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Grinding is an important process of ore beneficiation that consumes a significant amount of energy. Pretreating ore before grinding has been proposed to improve ore grindability, reduce comminution energy, and enhance downstream operations. This paper investigates hybrid thermal mechanical pretreatment to improve iron ore grinding behavior. Thermal pretreatment was performed using conventional and microwave approaches, while mechanical pretreatment was conducted with a pressure device using a piston die. Results indicate that conventional (heating rate: 10 °C; maximum temperature: 400 °C), microwave (2.45 GHz, 1.7 kW, 60 s), and mechanical (14.86 MPa, zero delay time) pretreatments improved the studied iron ore grindability by 4.6, 19.8, and 15.4%, respectively. Meanwhile, conventional-mechanical and microwave-mechanical pretreatments enhanced the studied iron ore grindability by 19.2% and 22.6%, respectively. These results suggest that stand-alone mechanical pretreatment or microwave pretreatment may be more beneficial in improving the grinding behavior of the studied fine-grain iron ore sample. The results of the mechanical pretreatment obtained in this study may be used in a simulation of the HPGR system for grinding operations of similar iron ore [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced polymer (CFRP) is an increasingly used lightweight material with a limited recyclability. This article investigates constructive, operating and material parameters of the comminution process, which is an unavoidable step of every recycling process chain for CFRP. A pendulum impact tester is used to determine the stressing energy, the energy loss because of friction and the resulting forces. The material properties and the stressing mode have significant effects on the comminution behavior of CFRP. The results lead to the material specific derivation of constructive measures to reduce the energy demand for the comminution process of CFRP. [ABSTRACT FROM AUTHOR]

This work compares the mechanical properties of two geomaterials: forsterite and magnesite. Various physical conditions are considered to investigate the evolution of stress–strain relationships for these two polycrystals. A molecular-scale study is performed on three-dimensional models of forsterite and magnesite. Three different temperatures (300 K, 500 K, and 700 K) and strain rates (0.001, 0.01, and 0.05 ps−1) are considered to initiate deformation in the polycrystals under tensile and compressive forces. The polycrystalline structures face deformation at lower peaks at high temperatures. The Young's modulus values of forsterite and magnesite are found to be approximately 154.7451 GPa and 92.84 GPa under tensile forces and these values are found to be around 120.457 GPa (forsterite) and 77.04 GPa (magnesite) for compressive forces. Increasing temperature reduces the maximum strength of the polycrystalline structures, but forsterite shows higher ductility compared to magnesite. Strain rate sensitivity and the effect of grain size are also studied. The yield strengths of the forsterite and magnesite drop by 7.89% and 9.09% when the grain size is reduced by 20% and 15%, respectively. This study also focuses on the changes in elastic properties for different pressures and temperatures. In addition, from the radial distribution function (RDF) results, it was observed that the peak intensity of pairwise interaction of Si–O is higher than that of Mg–O. Finally, it is found that the formation of magnesite, which is the product of mineral carbonation of forsterite, is favorable in terms of mechanical properties for the comminution process. [ABSTRACT FROM AUTHOR]

The objective of this study was to analyse bio-fibre comminution energy and particle size classification as the first step towards converting cellulose based agricultural residues into environment-friendly composite products. Bio-fibres used in the study were water retted, chemically modified and oven dried to remove any trace of moisture. The bio-fibres comminution was performed in a laboratory-scale knife mill at varying mill speed, and chemical treatment concentrations. The particle size classification was aided by mechanical sieving process. Nonlinear Least Square method using the cftool based on Gauss-Newton method of iteration available in MATLAB 2007b was used to fit the experimental data to Rosin-Rammler-Bennett’s (RRB) and Gaudin-Schuhmann’s (GS) size distribution models. Energy consumption was estimated via Kick’s, Rittinger’s and Bond’s models. The result showed that energy requirement for bio-fibre comminution increases with decreasing particle size, with coir fibres requiring the highest energy when compared with banana fibres. As the mill speed increases from 1400 rpm to 2100 rpm the energy consumed in comminution banana fibre increases from 357.46 J/g to 369.38 J/g for 2% NaOH treatment with the kick’s constant increasing from 52.97 J/g to 57.86 J/g for untreated banana fibres. Whereas for coir fibre, the energy consumed in comminution increases from 382.14 J/g to 411.07 J/g for 2% NaOH treatment with the Kick’s constant increasing from 57.25 J/g to 61.83 J/g for untreated coir fibres. Bio-fibre energy consumption was best described by Kick’s model with R2 > 0.910 and RRB model captured the bio-fibres size distribution better than GS model with higher R2 and lower value of SSE and RMSE. Scanning electron microscopy revealed that the surface of the fibres had changed, becoming rougher as a result of chemical modification. Findings also indicated that comminution of bio-fibres with high chemical concentration results in less fine sizes with median size (S50) ranging from 524 μm–1476 μm for banana fibres and 644 μm–660 μm for coir fibres. The data obtained at different speeds of comminution and from various bio-fibre treatment conditions might guide the selection of initial fibre size and other processing parameters to better exploit bio-fibres potential in particulate fibre reinforced composites products design.

