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1.
A major operating cost in dense-medium separation is in replacement of lost medium solids. The loss of medium solids, being costly, plays a crucial role in determining the economics of any preparation operation. Coal washeries that employ dense-medium cyclones often attempt optimization of the processes by varying the vortex or the spigot diameter and the feed relative density. While these changes help in closer control of the separation process, they also result in medium losses due to changes in the medium split ratio (ratio of the medium flow rate in overflow to underflow). Since medium solids are lost by adhesion to products and as magnetic separator effluent, the effect of the change in medium split ratio on the drain-and-rinse screens and, hence, the magnetic separator circuit needs to be studied. In Tata Steel's coal washeries, at Jharkhand India, which employs primary and secondary dense-medium cyclones in series to produce clean coal, middlings and rejects, reducing the relative density of feed medium, had an insignificant effect on the medium split ratio. On the other hand, changing the cone ratio (ratio of the overflow diameter to the underflow diameter) changed the relative density and the flow rates through the cyclone outlets, thus affecting the performance of the magnetite recovery circuit.A systematic study through laboratory tests and a detailed plant sampling campaign helped in identifying the causes of magnetite loss. Upon implementation of the recommendations, the magnetite losses decreased, resulting in a saving of approximately US$27,500 per annum. The study also helped in evolving some checkpoints for plant operators for identifying magnetite losses.  相似文献   

2.
Direct reduction of iron ore to produce electric furnace feed for steelmaking is becoming economically important on a worldwide scale. For this application an iron ore superconcentrate containing less than 2% silica is demanded. Pilot plant and commercial operations have shown that high-intensity wet magnetic separation is well adapted to meet this specification with high recovery and attractive capital and operating costs. Tests with the Jones separator have produced superconcentrates containing less than 1.5% silica with over 90% iron recovery from preconcentrates produced by sizing or by gravity or low-intensity magnetic separation. Estimated total capital and operating costs to produce a ton of superconcentrate by high-intensity wet magnetic separation are $0.43 for retreatment of specular hematite spiral concentrate, $0.47 for Brazilian hematite fines, and $0.49 for magnetite.  相似文献   

3.
A “straight-wire” flow-through magnetic ore separator has been designed, built, and successfully used to separate magnetite from synthetic slurries. The purpose of these experiments was to simulate the field profile of a “straight-wire” superconducting magnetic separator which would be capable of separating weakly-magnetic hematite ore from typical slurries. Magnetite is used as the test mineral because it experiences the same magnetic forces at low field as does hematite at high field; thereby making possible less expensive low-field simulation.The present separator concept is based on the fact that there is a particle concentration profile due to the gravity field for low-velocity turbulent flow. When an upward magnetic force is applied, the concentration profile of magnetic particles can be reversed leaving the nonmagnetic particles flowing alone at the bottom of the channel. By means of a divider at the end of the channel, the concentrate is separated from the tailings. It is shown that the time needed to deflect hematite particles in a narrow cylindrical channel concentric with the superconducting wire is small enough so that high throughputs in the turbulent flow region are possible. In the case of a high-field superconducting separator, the centrifugal force could replace gravity by rotating the flow around a straight-wire conductor.  相似文献   

4.
The influence of iron hydroxide/oxide coatings on the recovery of gold was studied using 13 stream sediment samples collected from an area of known gold mineralisation. Magnetic products collected from a Frantz isodynamic separator showed higher gold values than did non-magnetic fractions. An acid-treated magnetic product when run through the isodynamic separator yielded a significant amount of non-magnetic component which, when viewed by binocular microscope, showed the presence of gold grains in both bulk sample and in bromoform-separated heavy mineral concentrate. It is suggested that concentrates are treated with 10% HCl prior to magnetic separation where iron oxide coatings are conspicuous.  相似文献   

5.
The paper presents a method for separating the small metallic nonferrous particles from two component metallic nonferrous mixtures using a new type of dynamic eddy-current separator with permanent magnets. The so-called two successive steps eddy-current separator (TSECS) consists of a horizontal rotary drum covered with permanent magnets, alternately N–S and S–N oriented. The separation process takes place in two stages, first the strongly conducting particles are separated on the upper part of the drum, and then the remaining undecided and poorly conducting particles are separated at the lower part of the magnetic drum. The experimental results and comments regarding the values obtained for separation efficiency, grade and recovery for wastes consisting in Cu–Pb and Cu–Al mixtures are given. The obtained results are in good agreement with the theoretical analysis.  相似文献   

