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A mechanistic model for tumbling mills was developed based on breakage characteristics and tumbling mill operational features. The concept was presented at the IMPC (International Mineral Processing Congress) 2014, followed by progress in a sub-process of the model presented at the IMPC 2016. Additionally, a number of papers on the sub-models and breakage function have been published. This paper provides a consolidated summary of the outcomes and status of the model. The overall model structure is presented along with the sub-models such as appearance functions, breakage rate functions, energy distribution, transport, and dual component grinding interaction model. The strengths and capabilities of the model structure as achieved to date are presented. The approach developed can be used as a platform for building multicomponent models. The modelling work can be done quicker by using an existing structure such as the one presented in this paper. It is recommended that researchers assess compatibility prior to embarking on model development work if the intention is to use this model structure.

Granule breakage is an important rate process in wet granulation that promotes product uniformity and controls product size and strength. In this work, a model to predict granule breakage is proposed and experimentally validated. The model assumes exponential of the surviving granules, dependent on a probability of breakage; a function of powder and binder properties, as well as operating parameters. Validation experiments were performed with a breakage-only granulator, filled with cohesive, non-granulating sand. Premade pellets made from lactose monohydrate and silicone oils were granulated at several impeller speeds, and the number of survivors was observed over time. The results revealed that the number of granules did indeed decay exponentially. It was found that the overall probability of breakage was inversely proportional to the capillary number. Moreover, the pore saturation played an important role in determining the probability of breakage, with higher pore saturations reducing breakage overall. A comparison with experimental data from literature revealed that the developed models agrees qualitatively with the experimental data, but is unable to fully capture the effect of powder properties and powder-binder interaction.

Single particle breakage characterisation at fine sizes for use in mill modelling has been addressed by only a few researchers and is not utilised in engineering design. This is mainly due to the challenge of accurately imparting a range of impact energies to sub-millimetre particles and then measuring the progeny size distribution for the tiny resultant mass. In order to fill this gap, a dispersed monolayer multi-particle breakage method was applied with a mini JK Drop weight tester in this work to extend the single particle breakage test from 16 mm down to 425 μm, covering a specific energy (Ecs) range of 0.1 - 2.5 kWh/t to provide a wide range of test conditions. A challenge that had to be addressed was switching from single particle to dispersed mono-layer due to the physical constraints of drop-height and drop mass in maintaining accuracy in input energy over the orders of magnitude required to apply the required specific range of energy input. As only a limited size range could be subjected to both single particle and mono-layer bed breakage, it was necessary to establish if the two testing techniques provide the same breakage results. A novel application of the Fréchet distance was successfully applied to quantitatively evaluate the discrepancy of progeny size distribution between single particle breakage and monolayer multiple particle breakage. Extrapolation of an empirical Fréchet distance model indicated that the application of dispersed mono-layer breakage below 2 mm provides an acceptable comparison with the single particle breakage applied to coarser sizes, thus facilitating the fitting of a single appearance function across this wide range of sizes and applied breakage energies.

This work aims to build a generic dynamic model structure, which can accommodate interchangeable sub-models of each sub-process, making it amenable to continuous upgrade without the need for redevelopment, for multicomponent tumbling grinding mills. The Generic Tumbling Mill Model Structure (GTMMS) is based on a population mass balance framework which incorporates breakage characteristics, transport, classification along the mill, a discharge function, and energy consumption incorporated in a dynamic mill model structure. Version III builds on two earlier versions by incorporating energy distributions derived from discrete element modelling, an updated version of the 4D breakage appearance function which applies to a broader size range, and addresses multi-component ore breakage via the probability distribution of energy split based on material stiffness. The model has been tested against multi-component plant survey data. GTMMS III suggests a mechanistic insight into mixture prediction through component analysis and is a step forward towards the unified comminution model (UCM) with its mechanistic, generic, and dynamic prediction capability.

