Minerals Engineering最新文献

The reaction of pyrite (FeS₂) with dissolved oxygen (DO) in acidic media (pH 2.5, 3.0 and 4.0) was studied at 25 °C. In this regard, a series of experimental (potentiodynamic polarization, Electrochemical Impedance Spectroscopy (EIS) or cyclic voltammetry) and theoretical (quantum calculations) approaches were used. It was found that the proton concentration ([H⁺]) has not a significant influence on the oxidative dissolution of FeS₂. The oxidation current density (j_ox) varies little when the pH increases from 2.5 (j_ox = 1.02 μA cm⁻²) to 4.0 (j_ox = 0.80 μA cm⁻²), the order of reaction with respect to [H⁺] being 0.05 ± 0.10. EIS spectra indicate that the pyrite oxidation with dissolved oxygen is controlled by a surface electron transfer reaction. The results of quantum calculations show that protons spontaneously adsorb to the pyrite surface. The density of states of adsorbed protons is located far from Fermi level (between −0.3 and −0.2 Hartree) indicating that they are not available for subsequent reactions. The results of quantum analysis outline the main reasons why protons do not play a discernible role in the oxidation of pyrite with DO and the formation of acid mine drainage.

A two-stage direct leaching method has been applied to selectively recover calcium (Ca) and vanadium (V) from electric arc furnace slag obtained from pilot-scale smelting of hydrogen-reduced iron. Nitric acid-ammonium nitrate-water (HNO₃-NH₄NO₃-H₂O) medium was used in the first stage to produce leachate in which Ca and magnesium (Mg) composed over 99 wt% of the dissolved elements. Sodium carbonate-sodium hydroxide-water (Na₂CO₃-NaOH-H₂O) and ammonium carbonate-water ((NH₄)₂CO₃-H₂O) were investigated as alternative media for the V leaching stage. The effects of the medium composition, temperature, and liquid-to-solid ratio on element recoveries and selectivity were studied for both stages with the aid of experimental designs. Regression models were fitted that could adequately reproduce the general trends in the data and allowed the optimization of the process within the studied variable space. Under optimum conditions, 55 % Ca was recovered with 91 % selectivity. In the subsequent V leaching stage, (NH₄)₂CO₃-H₂O proved to be a more promising medium, achieving V recovery of 39 % and selectivity of 90 % under the optimum conditions.

The separation of galena (PbS) from chalcopyrite (CuFeS₂) requires strong oxidants for the depression of PbS, due to the excellent hydrophobicity of PbS. In this work, an advanced oxidation process, i.e., S₂O₈²⁻/Fe²⁺ treatment, was employed to selectively depress PbS. The parameters of the S₂O₈²⁻/Fe²⁺ process were determined via flotation tests as follows: pH 3, 1:1 S₂O₈²⁻: Fe²⁺ molar ratio, and 10 min reaction time. The S₂O₈²⁻/Fe²⁺ treatment selectivity decreased the hydrophobicity of the PbS surface. UV–vis spectroscopy results revealed that SO₄⁻ (major species) and OH radicals were produced in solution by the activation of Fe²⁺. The SO₄⁻/OH radicals reacted with the PbS surface, generating the SO₄²⁻ and PbSO₄ species. These species coated the PbS surface, forming a hydrophilic PbS surface and inhibiting the PbS flotation. By contrast, the S₂O₈²⁻/Fe²⁺ treatment generated only a minimal amount of SO₄²⁻ (5.98 % of the total S species) on the CuFeS₂ surface. Therefore, the CuFeS₂ surface was hydrophobic and CuFeS₂ particles could still be floated into the foam phase. This study provides a promising method for the selective depression of PbS in the PbS-CuFeS₂ mixture.

Energy transition from fossil- to a material-intensive energy system is highly dependent on the availability of Co and Ni. This has increased interest towards non-traditional raw material streams such as mining waste. In this work, leaching experiments were conducted on historical flotation tailings with low concentrations of Co (0.081 wt%), Ni (0.055 wt%), Cu (0.15 wt%) and Zn (0.17 wt%). This low grade may challenge the feasibility of industrial operation, and therefore water, and commonly used mineral acids, were investigated as lixiviants for the process. The electrochemical leaching behaviour was studied using various oxidants (O₂, Cu²⁺, Fe³⁺ and H₂O₂). The results showed that a substantial amount of Co (21 %) and Ni (37 %) could be leached using water, with no additional oxidants or pH adjustment (80 °C, 5 min). In water leaching, the system stabilized inherently to pH=3.7 and the redox potential to E_h < 0.3 V vs Ag/AgCl. This indicates that during the 32–67 years of piling, the weathering conditions had caused natural oxidation of Co– and Ni-bearing minerals such as pyrrhotite and pentlandite. The leaching yields of Co and Ni were slightly increased (5 % units for Co, 10 % units for Ni) by introducing additional acid (1 M) into the leaching system. Further addition of oxidants did not increase the leaching yield of Co, suggesting that the dissolution of Co-bearing minerals followed the chemical leaching mechanism. In contrast, some of the Ni leaching was found to be electrochemical in nature, as extraction increased up to 63 % with the use of strong oxidative (cupric chloride) conditions – most likely due to partial chalcopyrite or pentlandite leaching. Undissolved Co and Ni remained in refractory minerals such as chalcopyrite or pyrite. In addition to Co and Ni, 52 % of Zn and 37 % of Cu were also found to be soluble under acidic conditions. When considering the use of historical flotation tailings as a feed stream in hydrometallurgical processing, direct water leaching may provide an attractive and robust leaching strategy, with spontaneous inherent pH adjustment. An increase in solid-to-liquid ratio or solution circulation (higher acidity) could increase percentual Co and Ni yield and enable enrichment of the target metals in the pregnant leach solution (PLS). If flotation is considered for concentration of Co– and Ni-bearing minerals, water leaching prior to flotation is recommended, to improve both the flotation performance and overall flotation and metal recovery.

