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In this contribution a dynamic model of maize breakage in hammer mills of different scales is proposed through a population balance approach. The results of the pilot-scale experiments were used to fit the parameters of the breakage and classification functions, considering the effects of rotor speed and screen opening size. The model was validated with both pilot- and industrial- scales steady-state data, which also included variations in feed rates. The developed model was used to predict the dynamic behavior of the product mass geometric mean diameter and mill hold-up as a function of disturbances in the feed rate and the rotor speed. These results are highly valuable since they indicate the feasibility of using the fitted model to predict with confidence new operating points, study industrial milling performance and optimize hammer mill operation reducing the need to carry out expensive and time-consuming experimental tests. Unlabelled Image • A dynamic PBE model of maize breakage in different scales hammer mills is proposed • The model incorporates the effect of rotation speed and screen opening size • PSD, mass mean diameter and mill hold-up are predicted in pilot and industrial scales • The model correctly represents milling operation through different scales [ABSTRACT FROM AUTHOR]

Reducing the particle size of biomass is of great significance for rational and efficient utilization of biomass. In this study, maize grain, stover, and cob were comminuted at different speeds (2000-2800 r/min) by hammer mill with a mesh size of 2.8 mm. The mechanical energy for smashing three selected samples was obtained directly through the sensor and data testing system. Experimental results demonstrated that the maize cob had the highest total specific energy while the maize grain had the lowest (135.83-181.10 kW·h/t and 27.08-36.23 kW·h/t, respectively). In addition, for the same material, higher hammer mill speed generated more specific energy consumption. And the effective specific energy of maize stover had a similar trend to the total specific one. However, the effective specific grinding energy of maize cob and grain increased initially and then decreased with the increase of rotating speed. The fitting curves of the specific energy to mill speeds were determined, and the range of determination coefficients of the regression equation was 0.933-0.996. Particle size distribution curves were drawn by sieving the pulverized particles of the three samples based on a series of standard sieves. Fourteen relevant parameters characterizing the particle size distribution were calculated according to the screening data. Calculation results demonstrated that larger rotational speed leads to smaller particle sizes. Combining the size parameters, distribution parameters, and shape parameters, it was found that the distributions of the three samples all exhibit a distribution of "well-graded fine-skewed mesokurtic". The Rosin-Rammler function was considered to be suitable for characterizing the particle size distribution of maize grain, stover, and cob particles with a coefficient of determination between 0.930 and 0.992. [ABSTRACT FROM AUTHOR]

Dry or powdered formulations of food additives facilitate transportation, storage, preservation and handling. In this work, dry formulations of bacterial cellulose and carboxymethyl cellulose (BC:CMC), easily redispersible and preserving the functionality of the never-dried dispersions are reported. Different processing parameters and their effect on the materials properties were evaluated, namely: (i) wet-grinding of BC (Hand-blender, Microcut Head Impeller, High-pressure Homogenizer), (ii) drying of BC:CMC mixtures (fast drying at ≈ 130 °C and slow drying at 80 °C) and subsequent (iii) comminution to different particle sizes. The dispersibility of the obtained BC:CMC powders was evaluated, and their functionality after redispersion was assessed by measuring the dynamic viscosity, the effect in oil/water interfacial tension (liquid–liquid system) and the stabilization of cocoa in milk (solid–liquid system). The size of BC fibre bundles was of paramount relevance to its stabilizing ability in multiphasic systems. A more extensive wet-grinding of the BC fibres was accompanied by a loss in the BC:CMC functionality, related to the increasingly smaller size of the BC bundles. Indeed, as the Dv (50) of the wet BC bundles was reduced from 1228 to 55 µm, the BC:CMC viscosity profile dropped and the effect on interfacial tension decreased. This effect was observed both on the never-dried and dry BC:CMC formulations. On the other hand, the drying method did not play a major effect in the materials' properties. In a benchmarking study, the BC:CMC formulations, at a low concentration (0.15%), had better stabilizing ability of the cocoa particles than several commercial cellulose products. [ABSTRACT FROM AUTHOR]