6.
An influence of oil additions (0–3% w/w) on the vacuum filtration of fine coal has been investigated. The results show that an oil addition of 1% can lead to a lowering of filter-cake moisture from 26% (wet basis) to 16% (wet basis). This considerable lowering of filter-cake moisture is accompanied by an increase in both filtration rate and solids pick-up rate. The results are qualitatively interpreted in terms of a flocculation process in which oil droplets condense at the particle contact points to form pendular bridges.  相似文献   

7.
The Egyptian black sands contain several economic minerals, especially ilmenite. Monazite can reach concentrations up to 0.6 wt.%. The majority of monazite grains have light to deep canary and lemon yellow colors, whereas enigmatic monazite grains have brown, red, resinous, yellow and colorless to pinkish colors. The behavior of monazite with the electrostatic field setting of the roll-type electrostatic separator was studied for the different variables of the separator. Most of the monazite grains are reversible negative and are attracted towards the positively charged static electrode. Using wet gravity concentration, both low and high intensity magnetic separation, and electrostatic separation techniques, a high grade concentrate assaying 97 wt. % monazite with a recovery of 76.8% can be obtained. The Egyptian beach monazite contains high concentrations of Ce, La and Nd in addition to minor amounts of Y, Pr, Sm, Gd, Dy and Eu. It is particularly rich in the lighter rare earth elements (cerium subgroup). By a new method of ion exchange technique after chemically dissolving the mineral with sulfuric acid, both of REEs, Th and U, could be individually separated. The efficiency of the separation has been tested with sulfuric acid concentration at 2M H2SO4 where the thorium and uranium could be obtained with a cation exchange synthetic resin column, while rare earth metal ions are adsorbed and then individually separated. A highly pure thorium product could be obtained by oxalate precipitation followed by uranium precipitation as diuranate using NaOH.  相似文献   

8.
黏土单层击实试验与制样因子研究   总被引：1，自引：1，他引：0  
汪攀峰  丁启朔 《岩土力学》2010,31(6):1797-1802
使用非标准击实仪进行单层击样,获取非标准击实状态下单层击实样的密度与击实功及含水率之间的关系,并进一步以得到的击实样获得其抗剪强度。发现当击实功小到一定程度时,击实密度随含水率的增大而不断增大,两者近似线性变化,无峰值出现。密度峰值对应的含水率与抗剪强度峰值对应的含水率有一个差值,其值在3.4%～5.7%之间。内摩擦角随含水率增大而减小的规律仅适合于一定的击实功。内摩擦角在较小的击实功下有峰值出现,但随着击实功的增大,内摩擦角的变化呈线性而非曲线形式。另外,针对土工室内模型试验的重塑土样制备问题,结合试验数据,给出了试验最优制样参数,并初步提供了评价指标?。  相似文献   

9.
This study evaluates bioleaching treatments to remove copper from the Sarcheshmeh (Iran) molybdenite concentrate using a native strain of Acidithiobacillus ferrooxidans. Copper content of the concentrate was 0.83 wt.% as chalcopyrite. The tests showed selective dissolution of copper (chalcopyrite) from molybdenite concentrate. Up to 65% of copper content of molybdenite concentrate was removed via bioleaching with a native strain of A. ferrooxidans in less than 15 days. Ferrous sulfate, sulfur or pyrite was added to culture medium to enhance the activity of bacteria. Sulfur was the preferred additional source of energy for removing copper from molybdenite via bioleaching with A. ferrooxidans. In addition, 9K or Norris medium was also used as the culture medium in the experiments. The experiments showed that application of Norris medium would be better than that of 9K medium in order to remove copper from molybdenite via bioleaching. These results were backed up due to the fact that the cost of Norris medium was also less than that of 9K medium.  相似文献   