The inherent similarities in the physicochemical properties and floatability of specularite and chlorite pose challenges in their effective flotation separation. Exploration and utilization of efficient depressants is vital to improve the flotation separation performance. In this study, pullulan gum (PG) was employed as a depressant in the flotation separation of specularite and chlorite, employing dodecylamine (DDA) as a collector. PG’s inhibitory impact on the flotation performances of these minerals was evaluated through extensive flotation tests and systematically explored its inhibiting mechanism via various surface analytical measurements. Flotation experiments revealed that PG significantly depressed the floatability of specularite while exerting minimal effect on chlorite. Zeta potential tests and surface wettability analyses illustrated strong adherence of PG to specularite, hindering subsequent DDA adsorption, while its impact on DDA adsorption onto chlorite was negligible. Additionally, adsorption capacity measurements confirmed markedly higher PG adsorption onto specularite than chlorite. Further analyses via Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations indicated weak adsorption of PG on chlorite, contrasting with strong chemical adhesion observed between PG and specularite. This disparity resulted in distinct flotation behaviors of these minerals. Consequently, selective depression of specularite flotation and effective flotation separation from chlorite were achieved. Thus, PG emerges as an efficient and eco-friendly depressant, showcasing promise in enabling the flotation-based separation of specularite and chlorite.

The current suite of algorithms used in intelligent mineral sorting equipment is largely generic, lacking the necessary adaptability and the capability for simultaneous non-destructive structural detection and quantitative analysis. To address this, we have developed two specialized algorithms based on X-ray absorption spectroscopy: the Trans-LSTM algorithm based on Transformer and Long Short-Term Memory(LSTM), utilizing knowledge distillation for rough mineral sorting, and the RNN-overhead-xgboost algorithm based on Recurrent Neural Network(RNN) for fine mineral sorting. We collected 3000 X-ray absorption spectra from 15 types of minerals with similar appearances or compositions. We compared the performance of these proposed algorithms with three other general-purpose algorithms for mineral spectral classification. Our study specifically examined the impact of Trans-LSTM on rough mineral sorting and the effect of RNN-overhead-xgboost on fine mineral sorting. In the rough sorting stage, the Trans-LSTM model demonstrated a prediction time of just 0.0171 s per sample, maintaining a classification accuracy of 93.49%, thereby ensuring high precision with high efficiency. During the fine sorting stage, the RNN-overhead-xgboost algorithm significantly improved sorting accuracy to 99.21%, highlighting its effectiveness in achieving precise sorting. These findings underscore the potential of the Trans-LSTM and RNN-overhead-xgboost algorithms to enhance the adaptability and accuracy of intelligent mineral sorting systems, meeting the specific demands of different stages in mineral production.

Hyperspectral imaging (HSI), a promising technique integrating imaging and spectroscopy, can help sort iron ores with different total iron (TFe) contents. However, the adhesion of dust (caused by crushing) or water can affect the sorting process. Currently, the mechanisms underlying this influence and methods to conveniently mitigate it remain unclear, hindering the practical application of HSI-based sorting. This study aimed to investigate this issue. For the experimental materials, 300 ore samples (particle size: 20–40 mm) with different TFe contents were prepared. Subsequently, three sample conditions were prepared (“No dust, no water”, “With dust, no water” and “No dust, with water”) through washing and drying measures, and their hyperspectral images were acquired (953–2517 nm). Finally, the TFe content of each ore sample was measured. After preprocessing, the effects of water and dust on the spectra and sorting process were initially analyzed. Subsequently, a new spectral differential feature considering dust and water (DFDW) was proposed to mitigate this influence. Then, using the spectral and calculated proportion features as input, different grades of iron ore were classified into four classes using a machine learning classifier. For validation, models using several different input features and machine learning classifiers were tested for classification accuracy (the ratio of correctly predicted instances to the total number of predictions). On “No dust, no water”, “With dust, no water” and “No dust, with water” data, the model DFDW-random forest (RF) achieved accuracies of 87.7 %, 85.0 %, and 85.3 %, respectively, which was optimal. Overall, the results enhance the universality of HSI-based iron ore sorting and provide technical support for its practical implementation.

