A semi-mechanistic model of hydrocyclones - developed form industrial data and inputs from CFD.

The flow behavior in hydrocyclones is extremely complex, leading the designers to rely on empirical equations for predicting cyclone performance. A number of classifying cyclone models have been developed and used in mineral comminution circuit simulators in the past. The problem with these empirical cyclone models is that they cannot be used outside the range of conditions under which they were developed. A semi-mechanistic hydrocyclone model is developed using the dimensionless approach based on both the fluid mechanics concepts from Computational Fluid Dynamics (CFD) simulations and the wide range of industrial cyclone performance data. The improved model consist a set of equations for the water split to underflow (R), reduced cut-size (d), throughput (Q) and sharpness of the separation (α). The model for R, d, Q gives a very good fit to the data. The alpha model shows reasonable correlation for the cyclone design and operating conditions. Additional data sets were used to validate the new hydrocyclone model by comparing the predictions of the model equations with the experimental results

Possibilities for flotation acoustics monitoring - A review

Flotation research has matured enough to provide models that are able to predict outcomes under different scenarios. In order to achieve practical applications these models require key measurable descriptors, such as gas dispersion indicators in the pulp phase and stability, coalescence rate and recovery in the froth phase. Currently, these descriptors are measured using tools such as video processing, conductivity and more primitive mechanical instrumentation. However, these techniques still are not offering an adequate level of on-line and in real time information at a low cost. One technique that might address these problems, which has not been sufficiently explored and that can offer advantages in cost and ease of processing, is acoustic monitoring. Consequently, the aim of this paper is to review acoustic monitoring techniques applied in diverse fields that could be transferred to the flotation area. Different acoustic properties and measurement methods are reviewed and suggestions are made for their potential use either in the pulp or froth zones. It is concluded that important parameters could be estimated using acoustic monitoring. These parameters include bubble size and gas hold-up in the pulp zone and coalescence rate, gas hold-up and solids/liquid concentration in the froth zone

Separation of minerals using electrical fields

The mineral processing industry requires alternative separation techniques to help deal with rising energy costs and decreasing ore grades. Dielectrophoresis is one possible technology. It uses nonuniform electrical fields to separate particles on the basis of their permittivity. In order to determine its viability, the dielectrophoretic force was measured for individual chalcopyrite particles in ethanol. The measurements were made by attaching the individual particles to glass fi bres and measuring how far they were deflected by a non-uniform electrical field. Six sizes of chalcopyrite particles were tested and the force was found to increase as a function of particle radius cubed. The particles were also positioned at different points in the field in order to determine the effect of the electrical field gradient. The force was found to increase with the inverse cube of the distance from the centre of the particle to the pin electrode. With the effect of these parameters fully characterised, the single particle test cell can be used to determine the permittivity of single particles of various composition

Electrical properties of composite mineral particles and their effect on dielectrophoresis

Dielectrophoresis is a separation technique that uses a non-uniform electrical field to separate particles on the basis of their permittivity. There are many areas of mineral processing that might benefit from the application of dielectrophoresis. These include: coarse removal of gangue, recovery of ultrafine particles, upgrading of flotation concentrates or simply as a laboratory analysis technique. In order to determine the potential value of dielectrophoresis to the mineral processing industry, the response of composite particles was investigated. The electrical properties of composites involve complex relationships between the shape, distribution and permittivity of the individual grains within the rock. The relationship between mineral composition and dielectrophoretic force was measured on single particles from two ore types. The results were used to populate a model that could predict the separation characteristics of the ore. The insights gained from this model separator allowed potential applications of the technology to be examined and their performance evaluated

Multi-component modelling concept for hydrocyclone classifier

The flow in a hydrocyclone classifier is highly turbulent complex nature of multi-phase structure, which has led designers to rely on empirical mathematical models for predicting the performance. A number of classifying cyclone models have been developed and successfully used in mineral comminution circuit simulators over the past four decades (Plitt. 1976 and Nageswararao. 1978). However, most of the mathematical models currently available to describe hydrocyclone classifier performance are based on single average mineral density component behavior. In industrial comminution circuits, the feed to the cyclone composed of a mixture of particles of varying degrees of liberation and sizes. The behavior of multi-component particles in a hydrocyclone is poorly understood and unaccounted for in most of the mathematical model equations available in the literature. There is evidence from a number of experimental data sets indicating the significant influence of the multi-component particles on measured cyclone performance. A concept for modeling the performance of hydrocyclones based on multi-component behavior is proposed in this paper. A set of semi-empirical model equations for cutsize, sharpness of separation are presented and the corresponding model parameters evaluated from the measured data are given

The influence of particle shape in rock fracture

Understanding the fracture process of rock is of particular interest to the mining industry. In terms of energy utilisation, size reduction is an Achilles heel – utilising approximately two per cent of total global energy. Reducing this cost is a major driver in the industry. There are a number of ways to reduce this energy consumption. One of them is to gain a fundamental understanding of the fracture process of rock that can then be used to optimise breakage in various comminution devices and processes. Numerical tools such as Discrete and Finite element methods can be used to visualise and enhance the fundamental understanding of the fracture process. Successful quantitative modelling will enable researchers to quantify, and thus potentially control, the energy utilisation. There is little work looking at the infl uence of shape on rock fragmentation and utilising it to reduce comminution energy. It is hypothesised that particle shape and the way force is applied to the particle infl uence energy absorption and utilisation in fracture. The implication is that energy reduction during comminution can be achieved by controlling and using the shapes of rock particles to advantage. Controlled tests have been conducted to verify the effects of shape ranging from quasi static to dynamic breakage tests. Initial findings show that strength of ore is greatly influenced by shape and direction of loading. This information has significant implications to the standard test procedures used quantify the ore hardness in minerals industry

A review of flow modeling for dense medium cyclones

A critical assessment is presented for the existing fluid flow models used for dense medium cyclones (DMCs) and hydrocyclones. As the present discussion indicates, the understanding of dense medium cyclone flow is still far from the complete. However, its similarity to the hydrocyclone provides a basis for improved understanding of fluid flow in DMCs. The complexity of fluid flow in DMCs is basically due to the existence of medium as well as the dominance of turbulent particle size and density effects on separation. Both the theoretical and experimental analysis is done with respect to two-phase motions and solid phase flow in hydrocyclones or DMCs. A detailed discussion is presented on the empirical, semiempirical, and the numerical models based upon both the vorticity-stream function approach and Navier-Stokes equations in their primitive variables and in cylindrical coordinates available in literature. The existing equations describing turbulence and multiphase flows in cyclone are also critically reviewed

Multiphase modelling of hydrocyclones: prediction of cut-size

A comprehensive multiphase model of cyclone separators using Computational Fluid Dynamics is under development. The model is capable of predicting velocity profiles, flow splits, air core position and efficiency curves in classifying hydrocyclones. The model approach uses the Mixture model with the granular options and large eddy simulation (LES) to resolve the turbulent mixing of the particles. Multiphase simulations of Hsieh’s [Hsieh, K.T., 1988. A phenomenological model of the hydrocyclone, Ph.D. thesis, University of Utah] data show a very good prediction of the cyclone efficiency curve. Whilst further model development is needed, the approach is showing promise as a cyclone design tool