共查询到20条相似文献，搜索用时 15 毫秒
1.
P. Tucker 《International Journal of Mineral Processing》1984,12(4):273-284
The size distributions of the products from laboratory-scale batch grinds, of a leadzinc ore and a tin ore, were measured as a function of pulp density. A reduction in the overall grinding rate at high pulp densities correlated well with the increase in pulp viscosity. Enhanced fines production, apparent at the higher pulp densities, was however controlled largely by the particle packing and less by viscosity effects. The individual mineral distributions themselves responded differently to changes in pulp density. In particular, the extra fines generated at the high pulp densities consisted primarily of gangue material, with the softer ore minerals actually showing a drop in production. The addition of grinding aids, essentially viscosity modifiers, increased the grinding rate under certain conditions without producing any pronounced change in the selective grinding characteristics. 相似文献
2.
Electrochemical aspects of grinding media-mineral interactions in magnetite ore grinding are illustrated from the viewpoint of corrosive wear of grinding balls and changes in the surface properties of the ground minerals. The corrosive wear of mild steel and HCLA steel was found to be small in contact with magnetite, while the combined presence of pyrrhotite and oxygen accelerated the corrosion of the above ball materials. Austenitic stainless steel exhibited passive behavior under all the above conditions. Galvanic coupling of mild steel with magnetite or pyrrhotite resulted in the formation of a surface reaction product consisting of iron hydroxide species on the mineral. 相似文献
3.
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
4.
Ball milling is an energy-intensive unit operation and usually consumes a major proportion of the power drawn by a typical mineral processing plant. Hence, substantial economic benefits can be achieved by optimal design and by operating ball milling circuits under optimum process conditions. This requires an accurate ball mill modelling technique.In the multi-segment ball mill model, the size-dependent material transport within the mill varies systematically with the amount of coarse particles present in each segment. The ore-specific breakage distribution function can be determined from single particle breakage tests conducted using a computer-monitored twin pendulum apparatus. When the ore-specific breakage distribution function is used in the multi-segment, a constant relationship between the breakage rate parameters and mill diameter is observed. Thus, the performance of an industrial ball mill can be adequately described using the ore-specific breakage distribution function together with the systematic variation of the material transport and the breakage rate functions with process conditions and mill diameter, respectively.This ball mill modelling technique is illustrated using a case study on the design of a ball milling circuit for a particular grinding requirement and another case study on modelling the performance of an industrial ball milling circuit. 相似文献
5.
The performance of the secondary ball mill at the New Broken Hill Consolidated Ltd. concentrator is analysed using the perfect mixing model and an ore-specific breakage distribution function. This function was determined from single-particle breakage tests using a computer-monitored twin pendulum apparatus.The ratio of the breakage rate to the normalized discharge rate, r/d*, determined for the ball mill using the ore-specific breakage distribution function for a range of grinding conditions is related to the mill power consumption. The mill power consumption is related to the percentage of mill volume occupied by the ball charge and to the percentage of solids in the mill feed. 相似文献
6.
Kinetics of fine wet grinding of zeolite in a steel ball mill in comparison to dry grinding 总被引：1，自引：0，他引：1
Batch wet grinding of zeolite was studied with emphasis on a kinetic study in a laboratory size steel ball mill of 200 mm diameter. The breakage parameters were determined by using the single sized feed fractions of − 850 + 600 µm, − 600 + 425 µm and − 425 + 300 µm for the zeolite samples. The Si (specific rate of breakage) and Bi,j (primary breakage distribution) values were obtained for those feed size fractions in order to predict the product size distributions by simulation for comparison to the experimental data. The specific rates of breakage values for wet grinding in the first-order breakage region were higher than the dry values reported previously by a factor 1.7 at the same experimental conditions, but the primary breakage distribution (Bi,j) values were approximately the same. The simulations of the product size distributions of zeolite were in good agreement with the experimental data using a standard ball mill simulation program. The wet grinding of zeolite was subjected to slowing-down effect in the mill at 2 min of grinding, corresponding to an 80% passing size of about 400 µm. On the other hand, the slowing down effect in the dry grinding of zeolite was also seen at 4 min of grinding. In addition, effects of some operational parameters on dry and wet grinding of zeolite were determined by simulation using the breakage parameters obtained experimentally. 相似文献
7.
