Search Results (143)

To meet the requirements of large-scale visual physical model tests for typical slate strata in the Changsha area, this study aims to identify a similar material that can accurately reproduce the main mechanical characteristics of moderately weathered slate. Based on similarity theory, the target material parameters for a 1:100 scaled model test were derived, and a transparent soft-rock material system composed of fused quartz sand, mixed mineral oil, and fumed silica was used for mix-proportion optimization. Automatic quadruple quick direct shear tests were conducted to systematically investigate how the coarse-fine gradation of skeleton particles controls the shear strength of transparent soft rock. The results show that, under good refractive-index matching, the shear strength of the transparent soft rock increases with the mass fraction of coarse particles (1.0–2.0 mm). A fully coarse-particle skeleton can form stronger interlocking and a more stable cementation network. The optimized fully coarse-grained transparent soft-rock specimen has a cohesion of 42.05 kPa, and an internal friction angle of 34.6°. Under a 1:100 normal-gravity similarity ratio, it can equivalently simulate an in-situ rock mass with a cohesion of 7.53 MPa, and an internal friction angle of 34.6°. The physical and mechanical indexes of this material fall accurately within the target parameter range of moderately weathered slate in the Changsha area, providing scientific and reliable similar-material support for subsequent visual physical model tests of underground engineering in this region. Full article

Gold in the coarse-grained alluvial sediments of the Irgaity placer deposit (Kazakhstan) occurs predominantly as finely dispersed particles associated with mineral matrices, which limits the efficiency of conventional recovery methods. The proposed processing flowsheet demonstrated that thermal pre-treatment is an effective approach for enhancing ultrafine gold recovery, achieving an overall recovery of 86% from the treated concentrate. The Tescan TIMA “Bright Phase Search” workflow, optimized for gold detection by applying a minimum BSE brightness threshold of 75% and an Au phase filter calibrated using a gold standard, successfully identified gold-bearing grains within the analyzed mounts. Further mineralogical investigations revealed that gold particles ≤10 μm occur as native gold and Au-Ag-As-bearing phases, with silver content reaching up to 14 wt.% in some coarser grains. The significant association of silver with gold-bearing particles indicates the potential for incorporating silver recovery into the processing flowsheet, thereby improving the overall economic value of the deposit. Despite the low average gold grade (0.3–0.4 g/t), the large dimensions of the Irgaity placer deposit (approximately 12 km long, 1.5 km wide, and 60–70 m thick) suggest the presence of a substantial large-volume mineral resource. The combination of extensive mineralized sediments and high recovery achieved through thermal activation supports the potential economic viability of the deposit and warrants further evaluation of its development potential. Full article

Aluminum matrix composites (AMCs) reinforced with natural mineral ilmenite offer a cost-effective and thermally stable alternative to conventional cast iron brake drum materials. This study investigates the synergistic effect of fine (32–50 µm) and coarse (75–106 µm) ilmenite particles at four fine-to-coarse weight ratios (1:4, 2:3, 3:2, and 4:1) and three reinforcement contents (5, 10, and 15 wt.%) on the thermal stability and dry sliding wear behavior of stir-cast LM30 Al composites. Ilmenite reinforcement progressively reduces the coefficient of thermal expansion of the LM30 matrix, with the 15 wt.% 4:1 fine-to-coarse ratio composite (15DRP41) exhibiting the lowest coefficient of thermal expansion of ~16.54 × 10⁻⁶/°C, a ~33.3% reduction relative to the unreinforced alloy (~24.8 × 10⁻⁶/°C). The 15DRP41 composite demonstrates the lowest wear rate of all the fabricated composites, 1.82 × 10⁻³ mm³/m at 9.81 N and 9.56 × 10⁻³ mm³/m at 68.67 N at 200 °C. Under the most severe load condition (68.67 N, 200 °C), the coefficient of friction of 15DRP41 is reduced by up to 44% compared with the LM30 alloy. A comparative test against commercial grey cast iron shows that 15DRP41 has a similar wear rate up to 200 °C, while its density (~2.9 g/cm³) is significantly lower and it has excellent dimensional stability. Scanning electron microscopy and energy-dispersive X-ray spectroscopy of worn surfaces and debris confirm a progressive change from oxidative and mild abrasive wear at low loads and temperatures to severe wear by delamination at 68.67 N and 300 °C, as evidenced by the presence of a multi-component mechanically mixed layer. The results have confirmed that the optimum fine-to-coarse ratio for the reinforcement was 4:1, which led to the maximum wear resistance and thermal stability in ilmenite-reinforced LM30 composites for lightweight automotive brake drum applications, and that the optimum weight percentage for the reinforcement was 15 wt.%. Full article

