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).     

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%.     

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.     

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%.     

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.     

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.     

高磷赤铁矿两步法生物除磷实验研究

采用嗜酸氧化硫硫杆菌(At.t)直接浸出和两步法浸出,对鄂西高磷鲕状赤铁矿(铁品位43.50%,磷含量0.85%)进行生物除磷的实验研究。结果表明:矿浆浓度为2%时,At.t菌直接浸出除磷率为62.35%,且硫含量高达28.57%;采用两步法摇床培养At.t菌,24d菌液pH值接近0.8,磷含量可降至0.15%,硫含量为1.09%;采用自行设计制作的生物反应器培养At.t菌8d,菌液pH值接近0.98,分离菌液浸出原矿12h磷含量为0.18%。对磁选精矿进行的两步法浸出表明,当矿浆浓度为3%以下时菌液的除磷效果明显。     

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.     

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.     

Optimizing conditions for bacterial leaching of copper from discarded mines

1. IntroductionMany high-grade, easily exploited mineral depositsare becoming more and more scarce. Using biotech-nology to study discarded mines for the recovery ofmetallic values could present new business opportuni-ties and have a significant impact on…     

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.     

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.     

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.     

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.     

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.     

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.     

Zinc bioleaching from an iron concentrate using Acidithiobacillusferrooxidans strain from Hercules Mine of Coahuila, Mexico

The iron concentrate from Hercules Mine of Coahuila,Mexico,which mainly contained pyrite and pyrrhotite,was treated by the bioleaching process using native strain Acidithiobacillus ferrooxidans(A.ferrooxidans)to determime the ability of these bacteria on the leaching of zinc.The native bacteria were isolated from the iron concentrate of the mine.The bioleaching experiments were carried out in shake flasks to analyze the effects of pH values,pulp density,and the ferrous sulfate concentration on the bioleaching process.The results obtained by microbial kinetic analyses for the evaluation of some aspects of zinc leaching show that the native bacteria A.ferrooxidans,which is enriched with a 9K Silverman medium under the optimum conditions ofpH 2.0,20 g/L pulp density,and 40 g/L FeSO4,increases the zinc extraction considerably observed by monitoring duringl 5 d,i.e.,the zinc concentration has a decrease of about 95％ in the iron concentrate.     

Investigation of condition-induced bubble size and distribution in electroflotation using a high-speed camera

In the flotation process, bubble is a key factor in studying bubble-particle interaction and fine particle flotation. Knowledge on size distribution of bubbles in a flotation system is highly important. In this study, bubble distributions in different reagent concentrations, electrolyte concentrations, cathode apertures, and current densities in electroflotation are determined using a high-speed camera. Average bubble sizes under different conditions are calculated using Image-Pro® Plus (Media Cybernetics®, MD, USA) and SigmaScan® Pro (Systat Software, CA, USA) software. Results indicate that the average sizes of bubbles, which were generated through 38, 50, 74, 150, 250, 420, and 1000 μm cathode apertures, are 20.2, 29.5, 44.6, 59.2, 68.7, 78.5, and 88.8 μm, respectively. The optimal current density in electroflotation is 20 A/m². Reagent and electrolyte concentrations, current density, and cathode aperture are important factors in controlling bubble size and nucleation. These factors also contribute to the control of fine-particle flotation.     

Coal petrology characteristics of middlings from Qianjiaying fat coal mine

The objective of this paper is to evaluate the coal petrology characteristics of slack middlings (13–0.5 mm) of dense media separation and flotation middlings from Qianjiaying fat coal preparation plant. Phase composition, macerals distribution, microlithotype and mineral occurrence of the two middlings were studied by XRD analysis and polarized light microscopy observation. Macerals distribution and wettability of the float-and-sink products separated from the middlings after grinding was investigated to determine the liberation degree. Studies show that there are more vitrinite and mineral, but less inertinite in slack middlings than in flotation middlings. Macerals associated with mineral in slack middlings is 69.85%, by volume, which is 17.86% higher than that in flotation middlings. Minerals in slack middlings are dominated by pyrite and clay, which are disseminated with the diameter less than 2 μm. The main mineral in flotation middlings is clay with size range of 2–20 μm. Single macerals in the slack middlings are difficult to liberate due to the fine-grained minerals. After grinding, macerals associated with minerals in the slack middlings decrease to 46.73%, by volume, which is higher than in flotation middlings by 25.89%, by volume. For slack middlings with poor liberation degree, density fractions below 1.8 g/cm³ is hydrophobic with contact angle above 71.5°. For the well liberated flotation middlings, there is significant wettability difference among the float-and-sink products. This research is the theoretical basis to realize re-separation of middlings.     

Experiment and simulation on the pyrite removal from the recirculating load of pulverizer with a dilute phase gas–solid fluidized bed

In order to reduce the energy consumption and subsequent air pollution of coal-fired power station, based on the analysis to size and density distribution of particles from the recirculating load of the classifier of pulverizer, the separation experiment on sampling material from power plant with a dilute phase fluidized bed to remove pyrite and other minerals and numerical simulation on the separation process were done. The results show that the minimum fluidization velocity is 1.62 cm/s. Pyrite and other minerals in the material are separated. Ash of the upper and bottom layer material account for 33.34% and 73.42% respectively and sulfur content occupy 1.12% and 8.96% respectively. Scanning electron microscopy and spectroscopy tests show that sulfur in the bottom material exist in the form of pyrite. Numerical simulation on the flow field form of the dilute phase separation bed with gas–solid two phase and particle motion verifies the experimental results.