Motion behavior of particles in air–solid magnetically stabilized fluidized beds for separation

In order to study the settling mechanism of particles in an air–solid magnetically stabilized fluidized bed (MSFB) for separation, we carried out free settling and quasi-zero settling tests on the tracing particles. The results show that the main resistance forces as the tracing particles settled in an air–solid MSFB were motion resistance force and yield force. The motion resistance and yield forces greatly hindered the free settling of the particles by greatly decreasing the acceleration for settling process of the particles. The acceleration decreased from 3022.62 cm/s² to zero in 0.1 s, and in the end, the particles stopped in the air–solid MSFB. The yield force on particles increased with increasing the magnetic field intensity, resulting in decrease of the quasi-zero settling displacement. However, the yield force on particles decreased with increasing the fluidized air velocity, leading to increase of the quasi-zero settling displacement. When the structure and operating parameters of the air–solid MSFB were set up, the yield stress on particles stopped in an air–solid MSFB was a function of diameter and density of particles. The settling displacements of equal diameter particles increased with increasing their densities, and the settling displacements of equal density particles increased with increasing their diameters.     

Pretreatment of highly turbid coal mine drainage by a chemical agent free filtration system

A filtration system used without chemical agents for the pretreatment of turbid coal mine drainage is described in this paper. The influence of different aperture sizes and different motor speeds was investigated during the study. The experimental results show that for aperture diameters of 0.4, 0.6, or 0.8 mm smaller apertures provide more complete filtration. Rotations of 12, 20, 28, or 40 r/min show that higher speeds give more efficient filtration. Suspended solids decreased in both particle size and concentration after the filtration. The separated slime can be directly reused as a fuel. Efficient filtration pretreatment systems for coal mine drainage were investigated and the economic feasibility is analyzed in this article.     

Liberation characteristics of coal middlings comminuted by jaw crusher and ball mill

The associated minerals make coal middlings possess a relatively high ash content. Subsequent liberation through size reduction can cause recovery increase. However, effect of comminution facilities on mineral liberation of middlings was ignored. This paper studied the liberation characteristics of middlings crushed with different kinds of fragmentation forces. Middlings of ?3 mm + 0.5 mm sampled from a dense medium cyclone were comminuted by a jaw crusher and a ball mill to ?0.5 mm with similar size distribution respectively. The generating mechanism of fines was also analyzed. Full densimetric analyses indicate that mineral liberation of the product crushed by the jaw crusher is better than that by the ball mill at each fraction. For sizes of ?0.125 mm + 0.074 mm and ?0.074 mm, yields of the product with ash content 11% comminuted by jaw crusher are nearly 20% higher than that by the ball mill. Sectional micrographs observed by the scanning electron microscopy (SEM) also show the same law for these two fractions and some intergrowth particles still exist in the fraction of ?0.5 mm + 0.25 mm.     

Nano-microbubble flotation of fine and ultrafine chalcopyrite particles

As is well known to mineral processing scientists and engineers, fine and ultrafine particles are difficult to float mainly due to the low bubble-particle collision efficiencies. Though many efforts have been made to improve flotation performance of fine and ultrafine particles, there is still much more to be done. In this paper, the effects of nano-microbubbles (nanobubbles and microbubbles) on the flotation of fine (−38 + 14.36 μm) and ultrafine (−14.36 + 5 μm) chalcopyrite particles were investigated in a laboratory scale Denver flotation cell. Nano-microbubbles were generated using a specially-designed nano-microbubble generator based on the cavitation phenomenon in Venturi tubes. In order to better understand the mechanisms of nano-microbubble enhanced froth flotation of fine and ultrafine chalcopyrite particles, the nano-microbubble size distribution, stability and the effect of frother concentration on nanobubble size were also studied by a laser diffraction method. Comparative flotation tests were performed in the presence and absence of nano-microbubbles to evaluate their impact on the fine and ultrafine chalcopyrite particle flotation recovery. According to the results, the mean size of nano-microbubbles increased over time, and decreased with increase of frother concentration. The laboratory-scale flotation test results indicated that flotation recovery of chalcopyrite fine and ultrafine particles increased by approximately 16–21% in the presence of nano-microbubbles, depending on operating conditions of the process. The presence of nano-microbubbles increased the recovery of ultrafine particles (−14.36 + 5 μm) more than that of fine particles (−38 + 14.36 μm). Another major advantage is that the use of nano-microbubbles reduced the collector and frother consumptions by up to 75% and 50%, respectively.     