The coupled mechanisms governing carbon–nitrogen turnover across soil particle-size fractions remain unclear. This study investigated soil organic carbon (SOC) and total nitrogen (TN) dynamics across five particle-size fractions in Cambisols under conventional and organic orchard management. Results showed that particle size dominated δ¹³C variation (Partial η² = 0.36) while management practice regulated δ¹⁵N variation (Partial η² = 0.38), revealing a fundamental decoupling of C and N cycling within the particle-size matrix. The progressive linear increase in δ¹³C with declining particle size signaled a transition of SOC from net accumulation to net decomposition, accompanied by directional carbon translocation from coarse sand to clay fractions. A universal critical soil pH threshold ~5.3 was identified, where inter-particle-size carbon flow reached its maximum while microbial decomposition was minimized. Organic management reduced the intensity of plant-derived carbon translocation between particle-size fractions, yet substantially enhanced microbial anabolism, leading to drastically elevated stocks of microbial necromass carbon (MNC) in both particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) pools. Notably, the relative proportional distribution of POC and MAOC remained unchanged across the two management practices, which was intrinsically constrained by the inherent textural properties of the studied Cambisols. Counterintuitively, progressive soil acidification concurrently increased SOC lability and overall carbon stabilization, a paradox that directly demonstrated decoupling between chemical oxidizability and physical protection during particle-size carbon translocation. These findings confirmed incomplete carbon–nitrogen coupling within soil particle-size fractions, and demonstrated that SOC stabilization was co-regulated by organo-mineral interactions and microbial processing, whereas nitrogen dynamics were primarily modulated by exogenous management-derived inputs. This work provided novel insights for optimizing agricultural management strategies to synergistically enhance soil fertility and long-term carbon sequestration. Full article

Alternating marine inflow and continental outflow make southern Sweden a suitable region for investigating natural and anthropogenic contributions to background particulate matter (PM). However, interpreting dust and marine aerosol sources remains challenging because their source signatures often overlap during atmospheric transport. This study investigated aerosol sources at the Vavihill and Hyltemossa background stations using source apportionment, elemental analysis, transport modelling, reanalysis data, and particle-resolved microscopy. At Vavihill, filter samples provided elemental composition, while TEOM measurements provided PM₁₀ and PM_2.5 mass concentrations. The combined data were analysed using Positive Matrix Factorization (PMF). At Hyltemossa, online XACT elemental measurements were combined with FIDAS coarse PM observations to evaluate coarse PM source contributions. HYSPLIT backward trajectories, CAMS diagnostics, and SEM/EDX analysis supported the interpretation of selected dust-related episodes and particle mixing states. The analysis identified mineral- and marine-related aerosols, regional pollution, and mixed combustion particles as important components of background PM. Mineral-associated contributions increased markedly during spring, accounting for 39% of the measured coarse PM at Vavihill and 29% at Hyltemossa. In contrast, marine aerosol made its largest contribution to measured coarse PM during winter, accounting for 48% at Vavihill and 40% at Hyltemossa. The mineral-related factor reflected multiple source regions and transport pathways rather than a single recurring dust source. At both sites, mineral, marine, and anthropogenic components frequently co-occurred and underwent atmospheric processing and mixing. Together, these results highlight the chemically heterogeneous and seasonally variable nature of background PM in southern Sweden. Full article

