Effect of NaOH treatment on combustion performance of Xilinhaote lignite

The combustion characteristics of NaOH treated and untreated Xilihaote lignite was investigated by thermogravimetric analysis. The relationship between physico-chemical properties, including the ash content, oxygen-containing functional groups, mean pore diameter and specific surface area and combustion performance, was also studied in this paper. Combustion kinetic parameters were calculated through Coasts Redfern Method. The results show that ignition of treated samples takes place at higher temperature compared to raw lignite, and peak temperature also occurs at higher temperature. The maximum combustion rate of the sample, which was treated by 0.01 mol/L NaOH lignite, was the biggest. Reaction orders of 0.6, 2.0, and 0.8 were found to be effective mechanism for definite three temperature regions. Average activation energies of these three temperature regions of XLHTR, XLHT0.01, XLHT0.50 and XLTH1.00 are 19.17, 23.87, 10.77, and 10.93 kJ/mol, respectively. Treatment of lignite with NaOH can reduce the reactivity of lignite at proper concentration.     

Na_2Cr_2O_7和NaClO_4对水泥窑用煤燃烧特性的影响

以煤的着火点、燃尽点、燃烧烈度、平均放热强度和发热量为评价指标,利用TG-DSC分析添加剂Na2Cr2O7和NaClO4对水泥窑用煤燃烧特性的影响。结果表明,两类燃煤添加剂均能改变水泥窑用煤的燃烧特性。两类添加剂的加入降低了水泥窑用煤燃烧的着火点和燃尽点,使其能够在较低的温度下进行燃烧,提高煤的燃烧性和燃尽性,同时降低了煤的燃烧烈度,使煤的燃烧更加平稳,有利于煤在水泥窑内的燃烧;Na2Cr2O7和NaClO4均能使煤的发热量增加,且加快煤粉热量的释放,促进了煤的完全燃烧。     

Combustion characteristics of low concentration coal mine methane in divergent porous media burner

Low-concentration methane (LCM) has been one of the biggest difficulties in using coal mine methane. And previous studies found that premixed combustion in porous media is an effective method of low calorific gas utilization. This paper studied the combustion of LCM in a divergent porous medium burner (DPMB) by using computational fluid dynamics (CFD), and investigated the effect of gas initial temperature on combustion characteristic, the distribution of temperature and pollutant at different equivalence ratios in detail. Besides, the comparison of divergent and cylindrical burners was also performed in this paper. The results show that: the peak temperature in DPMB increases as the increasing of equivalence ratio, which is also suitable for the outlet NO discharge; the linear correlation is also discovered between peak temperature and equivalence ratios; NO emission at the initial temperature of 525 K is 5.64 times, larger than NO emission at the initial temperature of 300 K. Thus, it is preferable to balance the effect of thermal efficiency and environment simultaneously when determining the optimal initial temperature range. The working parameter limits of divergent burner are wider than that of cylindrical one which contributes to reducing the influence of LCM concentration and volume fluctuation on combustion.     

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.     

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.     

Removal of copper from molybdenite concentrate by mesophilic and extreme thermophilic microorganisms

Mixed mesophilic and extreme thermophilic bioleaching were evaluated to remove copper from the molybdenite concentrate. Bioleaching tests were carried out in shake flasks and in a 50-L bioreactor. The shake flask tests were performed with different inoculum size, solids density, pH, and temperature in order to identify optimum conditions. The highest amount of copper elimination, 75% was obtained with extreme thermophilic microorganisms (at 12% inoculation, 10% solids, 65 °C and a pH of 1.5). The highest copper elimination by mesophilic microorganisms was 55% (at 12% inoculation, 5% solids, 30 °C at pH 2). The optimum conditions in shake flask tests were applied to 7 days batch tests in a 50-L bioreactor. Extreme thermophilic experiment gave the best copper elimination of 60% (at 12% inoculation, 10% solids, 65 °C and pH 1.5). Mesophilic test removed 50% of the copper (at 12% inoculation, 10% solids, 35 °C at pH 2).     

