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[Display omitted] • Breakage of coke, iron ore lump, sinter, briquette and pellet studied. • Sinter and lump have low breakage strength; coke and pellet have high. • Coke and pellet suffer limited weakening and surface breakage. • High fines generation from simulation of degradation with briquette and lump ore. • Low fines generation from simulation of degradation with coke and pellet. Mechanical degradation of steelmaking materials can have significant economic and environmental implications. Such degradation typically occurs as result of impacts during transportation and handling from their production site to the steelmaking furnace, in operations that include transfers in chutes, ship loading, stockpiling, reclaiming, wagon loading and discharging, etc. Predicting the extent of such degradation and attempting to prevent it, is worthwhile. Fortunately, mechanical degradation during such operations can now be predicted using different approaches, but a proper breakage model is required. The work presents results from single-particle breakage tests of iron ore lump, sinter, briquette, and pellet samples, besides coke, followed by fitting parameters of the Tavares UFRJ Breakage Model. These are then used to simulate degradation in a hypothetical handling circuit. Predictions demonstrate the high susceptibility of iron ore lump and briquette to fines generation, when compared to the other materials, and the occurrence of conditioning for briquettes and sinter, which is the increase in strength of particles surviving handling. Iron ore pellets and coke remained comparatively unaffected by the handling operations simulated, which is explained by their greater resistance to either body or surface breakage. [ABSTRACT FROM AUTHOR]

Understanding ore breakage is the key for the development of appropriate breakage characterisation experiments. Hence, there has been significant effort to understand a single breakage event, both from the experimental and the modelling standpoints. One particularly interesting approach is to consider breakage of a particle, for instance in a drop weight tester, as a sequence of primary and secondary breakage components. Secondary breakage is defined as subsequent breakage of progeny that takes place after the primary fracture of the parent particle due to surplus energy that is provided by the comminution or breakage testing device. This influences the spatial distribution of fragments as well as their selection. Due to the complex nature of secondary breakage, most of the researches in the past have either been dedicated to understanding primary fracture as a basic element of every comminution process or to describe the breakage process as a whole. However, the progression of breakage may be modelled properly by incorporating the sequential breakage of fragments into a breakage process model. In the paper, a novel approach is proposed to describe a single breakage event by modelling it as a process through several stages of primary fracture while appreciating the effect of sequential fragmentation. The model has three main components: the primary breakage, the selection, and the classification functions. The data that served as the basis for demonstrating this model were a number of impact experiments in an impact load cell on quartz and apatite particles. The results indicate a good correspondence between experiments and model fit. Additionally, a sensitivity analysis to changes in selection and classification functions was performed, which indicated a strong dependency of a breakage event on its sub-processes. It is envisaged that this approach will allow decoupling the contributions of the ore and of the stressing conditions on the outcome of the breakage event. [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]

The performance of a comminution and classification process depends on the design and configuration of each process unit, the configuration of the plant, the design of the control and physical properties of the incoming feed. Comminution processes should be designed to have a stable and efficient production over a wide range of conditions. However, demands from the management, operational cost, investment, maintenance or any other related field can result in process alterations that are not beneficial for the stability of the circuit and, therefore, utilization and efficiency of the production. Furthermore, advanced process control and optimization rely heavily on understanding the dynamic behaviour of the process in achieving a more stable and consequently efficient process. This review aims to explore different dynamic aspects from particle, bulk, unit and process perspectives, their origin, and what consequences they may have on the operation. The aim is to illustrate a holistic view of process dynamics that should be considered when evaluating circuit performances and identifying risk zones that affect the process, considering the state-state performance and dynamic behaviour. Based on that, several dynamic related issues were formulated and ranked by experts within the field to get a subjective perspective. Issues such as process control design and configuration, ore variability, segregation and upstream disturbances ranked high in possible gains for comminution processes. [ABSTRACT FROM AUTHOR]