The stability of agglomerated/pelletized ores is one of the key properties for successful heap leaching of complex, low-grade nickel laterite minerals. In this paper, single pellets of saprolitic and goethitic nickel laterite with controlled binder type (tap water and 44 wt.% H2SO4), binder content and pre-set porosity were made by a pellet press and subjected to mechanical strength and rewetting stability tests. The effect of fine/coarse particles ratio on the mechanical strength was also investigated using siliceous goethitic ore. The failure strength of the pellets under different drying conditions was measured and the time taken for the pellets to disintegrate under saturated (soaking) and leaching conditions was recorded. The results showed that, with the same type of nickel laterite, the time taken to disintegration during leaching test is proportional to the pellets tensile strength. Pellets with water as binder are more stable under soak conditions. Furthermore, failure strength for oven dried pellets is greater than that of air dried. With saprolitic nickel laterite (SAP) pellets, their mechanical strength and re-wetting stability can be enhanced by drying the wet pellets or by increasing the binder content in the pellets. The pellets mechanical strength was found to be a good indication of their stability under leaching conditions as well. However, no relationship between the two was observed for goethitic nickel laterite pellets. Refereed/Peer-reviewed

In this research, TiO2 nanoparticles were treated with hydrophobic 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (fluorosilane) in acidic, neutral and alkaline conditions. The treated nanoparticles were characterized using FTIR spectroscopy, thermal gravimetric analysis, X-ray photoelectron spectroscopy, transmission electron microscopy and X-ray diffraction spectroscopy. Reflectance spectra were obtained using UV–vis diffuse reflectance spectroscopy and band gap energy of the various nanoparticles was determined. Zeta potential measurements were used to evaluate colloidal stability of nanoparticles in aqueous media. The mechanism of fluorosilane adsorption on the surface of TiO2 nanoparticles was investigated using ATR-FTIR spectroscopy and turbidimetric technique. The characterization results revealed that the amorphous fluorosilane adsorbs on the surface of TiO2 nanoparticles in both neutral (pH 6) and alkaline (pH 11) solutions. The values of the band gap energy for all treated nanoparticles were almost the same, in the range of 3.10–3.18 eV. Zeta potential measurements showed that isoelectric point of the TiO2 nanoparticles shifts from 6.8 for untreated TiO2 to 4.4 for treated one. Based on the zeta potential measurement results, it is expected that treated TiO2 nanoparticles in neutral or alkaline conditions have higher colloidal stability and better dispersion in the aqueous solutions. Hydrophobic character of fluoro specious on the surface of nanoparticles leads the treated nanoparticles migrate towards the suspension surface. Therefore, these treated nanoparticles may be useful for developing self-cleaning coatings with minimal destructive effect on the polymeric matrix. Refereed/Peer-reviewed

Nickel laterite pellets with controlled mass, porosity and binder were made by using a pellet press. Both water and sulphuric acid solution were used as binders. The wet pellets were then dried at different conditions and their mechanical strength was measured. Leaching tests were also conducted on single pellet with irrigation of sulphuric acid solution from the top of the pellet. The leached out solutions were collected and nickel recoveries were analysed. The time taken for the pellets to disintegrate during leaching test was also recorded. It was found that the mechanical strength of the pellets was directly related to their dryness, with completely dried pellets having much higher strength. The dry pellet strength was found to increase with increasing binder content and decreasing pellet porosity. The time taken for the pellets to disintegrate during leaching test increased with increasing pellet strength. In comparison to sulphuric acid solution-bound pellets at the same condition, water-bound pellets exhibited higher mechanical strength. Although the nickel leaching rate for water-bound pellets was low at the beginning of the leaching test, the pellets lasted for more than 200 h without disintegration, with 70% of nickel recovered. Refereed/Peer-reviewed

In this paper, ibuprofen from a commercial source and its fractioned samples with narrower size distribution were characterized to assess the effect of particle properties on compaction characteristics. The compaction behavior of binary mixtures of ibuprofen with spray-dried lactose was also studied. The tablet in-die densification rate and tablet out-of-die porosity and tensile strength were measured for all samples. It was found that the particle size of ibuprofen does not affect the yield stress as derived from a Heckel plot, however the yield stress increases with the increase of ibuprofen particle size in the binary mixtures. Particle size also affects the tablet out-of-die properties, with tablet porosity and tensile strength increasing with the decrease in particle size. The effect of adding a weak compacting powder such as lactose on the tablet tensile strength is very much dependent on the ibuprofen particle size and mass ratio of the binary mixtures. Mixing lactose with ibuprofen of similar size in equal mass has no effect on the tensile strength of the tablet whereas mixing it with ibuprofen of larger size reduces the strength compared to ibuprofen alone. Adding a smaller amount of lactose can lead to an increase in tablet strength, even though the particle size of ibuprofen and lactose is quite different. Theoretical analysis on the tablet strength based on particle–particle bond strength was also carried out to explain the experimental results.