10.
The paper presents a method for separating the small metallic nonferrous particles from two component nonferrous mixtures using a new type of dynamic eddy-current separator with permanent magnets. The so called Angular Drum Eddy-Current Separator (ADECS) consists of a horizontal rotary drum covered with permanent magnets, alternately N–S and S–N oriented. The rotor is placed oblique, under the superior part of a horizontal conveyor belt, coplanar with its surface. The axis of the drum and the direction of displacement of the belt make a certain angle, depending on the physical properties of the particles subjected to the separation process. The separator functions on the basis of the jump effect of the strongly conducting particles which assume different trajectories in the active zone of the field, namely, upper part of the drum. The experimental results and comments regarding the values obtained for grade and recovery for wastes consisting in Cu–Pb and Cu–Al mixtures are given.  相似文献   

11.
Industrial minerals of a high degree of fineness such as kaolinite, calcite and barite are used to an increasing extent in the chemical industries as filling material in the manu-facturing of paper, paints and plastics or as ingredients of ceramic products. Grains smaller than 5 μm can be produced by dry grinding in a jet mill or by wet grinding in drum mills. To avoid impurities due to wear, these mills are lined with rubber or plastic and ceramic balls are used as grinding bodies.Our investigations in a jet mill show that the fineness of the ground product depends on the feed rate and on the air volume. The grain sizes received in the drum mill are influenced by feed rate, pulp density, speed of rotation and by the grinding bodies (density, size).REM-photographs of mill discharge in the grain-size ranges 10-5 μm and below 5 μm indicate that in both the grains mainly show crystal planes as boundaries. After dry grinding the grains show smooth and clean faces; thus is traced back to the impact effect of the air streams. In wet grinding the fine grains are very prone to form agglomerates.  相似文献   

12.
A technological sample (50 kg) from Wadi Khamal Nelsonite ore was subjected to magnetic and flotation concentration techniques. Excellent recovery percentages of 72.95% and 71.22% were achieved by the dry/wet magnetic and flotation concentration techniques, respectively. The weight of the apatite concentrate reached a reasonable percentage of approximately 23.5% with an overall 40.23% P2O5 total content. Analytical data of the apatite concentrate after digestion in concentrated sulfuric acid revealed that the total content of the rare earth elements (REE) constitutes about 0.2% of the total apatite content. The REE content (0.2%) was partitioned between phosphoric acid liquor (65%) and gypsum precipitate (36%). The extraction of the REEs from the phosphoric acid liquor using oxalic acid and sodium carbonate–bicarbonate mixture (1:10?w/w) yielded the RE oxide cake which constitute about 1.2% (w/w). The produced rare earth oxide cake contains traces of various metal oxides, e.g., SrO, Na2O, etc. in addition to rare earth oxides. Attempts to determine quantitatively the constituents of the cake will be considered in future work.  相似文献   

13.
Yang  Song-Yue  Chang  Che-Hao  Hsu  Chih-Tsung  Wu  Shiang-Jen 《Natural Hazards》2022,111(3):2297-2315

Coupled 1D–2D hydrodynamic models are widely utilized in flood hazard mapping. Previous studies adopted conceptual hydrological models or 1D hydrodynamic models to evaluate the impact of drainage density on river flow. However, the drainage density affects not only river flow, but also the flooded area and location. Therefore, this work adopts the 1D–2D model SOBEK to investigate the impact of drainage density on river flow. The uncertainty of drainage density in flood hazard mapping is assessed by a designed case and a real case, Yanshuixi Drainage in Tainan, Taiwan. Analytical results indicate that under the same return period rainfall, reduction in tributary drainages in a model (indicating a lower drainage density) results in an underestimate of the flooded area in tributary drainages. This underestimate causes higher peak discharges and total volume of discharges in the drainages, leading to flooding in certain downstream reaches, thereby overestimating the flooded area. The uncertainty of drainage density decreases with increased rainfall. We suggest that modeling flood hazard mapping with low return period rainfalls requires tributary drainages. For extreme rainfall events, a lower drainage density could be selected, but the drainage density of local key areas should be raised.

