Search Results (1,214)

The conventional sulfidization–xanthate flotation of oxide copper minerals is often limited by reagent consumption and the mismatch between surface generation and sulfidization when sulfidization is carried out only during flotation conditioning. To address these limitations, this study proposes an in situ sulfidization strategy during the grinding stage and investigates the combined regulation of grinding media (conventional steel vs. 18% Cr cast iron) and atmosphere (ambient air vs. N₂ purging) on the flotation of a synthetic malachite–dolomite ore. Real-time pulp chemistry monitoring and ethylenediaminetetraacetic acid (EDTA) extraction indicate that the conventional grinding environment has two main disadvantages: Fe dissolution from steel media increases Fe-related surface contamination, while the air-ground pulp promotes the oxidation and consumption of active sulfidizing species. The combined use of high-Cr media and an N₂ atmosphere improved the chemical environment for grinding-stage sulfidization. Specifically, the high-Cr media reduced Fe release and associated surface contamination, while N₂ purging shifted the pulp to a lower-potential environment that was more favorable for preserving active sulfide species. Under standardized reagent conditions, the optimized in situ sulfidization protocol increased copper recovery from 29.79% to 57.47% and improved the concentrate grade from 9.71% to 11.11%. These results suggest that regulating the grinding environment can enhance in situ sulfidization flotation of malachite by reducing Fe interference and controlling pulp redox conditions, providing useful guidance for the efficient beneficiation of oxide copper minerals. Full article

Worm grinding is an effective approach for the precision manufacturing of face gears. However, pitch deviation and tooth thickness deviation inevitably arise during the grinding process. To reduce these deviations, this study proposes a compensation method applicable to complex topological surfaces in face gear grinding. Based on the structural configuration of a CNC face gear grinding machine, the dressing path of the grinding worm using the dressing wheel is first planned, followed by the generation of the grinding path for the face gear. Considering the tooth surface characteristics of the face gear, evaluation methods for single pitch deviation, cumulative pitch deviation, and tooth thickness error are established. The linkage polynomial method of the CNC machine tool is then employed to optimize the face gear grinding path and compensate for pitch deviation. Subsequently, a meshing tooth surface mapping method between the grinding worm and the face gear is developed to compensate for tooth thickness deviation. A compensation case study is conducted to verify the proposed method. The results indicate that the proposed compensation strategy effectively reduces both pitch and tooth thickness deviations in the face gear, with reduction rates ranging from 48.57% to 96.80%. Full article

This study examines the impact of regrinding on the interfacial properties of sulfide minerals and the flotation performance of weathered copper–porphyry tailings. The feed material is characterized by a low copper grade (0.17%) and a high proportion of oxidized species (53.84%), which contribute to its inherent chemical stability and poor flotation kinetics. The findings indicate that regrinding serves a dual role: facilitating the liberation of mineral intergrowths and inducing mechanical surface renewal. This renewal is characterized by a significant decrease in the oxidation–reduction potential (ORP) and an intensification of the surface reactivity. Experimental results identify an optimal grinding fineness of 77%–81% passing −0.045 mm, yielding a copper recovery of 16.26% in the absence of a sulfidizing agent. The integration of sodium sulfide (400 g/t) with regrinding significantly enhances recovery to 36.37%, driven by the establishment of a reducing environment (ORP ≈ −150 mV) and the chemisorption-mediated activation of mineral surfaces. While ultrafine grinding (90%–100% passing −0.045 mm) further increases recovery to 51.47%, it is accompanied by deleterious sliming effects and a subsequent loss of process selectivity. The study confirms that mechanical surface rejuvenation and the optimization of electrochemical conditions are critical for improving the processing efficiency of anthropogenic resources, providing a theoretical framework for establishing rational beneficiation regimes. 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

This study investigates the influence of the spatial distribution of specific grinding power within the contact zone on subsurface layer modification and the resulting modification depth effects. In surface grinding experiments on AISI 4140, the width of cut and depth of cut were deliberately modified to generate distinct thermal loads within the grinding contact zone, with simultaneous measurement of tangential and normal grinding forces to quantify the mechanical loading conditions. The distribution of specific grinding power was analyzed with respect to its localization along the contact length and across the width of cut. The results indicate a predominantly uniform distribution of grinding power density within the contact zone under the investigated process conditions. Subsurface integrity was characterized in terms of tempering effects in metallographic cross-sections, hardness and residual stress depth profiles. These findings were correlated with Barkhausen noise measurements to establish a non-destructive assessment methodology for thermally induced modifications. Also, roughness measurements were evaluated. The experimental results reveal a consistent relationship between specific grinding power input and subsurface modification depth. Furthermore, a uniform grinding burn threshold was identified, indicating a critical condition for thermally induced surface damage. Full article

