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Aggregation of nanoparticles in high ionic strength suspensions: Effect of Hamaker constant and particle concentration

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ADVANCED POWDER technology 2012年第4期23卷 478-484页

作者： Macpherson, Siubhan A. Webber, Grant B. Moreno-Atanasio, Roberto Univ Newcastle Sch Engn Ctr Adv Particle Proc & Transport Callaghan NSW 2308 Australia

The kinetics of aggregation of nanocolloidal particles in suspensions has been studied using computer simulations based on Discrete Element Method. This study presents the analysis of the influence of Hamaker constant, Brownian forces and particle concentration on the aggregation time of nanoparticles in high ionic strength suspensions. particle adhesion and cohesion were simulated using the van der Waals force equation. Half the particles were assigned a Hamaker constant of 9.0 x 10(-20) J and the other half of the particles had the Hamaker constant varied from case to case with values between 1.0 x 10(-20) and 9.0 x 10(-20) J. Aggregation times obtained from analysing the number of interparticle contacts and number of singlets in the suspensions have been used to characterise the speed of the aggregation process. The simulation results show that when the strength of the van der Waals interaction increases the aggregation time decreases following a power law. In addition, the presence of Brownian forces speeds up the aggregation process. Finally, the relationship between packing fraction and aggregation times for singlets and contacts has been very well expressed by power laws. (C) 2012 The Society of Powder technology Japan. Published by Elsevier B.V. and The Society of Powder technology Japan. All rights reserved.

关键词： Discrete Element Method (DEM) Colloidal suspensions van der Waals forces Binary mixtures

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Aggregation of nanoparticles in high ionic strength suspensions: Effect of Hamaker constant and particle concentration

Aggregation of nanoparticles in high ionic strength suspensi...

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particle technology and mineral processing sessions/conference on chemeca

作者： Macpherson, Siubhan A. Webber, Grant B. Moreno-Atanasio, Roberto Univ Newcastle Sch Engn Ctr Adv Particle Proc & Transport Callaghan NSW 2308 Australia

关键词： Discrete Element Method (DEM) Colloidal suspensions van der Waals forces Binary mixtures

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Upgrading of low-grade gold ore samples for improved particle characterisation using Micro-CT and SEM/EDX

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ADVANCED POWDER technology 2012年第4期23卷 498-508页

作者： Agorhom, Eric A. Skinner, W. Zanin, M. Univ S Australia ARC Special Res Ctr Particle & Mat Interfaces Ian Wark Res Inst Mawson Lakes SA 5095 Australia

There is a considerable challenge in accurate characterisation of gold (Au) particles in low-grade plant ore mineral samples. This is particularly true for automated mineralogical tools such as X-ray micro-computed tomography (Micro-CT) and scanning electron microscopy (SEM), where the need for statistically meaningful numbers of particles requires many sections to be analysed. Whiles the Vertical Gas Stream (VGS) elutriator is suitable for coarse particle upgrading (i.e. >38 mu m), the performance is poor for finer particles (i.e. <38 mu m). Consequently, the system has been modified to Vertical Water Stream (VWS) elutriator using higher density fluid (i.e. water) to enable analysis of Au particles below 38 mu m. In this work, the VGS system was used to upgrade Au particles in the -53 + 38 mu m size fraction (in rougher concentrate, rougher tailings, regrind mill discharge and regrind cyclone underflow) and the VWS system was used to upgrade Au particles in the -38 mu m size fraction of the regrind mill discharge sample. The VWS elutriator was calibrated using galena (specific gravity, S.G. of 7.58) and quartz (S.G. of 2.65) particles of <38 mu m size as model minerals. From the calibration tests, partition curves as a function of particle size were generated. Using these measurements, theoretical partition curves for Au (S.G. of 19.3) have been calculated. The VWS concentrate was characterised using Micro-CT and compared with SEM coupled with energy dispersive X-ray (EDX) analysis of -53 + 38 mu m ore size fraction of the VGS concentrate of the four sample streams. The Micro-CT analysis of VWS Au concentrate showed that sufficient particles (Au) can be upgraded. SEM/EDX results indicate that regrind does not affect changes in free Au particle morphology, aspect ratio and frequency of shearing damage in the -53 + 38 mu m size fraction. Cyclone classification of the regrind mill discharge in the -53 + 38 mu m size fraction appears to perform surface cleaning by expo