This study investigates the flow properties of binary mixtures of both commercial ibuprofen and reprocessed ibuprofen through high shear milling with lactose powders. Ibuprofen is recrystallized in a 30% water–ethanol mixture before high shear wet milling (HSWM). In-situ Process Analytical Techniques (PAT) (Labmax®) is used to study the HSWM process dynamics, with particle size measured by a Lasentec Focused Beam Reflectance Measurement, FBRM®. The flow properties of the binary mixtures of the different ibuprofen particles and its binary mixtures with lactose were measured using a Schulze® RST-XS ring shear tester. Results show that the morphology of ibuprofen was changed from needle to hexagonal like crystals during recrystallization and crystal size was reduced dramatically by HSWM for 1 h. The flowability of milled ibuprofen powders is reduced significantly due to its reduced size and change of surface morphology. Mixing the HSWM ibuprofen powders with lactose enhanced its flow properties. However, the increase of the mixture flowability for HSWM ibuprofen is less significant in comparison to the binary mixtures of lactose with commercial ibuprofen.

Agglomeration of fine mineral particles as a precursor to heap leaching is an important means of enhancing leaching rates and metal recoveries, particularly in processing low grade ores. In this paper, the modelling of a batch drum agglomeration process applied to nickel laterite using population balance model is explored. The coalescence kernels which are linked to feed material and agglomerator operating conditions are reviewed. The use of a physically based coalescence kernel which relates agglomerate layer thickness to binder content and agglomerate consolidation shows great promise for the modelling of the agglomerate size distribution of nickel laterite ore. The model parameters were then used to predict the effect of operating parameters such as binder content on agglomerate size distribution. Refereed/Peer-reviewed

Wet granule breakage is a significant mechanism, particularly in high shear mixer granulation. This paper presents a study of the wet breakage mechanism using a Breakage Only Granulator. Granules with varying powder and liquid binder properties were created using single drop nucleation. These granules were inserted in a Breakage Only Granulator, a high shear mixer granulator with non-granulating cohesive sand as the bulk medium. Two different impellers were used at impeller speeds of 500 and 750 rpm. An 11° beveled edge impeller was used to create both impact and shear in the granulator, and a flat plate impeller was used to minimize impact and maximize shear in the granulator. The fraction of granules which broke during the granulation process was used as a measure of granule breakage within the granulator. These results were compared with Stokes deformation numbers calculated using mean dynamic peak flow stresses measured in unconfined uni-axial compression tests. Results for the beveled edge impeller blade show increasing breakage with increasing Stokes deformation number. Significant breakage was observed at high Stokes deformation number. Increasing impeller speed increased the magnitude of breakage. The Stokes deformations number appears to be a reasonable predictor for granule breakage within the granulator. Results for the flat plate impeller show very little breakage at 500 rpm, and significant breakage for only one formulation at 750 rpm. This suggests that either impact is dominant over shear for breakage within the granulator, or that the two impeller designs give substantially different collision velocities in the granulator. The impeller speed, type and shape have a profound effect on granule breakage in high shear mixer granulators.

Wet granule breakage can occur in the granulation process, particularly in granulators with high agitation forces, such as high-shear mixers. In this paper, the granule breakage is studied in a breakage only high-shear mixer. Granule pellets made from different formulations with precisely controlled porosity and binder saturation were placed in a high-shear mixer in which the bulk medium is a non-granulating cohesive sand mixture. After subjecting the pellets to different mixing time in the granulator, the numbers of whole pellets without breakage are counted and taken as a measure of granule breakage. The experimental results showed that binder saturation, binder viscosity and surface tension as well as the primary powder size have significant influence on granule breakage behaviour. It is postulated that granule breakage is closely related to the granule yield strength, which can be calculated from a simple equation which includes both the capillary and viscous force of the liquid bridges in the granule. The Stokes deformation number calculated from the impact velocity and the granule dynamic strength gives a good prediction of whether the granule of certain formulation will break or not. The model is completely based on the physical properties of the formulations such as binder viscosity, surface tension, binder saturation, granule porosity and particle size as well as particle shape.