Modeling industrial thickener using computational fluid dynamics (CFD), a case study: Tailing thickener in the Sarcheshmeh copper mine

Separation of particles from liquid in the large gravitational tanks is widely used in mining and industrial wastewater treatment process. Thickener is key unit in the operational processes of hydrometallurgy and is used to separate solid from liquid. In this study, population balance models were combined with computational fluid dynamics (CFD) for modeling the tailing thickener. Parameters such as feed flow rate, flocculant dosage, inlet solid percent and feedwell were investigated. CFD was used to simulate the industrial tailing thickener with settled bed of 120 m diameter which is located in the Sarcheshmeh copper mine. Important factor of drag force that defines the rake torque of rotating paddles on the bed was also determined. Two phases turbulence model of Eulerian/Eulerian in accordance with turbulence model of k-ε was used in the steady-state. Also population balance model consists of 15 groups of particle sizes with Luo and Lehr kernel was used for aggregation/breakage kernel. The simulation results showed good agreement with the operational data.     

Effect of the column height on the performance of liquid–solid fluidized bed for the separation of coarse slime

A liquid–solid fluidized bed separator, used for the separation of coarse slime, was developed. Test particles sized in the range from 0.25 to 0.5, 0.5 to 1.0, and 0.25 to 1.0 mm were separated in the liquid–solid fluidized bed. Beds with column heights of 1200, 1500, and 1800 mm were tried. The clean coal and the tailings were subsequently analyzed by float–sink testing. The results showed that the ash and yield of clean coal both decreased with increasing column height, for all three size fractions, and that the ash of the clean coal obtained from tests on the broader size fraction was less than that from the narrower sized fractions. The separation density decreased with increasing column height. The lowest E value was seen for a column height of 1500 mm, for which conditions the separation density was 1.45 g/cm³. The E value was 0.084 for the 0.25–0.5 mm fraction but the corresponding separation density was 1.48 g/cm³, and the E value 0.089, for the broader 0.25–1.0 mm fraction.     

Application of response surface methodology and central composite rotatable design for modeling the influence of some operating variables of the lab scale thickener performance

This study discussed the application of response surface methodology (RSM) and central composite rotatable design (CCRD) for modeling and optimization of the influence of some operating variables on the performance of a lab scale thickener for dewatering of tailing in the flotation circuit. Four thickener operating variables, namely feed flowrate, solid percent, flocculant dosage and feedwell height were changed during the tests based on CCRD. The ranges of values of the thickener variables used in the design were a feed flowrate of 9–21 L/min, solid percent of 8%–20%, flocculant dosage of 1.25–4.25 g/t and feedwell height of 16–26 cm. A total of 30 thickening tests were conducted using lab scale thickener on flotation tailing obtained from the Sarcheshmeh copper mine, Iran. The underflow solid percent and bed height were expressed as functions of four operating parameters of thickener. Predicted values were found to be in good agreement with experimental values (R² values of 0.992 and 0.997 for underflow solid percent and bed height, respectively). This study has shown that the RSM and CCRD could efficiently be applied for the modeling of thickener for dewatering of flotation tailing.     

DEM simulation of particle flow on a single deck banana screen

A mathematical study of particle flow on a banana screen deck using the discrete element method (DEM) was presented in this paper. The motion characteristics and penetrating mechanisms of particles on the screen deck were studied. Effects of geometric parameters of screen deck on banana screening process were also investigated. The results show that when the values of inclination of discharge and increment of screen deck inclination are 10° and 5° respectively, the banana screening process get a good screening performance in the simulation. The relationship between screen deck length and screening efficiency was further confirmed. The conclusion that the screening efficiency will not significantly increase when the deck length L ? 430 mm (L/B ? 3.5) was obtained, which can provide theoretical basis for the optimization of banana screen.     

Experimental research on inorganic solidified foam for sealing air leakage in coal mines

In order to efficiently seal air leakages and control spontaneous combustion of coal, solidified foam was developed by adding a certain compound additive to fly coal ash and cement as the main materials. It was prepared basing on the foaming characteristic through physical and mechanical system. We studied the effects of the different types of foaming agents, the mass ratio of cement to fly ash, and the mass ratio of solid to water and content of cellulose on the performance of solidified foam. The results show that when adding the composite protein, surfactant and cellulose foaming agents. The cement-fly ash ratio of 0.75:1, the water solid ratio as large as 2:1, and the solidified foam with high properties and density of only 516 kg/m³ and compressive strength of up to 12.68 MPa were prepared. But the initial setting time, identity and compressive strength may be changed by varying the water solid ratio and/or the additives. We theoretically analyzed the influence mechanism of foam density, compressive strength and water solid ratio. The solidified foam is especially suitable for sealing surface leakage channels and filling the goaf with a wide application prospects.     

