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Abstract Prediction of continuous steady-state ball milling using the traditional population balance model requires knowledge of several functions, namely those describing the rate and distribution of breakage products, the mass transfer relationship between the mill hold-up and the discharge, the mode of transport within the mill, as well as the description of internal classification, whenever present. In spite of its long track record, there are comparatively few instances in which the population balance model of continuous ball milling has been validated in great detail under controlled conditions. The work analyzes how confidently one can predict continuous milling in a dry open-circuit pilot-scale operating under a wide range of feed rates, mill speeds, fillings and feed materials (an iron ore and a spent catalyst) using the population balance model. It relies on measured residence time distribution of the solids, the Austin model of grinding and the expressions recently proposed by Nomura to describe mass transfer from the mill to the discharge to predict continuous grinding. Breakage parameters of the materials studied were estimated on the basis of batch grinding tests. Parameters in Nomura's transport model were fitted on the basis of a few selected continuous tests and were used to estimate the mill hold up operating under a range of conditions. A comparison between experiments and predictions demonstrated that errors in the measurements of hold-up were, on the average, 6.0%, whereas those associated to the 80% passing size of the product were smaller than 5.6%. Graphical abstract Unlabelled Image Highlights • Modeling and simulation of grinding of spent catalyst and iron ore in pilot dry ball mill • Hold-up of continuous mill predicted using Nomura model • Product size predicted using Austin/Nomura models • Mean relative error of 6.0% for hold-up predicted using Nomura • Mean relative error of 5.6% for P80 predicted using Austin/Nomura models [ABSTRACT FROM AUTHOR]

In the early 1990s the discrete element method (DEM) was used for the first time to simulate media motion in tumbling mills. Although it has been over a quarter of a century since this tool was first used to predict media motion it has not yet reached maturity to be used in predicting product size distribution and throughput of tumbling mills. However, there has not been shortage of attempts to do so. The literature is relatively vast in the topic and researchers who embark in this area of research will find it difficult to understand the current status of development and also the similarities and fundamental differences that exist amongst the various approaches that have been proposed and pursued over the years. The paper reviews the literature on the application of models based on distributed collision energy information to predict size reduction in tumbling mills, in particular ball mills, analyzing critically various approaches proposed, their limitations and achievements, identifying areas that still require development until the technology becomes ready for being used for optimizing and designing ball mills. Finally, the advances recently accomplished on the approach proposed by the author and his co-workers are then reviewed in greater detail. [ABSTRACT FROM AUTHOR]

Abstract: Batch grinding tests have been a very good tool to aid in understanding the effect of design and operating variables in ball milling, as well as in providing data for a couple of successful scale-up methods. Recently, a mechanistic model of the ball mill has been proposed, and the present paper describes its application in the simulation of batch mills operating under a range conditions. First-order breakage rates have been estimated using data from these simulations, and used to investigate the effect of operating and design variables in milling. Predictions using the mechanistic model are then compared to those using the scale-up relationships proposed by Austin and collaborators and Herbst and Fuerstenau. The trends predicted using the mechanistic model are in general agreement with the empirical models. Good correlation has also been observed between the simulated specific breakage rates and the specific mill power, which is in agreement with the scale-up method proposed by Herbst and Fuerstenau. [Copyright &y& Elsevier]

Abstract: The understanding of how blends of materials grind is of great relevance in both the minerals and the cement industries. If benefits and challenges associated to it are properly understood, then decisions can be made on blending prior to grinding or grinding additives in separate during cement production, as well as different ores fed to mills in a processing plant. The paper investigates the size reduction of blends of materials with different grindabilities in a Bond ball mill, as well as in a continuous pilot-scale mill. The accumulation of the harder (tougher) component in the mill charge as grinding progresses is analyzed and a simple empirical model that describes this phenomenon has been proposed. It is found that the accumulation of hard component in the mill increases with the decrease in the ratio of Bond work index values of the individual soft and hard components, and with the increase in the circulating load ratio. It is also concluded that the Bond work index of the mixtures is often higher than the weighed-average value of the individual components in the mixture. As such, an expression is proposed for calculating the value for blends based on this modeled accumulation effect and has been found to remove the bias from predictions made on the basis of the weighed-average values from the feed. [Copyright &y& Elsevier]

