Filtration of copper concentrates in the mining industry is carried out in cycles, mainly cake formation, expression, and blowing. Each of these cycles depends on the solid (mineralogy, porosity, particle size distribution), water, and air (density, viscosity, permeability, and relative permeability) properties that define the performance in each cycle. The fundamental phenomenon in cake formation and expression is a one-phase flow (water) through a porous bed of solid particles (the cake), while in blowing it is a two-phase flow (water and air) through the cake. Sometimes, due to a change in the properties of the mineral, a filtration plant is unable to maintain the capacity at the specified humidity. One alternative to solve this problem is to heat the air during the blowing cycle, which in turn heats the water in the cake, this process significantly decreases the water viscosity and only marginally increases the air viscosity. In this work, this strategy was studied at a laboratory scale. The results show a significant decrease in the blowing time as the temperature of the air was increased.

The structural and operational simplicity of a hydrocyclone hides the high complexity of its classification mechanism. Efforts to describe hydrocyclone behavior have led to two types of models: empirical and phenomenological. Empirical models are based on experimental observation of hydrocyclone performance and consist of the statistical correlation of numerous experimental data. In some cases, simple conceptual models are used to interpret the results, while in others, the device is considered a black box. The best-known empirical models are those of Lynch and Rao [, , ], Plitt [, ], Nageswararao [] and Sepúlveda []. Experience has shown that these models have serious limitations. Their principle defect is that they must be used only in a small area of the conditions for which their parameters have been determined [] (Svarovsky []). They do not permit the reasons for the equipment behavior to be understood and, therefore, design optimization cannot be based on them.

It is common to call “design” the election of the sizes of the parts of hydrocyclones chosen from those provided by the manufacturers. It is really a geometric selection for which empirical formulas exist (see Chap. 9). In this chapter we will develop a design for hydrocyclones as a mixed-flow turbo machine including different inlet, vortex and apex geometry choices producing the greatest centrifugal energy from the angular momentum of the entrance to obtain the maximum fluid flow with minimum head loss when performing classification.

There are two types of empirical models: so-called design or selecting models and simulation models. The first is used to select commercial hydrocyclones that fulfill given capacity and classification conditions and the second, based on experimental work, is used to determine the capacity, split size, short circuit and classification function parameters that permit the simulation of a hydrocyclone or various hydrocyclones.

The purpose of this series is to focus on subjects in which fluid mechanics plays a fundamental role.As well as the more traditional applications of aeronautics, hydraulics, heat and mass transfer etc., books will be published dealing with topics, which are currently in a state of rapid development, such as turbulence, suspensions and multiphase fluids, super and hypersonic flows and numerical modelling techniques.It is a widely held view that it is the interdisciplinary subjects that will receive intense scientific attention, bringing them to the forefront of technological advancement.Fluids have the ability to transport matter and its properties as well as transmit force, therefore fluid mechanics is a subject that is particulary open to cross fertilisation with other sciences and disciplines of engineering.The subject of fluid mechanics will be highly relevant in such domains as chemical, metallurgical, biological and ecological engineering.This series is particularly open to such new multidisciplinary domains.The median level of presentation is the first year graduate student.Some texts are monographs defining the current state of a field; others are accessible to final year undergraduates; but essentially the emphasis is on readability and clarity.

The previous chapters showed that the problem associated with the mathematical modeling of flow patterns in hydrocyclones involves the solution of strongly coupled, non-linear partial differential equations of mass and momentum balances, which lies well beyond any analytical approach, except when major simplifications are assumed. In this chapter we will study the challenges related to the complex flow behavior arising from laminar and turbulent three-dimensional flows. Numerical simulation of partial differential equations with finite element and finite volume platforms such as Fluent has reached a reasonable level of maturity and is accepted as an analysis tool. Important aspects of the numerical simulation of hydrocyclones are the formulation of the governing equations, selection of the appropriate turbulence model, imposition of boundary conditions and proper representation of the computational domain.

Perturbations in the ore discharge of a grinding mill affects directly the classification in hydrocyclones and deviates the grinding-classification circuit from its optimal operating point. Operational variables, including the particle size, size distribution and volume fraction of solids in the feed should be subjected to control.

This chapter deals with the flow of fluids in circular pipelines as the basis to understand the feed, underflow and overflow piping necessary and the prevention of sedimentation in the tubes. Explicit equations of the settling velocities of suspensions in pipes for Newtonian in turbulent flow are presented and a general explicit equation for the velocity for turbulent flow of a Newtonian fluid in pipe flow is developed. Several critical transport velocities to avoid sedimentation are presented and the settling velocity of suspensions of spheres in non-Newtonian fluid is developed.

Classification in mineral processing is the operation of separating particle mixture components into two or more fractions according to size, with each resulting group more uniform in this property than the original mixture. There are two types of classifier: mechanical and hydraulic. During screening in the classical mechanical classifier, the material is subjected to the action of a series of screens through which small particles pass, while coarser particles greater than screen openings are retained. Like particle size, shape also has an important effect. The mechanism involved in separating particle sizes in a hydraulic classifier is sedimentation of the particles subjected to body forces such as gravity and centrifugal force. In this case, the factors affecting hydraulic classifications are the solid particle properties of size, density and shape and fluid temperature, density and viscosity.