关键词： Gold Galena Quartz Vertical water stream elutriation Surface analysis

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A DEM-based analysis of the influence of aggregate structure on suspension shear yield stress

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ADVANCED POWDER technology 2012年第4期23卷 437-444页

作者： Peng, Z. B. Doroodchi, E. Moghtaderi, B. Evans, G. M. Univ Newcastle Fac Engn & Built Environm Sch Engn Prior Res Ctr Adv Particle Proc & Transport Callaghan NSW 2308 Australia Univ Newcastle Fac Engn & Built Environm Sch Engn Prior Res Ctr Energy Callaghan NSW 2308 Australia

This study theoretically examined the effect of aggregate structure on the suspension shear yield stress. The aggregation process of colloidal particles was simulated using the discrete element model (DEM) combined with the well-known DLVO theory. The predicted aggregate structural characteristics, namely the coordination number and inter-particle forces were then used in a modified version of the Flatt and Bowen mechanistic model [6] to calculate the corresponding suspension yield stress. The effect of key parameters such as solid volume fraction, suspension pH and ionic strength on the aggregate structure and hence the yield stress of the suspension was investigated. The results showed that the yield stress increased significantly under conditions that were favourable for formation of complex net-like aggregate structures, such as high solid volume fractions, pH values near the iso-electric point, and high ionic strengths. In such cases, the mean coordination number reached a maximum value which was considered to be dependent on the particle size and size distribution. The suspension yield stress exhibited a power law dependency on the solid volume fraction. The interconnected network structure developed at high solid volume fractions was found to be the major contributing factor to the observed high suspension yield stress. As the particle-particle repulsion became significant, a decrease in both the number of bonds and the mechanical bonding strength of the aggregate structure was observed. That was considered to be responsible for the reduction in the suspension yield stress. The suspension yield stress became independent of the suspension ionic strength when the ionic strength exceeded the critical coagulation concentration. Satisfactory agreements were obtained between simulation results and the published experimental data. (C) 2012 The Society of Powder technology Japan. Published by Elsevier B.V. and The Society of Powder technology Japan. All rights reserv

关键词： Aggregate structure Coordination number Suspension shear yield stress DEM DLVO Aggregation rate

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Measurements of size distribution of titanium dioxide fine particles in a highly concentrated non-aqueous suspension by using particle self-assembly under an electric field

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ADVANCED POWDER technology 2012年第4期23卷 517-522页

作者： Otsuki, Akira Dodbiba, Gjergj Fujita, Toyohisa Curtin Univ Western Australian Sch Mines Dept Met & Minerals Engn Kalgoorlie WA 6433 Australia Univ Tokyo Grad Sch Engn Dept Syst Innovat Bunkyo Ku Tokyo 1138656 Japan

This paper describes the measurement of size distribution of TiO2 fine particles in a highly concentrated non-aqueous suspension by using self-assembly of particles under an electric field. Interactive force apparatus (IFA) was used to conduct the measurement. IFA first assembled pearl chains of particles between two electrodes, and then applied the compressive force to change the pearl chain structure by shortening the distance between electrodes. The repulsive force generated when the chain curved while the attractive force created when the chain was broken. The cycle of repulsive and attractive forces corresponds to the size of particles. The results obtained with IFA were compared with results obtained from size measurement by analyzing SEM photographs. IFA indicated the comparable results with the one obtained using SEM. The particle size distribution measured by IFA decreased as a result of increasing the supply voltages. Changes in correlation between size distribution measured by SEM and IFA at different supply voltages were observed in different size ranges. At smaller than 300 nm, result at 0.24 V fit well with the SEM result while at >600 nm gives better agreement with the results at 0.48 V. The difference is mainly due to the increase in number of particles in fine size fraction with increasing supply voltages. Decrease in size indicated that the breakage of aggregate particles and/or disintegration of doublet particles occurred due to the electrical fragmentation. The fragmentation was explained by monitoring the mean diameters and their deviation obtained from IFA measurements at different supply voltages. (C) 2012 The Society of Powder technology Japan. Published by Elsevier B.V. and The Society of Powder technology Japan. All rights reserved.

关键词： particle size distribution Titanium dioxide fine particles Non-aqueous solvent Interactive force apparatus Self-assembly Electric field Electrical fragmentation

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A DEM-based analysis of the influence of aggregate structure on suspension shear yield stress

A DEM-based analysis of the influence of aggregate structure...