• Particle replacement model was implemented in a DEM commercial code. • Breakage of particle beds by compression and impact was studied. • Fragmentation of iron ore pellets was modeled and simulated. • PR model calibrated on the basis of analytical models and experiments. • PR model validated by comparison with experiments. The present work introduces a particle replacement model implemented in the commercial software EDEM to describe breakage of particles. Several model parameters were initially estimated on the basis of single-particle breakage tests on iron ore pellets. The model was then used to simulate breakage of particle beds by both slow compression and impact. Model predictions were compared to experiments in terms of compressive force versus packing density, breakage probability of the particles versus compressive force applied to the bed, and the product size distribution in compression and impact. The model showed the expected trends as well as some agreement with the measured product size distributions both from confined and unconfined stressing conditions of the bed of particles, being a simple and effective approach to describe breakage in systems where particles are stressed as assemblies. [ABSTRACT FROM AUTHOR]

Polybutylene terephthalate (PBT) – polycarbonate (PC) multi-materials with a PBT mass content of 25% to 75% were produced for the powder bed fusion process by the means of co-grinding and spray agglomeration. The influence of the PC content and the process parameters on the thermal properties of the obtained powders are discussed in detail. Compared to pure PBT powder, the PBT/PC multi-materials crystallize at lower temperatures, which improves the handling during the additive manufacturing process. [ABSTRACT FROM AUTHOR]

Stirred media mills are used by the mining industry for ultrafine grinding to enhance liberation, and to decrease particle sizes of industrial minerals to tailor functional properties. This review describes stirred media mill technologies and operating principles, and summarises stress intensity theory which can be used for selecting efficient operating conditions. For fine and ultrafine grinding, the Bond work index is an inappropriate measure of grindability, so alternatives are discussed. Using literature data, the variation in the appropriate energy-size models between examples is assessed, and rationalised with stress intensity theory. A Rittinger operating index was found to be the best choice for assessing operation efficiency. Finally, a modification of stress intensity theory that tunes operating conditions based upon material properties, and the f mat mastercurve theory are discussed, with the conclusions that, although promising, laboratory-scale milling tests remain the most practical method of assessing material grindability and predicting industrial energy requirements. Unlabelled Image [ABSTRACT FROM AUTHOR]

An essential element for sustainable use of renewable resources is an efficient comminution process for which the relation between energy input and size reduction is of great importance. Fine comminution of beech, oak, and spruce wood chips in cutting and hammer mills at different moisture content levels is investigated. The influence of the different process parameters as well as the size reduction performed by the hammer and cutting mill on the specific comminution energy is reported and the particulate properties of the comminution products are reported. Considering the energy requirements, functional relations were derived from the experimental results, which describe the relation between comminution energy and size reduction. [ABSTRACT FROM AUTHOR]

Despite many attempts to establish material grindability in a milling process, it remains very difficult to predict the milling performance. In this study, impact milling tests were carried out under varying operational conditions in a UPZ100 impact pin mill. The product size distribution and fineness of milled alumina particle are reported and analyzed. A multiscale framework coupling discrete element method (DEM) and population balance model (PBM) is proposed to predict the milling performance of the mill. The impact velocity and impact frequency information from DEM is utilized to inform the mill operation parameters of the PBM model at the process scale, whilst the material grindability parameters are evaluated using constrained optimization to match a milling test. The predictions of the product size distribution show very good agreement with the experimental results. This indicates that the multiscale model is promising for optimizing the design and operation of mills. Unlabelled Image • Alumina particles were milled under varying operational conditions. • Particle statistics were obtained from DEM simulations of the pin mill. • A multiscale DEM-PBM model was proposed to predict milling performance. • Validation of the multiscale model was performed for the industrial pin mill. [ABSTRACT FROM AUTHOR]

As a waste product, oyster shells pose a major environmental pollution problem and the reuse of the material is becoming increasingly important. Since the comminution process in the recycling of secondary raw materials defines the properties of the material, oyster shells were grinded using a planetary ball mill and an impact mill and the fractions obtained were analyzed in terms of size and shape and compared with each other. A comminuted material from the impact mill was used for a series of wetting experiments, which helped to demonstrate the surface free energy of the material. [ABSTRACT FROM AUTHOR]

Due to increasing energy requirements for buildings, thermal insulation composite systems (TICS) have been used to insulate building facades since the 1970s. In view of the longevity of these composite materials, there has been an increased amount of TICS waste in recent years. Since there is no current recycling concept for these systems, an enormous resource efficiency potential remains unused. Due to the complexity of composite materials this study focuses on the pretreatment and discusses different processing steps in detail. [ABSTRACT FROM AUTHOR]