The global proliferation of plastic waste has made the search for sustainable chemical recycling strategies imperative to transition toward a circular bioeconomy. This study presents a dual-valorization approach for polylactic acid (PLA) waste, utilizing it both as a sustainable precursor for g-C₃N₄ catalyst synthesis and as a sacrificial agent for green hydrogen production via photoreforming. Platinum-modified graphitic carbon nitride catalysts were synthesized and evaluated using pure lactic acid and commercial PLA waste under solar-simulated irradiation. Results identified C₃N₄-NaOH-Pt as the most active material, while the simultaneous one-pot depolymerization/photoreforming of macroscopic PLA fragments exhibited a peak H₂ production rate of 1.5 mmol·h⁻¹·g⁻¹, remarkably surpassing both the pure monomer model and pre-depolymerized solutions. This enhanced performance is tentatively attributed to a “controlled release” mechanism that prevents catalyst surface saturation and minimizes light scattering effects inherent to fine powders. The study concludes that maintaining the macroscopic integrity of PLA waste provides a strategic advantage for chemical reforming by eliminating energy-intensive grinding and pretreatment. Future research into diverse operational and chemical parameters, including temperature and base-addition strategies, will be essential for scaling solar-driven upcycling technologies. Full article

To address the pervasive engineering challenges of rigid interference and subpar machining efficiency encountered during the complex freeform surface polishing of P20 mold steel, this study proposes and fabricates a structurally designed, five-petal composite compliant polishing tool via fused granulation fabrication (FGF). The tool structurally integrates a passive thermoplastic polyurethane (TPU) compliant buffer layer with an active PA66/diamond micro-cutting functional layer, achieving monolithic precision assembly through dual-temperature-zone 3D printing. Tensile mechanical characterization (n = 6) reveals that the composite interface attains an average ultimate tensile strength (UTS) of 59.39 ± 15.41 MPa (with a peak of 78.90 MPa) and an average elongation at break of 27.42 ± 7.41%, demonstrating exceptional structural robustness and fracture toughness under heavy-load abrasive machining conditions. During adaptive polishing validations on complex convex topographies and deep concave mold cavities, the compliant tool effectively compensated for normal vector spatial errors intrinsic to three-axis CNC machining via passive geometric adaptation. Topographical evaluations suggest a ductile-regime, differential asperity planarization material removal paradigm, which is attributed to the macroscopic 3D elastic deformation of the tool synergized with the proposed compliance of the polymer matrix. Following high-intensity sequential polishing regimens, the original macroscopic milling striations were substantially reduced. Quantitative profilometric analysis reveals that the average surface roughness of the convex profiles decreased from an initial 13.33 µm to 7.42 µm, while that of the restrictive deep concave features was reduced from 10.84 µm to 4.11 µm. Ultimately, this technological framework circumvents the traditional reliance on capital-intensive, six-degree-of-freedom robotic platforms, providing a scalable automated polishing protocol compatible with standard CNC systems for the cost-effective surface planarization of precision molds. Full article

This study presents the design, development, and experimental validation of an automated flat blade grinding machine for the wood processing and plastic recycling industries in Ecuador. The machine was engineered following the VDI 2221/2222/2225 design methodology, integrating SolidWorks-based 3D modeling and ANSYS finite element analysis (FEA) to validate critical structural components. The selected configuration includes a Type 6 alumina grinding wheel (38A-60-K-VS), a mechanical clamping system, cutting fluid cooling, and a hardwired electromechanical control system that does not require a programmable logic controller (PLC). FEA results confirmed adequate safety factors (ηs > 16; ηf > 14) for the ACME 3/4–8 power screw under operational loads. Experimental testing on blade specimens (thickness: 3 mm; length: 70 mm; steel up to 60 HRC) demonstrated that four grinding passes at a 45° inclination angle reduced mean surface roughness (Ra) from 5.39 ± 1.83 µm (used blades) to 0.162 ± 0.092 µm, achieving values comparable to new blades (Ra = 0.601 ± 0.153 µm): a point-estimate reduction of 97% in mean Ra relative to the used-blade condition. The automated process reduced average grinding time by approximately 30% compared to manual methods, while maintaining noise levels within the 85 dB occupational exposure limit. Operator satisfaction surveys rated the system above 4.5/5.0 across all ergonomic and usability criteria. These results validate the proposed machine as a cost-effective, locally manufacturable solution to standardize blade maintenance in small and medium enterprises (SMEs) across Latin America. Full article

