The Effect of Particle Size and Shape on Transport through Confined Channels in three-phase Froths

Multiphase systems (containing solid, liquid and gas) are increasingly common in a number of industries, with the most complex manifestation being three-phase froth. The interstitial suspension has to navigate tortuous channels and its transport is affected by drag, capillary and gravitational forces. Particle properties such as wettability, size, shape, and morphology results in a number of different types of interactions with the liquid-air interface and can have a significant effect on froth composition and stability. The effect of particle size and shape on its transport through these confined channels is thus of great interest for a number of industrial applications and is the focus of this work. This transport behavior is studied using a three phase transient froth that is produced in the froth flotation process for mineral separation. In this system, hydrophilic non-value particles present in the interstitial liquid phase do not attach to air bubbles, and their removal is desirable. The original hypothesis was that as particles become more anisotropic in shape, there is an increase in the froth interstitial viscosity, which results in reduced drainage rate of particles through the froth. Flotation experiments, froth sampling experiments, and rheological experiments were conducted to test this hypothesis. Froth zone sampling experiments were conducted using mixtures of sized platy mica, needle-like wollastonite, and fibrous chrysotile, all mixed with low aspect ratio silica in varying amounts. The froth zone suspension compositions were then used to prepare the froth interstitial suspension ex-situ, and bulk rheological measurements were conducted on the suspensions. The data showed that while the relative viscosities of the suspensions were much higher at even low concentrations of the fibrous ore in the mixture, there was no significant difference when mica was substituted for silica in the mixture at high concentrations (~50 wt%) at the solids volume fraction of interest (~7.5%). The bulk rheological measurements thus could not fully account for the difference in transport behavior between mica and silica. Flotation experiments were conducted with a copper mineral-containing ore augmented with additional hydrophilic minerals mica, silica (low aspect ratio), wollastonite or chrysotile. The results suggest increasing aspect ratios of the added non-value particles result in increased net transport (transport accounting for loss due to drainage) through the froth zone; mica transport is faster than silica. Froth zone sampling experiments (using pure mixtures of above minerals) confirmed that mica net transport was greater than that of silica. It was then hypothesized that this increase was due to increased drag experienced by high aspect ratio mica compared to low aspect ratio silica. The doped ore flotation data also suggested a decrease in transport as size of added platy mica increased until a local transport minimum was reached, beyond which another increase in transport was observed. It was further hypothesized that this was related to confinement of coarse mica particles in the plateau borders when the size of the constriction was comparable to particle size. Froth sampling experiments under high drag (upward flow dominated) conditions were compared with those under conditions where drag and drainage were more balanced (steady state froths). Under high drag conditions, mica mixtures showed more hydrophilic mineral mass in the froth zone compared to silica mixtures. Under drag and drainage-balanced conditions when the size of mica approached the size of the measured channel size, platy mica was found to be accumulating in the froth. This was not the case for silica particles with settling being more efficient for silica than for mica. The key parameters driving transport of particles through the froth are the bulk rheology of the interstitial suspension (driven by particle size and shape distributions and solids concentration), the size of constrictions in the plateau borders and vertices and the resulting confinement effects, and the mobility or elasticity of the interfaces (driven largely by the hydrophobic particles attached at the interface)

Fine coal flotation in a centrifugal field with an air sparged hydrocyclone

Journal ArticlePreliminary results are reported regarding the design and development of a pilot scale air sparged hydrocyclone for cleaning fine coal 590 \xm ("28 mesh) containing 24% ash and 1.6% sulfur. The principle of separation is the flotation of hydrophobic coal particles in the centrifugal field generated by the fluid flow in the air sparged hydrocyclone as discussed in another publication. This 152-mm (6-in.) hydrocyclone has a nominal capacity of 0.9 t/h (1 tph) and experimental results suggest that separations vastly superior to a watet-only cyclone are possible. In addition the separation efficiency is as good, if not better, than that achieved with conventional flotation cells. For example, typical results indicate that 75% clean coal can be recovered at 15% ash leaving a tailing product of almost 50% ash. These experimental results coupled with the high capacity of the air sparged hydrocyclone (imagine a retention time for flotation of only two seconds compared to two minutes for conventional flotation) may represent a significant breakthrough, not only in coal preparation technology, but in the flotation of fine particles in general

Vibration measurements for copper ore milling and classification process optimization