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.     

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.     

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%.     

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.     

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.     

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.     

Meso-structure and fracture mechanism of mudstone at high temperature

The meso-structure mineral composition and fracture mechanism of uniaxial compressed mudstone samples at high temperature were analyzed by XRD and scanning electron microscopy. The effect of temperature on mudstone composition and fracture mechanism were studied from a meso-structural perspective, and the relationship between meso-structure and macro-mechanical characteristics at high temperature was revealed. The findings demonstrated that the fluctuation in diffraction intensity of kaolinite in the mudstone caused the fluctuation in its mechanical properties. The overall structure underwent a phase change around 600 °C, which led to the sudden change in the mechanical properties of mudstone samples. When the temperature reached 600 °C, the crystalline state worsened and kaolinite disappeared; however, some illite was produced, indicating that the chemical reaction of the structure and sudden drop of bearing capacity of the mudstone. Mudstone fracturing at high temperature involves mainly intergranular and transgranular fractures, which are typical in micro-brittle tensile failure. Considering the macro-fracture characteristics of mudstone, the results suggested that macro-fracture under external force corresponds to the meso-fracture.     

污泥燃烧特性研究

利用TGA/DSC同步热分析仪,分析了不同NaOH掺量的污泥的燃烧特性.结果表明:污泥中的第一类有机物分解燃烧的温度范围为50～180℃,第二类有机物分解燃烧的温度范围随NaOH含量的不同而不同.NaOH的存在,使污泥中第二类有机物分解燃烧的温度起始点提前,而温度截止点滞后.NaOH降低了污泥着火温度,提高了燃烬温度....     

Study on kinetics of thermal decomposition of low LOI goethetic hematite iron ore

In the present study, the kinetics of thermal decomposition of hydrated minerals associated in natural hematite iron ores has been investigated in a fixed bed system using isothermal methods of kinetic analysis. Hydrated minerals in these hematite iron ores are kaolinite, gibbsite and goethite, which contribute to the loss on ignition(LOI) during thermal decomposition. Experiments in fixed bed have been carried out at variable bed depth(16, 32, 48 and 64 mm),temperature(400-1200 ℃) and residence time(30,45, 60 and 75 min) for iron ore samples. It is observed that beyond a certain critical bed depth(16 mm), 100% removal of LOI is not found possible even at higher temperature and higher residence time. Most of the solid-state reactions of isothermal kinetic analysis have been used to analyze the reaction mechanism. The raw data are modified to yield fraction reacted "α" versus time and used for developing various forms of "α" functions.f(α) is the inverse of first derivative of g(α) with respect to α. The study demonstrates that decomposition of hydrated mineral in hematite follows the chemical kinetics.The estimated activation energy values in all the experimental situations are found to high, of the order of 60 kJ/mol, reinstating that the reactions are indeed controlled by moving phase boundary and random nucleation.     

生物质与不同变质程度煤混合燃烧特性的研究

采用TG／DTG／DTA技术研究了不同变质程度煤(褐煤、烟煤和无烟煤)、生物质(小麦秸秆和玉米芯)以及煤和不同比例生物质的混合燃料的燃烧特性，升温速率为15c／min，温度范围为25～900℃，分析了燃烧特征参数如着火温度、燃烧速率最大时的温度、燃尽温度和最大燃烧速率以及燃烧特性指数．采用Freeman-carroll(FC)法计算了燃烧动力学参数．结果表明，生物质和煤相比具有较低的燃烧特征温度和较快的燃烧速率；在褐煤和烟煤中加入生物质后，燃烧特征温度降低，燃烧速率增大；无烟煤中加入生物质后，对其着火温度影响较小，燃尽温度降低；此外，加入生物质后煤的燃烧表观活化能降低，表观活化能E与指前因子A存在动力学补偿效应。     

Physical and mechanical properties of sandstone containing a single fissure after exposure to high temperatures

