A numerical simulation of the influence initial temperature has on the propagation characteristics of,and safe distance from,a gas explosion

A model roadway with a cross-sectional area of 80 mm × 80 mm and a length of 100 m was used to estimate the overpressure, the temperature, the density, and the combustion rate during an explosion. AutoReaGas software was used for the calculations and the initial temperatures were 248, 268, 308, or 328 K. The methane–air mixture had a fuel concentration of 9.5% and the tunnel had a filling ratio of 10%. The results show that the safe distance necessary to avoid harm from the shock wave increases with increasing initial temperature. The distance where the peak overpressure begins to rise, and where the maximum value occurs, increases as the initial temperature increases. These are almost linear functions of the initial temperature. At locations before shock wave attenuation has occurred increasing the initial temperature linearly increases the maximum temperature at each point following along the tunnel. At the same time, the peak overpressure, the maximum density, and the maximum combustion rate decrease linearly. However, after the shock wave has attenuated the attenuation extent of the peak overpressure decreases with an increase in initial temperature. The influence of the initial temperature on the explosion propagation depends on the combined effects of inhibiting and enhancing factors. The research results can provide a theoretical guidance for gas explosion disaster relief and treatment in underground coal mines.     

Study on “fracturing-sealing” integration technology based on high-energy gas fracturing in single seam with high gas and low air permeability

To improve the gas extraction efficiency of single seam with high gas and low air permeability, we developed the “fracturing-sealing” integration technology, and carried out the engineering experiment in the 3305 Tunliu mine. In the experiment, coal seams can achieve the aim of antireflection effect through the following process: First, project main cracks with the high energy pulse jet. Second, break the coal body by delaying the propellant blasting. Next, destroy the dense structure of the hard coal body, and form loose slit rings around the holes. Finally, seal the boreholes with the “strong–weak–strong” pressurized sealing technology. The results are as follows: The average concentration of gas extraction increases from 8.3% to 39.5%. The average discharge of gas extraction increases from 0.02 to 0.10 m³/min. The tunneling speeds up from 49.5 to 130 m/month. And the permeability of coal seams improves nearly tenfold. Under the same conditions, the technology is much more efficient in depressurization and antireflection than common methods. In other words, it will provide a more effective way for the gas extraction of single seam with high gas and low air permeability.     

Vacuum chamber suppression of gas-explosion propagation in a tunnel

To control and reduce the harm of a gas explosion, a new method is proposed for suppressing gas-explosion propagation in a tunnel by using a vacuum chamber. We studied the suppression effect on gas explosions by placing a vacuum chamber at dif-ferent positions along the tunnel. The results indicate that: 1) the vacuum chamber can absorb the explosion wave and explosion energy as much as possible at the beginning of the gas explosion, and; 2) when the vacuum chamber is used the closer it is to the ignition source the more significant the suppression effect. In addition, by using the vacuum chamber: 1) the flame propagation velocity decreases from ultrasonic to subsonic; 2) the flame propagation distance is remarkably shortened; 3) the maximum peak value of overpressure (Pro) decreases from 0.34 to 0.17 MPa or less, and; 4) the impulse of the blast wave (/) decreases from 20 to 8 kPa-s or less.     

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.     

Temperature influence on macro-mechanics parameter of intact coal sample containing original gas from Baijiao Coal Mine in China

Investigation of temperature effect on mechanical parameters of coal is very important for understanding the mechanical response of coal bed at high temperature. It is especially beneficial for mitigating the thermal-induced disasters occurred in those coal mines suffering from heat hazard. In this work, coal samples, obtained from the No. 2442 working face of Baijiao Coal Mine, were subjected to uniaxial compression ranging from 20 to 40 °C with an interval of 5 °C. The apparatus used was designed to obtain deformation of a stressed sample, as well as the emission of gases desorbing from coal matrix. The adsorbed gas desorption caused by heating is measured during the entire testing. It is evident that the concentrations of releasing gas (containing methane, carbon dioxide and ethane) slightly rise with increasing temperature. Gas movement observed is closely related to the deformation of coal sample. Both uniaxial compressive strength and elastic modulus of coal samples tend to reduce with temperature. It reveals that increasing temperature can not only result in thermal expansion of coal, but also lead to desorption of preexisting gas in coal which can in turns harden coal due to shrinks of the coal matrix. Even though desorption of adsorbed gas can contribute to the hardening effect for the heated coal, by comparison to the results, it could be inferred that the softening of coal resulted from thermal expansion still predominates changes in mechanical characters of coal sample with temperature at the range from 20 to 40 °C.     