Use of fly ash (FA), a by-product of coal-fired power stations, and basic oxygen furnace slag (BOFS), a by-product of steel production plants, in construction applications in Kazakhstan is limited due to their low quality and inherent problematic properties. For example, the concern with using BOFS as an aggregate in concrete is the volume expansion caused by the formation of calcium hydroxide (Ca(OH)₂) or magnesium hydroxide (Mg(OH)₂) in the concrete matrix generated by a chemical reaction between water and free calcium oxide (f-CaO) or free magnesium oxide (f-MgO) in BOFS. This issue can be addressed through geopolymerization and CO₂ curing (mineral sequestration). Moreover, the quality of FA does not meet ASTM Class F FA criteria (coarse particle sizes and low reactivity). This study investigated the physical, mechanical, microstructural, and durability properties of geopolymer mixtures composed of low-quality FA, ground granulated blast-furnace slag (GGBFS), and BOFS aggregates under various curing conditions. Six distinct curing regimes were assessed: air, water, 6 h steam, 12 h steam, 6 h steam combined with 6 h CO₂, and 6 h steam combined with 12 h CO₂ curing. The hardened properties, durability, and microstructural characteristics of geopolymer mixtures were mainly assessed by compressive strength, dielectric constant (DC), drying shrinkage, expansion (1 M NaOH solution and water expansions), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) images. Test results show that steam curing and combined steam and CO₂ curing significantly enhanced the performance of the mixtures containing BOFS aggregates. The combined steam and CO₂ curing accelerated the mineral sequestration of f-CaO in the BOFS aggregates, increasing the 28-day compressive strength by up to 27.7% and 19.2% (reaching 37.1 MPa) compared to air- and water-cured mixtures (29.1 and 31.1 MPa, respectively). While air (20.0 and 11.7), steam (28.7 and 12.4), and combined steam and CO₂ (23.6 and 12.6) curing at 1-day and 182-day yielded lower DC, water curing (30.5 and 32.2) had higher DC. The extended steam and CO₂ curing times further enhanced compressive strength growth (39.6 MPa) by 36.6% for air-curing and 27.1% for water curing, although curing duration did not significantly affect the dielectric constant. Importantly, the expansion of the BOFS aggregate in both water and 1 M NaOH solution was minimized up to 0.04% under combined curing, mitigating the inherent volumetric instability of the BOFS. Drying shrinkage was also reduced by 0.17% under combined curing conditions. Longer steam and CO₂ curing times reduced variability in dielectric constant, drying shrinkage, and the expansion characteristics. FTIR spectroscopy, SEM image, and XRD analyses confirmed that the mixture’s geopolymerization was more noticeable during the steam and CO₂ curing regimes than during water and air curing regimes. The longer steam and CO₂ curing times promoted extended hydration and the formation of stable carbonate compounds from the BOFS f-CaO, producing a significantly denser and microstructurally stable geopolymer matrix. Full article

The varying sensibilities of diverse proxies to Indian Summer Monsoon (ISM) variables lead to inconsistencies across individual studies. To attain a comprehensive understanding of the ISM driving mechanisms, it is essential to compile multi-proxy paleorecords from diverse monsoon-influenced areas. However, terrestrial ISM records spanning the last 200 ka remain sparse. Here, we performed a magnetic analysis of the PT2 core lacustrine sediments from the Heqing Basin, covering the past 184 ka, to reconstruct ISM variations from millennial to orbital timescales. According to the rock magnetic results, samples displaying strong magnetization are dominated by substantial amounts of magnetite and maghemite, accompanied by a broad grain-size distribution. Conversely, samples with weak magnetization show only limited quantities of fine-grained magnetite. The decrease in magnetic mineral concentration is attributed to the reduction in both coarse and fine-grained particles. Magnetic mineral dissolution intensity (MMDI) which combines magnetic susceptibility and frequency-dependent magnetic susceptibility, is highly sensitive to ISM changes. Consequently, we derived an ISM index from the MMDI and geochemical indicators of the PT2 core lacustrine sediments. This index exhibits pronounced “glacial–interglacial variations”, aligning with other regional ISM indicators from southwestern China and a variety of ISM-related proxies from a broader range of ISM-influenced areas. This suggests that ISM intensity is more sensitive to glacial boundary conditions in high-latitude ice sheets. Full article