In order to investigate the physical and mechanical properties of sandstone containing fissures after exposure to high temperatures,fissures with different angles α were prefabricated in the plate sandstone samples,and the processed samples were then heated at 5 different temperatures.Indoor uniaxial compression was conducted to analyze the change rules of physical properties of sandstone after exposure to high temperature,and the deformation,strength and failure characteristics of sandstone containing fissures.The results show that,with increasing temperature,the volume of sandstone increases gradually while the quality and density decrease gradually,and the color of sandstone remains basically unchanged while the brightness increases markedly when the temperature is higher than 585 ℃;the peak strength of sandstone containing fissures first decreases then increases when the temperature is between 25℃and 400℃.The peak strain of sandstone containing fissures increases gradually while the average modulus decreases gradually with increasing temperature,and the mechanical properties of sandstone show obvious deterioration after 400 ℃.The peak strain of sandstone containing fissures increases gradually while the average modulus decreases gradually with increasing temperature;with increasing angle αof the fissure,the evolution characteristics of the macro-mechanical parameters of sandstone are closely related to the their own mechanical properties.When the temperature is 800 ℃,the correlation between the peak strength and average modulus of sandstone and the angle α of the fissure is obviously weakened.The failure modes of sandstone containing fissures after high temperature exposure are of three different kinds including:tensile crack failure,tensile and shear cracks mixed failure,and shear crack failure.Tensile and shear crack mixed failure occur mainly at low temperatures and small angles;tensile crack failure occurs at high temperatures and large angles.     

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.     

Effect of temperature and stress on molecular structure and carbon monoxide generation of lignite from Kailuan mining area

In order to analyze the origin of carbon monoxide(CO) in coal seams, stress–strain experiments under temperature of 50, 150 and 250 °C were conducted using lignite from Kailuan mining area. Fourier transform infrared spectroscopy and elemental analysis were carried out before and after deformation of the samples. The results indicated that CO generated at 150 and 250 °C; the gas component was mostly oxygen(O_2), with small amount of carbon dioxide(CO_2), methane(CH_4) and hydrogen(H_2). At 50 °C, O_2 and a little CO_2 were observed and no CO was found. The carbon content of the coal samples increased slightly after deformation, and the oxygen content, H/C ratio, and O/C ratio decreased. The molecular structure of coal displayed different evolution characteristics at various temperatures. At 50 and 150 °C, the falling off of side chains, broken of ether bond and directional realignment of the aliphatic chains resulting in the formation of long chains were the main performance of coal molecular structure evolution. While at 250 °C, the side chains fell off and short chains formed. Furthermore, at both 150 and 250 °C, condensed degree of aromatic ring increased. Under the action of temperature and pressure, CO forms in two ways.The first is that ether bond breaks, oxygen and carbon atoms combine together and forms CO, or O_2 forming in the broken of ether–oxygen bond leads to the oxidation of free radicals and resulting in the formation of CO. And the second is that CO derives from falling off of C=O group.     

Nickel extraction from low grade laterite by agitation leaching at atmospheric pressure

This research work deals with the extraction of nickel from a low grade nickel laterite ore, taken from a deposit located in southwestern of Iran, through agitation leaching at atmospheric pressure. The assaying and mineralogical studies carried out on the nickel laterite sample, showed the 0.88% Ni, and principally consisted of oxide and silicate crystalline phases i.e. dolomite, quartz, magnetite, and goethite. Among numerous factors affecting such process, four major parameters i.e. temperature, agitator speed (r/min), leaching agents and their concentration were considered in a two-level full factorial experimental design. The agitation leach tests showed that the ore could be leached at atmospheric pressure with sulfuric acid while citric acid was almost unpromising. Analysis of variance (ANOVA) using DX7 software was employed to identify effective parameters. Sulfuric acid concentration and temperature were the most effective parameters on Ni extraction. Furthermore, the factorial models for experiment responses were developed. The results showed 83% Ni extraction after 4 h leaching, under optimized conditions i.e. temperature at 95 °C, acid concentration at 5 N and agitator speed at 1000 r/min. This study revealed that factorial experimental design can be implemented to identify effective parameters on the agitation leaching process of nickel laterite.