• Innovation is key to improving the environmental performance of the mining industry. • Benefits of adopting circularity (open-loop CDW recycling) in mining are exhibited. • Novel LCA scenarios in aggregates production combining state-of-the-art methods. • Mine-to-product simulation assists in reducing epistemic uncertainty in LCA. • Comprehensive and regionalized LCI considering both mine and product life cycles. Sustainability in mining must be envisioned from a more comprehensive perspective that involves the management of primary and secondary resources and that prioritizes the adoption of innovation beyond a techno-economic mindset. The holistic Life Cycle Assessment (LCA) methodology is useful to diagnose the environmental profile of mining operations seeking a greater contribution to sustainability. This work proposes an enhanced life cycle-based approach for the minerals industry, which is supported by mine-to-product process simulation, scenario analysis, and a comprehensive and context-specific data collection involving the life cycles of the product and the mining project. The convenience of this approach in terms of reducing epistemic uncertainty is demonstrated with a Brazilian case study of a large-scale granitic quarry operation. It is shown that mining can contribute to sustainability by adopting sustainability-driven innovation and circularity principles. The proposed methodology can be applied to other mineral commodities and geographic contexts. [ABSTRACT FROM AUTHOR]

• Manuscript describes approach to characterize fracture energies at wide size ranges. • Direct measurements of fracture energies of a few sizes are the basis of the model. • Data for a copper ore has been used to demonstrate application of the approach. Breakage probabilities and fracture energy distributions have now found application in several mathematical models that simulate both degradation during handling and comminution devices. Unfortunately, measurement of these at the range of sizes of interest, in particular in the case of fine sizes, is not a straight-forward task. The paper proposes a procedure to estimate breakage probability distributions over a wide range of particle sizes by combining direct measurements of fracture energies at a selected size to back-calculated values estimated on the basis of progeny size distributions from breaking single particles over a wider range. Whereas direct measurements of fracture energies were carried out in a short impact load cell device, energy-dependent progeny size distributions were conducted by propelling particles against a target in rotary breakage testing devices. The work demonstrates how the parameters that characterize the variation of particle fracture energies with size can be fitted in a stage-by-stage process, with successful application to characterizing breakage of a copper ore contained in the range from 37.5 to 0.25 mm. [ABSTRACT FROM AUTHOR]

• Strong size dependency in wear rates in Bond abrasiveness test. • Wear rates deviate from linearity at short times and also at long tumbling times, when sample replacement does not occur. • Variation of product fineness as a function of paddle hardness. • Good correlation between % −1 mm in Bond abrasiveness test and LA abrasion index. Nearly 80 years ago Fred Bond proposed his abrasiveness test, also known as Allis Chalmers abrasion test, together with empirical equations that have been used to predict the wear of mill and crusher liners, besides grinding media. Although those equations have been widely criticized over the years, in particular owing to the limited accuracy of the correlations originally proposed to predict wear, it remains the most widely used test to measure ore abrasiveness in the minerals industry. The work analyzes the test, through experiments conducted under conditions that differ from those originally proposed by Bond in order to gain insights on metal wear and particle breakage. The effects of particle size, ore competence, metal hardness and time of batch operation are analyzed. It is shown that initial particle size strongly affects the rate of wear, that the intensity of fragmentation varies with hardness of the paddle and that the size distribution from the ground material offers a valid proxy for ore competence that may be useful in geometallurgical studies. [ABSTRACT FROM AUTHOR]

Life Cycle Assessment (LCA) is a widely-used methodology for estimating the potential environmental impacts of technological systems in nature. Relative maturity of this method has been achieved thanks to recent standardization efforts, although there are still several challenges, particularly in the minerals industry where LCA still needs to be strengthened and extended in use. An exhaustive review of recent LCA studies on mining and mineral processing operations was conducted to identify how these have dealt with various methodological challenges. A total of twenty-nine studies were found, most of which focusing on developed regions and in three commodities: coal (28%), aggregates (21%), and copper ores (14%). The source of data for background processes has been the Ecoinvent database in 45% of the studies analyzed, whereas the SimaPro software has been the preferred LCA tool in 66% of such studies. Although important advances have been made, significant issues remain. For instance, inconsistencies were found in the definition of the functional unit and system boundaries (temporal and technological). Further, the adoption of allocation criteria and the use of normalization and weighting in impact assessment have not been considered in most cases. While climate change was the main environmental hotspot (more than 90% of the studies addressed this impact category), the impacts associated with water use and waste management have been overlooked in most studies. Furthermore, mining and processing operations have been described as generic, averaged values or as simple functional relationships between system inputs and outputs using parameters without physical significance ("black box models") in several production chains, making it difficult to identify opportunities for environmental sustainability enhancement within the sector. The work then discusses the opportunity of improvement in LCA in the minerals industry through the incorporation of process simulation from a bottom-up perspective. Evidence from other industries and recent advances in the computational development of such tools for the mineral sector are reviewed, which suggests that there is an opportunity for reducing the epistemic uncertainty in future LCA studies of mining and processing operations through the combination of both approaches. Image 1 • Critical evaluation of recent peer-reviewed LCA studies in the minerals industry. • Methodological challenges of LCA within this sector are discussed. • Potential improvements in LCA from a bottom-up approach are examined. • Process simulation coupled with LCA can become a reality for the mining sector. [ABSTRACT FROM AUTHOR]