  相似文献   

14.
Separation of metal laden waste using pulsating air dry material separator   总被引：1，自引：1，他引：0  
Separation of metal laden solid wastes for their recycling utilization using passive pulsed air and active pulsing air classifiers was studied. Laboratory investigation showed that the active pulsing air separator performs more efficiently than the passive pulsed air separator due to the ability to accurately control operating parameters. By studying the difference of drag coefficients of the particles moving through the airflow of varying Reynolds numbers, models of the dynamic particle motion were developed and a computer simulation was prepared. Results of the simulation were reported to predict the observed results with artificial tracing spheres being separated by the laboratory equipment. Two different, real world feed materials were separated with the laboratory scale active pulsing air classifier. The discarded catalyst consisting of precious metal components and sintered magnetic beads was separated with the separation efficiency, of 97.6 %. The second real-world feed, electronic scrap crushed to a size of 0.5 to 2 mm, showed a separation efficiency of 92.41 %. At the same time, the grade of the recovered concentrate of metals was above 98 %.  相似文献   

15.
测井评价煤层气储层的方法探讨   总被引：2，自引：0，他引：2  
根据煤层气储层实验室分析确定的体积模型（碳、灰分、挥发分、水分）,以测井曲线予以评价。其中以自然伽马测井确定湿灰分,该方法的前提条件是湿分主要是泥质且泥质不具放射性元素;以密度测井与人工伽马测井确定含碳量,并对密度测井作湿分校正;以灰分校正后的密度测井确定饱和水孔隙度;含气量的估算以声波测井和密度测井组成的复合参数ΔT/dDEN来确定,或以视电阻率曲线确定含气量。以某地区2个钻孔为例,讨论了煤层深度、压力等与水分、灰分、含气饱和度、含气量等参数的关系,认为含气量与深度成正比关系。  相似文献   

16.
Kaolin ores in Huichang contains these minerals of quartz sand, kaolin, mica and feldspars. In order to recover these valuable resources, some experiments of screening, classification, magnetic separation, grinding and flotation are carried out on the basis of the kaolin ore properties. The test results indicate that quartz sand concentrate can be directly obtained when vibrating screen size used is 10 meshes. Materials that are smaller than the screen hole are injected to hydraulic cyclones which controlling classification size is 325 meshes; kaolin concentrate containing above 33.70% Al2O3 and 0.37% Fe2O3 can be well beneficiated from the overflow through magnetic separation with one stage rougher and cleaner to remove iron. On the other hand, the hydrocyclone spigot flow to grinding and flotation with one stage rougher and two scavengers, mica and feldspars concentrate can be beneficiated in sequence. Therefore, these valuable minerals of kaolin ores can be realized comprehensive utilization.  相似文献   

17.
The kaolin industry has shown a phenomenal growth record from 1930 to the present and there is no indication that this growth will not continue. Innovative and efficient process developments enabled the kaolin industry to wet process over 5,000,000 tons in 1978 in Georgia and over 3,000,000 tons in the Cornwall district of southwestern England. These two regions supply the major tonnage of paper coating clays for the world's paper industry. The more important process developments are listed as follows: (1) development of chemicals for dispersion and flocculation; (2) continuous blungers to slurry the kaolin at the mine; (3) (continuous degritting by rake classifiers and hydrocyclones; (4) transport of kaolin slurry through pipelines from mine to plant; (5) continuous centrifuges for particle separation into coarse, medium, and fine sizes (6) chemical leaching of iron to improve brightness and color, (7) dewatering to high solids by: (a) continuous rotary vacuum filters; (b) automated plate and frame filter presses; (c) tube presses; (d) high speed contrifuges; (8) spray drying to low moisture and spherical shape to permit bulk hopper car shipments; (9) flotation to remove iron and titanium impurities to improve brightness and whiteness; (10) slurry clay shipments at 70 percent solids in tank cars; (11) high gradient magnetic separation to improve brightness and whiteness and to utilize marginal deposits; (12) delamination to utilize course kaolin stacks to make an improved product; (13) pugging and working the kaolin to improve viscosity; (14) a new development — dewatering to 80 to 85 percent solids using electrophoresis.Each of these developments is described and the future need to develop an efficient process to significantly lower the viscosity of high viscosity kaolins is discussed.  相似文献   

