control on pore structure in the overmature marine shales of the Wufeng–Longmaxi Formations in the Jianshi–Badong area, Middle Yangtze region. Total organic carbon analysis, Rock-Eval pyrolysis, organic petrography, organic matter reflectance measurements, petrographic thin-section observations, and scanning electron microscopy were integrated. The shale samples contain 0.10%–6.73% total organic carbon, with an average of 2.20%, and the organic-rich intervals are mainly concentrated in the middle to lower part of the Longmaxi Formation. The average equivalent vitrinite reflectance (EqRo), calculated from solid-bitumen reflectance, is 2.06%, indicating an early overmature stage. The original organic matter is inferred to have been dominated by Type II₁ kerogen, which was extensively transformed into indigenous solid bitumen during thermal evolution. Four principal occurrence types of solid bitumen were identified: laminated, dispersed, massive, and mineral-associated. Organic-pore development differs among these occurrence types. Nanometer-scale pores are locally preserved in laminated and mineral-associated solid bitumen, whereas dispersed solid bitumen in clay-rich matrices generally shows poor pore development. The pore structure is jointly controlled by the occurrence mode of solid bitumen, rigid-mineral support, clay-mineral compaction, thermal maturity, and hydrocarbon generation and expulsion. Quartz- and pyrite-associated solid bitumen is comparatively favorable for pore preservation, whereas clay-associated solid bitumen is more susceptible to pore deformation and closure. These results clarify the petrographic control of solid-bitumen occurrence on pore preservation in overmature marine shales. Full article

The reserves of non-refractory gold ores are continuously declining, while refractory gold ore deposits remain abundant. Therefore, developing more efficient technologies to utilize these ores is crucial for gold-related industries. Oxidation roasting is commonly used to eliminate the adverse effects of sulfur- and arsenic-bearing minerals, but its underlying mechanisms are still not fully understood. To address this gap, the present study investigated the effect of oxidation roasting on gold leaching rate. A combination of roasting–leaching experiments, X-ray diffraction (XRD), pore structure analysis, and scanning electron microscopy (SEM) was employed to examine the evolution of surface pore structures and their impact on leaching performance. The gold leaching rate of the raw material was only 10.13%, due to the encapsulation of gold particles within pyrite. Under optimal roasting conditions—600 °C for 2 h—the gold leaching rate reached a peak value of 88.06%. At this temperature, the dense surface of pyrite decomposed, forming a highly porous structure that allowed the JinChan lixiviant to fully contact the gold particles. However, increasing the roasting temperature or extending the roasting time promoted the formation of CaSO₄ and Mg₂SiO₄. These newly formed phases may have contributed to pore blockage on the hematite surface, which could explain the more compact structure and the subsequent decline in gold extraction. Based on these observations, a possible mechanism is proposed linking pore structure evolution and phase transformation during roasting to the leaching performance. Full article

Accurate oil saturation evaluation is critical for shale oil sweet-spot prediction and reserve assessment, but conventional resistivity-based interpretation is commonly challenged in clay-rich lacustrine shale oil reservoirs. In some favorable shale intervals, high oil-bearing potential is accompanied by low resistivity, which weakens the applicability of Archie-type saturation models and may lead to underestimation of oil saturation. To clarify the origin of this abnormal electrical response and improve saturation interpretation, this study investigates the upper fourth member of the Shahejie Formation in the Boxing Sag, Jiyang Sub-basin. Core description, thin-section observation, XRD mineral composition, porosity, measured oil saturation, TOC, S1 and conventional logging data were integrated to establish a core-calibrated and SOM-based reservoir classification workflow. Using GR, AC, CNL, DEN, Rt and Rs as input curves, the shale oil reservoirs were divided into Type I, Type II and Type III classes. Type I reservoirs exhibit better pore development and hydrocarbon enrichment, with mean porosity, oil saturation, TOC and S1 values of 4.95%, 59.18%, 2.21 wt% and 2.77 mg/g, respectively. However, their mean Rt is only 22.75 Ω·m, much lower than that of Type III reservoirs. This response defines a typical “three-high and one-low” logging pattern, characterized by high GR, high AC, high CNL and low resistivity. The resistivity-reversal behavior is mainly associated with clay-related conduction and relatively higher absolute water content, whereas organic matter and pyrite do not form continuous conductive pathways in the studied interval. Based on this mechanism, a class-dependent electrical–non-electrical log fusion model was developed by combining clay-corrected electrical saturation with neutron–density saturation constraints. Compared with the single electrical model and single non-electrical model, which yield mean absolute errors of 12.65 and 13.84 percentage points, respectively, the proposed fusion model reduces the error to 8.88 percentage points. Application to more than 40 wells identifies the central–western part of the Boxing Sag as the most favorable shale oil sweet-spot area. The cumulative thickness of Type I reservoirs generally exceeds 100 m in this area and locally reaches more than 150 m. The proposed workflow provides a practical method for identifying favorable low-resistivity lacustrine shale oil reservoirs using conventional logging data. Full article