The paper presents a new approach to optimize the comminution process by using accelerometer measurements of the mill shell. An installation performed in the KGHM Polska Miedź Division – Ore concentration Plant Lubin – one of the largest producers of copper and silver in the world – has been used. It is shown that the measurements are correlated with the lithological structure of the ore, and they can be used in a control system to improve effectiveness of the milling and classification processes

NML Technology Handbook

Technology on Standard Reference Materials ANC001 1 Arsenic Removal from Groundwater ACC001 2 Electroless Nickel Plating ACC002 3 Ethyl Silicate Based Zinc Rich Primer ACC003 4 Flux for Hot Dip Galvanising of Steel Components ACC004 5 Metasave ACC005 6 NML-Galvaflux ACC006 7 NML-Galvasave ACC007 8 NML-HCL Inhibitor ACC008 9 Reclamation of Coal Mine Water ACC009 10 Rust Stabilizer ACC010 11 Zinc Powder based Coating ACC011 12 Copper Powder from Copper Wastes Scrap MEF001 13 Fluxed sinter through Micro-Pelletization MEF002 14 Geo-Polymer Cement MEF003 15 Geo-Polymer Paving Blocks/Tiles MEF004 16 Iron Oxide from Waste Iron Rich Sources MEF005 17 Lead Recovery from Lead containing Residues MEF006 18 Lithium Chemicals MEF007 19 Mag Chem MEF008 20 Nickel From Spent Nickel Catalyst MEF009 21 Nickel Sulphate MEF010 22 Portland Pozzolana Cement MEF011 23 Tungstic Acid MEF012 24 Wear Resistant Ceramics using Fly Ash MEF013 25 Technology Code Page Acid /Metallurgical Grade Fluorspar MNP001 26 Agglomeration of Iron Ore & Concentrates from Slimes MNP002 27 Beach Sand Heavy Minerals MNP003 28 Beneficiation of Low grade Iron Ores MNP004 29 Beneficiation of Low grade Baryte Ores MNP005 30 Beneficiation of Tungsten Ores MNP006 31 Clean Coal(Coking/Non-Coking) MNP007 32 Copper Concentrate from Copper Ores MNP008 33 High Quality Magnesite MNP009 34 Pellets from Iron Ore Fines/Slimes MNP010 35 Phosphate Concentrate MNP011 36 Metal Values from Waste Printed Circuit Boards MNP012 37 Separation of Quartz & Feldspar MNP013 38 Utilization of Iron Ore Slimes MNP014 39 Alumina - (Ti, Zr) Borides Composite MST001 40 Biphasic Calcium Phosphate Nano-bio Ceramic MST002 41 Diamond Polishing Wheel MST 003 42 Magneto-Impedance based Magnetic Sensor MST004 43 Nano Crystalline Ferromagnetic Ribbons MST005 44 Ferro-fluids MST006 45 Magnetic Non-Destructive Evaluation (NDE) Device MST007 46 Magnetic Sensing Device MST008 47 Nanobioceramics MST009 48 Nano-composite Coating MST010 49 Portable Stress Strain Measuring System MST011 50 Rejuvenation of Hot Gas Path Components of Gas Turbine MST 012 51 Technology Code Page Wide Metallic Glass Ribbon MST013 52 Zirconium Diboride Powder MST014 53 Column Flotation NMC001 54 Electroless Nickel Alloy NMC002 55 Electrolytic Coloring of Titanium NMC003 56 Purification of Industrial Effluents NMC004 57 Removal of Pollutants from Industrial Effluents NMC005 58 TiO2 Nano Tubular Arrays on Ti and its Alloys NMC006 59 Zero Waste Phosphating Process NMC007 6

Performance of the vertical roller mill in a mineral processing application when coupled with internal and external classifiers