A laboratory sized jaw crusher with uniform movement of the jaws, the dual pivoted jaw crusher, was used to determine the relationship between wear and work. Wear was concentrated on the jaw plates opposing each other and was measured as mass loss of the specimens. Work was measured directly from the force and displacement of the instrumented jaw, which allowed work to accumulate only from the actual crushing events. The tests were conducted with several jaw geometries and with two motional settings, where the relation of compressive and sliding motion between the jaws was varied. The tests showed that the relation between wear and work was constant in many of the tested cases. In certain tests with larger lateral and faster contact speed, wear occurred at relatively lower amounts of work. This behavior was more definite when the relation of wear and work was investigated using modified Archards wear equation. The results indicate that the lower amount of needed work could stem from the material reaching a dynamic situation, where the flow stress becomes increasingly strain-rate dependent. [ABSTRACT FROM AUTHOR]

A series of axial loading and unloading compression tests was conducted on siliceous and calcareous sand, using a modified oedometer apparatus. Samples were prepared using aspect ratios of 6:1 and 1:1 (diameter:height) and loaded at uniform axial strain rates of 0.01 and 10%/s. Compression was arrested at various strains up to 30%, after which the size distribution of the sand particles was determined using a dynamic particle size analyzer capable of identifying particle shapes and sizes in the 10–3000 µm range. Samples responded slightly stiffer and experienced more crushing in the 1:1 aspect ratio tests. For silica sand, significant reduction in grain size was observed beyond 10% strain, with modest rate dependency observed. Faster breakage and greater rate sensitivity were seen in the softer coral sand, where particle breakage was observed to start at 5% strain. Strain-hardening behavior and hysteresis were observed in the stress–strain behavior and correlated with the size reduction observed in the arrested tests. In addition, it was noticed that smaller particles break more than larger particles. Both sands exhibited fractal particle evolution, i.e., when particles fracture, daughter particles preserve a similar sphericity to that of the parent material. [ABSTRACT FROM AUTHOR]

This paper presents the design and application of a multiple-input–multiple-output fractional order proportional-integral (MIMO FOPI) controller to a grinding mill circuit. The MIMO FOPI controller parameters are tuned using an off-line optimization process based on Particle Swarm Optimization (PSO). Its performance is compared to a single-input–single-output fractional order proportional-integral (SISO FOPI) controller designed and tuned using the same procedure based on PSO. The results show that the MIMO FOPI achieves better results compared to the SISO FOPI controller in most of the cases simulated, even in the presence of hardness and composition variations in the processed ore, and also in the presence of process noise. [ABSTRACT FROM AUTHOR]

In recent years, several definitions of entropy have been proposed and used in the literature to assess the efficiency of processes in the field of raw materials, including waste management, the circular economy and mineral separation. However, these definitions lack a common framework, making it difficult to compare them and assess their similarities, connections, and complementarities. In this contribution, we propose a common framework which describes the calculation of the entropy of particulate systems. This framework extends existing definitions and introduces new insights into their combination. Our approach focuses on describing disperse particulate systems in comminution, separation, and classification processes, with potential extensions to evaluate other processes of particle technology, such as mixing, sampling, and agglomeration. [Display omitted] • Common framework entropy analysis in the field of raw materials. • Description of liberation and comminution using statistical entropy. • Perfect liberation and perfect separation do not generate additional entropy. • Combined optimisation of comminution and separation using statistical entropy. [ABSTRACT FROM AUTHOR]

• Breakage function of coke breeze exhibited non-normalizable response. • Very good agreement of size-mass balance model for batch tests operated under different conditions. • Reduction of breakage rates with increase in moisture. • Good agreement between model predictions and full-scale rod mill surveys. Limited to less than 5 m in diameter and, as such, no longer found in large-scale circuits, rod mills remain popular in medium- and small-scale plants, primarily owing to their ability to prevent overgrinding. One successful application of rod milling is in size reduction of coke breeze, a material generated from mechanical degradation of coke during handling which is used as solid combustible in iron ore sintering. The work investigates the grinding response of coke breeze in a laboratory rod mill, through experiments conducted with narrow-size feeds under a range of conditions. Data has been described using the size-mass balance model, which demonstrated that coke exhibits non-normalizable breakage response, with an inflexion point at 0.27 mm. The model showed very good ability to predict grinding of different narrow sizes after being fitted form a single test. The validity of the Austin-Klimpel-Luckie scale-up relationship, incorporating an additional correction term for moisture, has then been demonstrated by comparing results from experiments with different rod sizes, mill fillings, interstitial fillings and moisture contents to predictions, with very good agreement. Finally, predictions of product size of an industrial mill operating at different throughputs were also in good agreements to data collected in plant surveys, demonstrating the great potential of the model in optimizing full-scale operations. [ABSTRACT FROM AUTHOR]