Abstract: Breakage rates of coarse particles in ball mills generally follow non-first-order kinetics and the distribution products from batch milling are often characterized by significant contributions of abrasion besides breakage by impact, which are not well described using traditional size–mass balance formulations. Under such conditions, particles are often subject to impacts of insufficient magnitude to produce breakage in each stressing event, so that they are broken by a combination of abrasion and impact and also particles undergo weakening due to unsuccessful stressing events. The paper presents a mathematical model of batch grinding which takes into account the distribution of stressing energies in the mill, the distribution of fracture energies of particles contained in the charge, describing breakage by impacts from grinding media producing catastrophic breakage, abrasion and weakening from repeated impacts. The model has been applied to describe the rate of disappearance of two materials in batch grinding with good results. [Copyright &y& Elsevier]

Abstract: Sugar cane bagasse ash, a byproduct of sugar and alcohol production, is a potential pozzolanic material. However, its effective application in mortar and concrete requires first the controlled use of grinding and classification processes to allow it to achieve the fineness and homogeneity that are required to meet industry standards. The present paper investigates the role of mill type and grinding circuit configuration in grinding in laboratory- and pilot plant-scale on the particle size, specific surface area and pozzolanic activity of the produced ashes. It was observed that, although different size distributions were produced by the different mills and milling configurations, the pozzolanic activity of the ground ash was directly correlated to its fineness, characterized by its 80% passing size or Blaine specific surface area. From a low pozzolanic activity of less than 50% of the as-received ash, values above 100% could be reached after prolonged grinding times. Electric power requirements to reach the minimum pozzolanic activity were estimated to be in the order of 42 kWh/t in an industrial ball mill. Incorporation of an ultrafinely-ground ash in a high-performance concrete in partial replacement of Portland cement (10, 15 and 20% by mass) resulted in no measurable change in mechanical behavior, but improved rheology and resistance to penetration of chloride ions. [Copyright &y& Elsevier]

Various approaches have been used over the years to describe quantitatively ball milling, with different levels of success. The present work presents the application and validation of a mechanistic model to describe ball milling of iron ore pellet feed. The approach started by estimating selected parameters describing the ore characteristics by back-calculation from batch grinding tests, followed by validation of the model in batch grinding as well as continuous open-circuit ball milling at a pilot-scale operating at a variety of solids concentrations, both with overflow and grate discharge. An industrial ball mill was then laser scanned and surveyed, including measurements of residence time distribution. Simulations using the discrete element method were then conducted and the model was applied to simulate closed-circuit operation, resulting in good agreement between measured and predicted size distributions and circulating load ratio. [Display omitted] • Mechanistic ball mill model applied to grinding iron ore pellet feed. • Particle breakage parameters back-calculated from bench-scale ball mill tests. • Model predictions validated for other batch milling conditions. • Open-circuit pilot-scale tests predicted with good accuracy. • Application to simulation to full-scale milling circuit provided valid results. [ABSTRACT FROM AUTHOR]

[Display omitted] • An energy-based ball mill model was applied to describe two industrial-scale operations that use large-diameter mills. • Very distinct breakage and selection functions appeared when comparing PGMs and itabirite iron ores. • Reduction in ball size increased the breakage rates of fine particles in PGM ores, at the expense of a reduction in the rates of coarser particlesItabirite iron ore showed higher ameneability to breakage compared to the PGMs even though minimal differences were noted at finer sizes. • Calibration of the model based on batch-grinding data showed ability to describe industrial grinding. Phenomenological models of ball milling are routinely used to optimize size reduction operations. A usual method adopted in the minerals industry relies on batch-grinding tests to calibrate models in a population balance model formulation describing the breakage behaviour and then scale-up the breakage parameters using an energy-based relationship. Despite the important advances and application of these methods, their application in describing grinding in large-diameter (>7.5 m) mills has not been widely demonstrated. The work demonstrates the calibration of industrial-scale ball mill model parameters from laboratory milling tests on Platinum Group Metals (PGM) and Itabirite iron ores. Minor fine-tunning of a single model parameter was required to simulate the large-diameter industrial mills, demonstrating the validity of the approach for ores as distinct as PGM and Itabirite iron ores. Estimation of the Arbiter Flow Number below 4.1 showed a regular slurry transport for all mills studied. This model can then be used in optimization of the ball mill performance. [ABSTRACT FROM AUTHOR]