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.     

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.     

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.     

Greenhouse gas emissions from shallow uncovered coal seams

This study discusses a method of quantifying emissions from surface coal mining that has been trialled in Australia. The method is based on direct measurement of surface emissions from uncovered coal seams in mine pits, concurrent measurement of residual gas content of blasted coal in mine pits, and measurement of pre-mining gas content of the same seam from cores retrieved from exploration boreholes drilled away from active mining. The results from one of the mines studied are presented in this paper. In this mine, the pre-mining gas content of the target seam was measured using cores from an exploration borehole away from active mining. Gas content varied from 0.7 to 0.8 m³/t and gas composition varied from 16% to 21% CH₄ (84–79% CO₂). In-pit measurements included seam surface emissions and residual gas content of blasted and ripped coal. Residual gas content varied from 0.09 to 0.15 m³/t, less than twofold across the mine pit. Composition of the residual gas was in general 90% CO₂ and 10% CH₄, with slight variation between samples. Coal seam surface emissions varied from 1.03 to 7.50 mL of CO₂-e per minute and per square meter of the coal seam surface, a sevenfold variation across the mine pit.     

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.     

Roasting and chlorine leaching of gold-bearing refractory concentrate: Experimental and process analysis

This paper deals with gold extraction from a refractory concentrate by chlorine leaching. The process considers a pre-treatment of refractory materials by low temperature oxidation carried out with low oxygen concentration. The oxidized material is treated by leaching with brine. After gold adsorption/reduction onto activated carbon, iron and base metals can be precipitated by NaOH. Roasting tests show the necessity to carry out a thermal pre-treatment at least at 550 °C to obtain a reduction of sulfur and mercury in the material (50% and 90%, respectively). Highest gold extraction yield (around 93%) is obtained in the leaching test performed with material sample treated at 650 °C. This result confirms the necessity to optimize the thermal pre-treatment to improve Au recovery and to reduce chlorine consumption. A comparison with conventional cyanidation confirms that chlorination could be an useful alternative: in fact, gold extraction yield is quite low: 57% in non-pre-treated material and 25% in pre-treatment material.     

Study on washability of microcrystal graphite using float–sink tests

This article presented an experimental research on washability of microcrystal graphite using float–sink tests. Chemical and X-ray analyses showed that graphite, semi-graphite, meta-anthracite, and anthracite existed together in this microcrystal graphite sample; and the intergrowth relationship between microcrystal graphite and gangues was very complicated based on optical mineralogy research. The results of float–sink tests revealed that: for the ?25 + 0.5 mm size fraction, about 68% (by weight) of microcrystal graphite was obtained at the density of 2.0 g/cm³, and the float product met the standard of commercial grade W65; for the ?0.5 mm size fraction, 58% (by weight) of microcrystal graphite was floated at the density of 2.0 g/cm³, which met the standard of commercial grade W70. It can be concluded that microcrystal graphite may be upgraded by dense media separation (DMS) providing a float product using as the raw materials of casting or refractories.     

Reservoir characteristics of Donghe well No.1 in Tarim Basin

Based on the techniques of X-ray diffraction analysis, identification of the thin sections of core cast, physical analysis and scanning electron microscopy analysis, this paper studied the reservoir characteristics of the Carboniferous strata in Donghe well No.1 of Tarim region. The results show that the reservoir lithology is mainly the fine-grained quartz sandstone with ferrocalcite and pyrite, mud cement-based, the permeability concentrated in 5–40 × 10–3 μm², a small part of the high permeability up to 150–327 × 10⁻³ μm² and porosity ranged from 10% to 20%. The most part of the reservoirs is low permeability with a small part of the layer in moderate-high permeability. The types of reservoir space include intergranular pores, intra particle-molding pores, micro-pores and cracks, which mainly are intergranular pores with the pore diameter of 15–200 μm, 95.5 μm on average. And the types of the throats are complex with the main type of constricted throats in this area and large contribution to the permeability.     

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.     

Preconcentration of rare earth elements from Iranian monazite ore by spiral separator using multi-response optimization method

The present work dealt with the preconcentration of rare earth elements in Saghand ore (Yazd province, Iran) which was achieved by Humphrey spiral using orthogonal optimization method after scrubbing the sample at 45% solid pulp density for 30 min. The pulp was diluted and was fed to a Humphrey spiral for upgrading. The process parameters considered were feed size, feed solids and feed rate, and Taguchi’s L₉ (3⁴) orthogonal array (OA) was selected for optimization of the process. The results show that the feed rate and feed size were more significant than the other operation parameters of the process. It was also found that under optimal conditions, the concentrate grade of rare earth elements increased from 2860 × 10⁻⁶ to 6050 × 10⁻⁶ and recovery reached to 58%.     