The depletion of high-grade ores has forced the utilization of low-grade ores. The small liberation sizes in the low-grade ores require fine grinding which is an energy intensive operation. In the present study, low-grade chromite ore bearing platinum group of elements (PGE) was used as an experimental material. The previous study concluded the liberation size of around 1–50 µm for chromite ore bearing PGE minerals. Therefore, the target product size for grinding was kept below 50 µm. The wet fine grinding experiments were performed in a vertical stirred mill. Four significant operating variables stirrer speed, grinding time, feed size, and solids concentration were investigated for their effect on the performance of stirred mills. The performance of the mill was assessed in terms of achieving small product size at lower energy consumption. The detailed investigations were carried out according to popularly adopted methods of statistical design of experiment. The results revealed that stirrer speed, grinding time, and feed size played crucial role on the performance of stirred mill. Mathematical correlations were developed for predicting product size and energy consumption. The models developed were then optimized using quadratic programing to minimize the combination of product size and energy consumption. [ABSTRACT FROM AUTHOR]

Experiments on comminution energy of different coals under conditions for CFB (circulating fluidized bed) boilers were carried out in a jaw crusher and a parallel roller crusher. The R–R (Rosin–Rammler) distribution was used to describe the size distribution of the crushing product. The size distribution of the product has a significant influence on comminution energy. With lower values of x P =63.2% (size modulus) or α (distribution modulus), the comminution energy increases. With a fixed particle size distribution of the product, the comminution energy increases gradually with the increasing of feed coal size, while, when the feed coal size is larger than 15 mm, the effect can be neglected. With a fixed outlet width of the crusher, the average product size tends to be finer when smaller sized particles or coal with higher HGI (Hardgrove grindability index) are fed into the crusher. Therefore, in coal preparation process, the adjustment of the crusher should be performed considering coal grindability or crushability and the feed coal size distribution. At last, an empirical model of comminution energy was proposed and validated by the measured values with ±25% of accuracy. [ABSTRACT FROM AUTHOR]

Abstract: Packing characteristics of particle beds, determined mainly by the particle size distribution, exert a critical influence on the interparticle breakage of minerals in confined beds under compression. This paper is concerned with the effects of feed size distribution on characteristic phenomena of confined-bed comminution. Minus 3.35-mm quartz and calcite feeds were prepared by proportionately mixing previously classified narrow-size fractions so as to construct particle size distributions having the Gaudin–Schuhmann functional form with distribution modulus values of 0.5, 0.7, and 0.9. These feeds were comminuted in a piston-die press at five levels of applied pressure ranging between 26.5 MPa and 283 MPa, generating specific energy inputs in the range 0.65 J/g to 8 J/g depending on the material and feed size distribution. The size distributions of the comminuted solids were analyzed for self-similarity, comminution kinetics and reduction ratios. Force–displacement data were analyzed for bed compaction, energy absorption and energy utilization phenomena. The results showed definite effects of feed size distribution on these latter phenomena and product particle size distributions. The relationship between the specific energy absorbed and applied pressure is linear. Self-similarity does not hold for the coarse-size range of the products, indicating greater deviations for feeds with greater proportions of the coarse material. Breakage fraction of the top-size class (3.35×2.36 mm) particles and production of fines (minus 75 μm) are significantly high with feeds having the size distribution modulus of 0.9. Reduction ratio-specific energy input relationship is curvi-linear; energy utilization becomes better with increasing value of the distribution modulus. The observed effects are explicable in terms of the packing density of particle beds and the amount of fines in the feeds. [Copyright &y& Elsevier]