Modification and separation of oil sand with ultrasonic wave and analysis of its products

Under the condition of ultrasonic wave heating, the ground oil sand from Daqing oilfield was preprocessed with compound modification reagent. In order to separate oil and sand, flotation machine is used and orthogonal test is carried out to optimize the process conditions. The test results show that under the conditions of modification reagent concentration of 10.0 g/L, ultrasonic wave intensity of 53 kHz, power of 75 kW, temperature of 50 °C and duration of 10 min, the Daqing ground oil sand with the initial oil content of 30.80% can be transformed into dry sludge with a sharply reduced residual oil content of 0.66% after being preprocessed with ultrasonic wave and separated by flotation machine. The solid particle size compositions and major components were analyzed with a laser particle size analyzer and X-ray analyzer (LS-100Q), and GC-MS as well as FITR were adopted to analyze the oil phase. The mechanism of action of intensifying separation of oil sand with the effect of ultrasonic wave was analyzed.     

Controlling the coal dust at transshipment point: A study of the foam-sol foaming device

In order to effectively control the dust at the transshipment point with foam-sol, this paper attempted to study the characteristics of dust diffusion at transshipment point and the foam-sol foaming device with diffusion outlet was also designed in this paper. To study the diffusion rules of coal dust, fluent discrete phase model was utilized in the numerical simulation, as the coal dust was thrown down at a horizontal velocity of 2.5 m/s. A foam-sol foaming device was designed, through which foaming agent could be automatically sucked into the Venturi by the negative pressure. The automatic controller was also equipped, which could transform the energy of the compressed air into the constant pressure difference so that the gelling agent could be qualitatively added into the gel container. The diffusion outlet that could spray out foam-sol in a continuous, conical and 3D manner was also designed. Moreover, this paper also carried out the contrast experiments on dust removal efficiency among water, aqueous foam and foam-sol. The results clearly show that the symmetrical whirlpools appeared below the inlet where the largest whirlpool diameter was 0.52 m, and the horizontal distance from swirl range to the inlet was approximately 0.69 m. By using the self-designed foaming device, the foaming was multiplied by 30 times and the volume ratio with water and foaming agent reached 95%:5%. In this context, the gas pressure was controlled at 0.3 MPa, with gas flow at 15 m³/h and water flow at 0.5 m³/h, with water pressure controlled between 0.34 and 0.36 MPa. The foam-sol has the highest dust removal efficiency than other agents.     

Determination of the desiccation behavior of clay slurries

The main objective of this study was to determine the desiccation behavior of clay slurries. A clay slurry with high water adsorption capacity(W_L = 180%,W_P 60%,W_s = 20) was used to determine the soil water characteristic curve(SWCC), shrinkage curve, and hydraulic conductivity. The last parameter was determined similar to the Instantaneous Profile Method using evaporation tests. Results indicated that the clay slurry had an air entry value(AEV) of 1000 kPa and a residual suction of 5000 kPa that occurred at the plastic limit and the shrinkage limit, respectively. The discrepancy between theoretical and measured shrinkage limit was due to the gradual increase in clay particle contact. Unlike soils, the saturated hydraulic conductivity varied by two orders of magnitude(4×10 ~10 m/s at 20 kPa to 3 x 10 ~12 m/s at AEV). The unsaturated k further decreased to 10 ~14 m/s at 6 x 10~4 kPa beyond which vapor flow took place.     

Modeling and process optimization for microbial desulfurization of coal by using a two-level full factorial design

The microbial sulfur removal was investigated on high sulfur content (1.9%) coal concentrate from Tabas coal preparation plant. A mixed culture of ferrooxidans microorganisms was isolated from the tailing dam of the plant. Full factorial method was used to design laboratory test and to evaluate the effects of pH, particle size, iron sulfate concentration, pulp density, and bioleaching time on sulfur reduction. Statistical analyses of experimental data were considered and showed increases of pH and particle size had negative effects on sulfur reduction, whereas increases of pulp density and bioleaching time raised microbial desulfurization rate. According to results of designing, and regarding statistical factors, the optimum values for maximum sulfur reduction were obtained; pH (1.5), particle size (?180 μm), iron sulfate concentration (2.7 mmol/L), pulp density (10%) and bioleaching time (14 d), which leaded to 51.5% reduction from the total sulfur of sample.     