In a previous paper, Hoornaert et al. ( Powder Technol. 96 (1998); 116-128) presented data from granulation experiments performed in a 50 L Lodige high shear mixer. In this study that same data was simulated with a population balance model. Based on an analysis of the experimental data, the granulation process was divided into three separate stages: nucleation, induction, and coalescence growth. These three stages were then simulated separately, with promising results. It is possible to derive a kernel that fit both the induction and the coalescence growth stage. Modeling the nucleation stage proved to be more challenging due to the complex mechanism of nucleus formation. From this work some recommendations are made for the improvement of this type of model.

The mechanical properties of a range of agglomerates and particulate coatings have been measured using a nanoindenter. The effect of formulation properties such as powder and binder properties on coating hardness is described. An attempt is also made to measure the fracture hardness with the nanoindenter. The use of indentation technology to measure fundamental agglomerate properties is critically analysed. Based on the indentation measurements and standard attrition test results, the coating hardness is found closely related to the attrition rate under standard conditions and can be used to screen different powder/binder formulations. (C) 2002 Elsevier Science B.V All rights reserved.

Granular gamma-Al2O3 support and 8 wt % CuO/gamma-Al2O3 catalyst were synthesized by a sol-gel granulation method. The pore structure, crush strength, hardness, and elasticity of these sol-gel-derived catalysts were studied and compared with similar commercial catalysts prepared by non-sol-gel methods. Alumina and CuO-coated alumina granular particles prepared by different methods have different macro- and microstructure. The sol-gel-derived granular gamma-alumina and CuO-coated gamma-alumina granular particles have a structure defined by compact packing of uniform, nanosized gamma-alumina crystallites. They are characterized by a more uniform pore size distribution and larger surface area as compared to similar commercial samples with a structure defined by packing of aggregates consisting of nonuniform gamma-alumina crystallites. Because of the differences in the macro- and microstructure, the sol-gel-derived granular samples offer higher crush strength and greater hardness than the commercial samples.

It was previously published by the authors that granules can either coalesce through Type I (when granules coalesce by viscous dissipation in the surface liquid layer before their surfaces touch) or Type II (when granules are slowed to a halt during rebound, after their surfaces have made contact) (AIChE J. 46 (3) (2000) 529). Based on this coalescence mechanism, a new coalescence kernel for population balance modelling of granule growth is presented. The kernel is constant such that only collisions satisfying the conditions for one of the two coalescence types are successful. One constant rate is assigned to each type of coalescence and zero is for the case of rebound. As the conditions for Types I and II coalescence are dependent on granule and binder properties, the coalescence kernel is thus physically based. Simulation results of a variety of binder and granule materials show good agreement with experimental data. (C) 2002 Elsevier Science Ltd. All rights reserved.

In this work coalescence of deformable granules in wet granulation processes is modelled. The model accounts for both the mechanical properties of the granules and the effect of the liquid layer at the granule surface. It is an extension to the model of Ennis ct al. (1991) to include the possibility of grannule plastic deformation during collisions. The model is written in dimensionless groups such as viscous and deformation Stokes numbers and the ratio of granule dynamic yield strength to granule Young's modulus (Y-d/E*). These variables are bulk parameters of the powder-binder mixture and also functions of the process intensify. The model glues the conditions for two types of coalescence - type I and type II. Type I coalescence occurs when granules coalesce by viscous dissipation in the surface liquid layer before their surfaces touch. Type II coalescence occurs wizen granules are slowed to a halt during rebound after their surfaces have made contact. The model explains some of the trends observed in the literature, ale pi preliminary validation of the coalescence criterion with drum granulation data is encouraging. An extension is also made to the case of surface dry granules, where liquid is squeezed to the surface during granule information.