In the minerals industry, froth flotation is a commonly used method for separating valuable minerals from gangue. The design and efficient operation of flotation cells require a knowledge of the interplay between the system hydrodynamics and its chemistry. These parameters however are often examined in isolation using bare bubbles due to the system complexity. This study aims at investigating the coupled effect of surfactant and turbulence on the rising dynamics of particle-laden bubbles of different bubble surface loadings. Specifically, the rise velocity and trajectories of particle-laden bubbles with bubble surface loadings of 0–87 % were examined in presence of methyl isobutyl carbinol surfactant in a near isotropic turbulent flow generated by oscillating grids. Particle-bubble aggregates were formed using a microfluidics T-Junction-based approach to attach coarse glass bead particles of 316 µm in size to bubbles with a diameter of 2.15 mm. The rising dynamics of the particle-laden bubbles were captured using a high-speed camera. The collected data on rise velocities and trajectories were then benchmarked against the rising behaviour of particle-laden bubbles in a quiescent water with no surfactant.

The experimental results showed that, in a quiescent water, addition of methyl isobutyl carbinol surfactant reduces the mean bubble rise velocity at low bubble surface loadings of less than 13%. At bubble surface loadings greater than 13%, the effect of methyl isobutyl carbinol surfactant on the bubble rise velocity was found to be negligible. The increased bubble surface immobility due to an increase in the bubble surface loading is believed to be responsible for the observed behaviour. Turbulence in the absence of surfactant on the other hand, consistently led to an increase in bubble rise velocity over the examined conditions.

Under the coupled effect of surfactant and turbulence conditions, the particle laden bubbles with bubble surface loadings greater than 13% exhibited an overall increase in the rise velocity indicating that turbulence was the governing factor at higher bubble surface loadings. At lower bubble surface loadings however, surfactant proved to counteract the effect of turbulence on the rise velocity, leading to an overall reduction of the velocity at loading below 13%.

In the absence of turbulence, the particle laden bubbles follow a path that is closer to rectilinear as the bubble surface loading increased or surfactant was added. This is the artefact of a reduction in bubble oscillation due to an enhanced bubble surface immobility. However, in presence of turbulence the trajectory of the particle-laden bubble was found to be generally non-rectilinear, due to stochastic interactions with the turbulent flow. The effect of surfactant on particle laden bubble trajectory was found to be negligible in turbulent flow conditions.

Copper mining produces immense amounts of tailings due to low ore grades. These residues are increasingly dewatered by filtration in recessed plate filter presses to ensure safer storage and high recovery of water. The process parameters filtration pressure, desaturation time, desaturation pressure and cake thickness have a significant influence on achieving water content as well as bulk material stability specifications and maintaining operation performance, especially with regard to cake detachment. In this study, copper tailings filtration tests in a laboratory filter press and directly connected measurements of cake-to-fabric shear adhesion as well as filter cake shear cohesion were carried out. It is shown that optimization of cake properties with regard to residual water content, suitability for detachment and bulk material stability by specific adjustment of the filtration and post-treatment parameters is possible. Furthermore, implementation of a mathematical model allows water content, cake saturation, cake-to-fabric shear adhesion and cake shear strength prediction dependent on filter cake desaturation time and pressure for tailings filtration applications in recessed plate filter presses.

The refractory metals tungsten, tantalum and niobium are considered critical raw materials in Europe. Diversifying the supply of such materials, for instance by recovering refractory metals from local low-grade ore materials could reduce their supply risks. However, the extraction processes require to be efficient with a low energy and material consumption and a minimal environmental impact. In this work, microwave (MW) assisted alkaline fusion was explored to extract tungsten from scheelite containing ore materials with different grades (high to very low) and tantalum and niobium from a columbite-tantalite [(Fe,Mn)(Nb,Ta)₂O₆] concentrate. During the fusion process scheelite was converted into soluble alkali tungstate salts [Na₂WO₄, K₂WO₄ and/or K₃Na(WO₄)₂] and the reaction temperature could be lowered to 150–200 °C by fusion with a low-melting eutectic alkali salt system of an 1:1 (m/m) NaOH:KOH mixture. The application of MW-assisted heating allowed for fast and volumetric heating, thereby lowering reaction times to 10 min – 30 min. After fusion, tungsten was extracted by a simple water leaching step leading to extraction efficiencies ranging from 77 % to 97 %. Noteworthily, also P, S and As, which all form soluble oxyanions were extracted from the studied materials. Extraction of niobium and tantalum was also achieved though MW-assisted alkaline fusion as an alternative to acidic fluorine-based hydrometallurgical processes. MW-assisted heating allowed for a fast conversion of the (Fe,Mn)(Nb,Ta)₂O₆ into alkali tantalate and niobate salts. Under optimal conditions, MW-assisted fusion with KOH (salt:sample = 3:1 (m/m)) at 400 °C for 10 min leached ca. 74 %–88 % of tantalum and 77 %–86 % of niobium into water (L/S=10) at 40 °C for 120 min, while the main matrix elements Mn and Fe displayed limited dissolution (<4%). Due to the low solubility of sodium tantalate and niobate salts in water, MW-assisted alkaline fusion in an eutectic NaOH:KOH mixture followed by water leaching was not efficient.