Pore structure characteristics of the relative water-resisting layer on the top of the Ordovician in Longgu Coal Mine

In order to study the permeability and water-resisting ability of the strata on the top of the Ordovician in Longgu Coal Mine, this paper tested the permeability and porosity of the strata, investigated the fracture and pore structure features of the strata, and identified the main channels which govern the permeability and water-resisting ability of the strata. The permeability of the upper, central and lower strata shows as 2.0504 × 10⁻³–2.782762 × 10⁻³, 4.1092 × 10⁻³–7.3387 × 10⁻³ and 2.0891 × 10⁻³–3.2705 × 10⁻³ μm², respectively, and porosity of that is 0.6786–0.9197%, 0.3109–0.3951% and 0.9829–1.8655%, respectively. The results indicate that: (1) the main channels of the relative water-resisting layer are the pore throats with a diameter more than 6 μm; (2) the major proportion of pore throats in the vertical flow channel and the permeability first increases and then sharply decreases; (3) the fractures occurring from the top to 20 m in depth of the strata were filled and there occurred almost no fracture under the depth of 40 m; and (4) the ratio of turning point of the main flow channel in the strata on top of Ordovician can be used to confirm the thickness of filled water-resisting layers.     

Evaluation of reduction roasting and magnetic separation for upgrading Mn/Fe ratio of fine ferromanganese

Low grade ferromanganese tailing was subjected to different mineralogical techniques, reduction roasting and magnetic separation to establish whether commercially acceptable manganese qualities and high Mn/Fe ratio could be obtained, and also to determine the best processing route for beneficiating this ore. The main manganese mineral within the feed sample is birnessite, with minor amounts of pyrolusite and todorokite. Size by assay analysis conducted presented a result with a yield of about 35.75% and Mn grade of 27.63% to coarse (?3.35 + 1 mm) and yield of 20.24% and Mn grade of 27.71% to (?1.18 + 0.50 mm) fraction. Two-stage high induced magnetic separations at 16,000 and 11,000 G produces Mn grades with similar grade to that obtained from the ferromanganese feed sample. Reduction roasting followed by magnetic separation on ?1.18 + 0.50 mm at 1000 G recovered 72.31% Mn with a grade of 58.44% Mn, 2.52% Fe and 3.29% Si at Mn/Fe ratio of 23.22. This study reveals the influence of roasting in converting the hematite and goethite to magnetite and the response of the roasted fraction to magnetic separation.     

Deformation mechanism of roadways in deep soft rock at Hegang Xing’an Coal Mine

Engineering geomechanics characteristics of roadways in deep soft rock at Hegang Xing’an Coal Mine were studied and the nature of clay minerals of roadway surrounding rock was analyzed. This paper is to solve the technical problems of high stress and the difficulty in supporting the coal mine, and provide a rule for the support design. Results show that mechanical deformation mechanisms of deep soft rock roadway at Xing’an Coal Mine is of I_ABII_ABCIII_ABCD type, consisting of molecular water absorption (the I_AB-type), the tectonic stress type + gravity deformation type + hydraulic type (the II_ABC-type), and the III_ABCD-type with fault, weak intercalation and bedding formation. According to the compound mechanical deformation mechanisms, the corresponding mechanical control measures and conversion technologies were proposed, and these technologies have been successfully applied in roadway supporting practice in deep soft rock at Xing’an Coal Mine with good effect. Xing’an Coal Mine has the deepest burial depth in China, with its overburden ranging from Mesozoic Jurassic coal-forming to now. The results of the research can be used as guidance in the design of roadway support in soft rock.     

