Mineral Processing Applications Research Articles

Temperature and Moisture Dependence of the Dielectric Properties of Silica Sand

The major objective of this work was to investigate the effects of temperature and moisture content on the dielectric properties of silica sand. The dielectric properties of moist silica sand at five temperatures between 20 to 100 °C, covering different moisture content levels at a frequency of 2.45 GHz, were measured with an open-ended coaxial probe dielectric measurement system. The wave penetration depth was calculated based on the measured dielectric data. The results show moisture content to be the major influencing factor for the variation of dielectric properties. Dielectric constant, loss factor and loss tangent all increase linearly with increasing moisture content. Three predictive empirical models were developed to relate the dielectric constant, loss factor, loss tangent of silica sand as a linear function of moisture content. An increase in temperature between 20 to 100 °C was found to increase the dielectric constant and loss factor. The penetration depth decreased with increase in moisture content and temperature. Variation in penetration depth was found to vary linearly with decrease in moisture content. An predictive empirical model was developed to calculate penetration depth for silica sand.This study offers useful information on dielectric properties of silica sand for developing microwave drying applications in mineral processing towards designing better microwave sensors for measuring silica sand moisture content.

Mass-Flow Estimation in Mineral-processing Applications

This paper evaluates mass-flow estimation capabilities of four online mass-flow sensors: Power transducer, laser profilometer, ultrasonic sensor, and strain gauge. Mass-flow estimates are generated with two methods, linear-regression and non-linear physical mass-flow estimation models. The results of this work indicate very good mass-flow estimation capabilities for all of the sensor types. These accurate and cost-effective mass-flow sensors increase online monitoring capabilities in the mineral-processing plants significantly, also allowing more effective manual process control, as well as the development and implementation of more advanced automatic process control and optimisation systems. However, a reference mass-flow measurement needs to be available for the calibration of the sensors.

Stability of sodium polyphosphate dispersants in mineral processing applications

Polyphosphates are commonly used industrially to provide electrostatic stabilisation to mineral and material suspensions. Polyphosphate solutions however have shown instability under processing conditions such as high temperature and acidic pH which may lead to a reduction in dispersion properties when added to mineral or material suspensions.In this study the influence of pH, temperature and divalent cation concentration pre-treatment on polyphosphate dispersion properties is reported. Dispersion properties are determined using rheological suspension analysis. The suspensions investigated are material-based model systems of titania pigment and high purity boehmite. Infrared spectroscopy studies of polyphosphate solutions were undertaken to directly investigate the polyphosphate structure after pre-treatment. The rheological measurements show reduced polyphosphate dispersion properties with reduced pH, increased temperature and at high calcium concentrations which correlate with directly measured and reported changes in the polyphosphate structure. When pH, temperature and high divalent cation concentrations are combined, the synergistic effect on reduced polyphosphate dispersion performance is particularly prominent.

Development of a TOF‐SIMS technology as a predictive tool for the needs of the mineral processing industry

AbstractRecently, upgrades towards a semiquantitative approach to mineral processing applications using the time of flight (TOF) SIMS (TOF‐SIMS) technique have been developed and implemented. Secondary ion yield at specific instrument parameters for matrix elements in the predominant ore minerals and their comparative normalization factors have been determined. Surface loading quantification for Cu on a variety of ore minerals has shown that signal intensity variability is related to the substrate matrix. Relative sensitivity factors for component loading have been determined and calibration curves for Cu loading on mineral surfaces have established with lower limits of detection in the range of 10 ppm.Given the new semiquantitative approach for surface characterization of minerals, a new test was developed to be used as a predictive tool in mineral flotation separation. The test protocol involved a two‐chamber ball mill where Cu transfer between the pulp and specimen surface was measured by the semiquantitative TOF‐SIMS approach. The test was applied to 13 ores. The reported experimental data on these ores demonstrated the ability of this technique to differentiate Cu transfer over a large dynamic range. The data also demonstrated that the surface loading of Cu on pyrite can be correlated, in some cases, with mineralogy. In others, however, the surface Cu loading observed is not congruent with the mineralogical assessment of the ore sample, but still linked with flotation behavior. This shows that the test could be used with mineralogy to better benchmark a sample before embarking on a flotation flowsheet development programme. Copyright © 2010 John Wiley & Sons, Ltd.

