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.     

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%.     

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.     

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.     

Determination of consolidation behaviour of clay slurries

The main objective of this study was to determine the consolidation behaviour of clay slurries.A finegrained clay with high consistency limits(W_L = 180%,w_P= 120%) was investigated using conventional oedometer and bench-top centrifuge tests.Results indicated that the slurry had an apparent preconsolidation(due to initial conditions,electrochemical interactions,tortuous drainage,and thixotropic strength) from e = 5.7 to e = 5.5 followed by virgin compression.Likewise,the low hydraulic conductivity(10~(-10)-10~(-12) m/s) was due to low porosity(small pore throats) and high tortuosity(long flow paths).Unlike consolidation of soils,the c_v and m_v decreased with increasing σ' but increased with increasing e and k.The data from the two tests correlated well in the range of σ' = 10-65 kPa,e = 5.5-3.86,k= 1.7 × 10~(-10)-5×10~(-11) m/s,F_c = 1-40 MN.New equations were developed to correlate the consolidation parameters(e,σ',k) with F_c.The deviation of k beyond 40 MN(e = 4.65) was due to deviation from the initial straight line portion of the settlement curve in the centrifuge test.     

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.     

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.     

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%.     

Discontinuities effect on drilling condition and performance of selected rocks in Nigeria

The study examined joint discontinuity spacing effect on drilling condition and performance in selected rocks in Ilorin and Ibese areas, Nigeria. Five samples for each rock type (gneiss and limestone) were tested in the laboratory for chemical, physical and mechanical properties. Dip direction and joint spacing were measured using compass clinometers. The chemical composition was determined using X-ray Fluorescence (XRF) spectrometer. The results show that gneiss has SiO₂ of 61.88% and limestone has CaO content of 52.3%. The average dry density of gneiss and limestone are 2.6 and 2.39 g/cm³, respectively. The uniaxial compressive strength of gneiss and limestone are 195 and 93.83 MPa, respectively. These rocks are classified as strong and moderately strong rock. Gneiss and limestone have mean joint discontinuity spacing of 0.79 and 0.25 m, which classified them as moderate and wide joint spacing respectively. Joint spacing was correlated with specific energy, bit wear and uniaxial compressive using Statistical Package for Social Science (SPSS). The regression model has multiple coefficient of correlation of R² = 0.791 and R² = 0.995 for gneiss and limestone, respectively. The variation in joint spacing could be attributed to specific energy, bit wear and uniaxial compressive strength which affect drilling condition and performance. Ultimately, as joint spacing gets closer, the drilling velocity increases, drill string will be stable.     

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.     

Geotechnical behavior of uranium mill tailings from Saskatchewan,Canada

This paper investigates the geotechnical behavior of uranium mill tailings from Saskatchewan, Canada.The 4% tailings were well-graded with 29% fines whereas the 5% and 6% tailings were gap-graded with 49% fines. All samples exhibited a negligible strength(0.4 k Pa) up to 60% solids, followed by a rapid increase. The 4% tailings exhibited a lower rate and amount of settlement than 5% and 6% tailings. The kidecreased from 10~(-2)to 10~(-4)m/s with a decrease in eifrom 16 to 4 and a decrease in ef from 8 to 4 such that 4% tailings showed one order of magnitude lower values than the 5% and 6%tailings. The settling potential decreased ten times(50%–5%) for 4% tailings and four times(60%–15%)for 5% and 6% tailings. The effective stress increased from 80 to 260 Pa in the settling tests. The 4%tailings were less prone to segregation when compared with 5% and 6% tailings. The average solids content after settling was 35% for 4% tailings, 40% for 5% tailings and 39% for 6% tailings with a solids content deviation of ±3%, ±8%, ±6%, respectively. All materials were essentially non-segregating at 40%initial solids.     

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.     