Leaching kinetics in cyanide media of Ag contained in the industrial mining-metallurgical wastes in the state of Hidalgo,Mexico

The leaching kinetics in cyanide media of the silver contained in the Dos Carlos waste tailings at the City of Pachuca de Soto, Hidalgo State, Mexico were carried out. The used material contained the following chemical composition: 56 × 10^-6 of Ag, 0.6 × 10⁻⁶ of Au and 70.43% (by weight) of SiO₂; 7.032% (by weight) of Al₂O₃; 2.69% (by weight) of Fe; 0.46% (by weight) of Mn; 3.98% (by weight) of K₂O; 3.34% (by weight) of CaO; 2.50% (by weight) of Na₂O; 0.04% (by weight) of Zn; 0.026% (by weight) of Pb. The mineralogical phases present were the following: Silica, albite, argentite, berlinite, orthoclase, potassium jarosite, and natrojarosite. In the leaching kinetics in cyanide media, and under the studied conditions, the effect of the CN⁻ concentration on the reaction rate has no effect on the whole process of alkaline cyanidation, of which the reaction order is n ≈ 0. Temperature has an effect on the cyanidation rate of the reaction, with an activation energy of 47.9 KJ/mol. At the same time, when the particle size decreases there is an increase in the reaction rate, which is inversely proportional to the particle diameter; when increasing the NaOH concentration there is an increase in the reaction rate K_exp, with a reaction order (n) of 0.215 under the studied ranges.     

Surface magnetization of siderite mineral

Surface self-magnetization of siderite is achieved by generating ferromagnetic substance on the surface of siderite by adjusting slurry temperature, pH value, stirring rate and reaction time. No addition of any iron-containing reagent is required. The temperature of 60 °C, NaOH concentration of 0.10 mol/L; stirring rate of 900 r/min and the reaction time of 10 min are the optimal conditions. The results show that the siderite recovery in magnetic separation increased from 26.9% to 88.8% after surface magnetization. Magnetization kinetic equation is expressed as 1 ? [1 ? (? ? 0.269)]^1/3 = Kt. Activation energy for the magnetization reaction is 4.30 kJ/mol. VSM, SEM and XPS were used to characterize the siderite, and results show that the saturated magnetization (σ_s) of siderite increased from 0.652 to 2.569 A m²/kg, the magnetic hysteresis was detected with a coercive force of 0.976 A/m after magnetization; Fe2P3/2 electron binding energy changed which reflects the valence alteration in iron on the surface and the formation of ferromagnetic Fe₃O₄.     

Study on hydrometallurgical process and kinetics of manganese extraction from low-grade manganese carbonate ores

In order to utilize low-grade manganese ore resources effectively, a hydrometallurgical process was developed for manganese extraction in dilute sulfuric acid medium, and the kinetics of leaching manganese was also investigated. At room temperature, manganese from low-grade manganese carbonate ores was extracted by sulfuric acid leaching without reductants. During the extracting process, single-factor analysis method was used to evaluate the effects of grinding fineness, sulfuric acid concentration, liquid-to-solid ratio, agitation rate and leaching time on the leaching efficiencies of Mn and Fe. The optimal leaching conditions are determined as coarse particles of below 2 mm size (without ball-milling), sulfuric acid concentration of 0.86 mol/L, liquid-to-solid ratio of 5:1, agitation rate of 150 r/min and leaching for 180 min at room temperature. Under the optimal conditions, the leaching efficiencies of Mn and Fe are 96.21% and 13.35%, respectively. In addition, through the experiments at different temperatures, it is found that the leaching process follows the shrinking core model under the conditions of changing acid concentration and intermittent reaction device. Moreover, the apparent activations of effective diffusion and chemical reaction in the kinetic model are calculated to be 18.83 and 27.15 kJ/mol, respectively.     

Fractured zone height of longwall mining and its effects on the overburden aquifers

As mining depth becomes deeper and deeper, the possibility of undermining overburden aquifers is increasing. It is very important for coal miners to undertake studies on the height of fractured zone during longwall mining and the effects of longwall mining on the underground water while mining under surface water bodies and underground aquifers. In order to study this problem, piezometers for monitoring underground water levels were installed above the longwall panels in an American coalmine. Large amounts of pre-mining, during mining and post-mining monitoring data were collected. Based on the data, the heights of fractured zones were obtained and the effects of longwall mining on the underground water were studied. The results demonstrate that when the piezometer monitoring wells had an interburden thickness of less than 72.7 m, the groundwater level decreased immediately to immeasurable levels and the wells went dry after undermining the face of longwall. The height of the fractured zone is 72.7–85.3 m in the geological and mining conditions. The results also show that the calculated values of fractured zones by the empirical formulae used in China are smaller than the actual results. Therefore, it is not always safe to use them for analyses while mining under water bodies.