Abstract: Aspects of the literature on single particle breakage test have been reviewed in this article. The test procedures that are commonly used by the researchers in examining and measuring the breakage characteristics of the ore and coal particles are also discussed. It appears that most of the common size distribution function fitting techniques were not suitable for accurate representation of the size distributions obtained from a pendulum breaking process. The single impact test, double impact test (drop weight test, pendulum test) and slow compression test can be used to study the behaviour of the single particle breakage events. The single impact test, slow compression test and drop weight test cannot measure the energy utilization pattern in single particle breakage events, but this can be determined from the pendulum test. The energy utilized for breakage was predominantly dependent upon the size and shape of the specimen, level of input energy and the breakage properties of the specimen. This review highlights that the size distribution curves were linear in the fine particle region and have varying curvature in the coarser region, the gradient of the linear fine particle region of the size distribution curves increases with an increase in the specific comminution energy. The comminution energy increases with input energy at lower levels of input energy but at the higher levels of input energy the comminution energy did not show the same proportional increase. At a given level of input energy, the size distribution resulting from the breakage of the particles by the pendulum apparatus can be represented by a one-parameter family of curves. [Copyright &y& Elsevier]

Single-particle breakage tests of South Blackwater and Ensham coal from the Bowen Basin area in Queensland were conducted by a computer-monitored twin-pendulum device to measure the energy utilization pattern of the breakage particles. Three particle sizes (-16.0 + 13.2 mm, -13.2 + 11.2 mm, -11.2 + 9.5 mm) of each coal were tested by a pendulum device at five input energy levels to measure the specific comminution energy. When particles were tested at constant input energy, the variation of comminution energy between the same size broken particles of Ensham coal was minimal, because Ensham coal is a softer and higher friability coal, which absorbs more input energy than harder coal during breakage tests. For different particle sizes, the specific comminution energy increases linearly with the input energy and the fineness of the breakage products increases with the specific comminution energy.The size distribution graphs are curved but approach linearity in the finer region. At a constant input energy, the twin pendulum breakage product results show that the fineness of the products increases with decrease in particle size and South Blackwater coal produced finer products than the Ensham coal. The t-curves are the family of size distribution curves, which can describe the product size distribution of the breakage particles during single-particle breakage tests. [ABSTRACT FROM AUTHOR]

Despite reservations of a number of researchers concerning the applicability of Bond''s equation for relating specific energy to the size reduction of rocks, his approach has become an industry standard.Data from a large number of pilot and full-scale autogenous (AG), semi-autogenous (SAG) and ball mill circuits are used to show that Bond''s equation does not hold over the particle size range -100 mm+0.1 mm. However, if suitable correction factors are applied its results can be made to approximate observed values. It is shown that a more appropriate relationship relies on a particle size exponent that is a function of size.This new relationship, which does not rely on the need for correction factors, is used to predict the specific energy requirements of a number of autogenous, semi-autogenous and ball mill grinding circuits. The results are compared to those obtained using Bond''s equation and are shown to provide a more precise prediction of specific power requirements. [Copyright &y& Elsevier]

Abstract: The Bond work index, W i, is defined in a Bond ball mill on the samples of standard size −3.327+0mm. In practice, it is possible to find materials of non-standard size that are finer than 3.327mm. In this work, a procedure for the calculation of the Bond work index is suggested for cases when the Bond grindability test is conducted on samples of non-standard size. [Copyright &y& Elsevier]

Abstract This article deals with a study performed at the Experimental Mine of the Research Center of Responsible Mining of the University of São Paulo, to examine the correlations between geological environment, blasting parameters and energy consumption in the primary crushing phase. The research is designed to appreciate the relationships between the energy provided for size reduction and the resistances to size reduction. For this purpose, Key Performance Indicators (KPIs) are used to describe the possible improvements on the energy consumption due to crushing. Four blast tests were performed: for each blast, KPIs were recorded regarding the blast design, the particle size distribution, the real power energy consumption at the primary crushing unit and its rate of utilization. The results show that energy consumption at the primary crusher is a sum of two components: energy directly involved in crushing the rock, and additional energy used for winning the inertial resistances of the moving parts of the crusher. We show how explosive energy and delay times influence the production of coarse fragments that jam the crusher, therefore influencing machinery stops and inertia loads related to putting the jaws back into movement.

Through the concept of fractals, the new non-integer dimensional world is introduced. Experimental results to show this new world are taken from the author and his colleagues' own works. A few words are given also to the scaling law in the "Critical phenomena" in relation to sol-gel transition, and Chaos, both of which are closely related to the fractal.