Two steps are usually involved in producing high impact polypropylene copolymer in a continuous process. The first is to polymerize propylene using Ziegler-Natta type or more recently metallocene catalyst, and the second is to add ethylene-propylene rubber (EPR). A narrow residence time distribution (RTD) of polymer particles is an important process design and operational target in this process. The broadening of RTD will lead to a widening of copolymer composition distribution in which results in inferior product properties. There are several techniques to obtain a narrower RTD, including by controlling size of particles leaving a well-mixed reactor. In this paper, a dynamic population balance model to track polymer particle age and size is presented. The model is applied to a well-mixed slurry reactor linked to a classifier. Polymer particle growth kinetics including catalyst deactivation with particle age are incorporated. The model agrees well with steady-state analytical solutions and process data for particle age and catalyst efficiency. The classifier acts to significantly narrow particle age distribution. However, the system is very sensitive to small change in feed catalyst size, catalyst deactivation can cause build up of small polymer particles trapped in the system if the feed catalyst size is too low. As a 'soft sensor', the RTD information from the validated model provides valuable insight for operational support. Further applications include strategies of reactor control design and optimization of grade transition policy. (C) 1999 Elsevier Science Ltd. All rights reserved.

In this work, a nucleation model that includes nuclei breakage/fragmentation is proposed. The model is based on the nucleation model of Hapgood and the Stokes deformation number calculated from the granule dynamic yield strength from the previously reported granule breakage work. It is proposed that breakage or fragmentation of primary nuclei from binder spray will occur if the Stokes deformation number exceeds a certain critical number. In the case where breakage occurs the model for secondary nuclei size distribution is proposed. To validate the model, the characteristics of the primary nuclei formed from nickel laterite ores with diluted sulphuric solutions as a binder were investigated. The nuclei were produced by dropping the binder solution onto a stationary powder bed. The mechanical integrity of the primary nuclei formed, the relationship between the nuclei diameter and binder drop diameter were studied. The Stokes deformation numbers for nickel laterite powders with different particle size in a lab scale drum granulator were calculated and the nuclei size distributions with different nickel laterite feed powders are predicted. Refereed/Peer-reviewed

In this study, the bed temperature profile of a conical/plasma fluidized bed without a distributor was studied. The same reactor was also used for growing diamond by chemical vapour deposition. It was found that the fluidized bed quenches the plasma gas quite significantly. The bed temperature increases with both the plasma gas flow rate and the plasma input power. A lateral temperature difference from the centre of the bed to the wall exists due to heat loss through the wall. The temperature profiles obtained are suitable for controlling of bed quenching conditions in particle processing and synthesis. The conical/plasma fluidized bed with a distributor on top of the plasma was then applied to diamond synthesis from a gas phase using a distributor between the bed and the plasma. The deposition mainly occurred in the plasma tail flame. Both the scanning electron micrographs and Raman spectra show the existence of diamond on seed particle surfaces, but with a rather low nucleation density. The limitations of the d.c. plasma fluidized bed system are discussed and modifications to the reactor are recommended.

The coating mass distribution from a 150 mm diameter spouted bed coater was studied. Three types of seed were coated with two types of fertilizer at various feed slurry rates, total coating mass added and spouting air velocity. The coating mass distribution was strongly dependent on the initial particle size distribution. The amount of coating on a particle was proportional to its mass. Over the range covered, spouted bed process parameters (slurry rate and spouting air velocity) had no effect on the coating mass distribution. A population balance model was developed to predict the coating mass distribution. This model, using a size dependent growth term, gave excellent agreement with experimentally measured coating mass distributions for all data sets. Model predictions were not as good using a size independent linear growth term. At this stage, it is not obvious why the larger particles are coated preferentially. The population balance model was extended to predict the coating mass distribution from a continuous spouted bed coater with both representative overflow and with overflow depending on particle mass.

The spouting properties of thirteen types of particles (twelve being agricultural seeds) were measured in a 150-mm diameter cylindrical column with a 60° conical base. The particles, with sphericities varying from 0.39 to 1 (one being 0.39, others being in the range of 0.66–1.0), were investigated to determine the effect of shape factor on the minimum spouting velocity and the fountain height of non-spherical particles. By using the effective particle size, ϕ d v , in the Mathur-Gishler correlation, the minimum spouting velocity was predicted within ±20%. Using the volume equivalent size d v , overpredicted the minimum spouting velocity for particles with sphericities less than 0.75. The fountain height is calculated by first solving the mass and momentum balance equations in the spout to calculate the particle velocity at the bed surface. By including the effect of particle shape on the particle drag coefficient in the spout, the fountain height could be predicted reasonably well (within ±40% for 12 of the 13 types of particles). If the effect of particle shape was ignored, the predicted fountain heights were much lower than the experimental values.