18.
Acid mine drainage (AMD), of which iron is a substantial component, is a potential by-product in the mining industry. Conventional neutralization is a common approach to treat AMD, although it creates a major disposal problem due to the generation of voluminous sludge. Sludge recirculation improves solid density by slowing down the rate of neutralization and allowing the growth of precipitates, while existing solids act as seed particles by providing necessary surface area for precipitation. The mechanisms of iron sludge densification are not fully understood, mainly because of the complex nature of iron chemistry, and the variety of amorphous, polymeric oxides that could be formed. In this work, the effects of alkaline reagents, flocculant addition, and dosing sequence, on the precipitation of iron (III) hydroxide and densification of the recycled sludge were investigated. Slowly dissolving lime (Ca(OH)2) was found to be more effective than caustic (NaOH) in producing sludge with higher solid contents. Polymers addition created stronger aggregates that could withstand shearing without significant size reduction, but the overall sludge density was lower than those produced without flocculant. Conditioning the sludge at pH between 3.5 and 4.5 by adding fresh lime in a specific dosing manner appeared to be conducive to the growth of large agglomerates. The final sludge solid content of ∼15 wt.% was considerably higher than others produced under different conditions. The plate-like structures of precipitates generated with more recycles in this instance, possibly helped ease the release of entrapped water between solids during shearing, thus producing sludge with higher solid density.  相似文献   

19.
Most of the topsoils encountered in United Arab Emirates and in the Arabian Peninsula are granular soils with small percentages of silt and clay. Determination of the compaction characteristics of such soils is an essential task in preparing for construction work. The accumulating experience over many years of soil testing in our laboratories suggested that there exists an underlying trend that governs the compaction characteristics of such soils. As such, a study was undertaken to assess the compaction characteristics of such soils and to develop the governing predictive equations. For the purposes of this study, 311 soil samples were collected from various locations in the United Arab Emirates, and tested for various including grain-size distribution, liquid limit, plasticity index, specific gravity of soil solids, maximum dry density of compaction, and optimum moisture content following ASTM D 1557-91 standard procedure C. Following the development of the predictive equations, a new set of 43 soil samples were collected and their compaction results were used to test the validity of predictive model. The range of variables for these soils were as follows: percent retained on US sieve #4 (R#4): 0–68; Percent passing US sieve #200 (P#200): 1–26; Liquid limit: 0–56; Plasticity index: 0–28; Specific gravity of soil solids: 2.55–2.8. Based on the compaction tests results, multiple regression analyses were conducted to develop mathematical models and nomographic solutions to predict the compaction properties of soils. The results indicated that the nomographs could predict well the maximum dry density within ±5% confidence interval and the optimum moisture content within ±3%. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

20.
Abstract Reliable predictions of wind erosion depend on the accuracy of determining whether erosion occurs or not. Among the several factors that govern the initiation of soil movement by wind, surface moisture is one of the most significant. Some widely used models that predict the threshold shear velocity for particle detachment of wet soils by wind were critically reviewed and evaluated. Wind‐tunnel experiments were conducted on pre‐wetted dune sand with moisture contents ranging from 0·00 to 0·04 kg kg?1. Sand samples were exposed to different wind speeds for 2 min. Moisture content was determined gravimetrically before and after each experiment, and the saltation of sand particles was recorded electronically with a saltiphone. Shear velocities were deduced from the wind speed profiles. For each moisture content, the experiments were repeated at different shear velocities, with the threshold shear velocity being determined by least‐squares analysis of the relationships between particle number rates and shear velocity. Within the 2‐min test runs, temporal changes in particle number rates and moisture contents were detected. A steep increase in the threshold shear velocity with moisture content was observed. When comparing the models, large differences between the predicted results became apparent. At a moisture content of 0·007 kg kg?1, which is half the moisture content retained to the soil matrix at a water tension (or matric potential) of ?1·5 MPa, the increase in ‘wet’ threshold shear velocity predicted with the different models relative to the dry threshold shear velocity ranged from 117% to 171%. The highest care should therefore be taken when using current models to predict the threshold shear velocity of wet sediment. Nevertheless, the models of Chepil (1956; Proc. Soil Sci. Soc. Am., 20, 288–292) and Saleh & Fryrear (1995; Soil Sci., 160, 304–309) are the best alternatives available.  相似文献   

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