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particle technology and mineral processing sessions/conference on chemeca

关键词： Aggregate structure Coordination number Suspension shear yield stress DEM DLVO Aggregation rate

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Upgrading of low-grade gold ore samples for improved particle characterisation using Micro-CT and SEM/EDX

Upgrading of low-grade gold ore samples for improved particl...

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particle technology and mineral processing sessions/conference on chemeca

作者： Agorhom, Eric A. Skinner, W. Zanin, M. Univ S Australia ARC Special Res Ctr Particle & Mat Interfaces Ian Wark Res Inst Mawson Lakes SA 5095 Australia

关键词： Gold Galena Quartz Vertical water stream elutriation Surface analysis

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Measurements of size distribution of titanium dioxide fine particles in a highly concentrated non-aqueous suspension by using particle self-assembly under an electric field

Measurements of size distribution of titanium dioxide fine p...

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particle technology and mineral processing sessions/conference on chemeca

关键词： particle size distribution Titanium dioxide fine particles Non-aqueous solvent Interactive force apparatus Self-assembly Electric field Electrical fragmentation

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processing of fine particles using closely spaced inclined channels

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ADVANCED POWDER technology 2010年第4期21卷 386-391页

作者： Walton, K. Zhou, J. Galvin, K. P. Univ Newcastle Sch Engn Ctr Adv Particle Proc Callaghan NSW 2308 Australia

A Reflux Classifier consists of a set of parallel inclined channels above a conventional fluidised bed. Recently Galvin et al. (2009, 2010)[3,2] discovered a new and powerful separation mechanism for elu-triating particles on the basis of density, utilising closely spaced channels. This arrangement suppresses the effects of particle size, thus promoting the effect of particle density. A series of particle fractionation experiments was conducted in this study to examine the effects of the channel spacing. Inclined channel spacings of 1.77, 4.2, 7, 9, and 18 mm were used in the work. A continuous distribution of coal and mineral matter, consisting of particles in the size ranges from 0.25 to 2.0 mm and 0.038 to 0.25 mm were used, with the particle density ranging from 1275 to 2600 kg/m(3). The results demonstrate the benefits of the new separation mechanism, with greatly improved fractionation achieved using the more closely spaced channels. (C) 2010 The Society of Powder technology Japan. Published by Elsevier B.V. and The Society of Powder technology Japan. All rights reserved.

关键词： Reflux Classifier Fluidization Narrow inclined channels Density separation

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Temperature responsive polymers as multiple function reagents in mineral processing

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ADVANCED POWDER technology 2009年第3期20卷 273-279页

作者： Franks, George V. Li, Haihong O'Shea, John-Paul Qiao, Greg G. Univ Melbourne Australian Mineral Sci Res Inst Chem & Biomol Eng Melbourne Vic 3010 Australia Alberta Res Council Edmonton AB Canada

A processing scheme which uses a single chemical that has multiple functions to achieve both efficient mineral flotation and solids dewatering is presented. Temperature sensitive polymers which display hydrophilic/hydrophobic transitions in response to changes in temperature such as poly (N-isopropyl acrylamide) (PNIPAM) have been found to be useful as such multiple function reagents. This polymer can cause the mineral particles' surfaces to be hydrophilic at temperature below the critical solution temperature (CST = 32 degrees C) and hydrophobic at temperature above the CST. Therefore, both particle surface wettability and inter-particle interaction forces are reversibly controllable. When the surface is hydrophilic, particle dispersion is achieved by repulsive inter-particle forces whereas when the surface is hydrophobic, particle aggregation is induced by inter-particle hydrophobic attractive forces. In addition, the hydrophobic surface condition allows for the attachment of particles to bubbles. Flotation and solid settling tests have been conducted With silica and kaolinite suspensions treated with (PNIPAM). Both effective suspension dispersion or hydrophobic aggregation and flotation without any additional collector have been demonstrated. In solid/liquid separation, rapid settling was obtained with hydrophobic aggregation at temperature above the CST and further sediment consolidation (and water release) occurred at temperature below the CST. The approach has the potential to reduce the amount and types of reagents required for mineral processing. (C) 2009 The Society of Powder technology Japan. Published by Elsevier BV and The Society of Powder technology Japan. All rights reserved.

关键词： Flocculation Flotation Inter-particle forces mineral processing Responsive polymers

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