Important advances have been made in understanding ball milling during the last 25 years or so, a great part of it owing to the widespread application of the discrete element method (DEM), which is now an integral part of several advanced ball mill models. These models, however, must rely on assumptions regarding the mill mechanical environment that can help make the problem more manageable. The paper analyzes the validity of some assumptions that have been the basis of several advanced ball mill models by conducting DEM simulations of dry batch mills including both grinding media and particles. The validity of the assumption of perfect mixing of grinding media and particles, as well as of simulating exclusively the grinding media in order to collect the collision energy information for prediction of breakage and, thus, saving computational effort, are analyzed in great detail. It is concluded that the assumption of perfect mixing in the radial direction is generally valid, except for mill frequencies that are unusually high and exceedingly large ratios of mean ball and particle sizes being ground. It is also observed that a fraction of the number of collisions inside the mill do not involve particles, so that an empirical expression that is based on the ratio of surface areas of the ball and particle charge is proposed to estimate such proportion of unsuccessful collisions. Finally, a model from the authorś laboratory, that assumes that each collision in the mill will involve a monolayer bed of particles, is tested, demonstrating reasonable agreement when compared to simulations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effects of solids content, pH, slurry temperature, coagulant and surfactant dosage were studied. • Ceramic filtration performance of iron ore slurries analyzed through cake moisture and thickness and capacity. • Solids content has the greatest effect on the system studied. • Coagulant addition improved capacity at low solids content. Although ceramic capillary filtration is a novel technology, it is proving rapidly to be an attractive alternative for dewatering slurries in the minerals industry. For instance, it has demonstrated great potential for application to iron ore slurries. However, the current understanding of effects of its variables on the performance of the process is still limited. The present work investigates the effects of solids content, pH, slurry temperature, and coagulant and surfactant dosage on ceramic filtration performance of iron ore slurries. The experiments were conducted both varying one variable at a time and following a response surface approach (Box-Behnken design), being carried out either in batch or pilot-scale. The results show that solids content is the variable with the greatest impact on ceramic filtration and that addition of a coagulant increased capacity of the filtration system at lower solids content. Furthermore, it is concluded that the addition of neither of the surfactants studied is recommended for ceramic filtration of the ore in question due to significant reduction in productivity of the plates. [ABSTRACT FROM AUTHOR]

Abstract: In spite of its relative operational simplicity and earlier attempts to model its performance, the Vertical shaft impact (VSI) crusher is still lacking a comprehensive mathematical description that allows predicting its performance accurately. One of the reasons is the limited knowledge of particle interaction and solids flow inside the machine. The paper deals with the application of the discrete element method (DEM) in the prediction of solids flow within a pilot-scale VSI crusher operating under different conditions. A large amount of data has been generated and used to calculate the collision energy spectra, as well as the residence time distributions of rock particles that are fed to the machine. It is shown that the collision energy distribution and frequency change significantly if rock or a ring of steel anvils is used as the target and also if a cascading flow of material bypasses the rotor directly into the crushing chamber. Finally, it is discussed how these data, along with models that describe breakage and damage of single particles, can serve as the basis for the development of a fully-predictive model of comminution in this machine in the future. [Copyright &y& Elsevier]