Effective goaf gas capture design at Ravensworth Underground Mine

This paper highlights a reliable goaf gas capture system developed and used at Ravensworth Underground Mine since its trial in 2009. The method utilises horizontal holes drilled from underground sites and connected to an underground gas pipeline. This system incorporates a gas suction and flaring plant designed specifically for this method. The current method has captured effectively a total longwall, and adjacent goaf gas accounts for over 85%. The design of the holes drilled has been the success of the gas flow reliability. The flow is extraordinarily consistent and predictable. The management of the underground pipeline determines the overall reliability of flow. The design has resulted in Ravensworth Management being confident to remove a gas bearing bleeder roadway and still manage the existing tailgate roadway for allowing access as required. The reduction of CO₂ equivalent emissions recorded is approximately 0.35 × 10⁶ tons annually. This design has further improvements to be added to allow use at any other site with gas in the overlying strata.     

Time evolution of coal structure during low temperature air oxidation

The time evolution of coal structure during low temperature oxidation was investigated by oxidizing coal samples in air at 120 °C for periods of up to 14 days. The structure of the oxidized coal samples was characterized by Fourier transform infrared spectroscopy (FTIR) and curve fitting analysis. The results show that carboxyl and ether groups are the main oxygen containing moieties in oxidized coal. Ethers are most abundant during the first 3 days of oxidation, thereafter carboxyl groups predominate. The content of carboxyl and ester functionality increases with oxidation time. The other oxygen containing groups vary in concentration over time. The amount of hydroxyl groups first decreases then increases and finally decrease again during the oxidation. The aliphatic structure and the degree of branching of the aliphatic chains is reduced as the oxidation proceeds. The proportion of aromatic structure increases with oxidation time. Obvious decomposition of aromatic rings occurs after about 9 days of oxidation. The aryl ester bands and the CH₃/CH₂ ratio both have a good linear relationship to oxidation time.     

Effects of different factors during the de-silication of diaspore by direct flotation

Most of the bauxite resources in China are kaolinite-diaspore bauxite of middle to low grade, with a fine dissemination, and are difficultly separated. Direct flotation de-silication has been shown to be an effective method for de-silication of diaspore. In this study the effect of different factors, including pulp temperature, density, pH value, depressant, and collector dosage, on direct flotation of diaspore were investigated by laboratory experiments. The optimum conditions were identified and the flotation performance was improved. The results show that under optimum conditions (a pulp temperature around 40 °C, a pulp density from 30% to 33%, a pH value from 9.0 to 10.0, an air flow rate of 0.5 m³/(m² min), a dispersant level from 35 to 70 g/t, and a collector level around 1000 g/t) an Al/Si ratio of 6.97 is obtained starting from an initial Al/Si ratio of about 4.71. The recovery of Al₂O₃ under these conditions was 86.94%.     

Deformed coal types and pore characteristics in Hancheng coalmines in Eastern Weibei coalfields

Based on SEM observance, the methods of low-temperature nitrogen and isothermal adsorption were used to test and analyze the coal samples of Hancheng, and pore structure characteristics of tectonic coals were discussed. The results indicate that in the same coal rank, stratification and crack are well developed in cataclastic coal, which is mostly filled by mineral substance in the geohydrologic element abundance, results in pore connectivity variation. Granulated and mylonitic coal being of these characteristics, as develop microstructures and exogenous fractures as well as large quantity of pores resulted from gas generation and strong impermeability, stimulate the recovery of seepage coal, improve coal connectivity and enhance reservoir permeability. Absorption pore (micro-pore) is dominant in coal pore for different coal body structure, the percentage of which pore aperture is from 1 to 100 nm is 71.44% to 88.15%, including large of micro-pore with the 74.56%–94.70%; with the deformation becoming more intense in the same coal rank, mesopore enlarge further, open-end pores become thin-neck-bottle-shaped pores step by step, specific surface area of micro-pore for cataclastic coal is 0.0027 m²/g, while mylonitic coal increases to 7.479 m²/g, micro-pore gradually play a dominant role in effecting pore structural parameters.     

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.