Comminution is applied in all mineral processing plants where mineral liberation is needed for separation and concentration of valuable minerals. The process is energy intensive and is predominantly carried out in tumbling mills which are known to be highly inefficient. Comminution technologies utilised in other industries, such as the vertical roller mill (VRM), a high compression dry grinding device, have the potential to contribute towards enhancing the energy efficiency of comminution and the sustainability of mineral processing. The vertical roller mill is used extensively in cement and coal grinding applications, where it is known to be more energy efficient than traditional tumbling mills. The VRM has a larger reduction ratio and greater flexibility in terms of product quality control and throughput. However, in the majority of operations where the vertical roller mill is applied, the device is coupled with an internal dynamic air classifier. These classifiers are significantly more energy intensive than other classifiers typically used in the mineral processing industry. Operating the vertical roller mill with less energy intensive classification devices could have the potential to further reduce the total comminution circuit energy. Reducing the comminution energy usage in mineral processing is important, however there are other factors which also need to be considered before the vertical roller mill can be considered as a viable alternative to tumbling mills. The effect of grinding with the vertical roller mill on product quality and mineral liberation, and their impact on downstream processing is of critical importance and has not yet been extensively investigated. This study investigates the grinding of the platinum group mineral (PGM) bearing Platreef ore, in a pilot scale vertical roller mill. The research explores the effects of milling variables and methods of classification on the mill performance, energy consumption, throughput, product characteristics and flotation response. The energy efficiency of the vertical roller mill and product flotation response is also compared with that of a traditional ball milling circuit. Vertical roller mill products of three target grinds, typical to primary, secondary and tertiary grinds in PGM circuit, were generated with the VRM operated in the standard airflow mode, with the internal dynamic air classifier, for a variety of grinding pressures (an online control used for maintaining product quality), and dam ring heights (a design variable affecting residence time on the grinding table). The specific grinding energy for the vertical roller mill was found to increase as the target grind became finer, conforming to general comminution theory. Vertical roller mill specific grinding energies were lower than those for a ball mill at all product sizes, and when estimates of classification energy and scale-up of the VRM are included, the specific energy for the vertical roller mill is up to 35% lower than for a ball mill in closed circuit. Grinding at higher pressures yielded greater throughputs and was found to generate products of less steep particle size distribution (PSD), but did not affect specific grinding energy. The effect of varying dam ring height was found to be target grind dependent. Higher dam rings yielded products with a greater proportion of fines, for higher specific grinding energies with the differences more pronounced at coarser target grinds. The grinding component of the vertical roller mill was operated in conjunction with three classification devices - the internal dynamic air classifier, external hybrid air classifier and an external vibrating screen. The external air classification circuit had a lower throughput than the internal air classification circuit, and operated with a 20 - 40% higher specific grinding energy. When including pilot scale estimations for classification energy, the external air classification circuit overall specific energy is lower at intermediate and coarse grinds, and comparable at finer target grinds, to that of the internal air classification circuit. The specific grinding energy in the VRM - external screening system was higher than both air classification circuits, however when considering the lower energy intensity of screening, this circuit may prove more efficient. The flotation response of the tumbling mill product and the vertical roller mill product prepared under different operating conditions in circuits with different classification devices was assessed using a standard reagent suite, in terms of platinum, palladium, gold (3E PGE), and copper, nickel (Cu, Ni) concentrate grades and recoveries. Both vertical roller mill and tumbling mill products yielded greater recoveries as the products became finer and valuable mineral liberation increased. The vertical roller mill products however had substantially higher recoveries, which was linked to higher froth recoveries and differences in oxidation potential within the flotation pulp. Increasing the compressive force in the VRM through the application of higher grinding pressures led to an increase in fines causing a decrease in froth stability during flotation, which corresponded with lower valuable metal recoveries. Variation in dam ring height caused small decreases in discrete PGM liberation but an increase in effective PGM liberation (considering PGMs liberated and locked in floatable base metal sulphide minerals). Flotation recoveries followed changes in froth stability with products prepared at the highest dam ring height, which had greater fines contents, yielding lower valuable metal recoveries. An optimised reagent suite for VRM products should be developed to address issues with froth stability caused by the increase in fines component at higher grinding pressure and dam ring heights. This will allow for the improvements in valuable mineral liberation with these grinding conditions to be realised as increased flotation recoveries. When operating the VRM grinding components with different classification devices, flotation performance was influenced by variation in the particle size distributions of products. External and internal air classification products with closely comparably particle size distributions yielded similar 3E PGE flotation recoveries. Flotation recoveries were however lower for the finest external air classifier product, which had a less steep PSD. A similar difference in PSD was observed for the screening vertical roller mill circuit products, which also had lower flotation recoveries than products generated with the internal dynamic air classifier. The research indicates that the vertical roller mill is able to efficiently prepare material for valuable mineral concentration through flotation. The effects that the vertical roller mill variables grinding pressure and dam ring height have on operation and the comminution product has been investigated. Furthermore the VRM has been successfully coupled with different classification devices to generate a product with flotation response better than that of tumbling mill products