Anatase-bearing lateritic ores from Qinglong, Guizhou Province, China, are characterized by extremely low TiO₂ grade, high clay content, fine-grained dissemination, and complex intergrowths with iron oxides, which severely hinder efficient beneficiation. In particular, anatase commonly occurs as ultra-fine particles encapsulated by clay minerals or closely associated with iron oxides, and its surface is often covered by nanoscale goethite films, resulting in surface passivation and pseudo-magnetic behavior. These characteristics lead to a pronounced contradiction between mineral liberation and excessive slime generation during conventional grinding processes. To address these challenges, a high-efficiency pre-concentration flowsheet was developed based on selective desliming, stage grinding, intensive scrubbing, flotation, and weak magnetic separation. Selective desliming via hydrocyclones was adopted, which is inferred to preferentially discard true slimes finer than 10 μm while potentially retaining most fine anatase particles within the underflow. Stage grinding was then applied, which may promote the improved liberation of anatase and early rejection of coarse gangue, and may help reduce overgrinding. Intensive scrubbing was introduced, which is expected to weaken or partially remove iron oxide coatings from the anatase surface, thereby potentially restoring surface activity and reducing pseudo-magnetic interference. Subsequent flotation and low-intensity magnetic separation were optimized to increase the concentrate TiO₂ grade and cut iron impurities, which may be associated with improved surface selectivity and weakened pseudo-magnetic responses. Closed-circuit beneficiation tests demonstrated that a TiO₂ concentrate with a grade of 29.62% and a recovery of 65.4% could be obtained from an ore with an initial TiO₂ grade of only 4.39%. Moreover, approximately 40% of the feed mass was rejected at the pre-concentration stage, significantly reducing the load on downstream separation processes. The proposed process demonstrates promising potential as a technical route for the beneficiation of similar refractory anatase-bearing lateritic ores. Full article

Morphological characteristics of coarse aggregates, namely shape, angularity and surface texture, are closely related to rock mineral compositions and crushing mechanisms. Aggregates with different mineral compositions should be crushed using a suitable crusher. To explore the influence of mineral and crusher types on aggregate morphology, this study investigated the effect of the mineral compositions and crushing operations on the morphologies of coarse aggregates. Six types of major rock-forming minerals (i.e., quartz, amphibole, potassium feldspar, sodium feldspar, calcite and pyroxene) were selected and two typical crushers (i.e., jaw crusher and impact crusher) were used. The morphology parameters (i.e., angularity, texture, sphericity and F&E) of coarse aggregates were measured using the Aggregate Image Measurement SystemII (AIMSII). Further, the morphologies of different aggregates produced by two crushers were compared. The results showed that the angularity values of some aggregates crushed by a jaw crusher (average 3451) were bigger than those by an impact crusher (average 3067) and the angularity of the harder mineral was less affected by the crusher. For surface texture, there was no significant difference between these two crushers, with average texture index of 333.83 for the impact crusher and 332.67 for the jaw crusher, indicating that the surface texture of aggregates was mainly affected by their compositions and barely influenced by the crushing operations. The shape results indicated that the impact crusher produced more cubical aggregate particles compared to the jaw crusher, with average sphericity of 0.666 versus 0.607, whereas the jaw crusher produced aggregates with more elongated or flat particles, with an average F and E index of 3.331 versus 2.726. This study fills the research gap that few previous investigations focused on—the crushing morphology of single mineral aggregates—and the findings help us to understand the effect of the mineral compositions and crushing operations on the morphologies of coarse aggregates, which in turn guides the selection of suitable crushers for different minerals. Full article

The mineralogical characteristics of low-grade hard-rock uranium ore from the Zoujiashan deposit were systematically investigated via multiple analytical techniques, including chemical analysis, X-ray fluorescence (XRF) spectrometry, uranium occurrence analysis, 3D X-ray micro-computed tomography (CT), an automated mineral identification and characterization system (AMICS), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). The results revealed that the uranium grade of the ore was only 0.202%, among which 65.87% existed in the form of independent uranium minerals, while the remaining 34.13% existed in a dispersed ionic state. Except for quartz, most uranium minerals and gangue minerals were finely disseminated and closely intergrown. The pre-concentration of the ore is therefore necessary to separate uranium-rich particles from barren particles at a coarse particle size. Ore density analysis demonstrated that the feed particle size exerted a significant impact on the separation performance, and the optimum feed particle size was determined to be 20 mm. Subsequently, dense medium cyclone (DMC) separation tests were conducted. The experimental results indicated that fine grains were prone to report to low-density products (tailings) during mixed-size beneficiation. Under a tailings yield of 54%, for the −20 + 8 mm coarse fraction, the tailings uranium grade was 0.025% and the uranium recovery of the concentrate was 88.05%. Therefore, classified separation can effectively promote separation efficiency. To reveal the density control mechanism of the particle separation behavior inside the DMC, computational fluid dynamics (CFD) simulations were implemented with the Eulerian–Eulerian multiphase model in ANSYS-Fluent (version 2020R2). The simulation results suggested that a density difference of 8.6% realized effective separation. This work achieved the effective treatment of low-grade hard-rock uranium ore via DMC separation, providing a novel technical route for uranium ore pre-concentration. Full article