Fractal dimension of coal particles and their CH4 adsorption

We describe the fractal analysis of three differently sized coal samples (0.350–0.833 mm, 0.245–0.350 mm, and 0.198–0.245 mm). The influence of fractal dimension on CH₄ adsorption capacity is investigated. The physical parameters of the samples were determined via the Brunauer–Emmett–Teller (BET) theory. A CH₄ adsorption study over the pressures range from 0 to 5 MPa was carried out with a new volumetric measurement system. The CH₄ adsorption was measured using the differently sized coal. Two fractal dimensions, D₁ and D₂ were determined over the pressure ranges from 0 to 0.5 MPa and from 0.5 to 1 MPa, using the Frenkel-Halsey-Hill (FHH) method. We conclude that the two fractal dimensions correlate with the CH₄ adsorption capacity of the coal: increasing CH₄ adsorption capacity occurs with a corresponding increase in fractal dimension. Furthermore, D₁ and D₂ are positively correlated with surface area, pore volume, and samples size. The size distribution of the samples has fractal characteristics.     

Effect of galvanic contact on the flotability of galena in the presence and absence of a collector

In this paper, the effect of various electrochemical environments in the galena flotation is investigated. The electrochemical environments consisted of a ball mill for grinding of galena ore and a Denver flotation cell for flotation of galena in the laboratory scale. In order to achieve the maximum recovery with sodium hyposulfite, the concentrations of 0.06 and 0.12 M of air and nitrogen gases have been used to control the pulp potential in the Denver flotation cell. The galena sample was from the “Era mine” which is located in the Kiyasar area, north of Iran. This mine contains: Galena (PbS) at least 22%, Fluorite (CaF₂) 73.37%, Quartz (SiO₂) 2.54% and other minerals such as Cerussite (PbCO₃) and Kaolinite (Al₂Si₂O₅(OH)₄). Flotation of Galena was conducted in a 0.12 M of sodium hyposulfite solution. It was found that the amount of recovery by this process was 85% and 63% in the presence and absence of potassium amyl xanthate (KAX) and at an estimated potential of 280 to 350 mV respectively while the recovery was 70% and 52% at an approximate potential of 175 to 210 mV in water in the presence and absence of collector (KAX).     

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.     

Identification of large-scale goaf instability in underground mine using particle swarm optimization and support vector machine

An approach which combines particle swarm optimization and support vector machine (PSO–SVM) is proposed to forecast large-scale goaf instability (LSGI). Firstly, influencing factors of goaf safety are analyzed, and following parameters were selected as evaluation indexes in the LSGI: uniaxial compressive strength (UCS) of rock, elastic modulus (E) of rock, rock quality designation (RQD), area ration of pillar (S_p), the ratio of width to height of the pillar (w/h), depth of ore body (H), volume of goaf (V), dip of ore body (α) and area of goaf (S_g). Then LSGI forecasting model by PSO-SVM was established according to the influencing factors. The performance of hybrid model (PSO + SVM = PSO–SVM) has been compared with the grid search method of support vector machine (GSM–SVM) model. The actual data of 40 goafs are applied to research the forecasting ability of the proposed method, and two cases of underground mine are also validated by the proposed model. The results indicated that the heuristic algorithm of PSO can speed up the SVM parameter optimization search, and the predictive ability of the PSO–SVM model with the RBF kernel function is acceptable and robust, which might hold a high potential to become a useful tool in goaf risky prediction research.     

Improved recovery of a low-grade refractory gold ore using flotation–preoxidation–cyanidation methods

In this work, different flotation–preoxidation–cyanidation methods are considered for treating a low-grade refractory gold ore. On the one hand, the results of selective flotation show that 22% and 31.1% of total Sb and As, respectively, remained in the final tailings and only about 28% of the total Au remained for further cyanidation processes. On the other hand, in bulk method of flotation the maximum Au recovery of 90.6% achieved after 60 min of flotation at the grind size with K80 of 146 micron. In addition, the bulk flotation method resulted in the concentrate with low concentrations of Sb and As elements. To improve the recovery of low-grade refractory gold ores, flotation should be followed by roasting, biological, or pressure oxidation processes so that the gold could be liberated prior to cyanidation processes. It is also found that the pressure oxidation pre-treatment of the concentrates prior to cyanidation may yield high gold recoveries of over than 83%. In these processes, recoveries are controlled by the temperature and the oxygen partial pressure in the solvent. However, by utilizing the bio-oxidation technique, the oxidation of sulfur to sulfate cannot be completed and, consequently, the gold recovery may be limited to only 72.2%.     