Modelling the transient drainage of liquid in foams

Froth flotation is the largest tonnage separation process worldwide and is used for paper deinking, water purification and, particularly, mineral separation. One of the key aspects of the performance of flotation cells is the behaviour of the liquid within the froth, as it is crucial to the purity of the product and a major influence on the overall recovery. Nonlinearities in models for liquid motion in the froth make them complex to solve and existing numerical solutions have been in two dimensions at most. In order to predict the performance of industrial flotation cell designs, a three-dimensional solution for these equations is desirable. Moreover, the understanding of the process would be enhanced if a transient model were used to predict the dynamics of foam drainage. In this work, the equations for the liquid drainage have been rearranged in order to make them analogous to a compressible version of the Navier-Stokes equations, coupled to an equation of state. A model for predicting the movement of the flowing foam has also been developed, which is able to solve for the foam velocity in two and three dimensions. This has allowed the transient behaviour of liquid in flotation foams to be modelled using Fluidity, a general purpose finite element method code that allows simulations to be carried out on unstructured adaptive meshes. This is an important feature for improving the computational cost of modelling these systems, as there are boundary layers present in the process, whose size is independent of the scale of the flotation system being modelled. These models have allowed, for the first time, to carry out numerical investigations of drainage for arbitrary flotation tank geometries in up to three dimensions, and have been verified against analytical solutions and compared to laboratory scale experiments with satisfactory agreement

The Feasibility of Reclaiming Shell Material from Investment Casting

This report examines the feasibility of investment shell component reclamation. Shell material components and their compositions are investigated with an industry survey, a study of the available literature, and analysis of specimen shell materials. physical properties and factors related to the reclamation and reuse of shell materials are described. Well known mineral processing methods are capable of producing concentrates of the various shell components. The theory and techniques of some applicable processes are discussed to assist with the development of reclamation operations. The recommended methods are; comminution by roll crushing, component concentration by screening, gravity settling or heavy medium separation. Aluminosilicate stucco (a major component of many investment shells) can be recovered in a form suitable for reuse as backup stucco. Zircon (a minor component in many shell compositions) -can be concentrated in an impure form, and subsequent caustic liberation treatments can remove the intermixed silica phases. Reuse of such zircon in investment casting may be possible but will require careful qualification testing. Fused and crystalline silica (major components of most shell compositions) are not reusable for investment casting. The feasibility of reclamation will be influenced by individual foundry choices of materials, composition and shell practice.HWRIC Project No. RRT-10NTIS PB92-16219

Bubble size, coalescence and particle motion in flowing foams

In minerals processing, froth flotation is used to separate valuable metal minerals from ore. The efficiency of a froth to recover these valuable minerals is closely related to the bubble size distribution through the depth of the froth. Measurement of the bubble size entering the froth and at the froth surface has been achieved previously; however measurement of the bubble size within the froth is extremely difficult as the mineral laden bubble surfaces are opaque and fragile. This work developed a flowing foam column to enable new measurement techniques, in particular visual measurement of the bubble size distribution and velocity profile throughout the depth of the foam. Two phase foam systems share their structure with three phase froth flotation systems, but are transparent in a thin layer. A foam column was constructed to contain a monolayer of overflowing and coalescing foam. This enabled direct measurement of the dynamic bubble size and coalescence through image analysis. The results showed a strong link between column geometry and the foam behaviour. In addition, the measured bubble streamlines closely matched simulated results from a foam velocity model. Positron Emission Particle Tracking (PEPT) is the only existing technique to measure particle behaviour inside froths. In this work, tracer particles with different size and hydrophobicity were tracked in a foam flowing column with PEPT. The particle trajectories were verified with image analysis, thereby increasing confidence in PEPT measurements of opaque flotation systems. The results showed that as hydrophilic tracer particles passed through the foam, their trajectory was determined by the local structure and changes of the foam, such as coalescence events. A hydrophobic tracer particle was involved in drop–off and reattachment events, however in the majority of cases still overflowed with the foam. The tracer particle did not always follow the bubble streamlines of the flowing foam, taking instead the shortest path to overflow which cut across streamlines. This work has developed an experimental methodology to validate flowing foam and coalescence models and has developed the necessary techniques to interpret PEPT trajectories in froth flotation

Effect of VRM on a polymetallic sulfide ore and the flotation response as compared to conventional wet and dry rod milling