Microwaves in extractive metallurgy: Part 1 – Review of fundamentals

Microwave radiation is a relatively new energy source, which has considerable potential for various applications in mineral processing and extractive metallurgy. However, the strengths of the interaction of the microwave radiation with the materials of interest are largely unknown. Additionally, in contrast to the aqueous solutions used in hydrometallurgy, the microwave interaction with the heterogeneous solids used in pyrometallurgical processes is difficult to model from fundamentals. Since the microwave heating characteristics of most of the materials cannot be predicted, research is being performed to determine the underlying factors which govern the microwave response of ores, concentrates, reducing agents and other feedstocks used in pyrometallurgical processes. In the present research, the techniques used to measure the microwave coupling characteristics are outlined and the application of these techniques to some relevant pyrometallurgical materials is reviewed.

Alternative ways of coupling particle behaviour with fluid dynamics in mineral processing

Research in particulate multiphase hydrodynamics is especially important in mineral processing applications that involve complicated physical processes and complex geometry. Numerous numerical methods have been developed to address the coupling physics. However, there is no single solution for all applications, especially after considering computational costs and model accuracy.This article presents alternative numerical coupling approaches to capture the physics of interest. A one-way coupling of conventional grid-based CFD with discrete element method (DEM) is applied to simulations of slurry pumps. FLUENT is used to compute the fluid field in the pump, which is imported into our DEM code. The DEM is used to capture dynamics of the detailed behaviour of individual solid particles, including inter-particle collisions and particle impacts into structure (boundaries).A Lagrangian–Lagrangian multiphase model is proposed for simulation of dense particulate flows in a grinding mill. This work is motivated by developing totally meshfree approaches for particulate flows due to complex and rotating geometry in many pieces of equipment in the mining industry. The particle-based multiphase model is an integration of DEM with smooth particle dynamics (SPH). SPH is extended to the multiphase version where an extra variable, volume fraction, is introduced into the governing equation in order to account for interpenetrating multiphase fluid dynamics. The interaction between the solid particles and the fluid phase consists of three contributions: volume fraction, pressure and drag force. The time stepping scheme can be either explicit Euler for speed-up or lower order Runge–Kutta for more accuracy, and the time step is controlled by the Courant condition. The model is applied to a preliminary study of a semi-autogenous grinding mill.

Evaluation of grain size distribution of unbroken chromites

Knowledge of prediction of grind size for liberating minerals to recover minerals is very important for mineral processing applications. The grind size for mineral beneficiation can be established by determining the particle size distributions (PSDs) of minerals in an unbroken ore by image analysis. PSDs determined by fractals in natural cataclasites reveals the degree of cataclastic deformation in the chromites. PSDs have been described by relations between particle mass and size, volume and size, number and size and number and mass. Different mathematical formulas and approaches have been suggested to express relationships against size, and total mass/volume/number is given against increasing size (mass/volume/number undersize). In this paper, grain size distribution was estimated from the distribution of mean Feret diameters ( d F) of individual grains by image analysis. It was found by fractal evaluation that the relation is not linear and the cataclastic deformation of the chromite ores studied is dominated by extension microstructure due to fragmentation by microfracturing. The suitability of the lognormal distribution function was studied for linearization of number-based size distribution curves measured on polished sections of unbroken samples of five chromite ore types from Turkey. Data analysis revealed that lognormal evaluation of the distribution of the mean Feret diameters ( d F) gives excellent fits for all types of chromite samples which have different degree of cataclasis and wide size ranges.

Using turbulent pipe flow to study the factors affecting polymer-bridging flocculation of mineral systems

Batch flocculation tests in cylinders (jars) or stirred vessels suffer from poor control over the reaction time and involve broad shear rate distributions. The use of a linear pipe reactor provides continuous turbulent mixing of flocculant and slurry at well-defined mean shear rates. Combined with in-line, real-time monitoring of the aggregation state with a focused beam reflectance measurement (FBRM) probe, reaction times can be determined to within a fraction of a second. The resultant reaction profiles of aggregate growth and breakage obtained while varying different conditions (dosage, solids concentration, shear rate, split dosing) provide new insights into flocculation kinetics that are more relevant to mineral processing applications. In this study, the reaction profiles are examined in terms of the effects of flocculant adsorption, applied shear and solids dilution on the aggregate structures formed. Also presented is the first definitive evidence of “post-aggregation”, where surface adsorbed flocculant remains active at short reaction times (up to the peak in aggregate size in the measured profiles), allowing additional aggregate growth under subsequent reduced shear. At reaction times beyond the peak, little or no additional growth is observed. This behaviour explains the observed discrepancy between size and settling rate reaction profiles, and highlights the importance of optimising hydrodynamics in industrial flocculation applications to maximise settling flux.