Analysis of vacuum chamber suppressing gas explosion

In order to suppress the harm of gas explosion, the current study researched on the body of vacuum chamber. The previous studies verified that it could obviously lower the explosion overpressure by reasonably arranging vacuum chamber on pipe. That is to say, the vacuum chamber has the effect of absorbing wave and energy. To further deeply analyze the vacuum chamber suppressing gas explosion, this research designed the L-type pipe of gas explosion, and compared the experimental results of gas explosion with vacuum chamber and without vacuum chamber. Besides, using the gas chromatograph, this study also investigated the gas compositions in the pipe before and after explosion. The results show that: (1) without vacuum chamber, the maximum value of explosion overpressure is 0.22 MPa, with 60 ms duration, and after explosion, the concentration of oxygen drops to 12.07%, but the concentration of carbon monoxide increases to 4392.3 × 10^?6, and the concentration of carbon dioxide goes up to 7.848%, which can make the persons in danger suffocate and die; (2) with vacuum chamber, explosion overpressure drops to 0.18 MPa, with 20 ms duration or less, and after explosion, the concentration of oxygen still remains 12.07%, but the concentration of methane is 7.83%, however the concentration of carbon monoxide is only 727.24 × 10^?6, and the concentration of carbon dioxide is only 1.219%, at the this moment the concentration ratio of toxic gas drops by more than 83% in comparison to be that without vacuum chamber. Consequently, the vacuum chamber can guarantee that most methane does not take part in chemical reaction, and timely quenches the deflagration reaction of gas and oxygen. Because of the two points mentioned above, it reduces the explosion energy, and lowers that the overpressure of blast wave impacts and damages on the persons and facilities, and also decreases the consumption of oxygen and the production of the toxic gas. Therefore, it is safe to conclude that the vacuum chamber not only absorbs wave and energy, but also prevents and suppresses explosion.     

Seismic studies of coal bed methane content in the west coal mining area of Qinshui Basin

The coal bed methane content (CBMC) in the west mining area of Jincheng coalfield, southeastern Qinshui Basin, is studied based on seismic data and well-logs together with laboratory measurements. The results show that the Shuey approximation has better adaptability according to the Zoeppritz equation result; the designed fold number for an ordinary seismic data is sufficient for post-stack data but insufficient for pre-stack data regarding the signal to noise ratio (SNR). Therefore a larger grid analysis was created in order to improve the SNR. The velocity field created by logging is better than that created by stack velocity in both accuracy and effectiveness. A reasonable distribution of the amplitude versus offset (AVO) attributes can be facilitated by taking the AVO response from logging as a standard for calibrating the amplitude distribution. Some AVO attributes have a close relationship with CBMC. The worst attribute is polarization magnitude, for which the correlation coefficient is 0.308; and the best attribute is the polarization product from intercept, of which the correlation coefficient is ?0.8136. CBMC predicted by AVO attributes is better overall than that predicted by direct interpolation of CBMC; the validation error of the former is 14.47%, which is lower than that of the latter 23.30%. CBMC of this area ranges from 2.5 m³/t to 22 m³/t. Most CBMC in the syncline is over 10 m³/t, but it is below 10 m³/t in the anticline; on the whole, CBMC in the syncline is higher than that in anticline.     

A damage-based constitutive model for rock under impacting load

Using the Splitting Hopkinson Pressure Bar (SHPB) experimental system, investigations were made into the dynamic mechanical performances of underground soft rocks. The experiments proved that the measured stress–strain curves display the characteristics of plastic deformation. By making use of a revised overstress constitutive formula for the stress model and by taking into account that the strain rate and strain are a function of 1 − E(t)/E₀, a revised overstress constitutive formula for the stress model was simplified by applying dimensional analysis and consequently, a simplified overstress formula was obtained for the stress model. Then, by taking into consideration the effects of damage under a dynamic load on the dynamic loading strength of the rock, the continuous damage theory and the statistical strength theory were introduced into the development of the simplified overstress constitutive formula for the stress model. Hence, a damage-based constitutive formula for an overstress model, which can be appropriately applied to the analysis of full dynamic stress–strain curves, was developed. By using the simplified damage-based constitutive formula for an overstress model, the actually measured curves are fitted, indicating that the fitting curves and those actually measured are in good agreement.