The workability of abrasive tools for precision grinding is significantly affected by the quality of active surface of grinding wheel in terms of the number, form, and sharpness of active abrasive grains. The aim of this study is to introduce a method for optimizing the abrasive tools based on active surface topography analysis, tool wear diagnostics, and numerical simulation of micro-cutting by one active grain and abrasive aggregate. Particular attention is given to the Shos parameter, which characterizes the machining potential of a grinding wheel by combining information on the height and sharpness of active abrasive grain vertices. Changes in this parameter allow observation of the blunting and wear of the active surface. Numerical simulation shows that material removal by one active grain and by an abrasive aggregate differs significantly. According to the obtained data, under the assumed micro-cutting conditions, the aggregate geometry reduced lateral material displacement and promoted chip formation. The coefficient of material removal efficiency for aggregate was equal to kr = 0.93 compared to kr = 0.37 for one grain. Therefore, abrasive aggregates have an effect on the material removal process and may support the improvement of the stability of precision grinding. Thus, it can be concluded that further improvements in abrasive tools require considering controlled active surface structures and abrasive aggregates, as well as diagnostic parameters that relate tool topography to wear and machining efficiency. Full article

To improve the form accuracy of spherical surfaces generated by cup-wheel grinding, this paper presents a geometric modeling and error compensation method for concentric grinding of spherical surfaces. A cup-shaped arc grinding wheel, hereafter referred to as a cup wheel, is used as the grinding tool. The relative motion between the cup wheel and the workpiece is formulated so that the contact arc center of the wheel follows a trajectory that is concentric with the target spherical surface. Based on this principle, trajectory models for both convex and concave spherical surfaces are established, and the geometric constraints for cup-wheel dimension selection are analyzed. To compensate for tool-setting errors and wheel-wear-induced deviations, a central-peak-based error compensation model is further developed. Grinding experiments on a convex spherical sample were conducted to verify the proposed trajectory and compensation models. The results show that the form error PV value was reduced from 57.7 μm to 0.3 μm after compensation, demonstrating the effectiveness of the proposed model in improving spherical form accuracy. Full article

Pisha sandstone (PS) has potential as a low-cost adsorbent due to its abundant surface-active adsorption sites. In this work, mechanical grinding coupled with high-temperature calcination was employed to activate and modify raw PS for improved chloride ion adsorption performance and efficient resource utilization. Adsorption kinetic experiments demonstrated that the PS modified via 15 min of mechanical grinding (PSM15) exhibited the optimal chloride adsorption performance and achieved adsorption equilibrium within 240 min. The adsorption kinetics data were well fitted by the pseudo-second-order model, indicating that chemisorption dominates the chloride adsorption process. The chloride removal efficiency of PSM15 reached a maximum value of 33.3%, which was superior to that of calcined PS (30.1%) and raw PS (23.6%). Combined characterization results from XRD, FTIR, and SEM-EDS revealed that mechanochemical activation does not alter the main crystalline phases of the material. Instead, it significantly enhances chloride adsorption capacity by refining crystallite size, exfoliating layered microstructure, and exposing surface active sites. Moreover, the in situ formation of C–S–H gel reinforces chloride immobilization via physical encapsulation and electrostatic attraction. Collectively, the enhanced chloride adsorption by modified PS can be attributed to synergistic mechanochemical activation, surface and interlayer retention, and gel-mediated immobilization. As a low-cost and eco-friendly adsorbent, the PS-based cementitious material shows promising application potential in chloride-containing wastewater purification. Full article