Comminution is an energy intensive, size reduction and mineral dressing process which consumes up to 50% of concentrator energy consumption. Conventional methods use mainly a combination of crushers and tumbling mills in comminution circuits. Energy consumption in these circuits has been found to be relatively high. To reduce the energy requirements, compression grinding equipment, Vertical Roller Mills (VRMs) and High-Pressure Grinding Rolls (HPGRs) have been identified as potential solutions, and they have been adopted in the cement industry. Reports from plants where these technologies have been installed in circuits indicate they are more energy efficient than the conventional comminution circuits. Studies have also suggested that the use of VRMs results in comminution products with relatively higher mineral liberation degrees. Unlike in the cement industry, comminution equipment in mineral processing circuits are also required to produce particles that can be separated and recovered in downstream processes. Froth flotation is a selective separation process that utilises differences in surface properties to separate value minerals from unwanted gangue. The success of flotation is dependent on chemistry, operational and equipment factors. The chemistry factors consider the interaction between flotation reagents and solids particles surface. The operational factors consider the effect of particle size distribution, mineralogy, feed rate, pulp density, pulp potential (Eh), bubble size, temperature and circuit design on flotation. The use of different comminution procedures may result in flotation feeds of different particle size distributions (PSDs), mineral liberation characteristics and pulp potential. Due to these differences, the resultant flotation response may differ. The present study was aimed at assessing the particle size distribution, mineral liberation profiles and the flotation response from material comminuted using the VRM floated under batch flotation conditions in a 3 litre Barker flotation cell. A complex polymetallic sulfide ore containing chalcopyrite (1.3 %), galena (2.4 %) and sphalerite (1.8 %) as the main value minerals and magnetite (68.0 %) and quartz (15.7 %) as dominant gangue minerals was used for the study. The ore was milled to target grinds of 55 %, 60 %, 65 %, 70 % and 75 % passing 75 µm respectively, at a grinding pressure of 600 kPa, air temperature of 300 K. For the benchmarking grind of 65 % passing 75 µm, the ore was also milled using heated air of temperature of 373 K and at elevated grinding pressures of 800 kPa and 1000 kPa. Further work was performed to evaluate if the VRM results are comparable to conventional dry and wet rod milling products floated under the same batch flotation conditions. An increase in grinding pressure was observed to result in an increase in throughput and a general decrease in specific energy consumption without a change in product particle size distribution nor the recovery of chalcopyrite, galena and sphalerite. Using heated air (373 K) resulted in the production of slightly less fines in the comminution products. The recovery of chalcopyrite, galena and sphalerite were not affected by the change in operating temperature. However, concentrate grade (selectivity) was compromised at elevated temperatures of comminution probably due to surface oxidation. The results indicated that the grind range to achieve the best flotation performance when using the VRM as a comminution device is between 60 % and 70 % passing 75 µm. The results also indicated that at the benchmarking grind of 65 % passing 75 µm, the specific energy consumption for comminution using the VRM was 54.3 % lower than that of the conventional tumbling mill circuit. The grind of 55 % passing 75 µm resulted in lower flotation efficiencies as the minerals were unlikely liberated enough whereas the grind of 75 % passing 75 µm resulted in poor performances due to low water recovery. Comparing VRM with wet and rod milling, the different comminution procedures resulted in flotation feed of similar PSDs for all grinds compared. The wet and dry rod milling products of grinds 55 % and 75 % passing 75 µm achieved better recoveries of chalcopyrite, galena and sphalerite as compared to the VRM performance mainly due to high water recoveries achieved. While mineral recoveries were above 90 % for the grinds of 60 % and 70 % passing 75 µm, the rod milling products had statistically better flotation recoveries at 95 % confidence compared to the VRM products. The mineral recoveries after dry rod milling were marginally better than after wet rod milling due to the minimisation of galvanic interactions during dry rod milling. For the benchmarking grind of 65 % passing 75 µm, VRM grinding resulted in 84 %, 84 % and 90 % liberated chalcopyrite, galena and sphalerite respectively. The liberation of chalcopyrite, galena and sphalerite after wet and dry rod milling were 80 %, 78 % and 90 % respectively. Chalcopyrite recovery was 96.7 %, 96.3 % and 96.7 % for the VRM, dry rod mill (RD) and wet rod mill (RW) products respectively. Galena recovery was 94.3 %, 94.3 % and 92.9 % for the VRM, RD and RW products respectively. Sphalerite recovery was 96.6 %, 97.4 % and 97.4 % for the VRM, RD and RW products respectively. The differences in recovery were statistically insignificant at 95 % confidence. Liberation differences did not translate to differences in recoveries as the ore was coarse grained. The recovery kinetics were very fast and independent of comminution procedure. Reference to the benchmarking grind therefore, the VRM can be retrofitted into existing plant installations as it is more energy efficient and the flotation performance was similar when using the flotation procedure tailored for tumbling mill-flotation systems