High-pressure grinding rolls (HPGRs) are critical in mineral processing, making comprehensive research and analysis of their performance of great significance. This study focuses on the HPGR-3516 test prototype and develops an analytical model that combines the discrete element method (DEM) with multi-body dynamics (MBD). The influences of feed top size, roll speed, and specific press force on equipment performance were examined using analysis of variance (ANOVA) in conjunction with response surface methodology (RSM). A performance prediction model was established through regression analysis, followed by multi-objective optimization and experimental validation. The results indicate that increasing roll speed under high specific press force significantly reduces the roll gap, while the effect is negligible under low specific press force. Increasing roll speed improves throughput more substantially for fine feed than for coarse feed. The optimal process parameters were determined to be a feed top size of 8 mm, a roll speed of 0.37 m/s, and a specific press force of $4.84 \mathrm{N}/{\mathrm{m}\mathrm{m}}^2$. In comparison to the original parameters, throughput increased by 15.81%, qualified particle size passing rate (QPR) improved by 7.85%, and roll gap decreased by 10.24%. This study offers valuable insights into predicting the dynamic performance of HPGRs and has significant engineering implications. Full article

Artisanal gold mining (AGM) activities are increasing globally and rely on rudimentary methods, such as amalgamation, to recover gold. In this study, mercury (Hg) metallurgical balances were conducted in 18 operations and gold (Au) balances in 35 operations, at a processing site serving approximately 4000 miners in the Korokpa mining area in Minna, Niger State, Nigeria. Ore processing involves grinding ore in hammer mills to below 1 mm, concentrating gold in sluice boxes, followed by amalgamating free gold particles in the concentrate. The results showed an average Au feed grade of 1.74 g/t and an average Au recovery from gravity concentration of 42.7%. Chemical analysis of the gravity separation tailing size fractions indicates that Au is lost in coarse fractions due to poor Au liberation and in fine fractions due to inefficiency in the sluicing process. Hg lost in the tailings was calculated as the mass balance difference between Hg added and the sum of Hg recovered through filtration and volatilized Hg in bonefires. It was found that 34% of Hg was lost during amalgamation, by volatilisation (18%) and with tailings (17%). The Hg lost-to-Au produced ratio was 2.6. By optimising procedures for grinding, classification, and concentration, the efficiency of recovery can be improved. Implementing a simple Hg recovery method, such as using a retort for condensation, and improving amalgam heating time can help miners minimise environmental loss. Full article

As an efficient solid–liquid separation device, the hydrocyclone is widely applied in various industrial fields such as coal preparation and oil impurity removal, and its classification performance directly determines the efficiency of industrial separation operations., As the core separation zone of the hydrocyclone, the cone segment, its structure and the number of cone angles directly affect the flow field distribution characteristics and particle classification performance of the hydrocyclone. To reveal the regulation mechanism of the combined cone angles on the classification performance of hydrocyclones, numerical analysis and experimental verification methods were adopted to investigate the internal flow field and classification performance of hydrocyclones under different cone angle combinations. The evolution laws of velocity field, pressure field, turbulence characteristics, and particle classification effect under different configurations were systematically explored. The results show that the basic characteristics of the core flow field of the hydrocyclone do not change essentially with the increase in the number of cone segments, but the amplitude, distribution, and stability of flow field parameters are significantly regulated. The three-cone configuration achieves the optimal flow field synergy effect: the amplitude of the high turbulence intensity zone is lower and concentrated near the central axis; the zero-velocity envelope surface is stably maintained at approximately 8 mm in the core separation zone; and the full axial fluctuation of the air core is gentle, which effectively inhibits random particle diffusion and flow pattern mixing. In terms of separation performance, the three-cone configuration exhibits the highest classification efficiency in the core range of sub-coarse particles (10~30 μm), with the cut size (approximately 17.5 μm) in a reasonable range, the steepness index reaching a peak value (approximately 0.55), and the pressure drop (approximately 1.8 × 10⁵ Pa) and split ratio (2.8%) achieving synergistic optimization, balancing separation accuracy and energy consumption control. The single-cone configuration causes flow field disturbance due to the one-time contraction of the flow channel, while the four-cone configuration falls into the dilemma of “high pressure drop–marginal performance gain”, and neither achieves optimal performance. The regulation law of the number of cone segments revealed in this study provides a scientific basis for the structural optimization and engineering application of multi-cone hydrocyclones, and is of great significance for improving the particle classification efficiency in fields such as wastewater treatment and mineral processing. Full article