The efficient removal of tenacious oxide scales from hot-rolled steel surfaces represents a persistent challenge in advanced manufacturing, as traditional manual grinding methods exhibit poor efficiency and environmental compatibility. This investigation develops an innovative methodology, i.e., a “coarse-to-fine” hierarchical cleaning paradigm consisting of dual-stepwise laser cleaning with variable parameters that successfully addresses the restrictive process window inherent to conventional single-parameter techniques. Through a strategically designed sequential treatment protocol—employing initial low-frequency (20 kHz), high-energy-density (200 mm/s) laser irradiation for primary oxide ablation, succeeded by high-frequency (60 kHz), low-energy-density (4000 mm/s) processing for residual scale elimination—we demonstrate an optimal synergy between ablative and thermomechanical vibration mechanisms. Rigorous multi-modal characterization incorporating SEM-EDS microscopy, oxygen content quantification, and metallographic analysis confirms exceptional performance metrics, including 98.7% oxide removal efficiency and 43.2% reduction in substrate surface roughness relative to standard methods. The developed protocol achieves a 2.8-fold expansion of the operational parameter space while establishing a novel “coarse-to-fine” hierarchical cleaning paradigm. These findings offer fundamental insights into laser–matter interactions while delivering a transferable technological framework for high-value manufacturing sectors, particularly in automotive and aerospace component production. Full article

Direct cyanide leaching of high-carbon gold ores typically results in poor gold extraction due to the “preg-robbing” effect of carbonaceous matter. This study investigates a refractory high-carbon gold ore from Laos. Based on detailed process mineralogy that identified the occurrence state of gold and the distribution of harmful impurities, a combined process consisting of flotation pre-concentration, oxidative roasting, and a Mill–Leach Coordination (MCL) process was developed. The MCL process, which integrates simultaneous grinding and leaching, continuously renews the particle surface and eliminates product-layer diffusion resistance, thereby significantly enhancing gold dissolution efficiency. Kinetic studies demonstrate that the leaching reaction follows the Avrami model and is controlled by internal diffusion, with a derived semi-empirical kinetic equation. This research provides a novel and efficient technical route for treating high-carbon gold ores and offers theoretical guidance for industrial scale-up. Full article

Rust removal on pipe surfaces is hazardous and labor-intensive, yet it is a prerequisite for inspection and recoating in maintenance. Existing solutions rely on industrial robots or specialized robots with limited obstacle-negotiation capability and cable entanglement risks. This work presents a Robotic Pipe Grinding System (RPGS) for straight pipes and focuses on the latest generation, RPGS-III. Driven by a single motor, RPGS-III integrates cutter self-rotation, revolution about the pipe axis, and axial translation through planetary-gear and bevel-gear transmissions. Passive mechanisms enable adaptation to different pipe diameters, obstacle negotiation, and dust containment during grinding. Kinematic and static analyses, motion simulations, and prototype experiments were conducted to validate the system, with feasibility demonstrated through in situ maintenance tests. The validated design demonstrates a practical solution for automated pipe maintenance in field environments, reducing actuation complexity while maintaining operational effectiveness. Full article

This study investigates the influence of normal and cryogenic grinding on the antioxidant properties and bioactive compound profiles of fennel seed (Foeniculum vulgare) powder at varying particle sizes. Methanolic and ethanolic extracts were evaluated for DPPH radical scavenging activity (AAO), total phenolic content (TPC), and total flavonoid content (TFC) using conditions optimised through Response Surface Methodology (RSM) employing an I-optimal quartic design. Statistical analysis confirmed that grinding type and solvent type were the dominant factors influencing all three responses, with their interaction significantly governing flavonoid content recovery. The optimal extraction conditions were identified as cryogenic grinding, methanol as solvent, and a particle size of 200 µm, with an overall desirability of 0.887. Validated experimental values under these conditions were AAO = 87.11%, TPC = 11.31 mg GAE/g, and TFC = 14.18 mg QE/g, with prediction errors within ±5% of model-predicted values confirming the robustness of the developed models. HRLC-MS analysis confirmed that cryogenic grinding preserves a broader and more concentrated phytochemical profile compared to normal grinding. These findings demonstrate that cryogenic grinding combined with methanol extraction at fine particle sizes significantly enhances the yield of antioxidant-rich phytochemicals from fennel seeds, supporting their potential application in functional food and nutraceutical development. Full article