Abstract: Mathematical models of grinding mills and crushers are undergoing significant advances in recent years, demanding ever more detailed information characterizing ore response to the mechanical environment. In a mechanistic model of a comminution machine, the type of characterization data used should cover, as much as possible, the conditions found inside the size reduction machines. This applies to the particle size, the stressing energy and rates that particles are subject to, the breakage mechanism and the level of interaction of the particles during stressing, which all must be described appropriately. Whereas, a very large number of experimental techniques and published data exist that allows understanding and quantitatively describing the response of single particles to stressing, comparatively little information exists on the breakage of particles contained in beds. The present work investigates breakage of particle beds impacted by a falling steel ball in unconstrained conditions, such as those that are likely to be found in tumbling mills. The influences of particle size, impact energy, ball size and bed configuration are investigated for selected materials and a mathematical model is proposed that describes the influence of all these variables. The key element of this model is that it allows predicting breakage in monolayer unconfined particle beds with a combination of single-particle breakage data and functions that describe energy partition and volume of material captured in the bed. This model has been calibrated and validated using data from quartz, granulite, limestone and a copper ore, with good agreement. [Copyright &y& Elsevier]

• DEM-MBD-PRM coupling simulations used to study roll skewing. • Uneven feed regarding rate, top size and fracture energy causing skewing were studied. • When uneven feed to the HPGR no longer occurs, simulations show that skewing ceases. • Simulations show the application of differential pressure on the pistons to reduce skewing. • Heterogeneity in force profile is higher when skewing is disabled. Roll skewing is an integral part of the operation of most HPGR designs presently used and is the result of the system attempting to compensate for uneven reaction from the particle bed along the length of the rolls to the applied forces. Several studies in recent years have simulated HPGR performance using the discrete element method (DEM). However, even when coupled to multi-body dynamics (MBD), these simulations have been limited to the description of one-dimensional motion of the rolls. The present work uses a combination of DEM and MBD to describe two-dimensional motion of the floating roll, making predictions of HPGR operation under skewing possible. Simulation case studies were carried out of a pilot-scale HPGR considering the case of uneven feeding, besides cases in which the feed is segregated with respect to particle size and also strength, represented by different median particle fracture energies, fed to each section of the rolls. Results show that the force profile along the bed and the product fineness along the length of the rolls become more uniform if skewing is allowed in the presence of uneven feed. [ABSTRACT FROM AUTHOR]

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]

• RHA's pores improved paste hydration kinetics and acted as an internal curing agent. • RHA meso/macropores volume decreased during grinding affecting RHA pozzolanicity. • Until 28 days, reduction on RHA particle size increased the compressive strength. • At 91 days, interaction of RHA replacement and size increased compressive strength. • Coarse RHA should be used in higher contents for increasing compressive strength. Compressive strength evolution of high strength concrete with rice husk ash (RHA) was evaluated as a function of RHA particle size , porous structure and replacement content. RHA porous structure was investigated by N 2 absorption isotherm and its effect on hydration evaluated using isothermal calorimetry and thermogravimetry. Results indicated that RHA particle size influenced compressive strength until 28 days, whereas at 91 days replacement content became the significant factor. Preserved porous structure of RHA particles besides improving hydration kinetics enabled its action as internal curing agent improving compressive strength at late age. [ABSTRACT FROM AUTHOR]

[Display omitted] • Size-dependent fracture energy distribution and progeny size distribution characterized by uniaxial slow compression tests. • An energy-based model describing single-particle breakage by slow compression is proposed. • Energy absorbed by single particles during compression is modeled as function of particle thickness. • Model able to capture changes in particle fracture energy, stiffness, shape and breakage intensity. • Model validity demonstrated by predicting progeny distribution and energy consumption in double roll crusher. Compression of particles to a fixed final gap is the mode of application of stresses in many crushing devices. Understanding and modelling this particle fracture process is indispensable for comminution operations. The present work is based on detailed compression tests conducted with a polymetallic ore to different applied deformation ratios to characterize the size-dependent fracture energy distribution and progeny size distribution. An energy-based model is then proposed that accounts explicitly for particle thickness and maximum deformation to define if the particle is classified for breakage (classification function), the likelihood that the classified particle is sufficiently nipped to break (breakage probability) and the extent of breakage the particle will undergo (breakage distribution). Expressions that allow calculation of the energy absorbed by the particle in both primary and secondary breakage regimes are proposed. The validity of the model is demonstrated by accurately predicting, without any fitting, the progeny and energy consumption of compression using fixed gaps and breakage in a double roll crusher. The advantage of the approach not only lies in its ability to accurately predict the product size distribution, but also the energy demanded in the operation. [ABSTRACT FROM AUTHOR]