Australian Synchrotron—applications in geochemistry, mineral exploration and mineral processing

Australian Synchrotron—applications in geochemistry, mineral exploration and mineral processing

OPTIMIZATION-FREE CONSTRAINED NONLINEAR PREDICTIVE CONTROL – MINERAL PROCESSING APPLICATIONS

A difficulty with constrained nonlinear control is the minimization of the cost function. With complex system representations such as fundamental models, the required optimization algorithm may be complex to implement, setting its parameters may be difficult and the calculation time may be long. To overcome these problems, an innovative optimization-free predictive control scheme is proposed. The minimization of the cost function is replaced by a simple and easy-to-compute simulation. Two mineral processing applications illustrate the very good performances of this new algorithm.

ISRM Suggested Methods for land geophysics in rock engineering

Microwave assisted mechanical rock breaking is a hybrid rock breaking method that combines microwave heating and mechanical rock breaking technologies and is proven to have potential applications in mineral processing, mining, and geotechnical engineering. It is, thus, important to understand the effect of microwave-induced damage on rock fracture characteristics. In this study, granite specimens of the Cracked Straight Through Brazilian Disc (CSTBD) were used to carry out the mode I fracture test of the samples irradiated by microwave for different time and thermal cycles. The results showed that the heating rate of the surface temperature of granite is about 1 °C/s, under microwave power of 0.9 kW. When the heating time exceeds the 60 s and after 3 cycles, the fracture toughness of the granite hardly changes with the heating time and cycles. Before 100 °C, the fracture toughness and fracture energy of granite decrease by about 40% with the increase of temperature. Under microwave irradiation, the medium absorber (biotite) in granite is heated and expanded, which results in thermal damage to the rock. Moreover, the polar materials in fluid inclusions move more violently than under conventional heat conduction heating, resulting in a lower decrepitation temperature of the inclusions than under conventional heating and decrepitation degree is more severe, which further leads to an increase in the density of microcracks in mineral crystal and a significant decrease in fracture toughness. When the surface temperature is 300 °C, the bending degree of the crack increases and deviates from the straight line obviously.

Axial inlet cyclone for mineral processing applications

An axial inlet cyclone was developed and tested for wet size classification of particulate materials with the purpose of providing an alternative to the tangential inlet cyclone used traditionally in the mineral processing industry. The proposed device shared many of the fundamental features of a conventional cyclone, but had a circular opening on the roof of the cylindrical section and surrounding the vortex finder for feed entry, instead of a tangential inlet. The feed material spiraled down through that opening and generated the necessary spin for separation inside the cyclone. Experimental work was carried out on a sample of copper–nickel mill tailings having a particle size of 91% passing 300 μm, and the performance of the cyclone was evaluated at different inlet pressures, feed pulp densities and vortex finder lengths. In comparison to the tangential inlet cyclone, the axial inlet cyclone provided higher throughputs, coarser cut-sizes in relatively dilute pulps, and greater flexibility and control over the cyclone separation process.

Rational polymer design for solid–liquid separations in mineral processing applications

Designing polymers for improving solid–liquid and solid–solid separations in mineral processing requires a sound knowledge of the fundamentals of colloid stability, adsorbed polymers, and floc formation. This article outlines these fundamentals, and illustrates the use of such principles in two examples: the design of red-mud flocculants for use in the Bayer process, and the design of polymeric depressants for use in mineral-specific separation by means of flotation.

Assessment of the erosion resistance of steels used for slurry handling and transport in mineral processing applications

The wear environment of steels used for containing, transporting and processing erosive mineral slurries is often such that fluid borne particles form a layer moving at high speed across the wearing surface. Information on the performance ranking of such materials is limited, particularly with respect to the influence of steel hardness and microstructure on the resistance to erosion. This is particularly important for the oil sands industry of Northern Alberta where handling and processing of essentially silica-based solids results in extremely severe wear conditions. This paper presents slurry erosion data obtained on 11 commercially available wear resistant plate and pipeline steels with hardness values up to ∼750HV. These data were obtained using a Coriolis erosion tester operated at 5000rpm with an aqueous slurry containing 10wt.% of 200–300μm silica sand particles.The Coriolis erosion tester was selected because it provides a low-angle scouring action that simulates the erosive conditions encountered in oil sands and tailings pipeline transport and in some related processing operations. Results show that this test method is able to discriminate clearly between the erosion resistance of these steels, expressed in terms of specific energy (the energy necessary to remove unit volume of test material), with the most erosion resistant steel being more than five times superior to the least resistant. A graphical relation between steel hardness and erosion resistance is given. A comparison is also made between slurry erosion data and the performance of the materials in the ASTM G65 dry sand rubber wheel (DSRW) sliding abrasion test. Comments on the influence of the macro- and microstructures of the steels on their wear behaviour are included.