The planetary mill is one of the most commonly used mills for ultrafine grinding in the laboratory, given its ability to reach higher intensity of the collisions as the result of increase in rotational frequency and ball acceleration without the undesired centrifugation of the grinding charge. Several attempts have been made in the literature to develop a predictive model of this mill, with limited success. The work applies the mechanistic UFRJ mill modeling approach to predict the size distribution in a laboratory planetary mill, on the basis of single-particle slow compression data obtained using a micro compression tester, besides simulations using the discrete element method. At first, careful verification of the Hertz-Mindlin contact parameters was conducted using a video recording system that moves along with the jar during milling. Grinding tests were conducted with hematite for the mill operating at frequencies that varied from 150 to 300 rpm, resulting in generally very good agreement between model and experiments. However, agreement between the two was found to reduce for the highest rotational frequency studied. This was attributed to the reduction in grinding efficiency in the experiments that was not observed in the simulations, which resulted in predicted values overestimating fineness of the product. Finally, simulations were compared to experiments for quartz, silicon carbide and blast furnace slag under identical conditions and it was shown that the model provided very good predictions, with the exception of quartz. Overview of application of UFRJ Mechanistic Mill Model to predict planetary milling. [Display omitted] • Media motion in a planetary mill recorded using special video recording system. • Fine particle breakage data used to model key breakage parameters. • Good ability of mechanistic model in predicting planetary milling of hematite. • Predictions were optimal at lower mill frequencies. • Very good predictions for other materials at 200 rpm, with minimal model fit. [ABSTRACT FROM AUTHOR]

Characterizing the response of individual particles to stresses is of great relevance in a number of fields. In the field of grinding, important advances in mill modeling by decoupling material from machine contributions to the outcome of the process have been made in recent years that require direct information on the distribution of strengths of particles being ground. Although a number of methods and experimental devices have been proposed to measure the breakage strength of individual particles, only recently alternatives have become commercially available for testing particles in the fine size range. The paper demonstrates that a micro compression testing machine allows measuring the distribution of strengths and fracture energies of non-spherical fine particles, although great care should be taken while doing the measurements. It then shows that the mean strength of particles contained in a narrow size range is closely related to the rate of breakage of particles in the same size range in a planetary ball mill, thus demonstrating the validity of the measurements. [ABSTRACT FROM AUTHOR]

• Relationships appeared between iron ore concentrates composition and breakage characteristics in 150–45 μm sizes. • Single-particle compression tests discriminated well iron ore concentrate characteristics. • Energy utilization appeared as a good measure to discriminate between materials amenability for breakage at such fine sizes. • Higher efficiency for rigidly-mounted roll mill and piston-and-die, followed by lab-HPGR and ball mill. Production of iron ore pellets typically requires regrinding of the iron ore concentrates. Although these concentrates are produced following close control of chemical composition, substantial differences may exist in their response to the size reduction operations that are used prior to pellet formation in the pelletizing disc or drum. Establishing relationships between some intrinsic characteristics of these concentrates and their response to size reduction is, therefore, worthwhile. Single-particle breakage testing has long been used to characterize the material intrinsic response to comminution. However, application of traditional breakage tests to iron ore concentrates is not possible, given their fine sizes. The present work analyzes the application of recent single-particle testing methods that are suitable for particles in the –150 µm size range to characterize breakage of four iron ore concentrates from Brazil. The response of particles when assembled in beds is then analyzed in great detail through piston-and-die testing, as well as by comminution tests in a bench-scale ball mill and high-pressure grinding rolls. Relationships between the results in the various devices, which represent the different levels of particle interaction, have been analyzed in light of their energy utilization. Furthermore, implications of differences in particle characteristics on the differences observed in breakage response are also analysed. [ABSTRACT FROM AUTHOR]