The performance of the bacterium Acidithiobacillus ferrooxidans and sodium metabisulfite (MBS) as pyrite depressants in seawater flotation was compared. Microflotation experiments were conducted using pure pyrite, while batch flotation tests were performed using a sulfide ore sample containing pyrite. The results showed that A. ferrooxidans was more effective than MBS in depressing pure pyrite flotation. In the presence of the bacterium, pyrite recovery decreased from 95% to 64% at pH 8 and from 96% to 21% at pH 10. In contrast, MBS exhibited superior performance during flotation of the sulfide ore sample, reducing pyrite recovery from 81% to 57% at pH 8 and from 86% to 57% at pH 10. The results suggest that dissolved copper ions present during flotation of the sulfide ore promote the interaction between MBS and pyrite, thereby enhancing its depressant effect. Conversely, the performance of A. ferrooxidans appears to be reduced in complex ore systems because the bacteria may adhere to other mineral surfaces, decreasing their interaction with pyrite. This phenomenon was not observed during flotation of pure pyrite. SEM–EDS analyses confirmed the presence of copper-containing species on the pyrite surface after exposure to copper ions. These findings indicate that MBS is more suitable than A. ferrooxidans for pyrite depression in complex sulfide ores under seawater flotation conditions, particularly when copper-bearing minerals are present. Full article

Datangpo-type manganese (Mn) deposits in South China constitute a key archive of Cryogenian postglacial oceanic evolution and large-scale Mn mineralization. However, systematic comparisons between western and central Hunan remain limited, particularly regarding redox conditions, Mn precipitation pathways, and Mn sources. This study investigates Mn ores hosted within the Datangpo black shale succession in western and central Hunan through integrated petrographic, mineralogical, and whole-rock geochemical analyses. The ores are dominated by rhodochrosite and dolomite, with subordinate quartz, pyrite, and illite. Pyrite framboid characteristics together with redox-sensitive trace element systematics record increasingly reducing conditions from high- to low-grade ores, highlighting the control of redox conditions on Mn enrichment. Medium- to high-grade ores show limited terrigenous input and generally shift toward hydrothermal Fe–Mn end members, consistent with a hydrothermal contribution to Mn supply. Mn enrichment generally involved oxidative fixation during deposition, followed by reductive carbonatization during early diagenesis. Locally intensified hydrothermal input may also have promoted limited direct precipitation of Mn carbonate under reducing, Mn-rich, and alkaline conditions. This model may provide a useful basis for interpreting other Datangpo-type Mn deposits in South China. Full article

Acid mine drainage (AMD) generation in sulfide waste rock deposits involves complex hydrogeochemical processes that require controlled experimental approaches to improve our understanding of them. In this study, a laboratory-scale waste rock dam reactor was operated for 31 weeks using representative materials from the Iberian Pyrite Belt. Continuous monitoring of physicochemical parameters and weekly chemical analyses generated a big dataset that was evaluated using graphical and statistical approaches. The reactor successfully reproduced the principal hydrogeochemical processes characteristic of AMD environments, including sulfide oxidation, contaminant transport and attenuation. Graphical and statistical analyses consistently validated the proposed conceptual hydrogeochemical model. Sulfate concentrations were identified as the main control on electrical conductivity, while alternating wet and dry periods governed pH fluctuations through precipitation–dissolution and redissolution processes. The progressive decrease in dissolved metals and sulfate along the reactor reflected precipitation processes comparable to those observed in natural AMD systems. The reactor reproduced, at a small scale, both the temporal evolution and the three hydrological phases described for natural waste rock dams, demonstrating its reliability as a reproducible experimental platform for hydrogeochemical modeling and the investigation of AMD generation under controlled conditions. An effective diagnosis of contamination processes in mine waters is essential for future remediation interventions. Full article