Droplet size is a key factor in minimizing spray drift. Different types of adjuvants and sprayer operating pressures can affect the droplet size distribution in various ways. This study aimed to evaluate the effects of commercial adjuvants, namely, acids and surfactant (AS), silicone surfactant (SS), organosilicone surfactant (OS), mineral oil (MO and MO₂), and copolymer (CP) adjuvants, on the droplet spectra and physicochemical properties of aqueous solutions. Hydrogen potential (pH), volumetric mass ($VM$), electrical conductivity (EC), surface tension (ST), contact angle (CA), and droplet spectra were measured. The droplet spectrum variables, including volumetric diameters ($D_{v0.1}$, $D_{v0.5}$, and $D_{v0.9}$), the Relative Span Factor ($RSF$), and percentages of the total volume of droplets with a diameter smaller than 100 µm (V100) and larger than 500 µm (V500), were determined using a laser diffraction particle analyzer (Malvern Spraytec). Spraying tests were carried out using the AXI 11003 flat fan nozzle at pressures of (0.1, 0.2, 0.3, 0.4, and 0.5) MPa. The increase in pressure increased the V100 and the $RSF$, with greater sensitivity observed for SS. Adjuvants such as AS, MO₂ and OS showed a more balanced trend, with a smaller increase in fine droplets and a greater reduction in coarse droplets. The principal component analysis (PCA) revealed that the droplet spectrum variables were the ones that best explained the variation among the solutions. A negative correlation was identified between EC and other physicochemical properties, such as pH, ST, and CA. Therefore, these properties alone did not determine the atomization pattern. The study demonstrates that optimizing spray quality and minimizing drift require a combined consideration of adjuvant physicochemical properties and their interaction with operational pressure. Full article

The escalating global waste crisis necessitates sustainable valorization strategies, with biochar production emerging as a promising solution for converting organic residues into a carbon-rich material. This study evaluated biochar derived from corncob and khat waste pyrolyzed using allo-thermal and auto-thermal multi-purpose stoves. Biochar was fractionated into four particle sizes (>2 mm, 1–2 mm, 0.6–1 mm, and <0.6 mm) and characterized for ash content, pH, and electrical conductivity (EC). Results demonstrated that the auto-thermal stove, operating at higher temperatures (up to 800 °C), consistently produced biochar with greater ash content (khat: 12–19%; corncob: 11–14%), alkaline pH (9.2–10.0), and significantly higher EC compared to the allo-thermal stove (maximum 350 °C). EC values ranged from 0.38 mS/cm (coarse allo-thermal corncob) to 6.6 mS/cm (fine auto-thermal khat), with auto-thermal biochar exhibiting EC values 5–10 times higher than their allo-thermal counterparts. khat waste consistently yielded biochar with higher ash content, pH, and EC than corncob, reflecting its richer mineral composition. Particle size fractionation revealed that pH and EC increased progressively with decreasing particle size across all treatments, with the finest fraction (<0.6 mm) showing the highest values. For auto-thermal khat, EC increased from 2.43 mS/cm (>2 mm) to 6.6 mS/cm (<0.6 mm). This study demonstrates that decentralized biochar production using multi-purpose stoves can yield materials with tunable properties, and that khat waste—an underutilized regional resource—shows particular promise for producing high-ash, high-EC biochar suitable for acidic soil amendment. Full article