On some upwind difference schemes for the phenomenological sedimentation-consolidation model

In one space dimension, the phenomenological sedimentation-consolidation model reduces to an initial-boundary value problem (IBVP) for a nonlinear strongly degenerate convection-diffusion equation with a non-convex, time-dependent flux function. The frequent assumption that the effective stress of the sediment layer is a function of the local solids concentration only which vanishes below a critical concentration value causes the model to be of mixed hyperbolic-parabolic nature. Consequently, its solutions are discontinuous and entropy solutions must be sought. In this paper, first a (short) guided visit to the mathematical (entropy solution) framework in which the well-posedness of this and a related IBVP can be established is given. This also includes a short discussion of recent existence and uniqueness results for entropy solutions of IBVPs. The entropy solution framework constitutes the point of departure from which numerical methods can be designed and analysed. The main purpose of this paper is to present and demonstrate several finite-difference schemes which can be used to correctly simulate the sedimentation-consolidation model in civil and chemical engineering and in mineral processing applications, i.e., conservative schemes satisfying a discrete entropy principle. Here, finite-difference schemes of upwind type are considered. To some extent, also stability and convergence properties of the proposed schemes are discussed. Performance of the proposed schemes is demonstrated by simulation of two cases of batch settling and one of continuous thickening of flocculated suspensions. The numerical examples focus on a detailed error study, an illustration of the effect of varying the initial datum, and on simulation of practically important thickener operations, respectively.

Modelling confined multi-material heat and mass flows using SPH

Many applications in mineral and metal processing involve complex flows of multiple liquids and gases coupled with heat transfer. The motion of the surfaces of the liquids can involve sloshing, splashing and fragmentation. Substantially differing material properties are common. The flows are frequently complicated by other physical effects. Smoothed particle hydrodynamics (SPH) is a computational modelling technique that is ideally suited to such difficult flows. The Lagrangian framework means that momentum dominated flows and flows with complicated material interface behaviours are handled easily and naturally. To be able to model complex multi-physics flows, many aspects of SPH need to be explored. In this paper we describe developments that allow conductive and convective heat transfer to be modelled accurately for a sequence of idealised test problems.

An empirical model of hydrocyclones incorporating angle of cyclone inclination

Experimental work has been undertaken to quantify the influence of angle of inclination on hydrocyclone performance in mineral processing applications. Testwork was undertaken at Mount Isa Mine on copper and lead-zinc slurries and in the JKMRC laboratory on a gold ore and other ores. In both cases the cyclone performance was monitored at a range of cyclone inclinations from zero to 112°C to the vertical. Cyclone diameter varied from 102 to 508mm. The results show that cyclone inclinations greater than 45° can strongly affect the performance of industrial cyclones. A new empirical model of classifying hydrocyclone performance has been developed on the basis of this data, incorporating angle of inclination and slurry viscosity as variables, and including prediction of cut-size, separation quality, water recovery and the pressure-flowrate relationship.

The calculation of contact forces between particles using spring and damping models

Discrete element simulations can be used to model the behaviour of both fluids and contacting particles in a very flexible manner. These simulations have wide applications in both mining and mineral processing. They require the calculation of forces between the discrete elements used in the simulation typically by assuming spring, dashpot and slider components at the contact points. The accuracy of the simulations depends on the assumptions mide in the calculation of interelement forces. The different methods that can be used to calculate the forces have been examined and unrealistic behaviour found for most of methods commonly used. The non-linear force formula of Tsuji et al., Powder Technol., 71 (1992) 239, with the particles separating when the force returns to zero rather than when the distance between the centres exceeds the sum of the radii is found to give realistic results.

Rare earth permanent magnet separators and their applications in mineral processing

Rare earth permanent magnet separators and their applications in mineral processing

Expert system development using ellipsoid-based clustering

Most classification systems classify given data into one of a number of predefined groups, which have an associated response or action. These groups form a knowledge base, whose acquisition is crucial for successful data classification. This paper describes the design and implementation of an expert system, whose knowledge base is made up of elliptical clusters. The clusters are acquired using a clustering technique specifically designed and developed for mineral processing applications. The use of clustering techniques provides significant advantages over rule-based and neural network expert systems for many applications. The expert system is demonstrated using the classification of colour density tracer samples used in spiral separator experiments.