• Comminution for mining and cement industries accounts for over 2% of global energy consumption. • Innovative Gyratory Rolls Crusher (GRolls) technology has been developed in South Australia to reduce energy and water consumption, providing dry and wet crushing. • The GRolls simultaneously applies pulsed compression and shear forces to a packed particle bed inducing compression crushing, inter-particle compression, induced tensile failure and particle shear forces. • The gyratory eccentric off-set is equivalent to an open and closed size setting for a cone crusher, with off-sets of < 0.1 mm targeting particle generation of < 100 µm, resulting in fines (<75 µm) generated during a single pass ranged from 19 % to 64 %. • Commercialisation pathway includes extensive testing of a proof of concept lab unit leading to a concept design for pilot scale unit semi-commercial testing programs. Comminution for mining and cement industries accounts for over 2 % of global energy consumption and an innovative Gyratory Rolls Crusher (GRolls®) technology has been developed in South Australia to reduce energy and water consumption, providing dry and wet crushing from ∼ 20 mm to 20 µm fractions without media, replacing up to two stages of size reduction. The GRolls® is a compression based particle size reduction device, designed to generate fine and ultra-fine products from coarse feeds, by simultaneously applying pulsed compression and shear forces to a packed particle bed. The breakage mechanisms initiated by these forces include compression breakage, inter-particle compression, induced tensile failure and particle shear forces generated by a gyrating roll. The paper presents the commercialisation pathway of the GRolls® technology, from "proof of concept" laboratory scale Alpha prototype and concept design of an upscaled Beta prototype for a pilot plant. A systematic progression of laboratory scale testing of a wide range of feed materials through the Alpha prototype was undertaken to confirm the '"proof of concept" design and identify the many design variables and operational configurations that affect the GRolls® crushing and energy performance. The test results were evaluated against currently available comminution solutions such as the High Pressure Grinding Rolls (HPGR) and Vertical Rolls Mill (VRM) in which the mining section is moving towards to provide more economical dry comminution and a progression towards partial to full dry process flowsheets. The commercialisation pathway has confirmed the broad performance range and energy consumption of the GRolls® which could be modularised in the near future to support new and existing low grade mining operations in remote areas restricted by limited water and power infrastructure. [ABSTRACT FROM AUTHOR]

There is no doubt about the practical interest of Fred Bond’s methodology in the field of comminution, not only in tumbling mills design and operation but also in mineral raw materials grindability characterization. Increasing energy efficiency in comminution operations globally is considered a significant challenge involving several Sustainable Development Goals (SDGs). In particular, the Bond work index (wi) is considered a critical parameter at an industrial scale, provided that power consumption in comminution operations accounts for up to 40% of operational costs. Despite this, the variability of wi when performing the ball mill Bond’s standard test is not always understood enough. This study shows the results of a variability analysis (a 33 factorial design) performed to elucidate the influence on wi of several parameters obtained from the particle size distribution (PSD) in feed and product. Results showed a clear variability in the work and grindability indexes with some of the variables considered.

Six different particle size distribution (Gates–Gaudin–Schuhmann (GGS), Rosin–Rammler (RR), Lognormal, Normal, Gamma, and Swebrec) models were compared under different metallurgical coke grinding conditions (ball size and grinding time). Adjusted R2, Akaike information criterion (AIC), and the root mean of square error (RMSE) were employed as comparison criteria. Swebrec and RR presented superior comparison criteria with the higher goodness-of-fit and the lower AIC and RMSE, containing the minimum variance values among data. The worst model fitting was GGS, with the poorest comparison criteria and a wider results variation. The undulation Swebrec parameter was ball size and grinding time-dependent, considering greater b values (b > 3) at longer grinding times. The RR α parameter does not exhibit a defined tendency related to grinding conditions, while the k parameter presents smaller values at longer grinding times. Both models depend on metallurgical coke grinding conditions and are hence an indication of the grinding behaviour. Finally, oversize and ultrafine particles are found with ball sizes of 4.0 cm according to grinding time. The ball size of 2.54 cm shows slight changes in particle median diameter over time, while 3.0 cm ball size requires more grinding time to reduce metallurgical coke particles.