A centrifugal mill is a high-power intensity media mill that can be used for ultra-fine grinding, employing centrifugal forces generated by gyration of the axis of the mill tube in a circle. The mill charge motion is quite different depending on the ratio of the gyration diameter to the mill diameter (G / D ratio), varying from a motion similar to that of a conventional tumbling media mill to that of a vibration mill. In this study, a centrifugal mill was constructed with an arrangement where the gyration diameter could be readily adjusted. The batch grinding characteristics of three different minerals (limestone, talc and illite) in water with dispersing agent were investigated at various G / D ratios. It was found that the optimum G / D ratio in terms of the specific energy consumption to give a desired fineness of product was different for the three minerals. This was due to their different reactions to the breakage mechanisms provided by the mill charge motion at varying G / D ratios. The size distributions became progressively narrower at increased grinding times, and particles finer than about 0.1 μm were not detected even for prolonged grinding times. Measurement of specific surface areas indicated that this was not due to an artifact of the size measurements by laser diffractometry. This implies that there is a limitation in which particles finer than 0.1 μm are not produced under the conditions tested in this type of mill, but further investigation is needed for experimental verification of this limit of comminution. 相似文献
8.
Grinding mills are commonly used in the Florida phosphate industry to reduce particle size. The corrosion of metallic grinding media and mill liner is a very serious problem, particularly under acidic conditions as encountered in the Florida phosphate fertilizer industry. A statistical Box–Behnken Design (BBD) of experiments was performed to evaluate the effects of individual operating variables and their interactions on the wear rate of high chromium alloy during phosphate grinding. The variables examined in this study included grinding time, solution pH, rotation speed, mill crop load, and solids percentage. The wear tests were conducted using a specially designed grinding mill whose electrochemical potential can be controlled. The most significant variables and optimum conditions were identified from statistical analysis of the experimental results using response surface methodology (RSM). It has been shown that solution pH had the most significant effect on the wear rate. The optimum process parameters for minimum wear rate were solution pH at 8.7, rotation speed at 61 rpm, solid percentage at 65% and crop load at 58%. 相似文献
9.
目前球形全流贯入被仪广泛应用于岩土离心试验中,以表征软弱黏土土样的抗剪性能。然而,在离心加速度作用下离心机试验中的球贯入仪比现场使用的标准球贯入仪有更大的加载杆与球的面积比a、更大的等效原型直径以及不一样的球-土摩擦系数,从而使得离心机球体会出现不一样的贯入特性,进而导致不一样的土体抗剪承载力校验系数。通过大变形有限元（large deformation finite element,简称LDFE）方法对中国常见离心机球形贯入仪贯入单层黏土进行分析,获得不同几何尺寸和摩擦系数下球形贯入仪的贯入特性。计算结果通过与有关解析解以及其他前人研究结论的对比分析,验证了有限元分析结果的合理性。通过大量参数分析表明,球摩擦系数对空腔的临界深度以及深层破坏深度的影响较小,面积比a对浅层和深层承载力系数以及达到深层破坏深度有显著的影响。根据数值模拟的结果,提出了不同面积比和摩擦系数下的极限间隙深度Hc、浅层和深层临界破坏模式深度Hd、不同摩擦系数和面积比情况下的深层承载力系数和浅层承载力校准系数的计算公式,从而能获得更精确的土体抗剪强度,为离心机中球形贯入仪的应用提供了理论依据。 相似文献
10.
A detailed comparison is made of the capability of population balance models to predict steady-state product size distributions of a pilot-scale ball mill. The mill was operated at 60% solids with feed rates of crystalline limestone ranging from 90 to 450 kg/hr (200 to 1000 lb/hr). Two types of lumped parameter models are compared: a linear model in which size reduction parameters are independent of size consist and a nonlinear model in which these parameters are dependent on size consist. The nonlinear model is based on an empirical correlation between rate of breakage and size consist in the mill. Results indicate that the nonlinear model gives the most accurate predictions of product size distributions, however, at the cost of significantly more complex computations. 相似文献
11.