Understanding hydrogeochemical change after coal mine closure is needed to protect groundwater in multi-layer aquifer systems, but predictions that span decades are scarce. Earlier FEFLOW–PHREEQC studies of mine hydrogeochemistry have reduced the subsurface to one aquifer, so they cannot resolve the goaf-to-aquifer transport that governs post-closure risk. This study presents a decadal-scale (10-year) reactive transport simulation for a 9-layer mine system with layer-specific kinetics, a step beyond the single-aquifer simplifications of earlier applications. We modeled groundwater rebound and water–rock interaction at a permanently closed deep coal mine in Xuzhou, China, with a three-dimensional FEFLOW–PHREEQC framework. The four aquifers (Q, 7S, L4, O) each received their own reactive parameters, so the goaf and surrounding units were coupled yet chemically distinct. Pyrite-driven acid mine drainage was set as a non-point source in the mined-out zone, with initial pH 2.1 and pyrite content 0.225 mol/L. pH in the stope rose from 2.1 to 5.6 in 5 years and to 6.6 at year 10, a result of fast neutralization by carbonate-buffered alkaline water. Sulfate and total Fe in the overlying 7S aquifer rose without interruption, and Fe passed the 0.3 mg/L drinking-water limit in every monitored aquifer (0.34 to 14 mg/L). Plumes stayed within the mined area for the first 5 years, then moved down-gradient toward dewatering centers. A sensitivity test found that longitudinal dispersivity and porosity controlled SO4²⁻ transport, while transverse dispersivity had little effect. The 7S aquifer is the most vulnerable receptor of post-closure contamination. The deep Ordovician aquifer stayed stable because carbonate buffering and hydraulic isolation protected it. Because each aquifer carries its own parameters, the framework transfers to other abandoned coalfields and supports long-term groundwater-quality forecasting there. Full article

The Dajing Cu-Sn polymetallic deposit, situated within the southern Great Xing’an Range of northern China, is a representative Mesozoic magmatic–hydrothermal system within a major Cu–Sn–Ag–Pb–Zn metallogenic belt. Located at the junction between the Siberian and North China plates, the deposit occurs within a composite tectonic domain overprinted by the Paleo-Asian, Mongol–Okhotsk, and Paleo-Pacific systems. Building on field geological constraints and detailed ore petrography, this study utilizes SEM–CL imaging and in situ LA–ICP–MS trace-element analysis of hydrothermal quartz to reconstruct the multistage physicochemical evolution and fluid dynamics of the ore-forming system. Three quartz generations record successive mineralization stages: early QI forms grain cores associated with Stage I cassiterite–arsenopyrite–quartz mineralization; main-stage QII crystallized during or shortly after Stage II chalcopyrite precipitation and exhibits well-developed oscillatory zoning; and late QIII occurs mainly as rim overgrowths and fracture fillings and postdates Stage III ore-mineral precipitation. Quartz is characteristically Ti-poor (4.7–22.8 ppm), and its trace-element systematics indicate a low- to intermediate-temperature hydrothermal signature and a granitic magmatic–hydrothermal affinity. Al, Li, Na, K, and Ge show coupled behavior consistent with heterovalent substitution and vary markedly among quartz generations, with CL-bright QIIa showing relatively higher Al, Ge, and Na relative to CL-dark QIIb, whereas QIII is generally characterized by lower Al, Li, and Ge. Localized anomalously high Cu and Sn values are mainly attributed to the co-ablation of fine-grained mineral inclusions, metal-rich fluid inclusions, or fracture-filling components. These features indicate a chemically heterogeneous fluid reservoir with inferred relatively acidic conditions during the initial Sn-mineralization stage. The fluid system subsequently experienced recurrent physicochemical fluctuations associated with pulsed fluid input during the principal Cu-mineralization stage. QIII records a trace element-depleted late-fluid system associated with the terminal pyrite–quartz stage. Late fluids migrated along earlier quartz boundaries and fractures and may have undergone further cooling and dilution through fluid mixing and/or water–rock interaction. Overall, the fluid system shows a progressive shift in inferred fluid chemistry, consistent with decreasing acidity during hydrothermal evolution. Full article

Pore heterogeneity in marine shales critically controls gas storage and transport; yet, how pore surface fractal attributes and pore network geometry differentially regulate adsorbed and free gas among lithofacies remains unclear. This study investigates Longmaxi marine shales from the Weiyuan area, Sichuan Basin, using XRD, FE-SEM, low-pressure N₂ adsorption, and high-pressure CH₄ isothermal adsorption. According to mineral composition, samples are divided into four lithofacies: quartz–calcite (#QC), quartz–pyrite (#QP), quartz–dolomite (#QD), and quartz–illite (#QI). Results show that adsorbed and free gas are controlled by different pore structure descriptors. Adsorbed gas content decreases as #QC > #QP > #QI > #QD and is mainly governed by micropore development, specific surface area, and surface roughness/complexity. Free gas content follows #QP > #QC > #QI > #QD and is primarily controlled by pore network effectiveness: connectivity enlarges connected pore space, whereas the tortuosity factor increases flow resistance and restricts migration. The #QP lithofacies have the most favorable network conditions, with high connectivity and a low tortuosity factor, indicating the greatest free gas enrichment potential. These findings provide a lithofacies-specific framework for reservoir assessment and sweet spot identification in Longmaxi shale. Full article