After a summary of maximum likelihood (ML) estimation, the application of the ML-method is demonstrated by estimating parameters in a ball mill-hydrocyclone grinding circuit from flow and density measurements. The model with the estimated parameters is used to determine the time propagation of mill contents and size distribution. 相似文献
12.
13.
This paper presents the experimental results of the mechanical production of silica and carbonate colloidal particles below 100 nm using two types of stirred bead mills (i.e., DCP Superflow 12 and PML H/V). It is shown that the stirred bead mill with very small beads can be used as an efficient equipment for the production of the colloidal particles in nanoscale from the feed materials of several microns in sizes at high energy consumptions. The DCP Superflow mill with high power densities is superior for the effective size reduction and production rate, compared to the conventional PML H/V mill with lower power densities. The smaller particles could be produced by the DCP Superflow mill at the same level of high energy inputs as from the PML H/V mill. The “grinding limit” for the processes in the mills has been discussed. 相似文献
14.
S. Narayanan N. Raghunathan U. B. Nayak A. K. Lahiri 《International Journal of Mineral Processing》1983,10(4):309-317
The effect of surface-active agents in improving the grinding efficiency for haematite, expressed as a measure of reduction ratio, has been studied. Drying of the feed before grinding has been found to improve the grinding efficiency. The effect of surfactant additions on hardness, microhardness, crushing strength and wet grinding of haematite has shown that dispersants are better than flocculants, and each dispersant has a critical concentration at which the grinding efficiency is maximum. 相似文献
15.
The conversion factor for specific rates of breakage, to change from results in a 200-mm diameter laboratory mill with 25.4-mm diameter balls, at Bond filling conditions, to a 4-m diameter production cement mill was found to be 2.75. The residence time distribution of the 10-m long, 2-compartment production mill was equivalent to 10 equal fully-mixed reactors in series, with a mean overall residence time of 5.58 min. A mathematical simulation of the mill circuit using experimental separator selectivity values gave a reasonably close match between simulated and experimental size distributions at various points in the circuit.The steady-state simulation model was used to predict how design schemes for different operation conditions would influence the product size distributions and output rates, assuming that the discharge diaphragm could be redesigned to preserve design mill filling conditions at different circulating loads. It was concluded that the increase of circuit output from the breakage view-point due to separation and rejects recycle was slight, and that improved separator efficiency to produce the same product would not result in significant increase in output, primarily because the size distribution of the finish product is close to that predicted from open-circuit operation. 相似文献
16.
The results of experiments on a 40 cm × 40 cm grate-discharge ball mill have been analysed for variation of mill hold-up weight of solids with solids feed rate, weight percent solids, mean feed particle size, material specific gravity and work-index. It is shown that mill hold-up weight is independent of the material specific gravity and mean feed particle size, and it varies linearly with solids feed rate and weight percent solids, at least over the range of practical interest. The variations in the transport behaviour of different materials have been attributed to the differences in the size distribution of the mill hold-up solids. It is shown that work-index can be used as the material characteristic for the development of an empirical correlation. Variation of mean residence time of solids with solids feed rate and weight-percent solids is also discussed. 相似文献
17.
M. Sri Raj Rajeswari K.A.M. Azizli S.F.S. Hashim M.K. Abdullah M. Abdul Mujeebu M.Z. Abdullah 《International Journal of Mineral Processing》2011,98(1-2):94-105
This paper presents a three dimensional Computational Fluid Dynamics (CFD) model to investigate the flow dynamics of solid–gas phases during fine grinding in an air jet mill. Alpine 100AFG fluidized bed air jet mill is considered for the study and the jet milling model is simulated using FLUENT 6.3.2 using a standard k-ε model. The model is developed in GAMBIT 2.3.16 and meshed by tet/hybrid (T-Grid) and Triangular (Pave) meshes. The effects of operating parameters such as solid feed rate, grinding air pressure and internal classifier speed on the performance of the jet mill are analyzed. The CFD simulation results are presented in the forms of dual phase vector plot, volume fraction of phases and particle trajectories during fine grinding process. The mass of ground feed entering and leaving the cyclone (underflow) is also computed by simulation. The proposed model gives realistic predictions of the flow dynamics within the jet mill. Experiments are conducted on the Alpine 100AFG jet mill to study the particle size, morphology and mass of the ground product. The numerical results are found in good agreement with the experimental results. 相似文献
18.