The reactive transport of hexavalent chromium (Cr(VI)) in anthropogenically disturbed sites (e.g., mine waste rock dumps, chromium salt industrial sites) is critically influenced by physico-chemical heterogeneity, yet the interplay between physical and chemical heterogeneities remains poorly understood. This study employed a series of experiments and numerical modeling to investigate the transport of Cr(VI), focusing on the implications of physical heterogeneity—represented by preferential flow paths—and chemical heterogeneity—characterized by reductive mineral lenses. Key findings indicate that physical heterogeneity accelerates Cr(VI) breakthrough by 1.4 to 2.1 pore volumes (PV) relative to homogeneous columns. The presence of pyrite lenses delays breakthrough by 0.6–1.2 PV under neutral pH and 1.6–2.0 PV under acidic pH. At a flow rate of 3.0 m/day, the apparent sorption capacity decreases by ~62.5% compared to 0.3 m/day, indicating that physical advection largely suppresses chemical retention under high-flux conditions. The above results demonstrate that physical heterogeneity governs flow paths and advection rates, whereas chemical heterogeneity impedes transport through heterogeneous adsorption and reduction in Cr(VI) to Cr(III) along these pathways. Furthermore, the presence of preferential paths leads to greater spatial variability, which subsequently influences the interaction dynamics between Cr(VI) and reactive minerals in the aqueous environment. The dominance shifts between physical/chemical controls based on flow rates and pH. At higher flow rates, the influence of physical heterogeneity becomes more pronounced, diminishing chemical reactions due to insufficient residence time of Cr(VI). Conversely, a lower pH environment enhances pyrite dissolution, which decouples the dependency on physical heterogeneity by promoting homogeneous reactions. Further evidence was obtained through X-ray photoelectron spectroscopy (XPS) analysis. The experimental observations are complemented by TOUGHREACT-based reactive transport simulations, which further reveal that the apparent dominance shifts arise from competing timescales between advection and surface reaction. The insights gained from the study emphasize the necessity of integrating both physical and chemical spatial variability in risk assessments, transport modeling, and designing targeted remediation strategies. Full article

Effective iron removal from highly acidic leachates without neutralizer addition is a long-standing challenge in hydrometallurgy. For Cu-Co-bearing pyrite cinder, we demonstrate that a cyclic leaching process achieves this outcome. Operating entirely without neutralizers, the process consumed 96% of residual acid, enriched Cu and Co 4.76- and 3.88-fold, and removed 48.2% of iron, all while maintaining pH below 1.5 across four closed-loop cycles. Thermodynamic analysis reveals that Fe³⁺-${\mathrm{SO}}_4^{2-}$ complexation suppresses free Fe³⁺ to approximately 10⁻⁸ mol/L, ruling out conventional hydrolytic precipitation and directing precipitation towards schwertmannite-type basic ferric sulfate (Fe₈O₈(OH)₆SO₄). The formation of this sulfate-bearing Fe precipitate is consistent with the thermodynamic analysis, the iron mass balance, and a 176% increase in solid-phase sulfur. This neutralizer-free strategy offers a sustainable paradigm for recovering critical metals from iron-rich secondary resources. Full article

Permian sedimentary manganese carbonate deposits in the Qiling Basin exhibit substantial resource potential, yet their depositional environments and precipitation pathways remain insufficiently constrained. This study integrates petrographic, mineralogical, whole-rock geochemical, and carbonate C–O isotope data from the Shuibutou Mn deposit in southern Hunan. We compare this deposit with the coeval Dongxiangqiao deposit and other Permian marine sedimentary Mn deposits to constrain its depositional setting, Mn-carbonate precipitation mechanisms, and potential Mn sources. The Shuibutou ores contain 10.88–17.18 wt.% MnO and are characterized by spherulitic–oolitic textures, abundant bioclasts, and framboidal pyrite. Mo–U enrichment indicates anoxic bottom waters, whereas the near-marine δ¹³C_carb values of ore carbonates (−0.24‰ to 1.28‰) are consistent with precipitation within a marine carbonate system and suggest direct precipitation of Mn(II) carbonates from dissolved Mn²⁺ under anoxic conditions. In this setting, dissolved Mn²⁺ accumulated below the chemocline. Partial dissolution of platform-derived calcite grains near the chemocline increased local dissolved inorganic carbon and alkalinity, driving Mn-carbonate supersaturation and the authigenic precipitation of manganoan calcite, ultimately forming manganese carbonate ores. The low Al/(Al + Fe + Mn) ratios, high Fe/Ti ratios, and Co–Ni–Zn and REY geochemical characteristics are consistent with a possible contribution from Mn-rich deep fluids to the dissolved Mn²⁺ inventory of the basin waters. Similarities in mineralogy, geochemistry, and depositional setting between Shuibutou and Dongxiangqiao point to a possible regional role for the direct precipitation of Mn(II) carbonates under anoxic conditions in the Middle Permian Qiling Basin. Relatively deep intraplatform basins may therefore represent favorable targets for manganese carbonate exploration and provide a reference for exploration targeting of Permian sedimentary Mn deposits within the Qiling Basin. Full article