Xiaoli Wang Weihua Gui Chunhua Yang Yalin Wang 《International Journal of Mineral Processing》2011,98(1-2):113-117
The grindability of a diasporic ore was studied by wet grinding in a laboratory ball mill and its breakage parameters were determined based on the population balance model (PBM). Four different feeds with unnatural size distributions were designed to save grinding and sieving work. It was found that three size-intervals fitted the first-order breakage, but the coarsest interval did not. The non-first order breakage was most probably caused by the heterogeneity of the material. The heterogeneity was then confirmed by experiments. The breakage rate and the breakage distribution parameters were back calculated by treating the non-first order breakage as two linear segments according to the grinding time. The back-calculated breakage rates were in good agreement with the values calculated directly from the experimental data, and non-normalizable breakage distribution was observed. The model with the obtained parameters simulated the experimental product size distributions with good accuracy. These findings are valuable to the simulation and optimization of the industrial grinding processes of diasporic ores. 相似文献
19.
Hematite concentrate was mechanically treated using different milling machines and experimental conditions in air atmosphere. The changes in phase constitution, particles size, specific surface area, lattice parameters and X-ray amorphous phase fraction of activated hematite were determined. It was found that the agglomeration of the particles take place during extended milling with accessible pores for Nitrogen gas. The higher media surface brought about the largest specific surface area whatever milling devices used. After 9 h of grinding with higher media surface, the maximum and minimum specific surface area resulted from the grinding in the tumbling and vibratory mills, accounting for 6.83 m2/g and 18.42 m2/g, respectively. For the same grinding condition, tumbling mill produced the lowest X-ray amorphous phase. The maximum X-ray amorphous material estimated around 85% from the grinding in the planetary mill with higher media surface for 9 h of milling. 相似文献
20.
Paul C. Lyons Carolyn L. Thompson Patrick G. Hatcher Floyd W. Brown Michael A. Millay Nikolaus Szeverenyi Gary E. Maciel 《Organic Geochemistry》1984,5(4):227-239
An evaluation was made of the degree of coalification of two coal balls from the Illinois Basin of the Pennsylvanian (upper Carboniferous) of the United States. Previous interpretations are mainly misleading and contradictory, primarily because of the assumption that the brown color and exceptional cellular and subcellular preservation typical of American coal balls imply chemical preservation of cellulose and lignin, the primary components of peat. Xylem tissue from a medullosan seed fern contained in a coal ball and the coal attached to the coal ball from the Calhoun coal bed, Mattoon Formation, Illinois, was analyzed by elemental, petrographic, and nuclear magnetic resonance (NMR) techniques to determine the degree of coalification. The NMR and elemental data indicate the lack of cellulose and lignin and a probable rank of high-volatile C bituminous coal. These data corroborate data for a coal ball from the Herrin (No. 6) coal bed (Carbondale Formation, Middle Pennsylvanian) and support our hypothesis that the organic matter in coal balls of the Pennsylvanian strata of the United States is coalified to about the same degree as the surrounding coal. Data presented show a range of lower reflectances for xylem tissue and vitrinite in the analyzed coal balls compared with vitrinite in the attached coal.The data reported indicate that physical preservation of organic matter in coal balls does not imply chemical preservation. Also our study supports the hypothesis that compactional (static load) pressure is not a prerequisite for coalification up to a rank of high-volatile C bituminous coal.A whole-rock analysis of the Calhoun coal ball indicates a similarity to other carbonate coal balls from the United States. It consists primarily of calcium carbonate and 1–2% organic matter; silica and alumina together make up less than 0.5%, indicating the lack of minerals such as quartz and clays. 相似文献