Hydrocyclones are used for classification purposes in the mining and mineral processing industries. According to their geometry and under certain operating conditions, hydrocyclones may present roping, which is a defective operation. Studies have related the roping phenomena to many variables such as hydrocyclone geometry and operating conditions. Some authors established a connection between the solids concentration of the feed and the discharge as one of the factors that generate roping. Other authors presented factors such as the apex and the vortex finder diameters, inlet pressure and the relationship between roping generation and the air core. This research aims to study the effect of inlet pressure and particle size distribution in the feed on roping in hydrocyclones. We develop a model using computational fluid dynamics (CFD) in order to study a 75-mm hydrocyclone operating with a variable flowrate and fed with two different materials. Each material is characterized by five granular phases interacting with each other and the model is validated by comparison with experimental data. The turbulence is treated using the Reynolds Stress Model (RSM) and the Eulerian Multiphase Model is used for the interactions between phases. The granular phases are described by the kinetic theory of granular flows (KTGF). The characteristics studied were: (i) air core and material distribution inside the hydrocyclone, (ii) underflow shape and spray angle, (iii) flow and solid concentrations, (iv) efficiency curve and separation size and (v) particle size distribution in the underflow and the cut sizes. According to the results, the particle size distribution of material in the feed has a direct impact on underflow behavior; when operating with coarser material the device tends to rope as the spray angle decreases. The same happens with an increase in the feed pressure. The roping condition generated by the coarse material directly affects the efficiency of the hydrocyclone, triggering an increase in separation size. The underflow particle size distribution tends to be coarser with an increase in the inlet pressure. When the inlet pressure decreases, the overflow particle distribution tends to be finer.

Water scarcity is a global issue that is threatening social and economic development. One approach to alleviating scarcity is the incorporation of new water sources into supply systems, including desalinated seawater for industrial and municipal use. In Chile, large volumes of water are used in water-scarce regions where mining takes place, alongside agriculture and small communities. This situation has driven a debate around policies to increase the use of seawater to satisfy the water demand of the mining industry. The economic, social and environmental implications of such a policy, however, are poorly understood and the current regulatory framework to address concerns and uncertainties is inadequate. This paper presents a technical, legal, economic and environmental appraisal of such a policy and considers options to improve outcomes. The appraisal suggests that clear regulations derived from economic, social and environmental analysis must be generated to provide legal certainty and reduce risks. Alternative or complementary water supply options should be allowed where mining operations can demonstrate negligible hydrological and social impacts or use innovative solutions such as stakeholder water rights swaps and water efficiency technologies. We provide insight that will help to drive a better policymaking process aimed at tackling water scarcity in Chile and in similar areas of the world.

Flocculation presents one of the most effective methods for enhancing separation of both anthropogenic and natural suspensions by sedimentation, filtration and flotation techniques.The flocculation effectiveness much depends on the medium shear rate in a flocculator. The objective of this research comprises the study how the suspension dispersity and concentration effect the efficiency of its flocculation in a static tubular flocculator and in a dynamic Couette flocculator. The studies used aqueous suspensions of ultra-fine calcium carbonate (<7 μm) and fine silica (<90 μm) as objects. It was established that treatment of ultra-fine calcium carbonate suspension in a static flocculator produced in the range 400-450 s-1 a pronounced primary maximum in the dependence "flocculation efficiency/shear rate". The increase of the suspension concentration to 70 g/l and above resulted in a small secondary maximum of the flocculation efficiency in the region of around 950 s-1. This can be due to a higher dissolution rate of flocculant and a corresponding increase of particles adhesion forces in flocs, which counteract viscous forces destroying them. In silicon dioxide suspension treatment, the primary and secondary peaks occur at both small and high suspension concentrations, but in a latter case, they are by far more pronounced and comparable in magnitude.

Hydrocyclones are industrial devices used as processing units in fluid and particle technology. In a hydrocyclone the fluid and the transported particles experiment high centrifugal forces which force them to move outwards towards the solid walls and then to the bottom exit. On the other hand, the fluid and the particles suffer also an inwardly acting drag which can drive them towards the upper outlet. Thus, the performance of a hydrocyclone depends on the 3D character of this flow and the anisotropy of its turbulence. In this work we have developed a 3D model of the swirling flow in a hydrocyclone by using COMSOL Multiphysics®. Turbulence is modeled by using the Reynolds-Averaged Navier-Stokes equations and the v2-f turbulence closure. The results of the simulations are satisfactory, being able to reproduce the general flow pattern. Finally, the computed velocity profiles are compared with laser Doppler measurements, in order to assess its goodness.

The efficient use of water has become an important issue in the mining industry, especially in countries where it is located in desert areas with low water reserves, as is the case in Chile. In addition, low ore grades necessitate efforts to recover the maximum amount of minerals in solid–liquid separation processes. Fine particle flocculation is a preliminary stage in various solid–liquid separation processes. The conventional flocculation process is done at low shear rates, ensuring that large flocs remain unbroken. However, it has been seen that the application of high shear rates at the beginning of the process for a short period of time significantly improves the solid removal efficiency, reducing the flocculant dosage and the duration and cost of the process, which is known as ultra-flocculation. This work presents a numerical CFD study of the hydrodynamic behavior in five hydraulic reactors for ultra-flocculation, analyzing the shear rate curve over treatment time, dissipation efficiency and average shear rates. A new mean shear rate, which uses hydraulic variables to estimate the average agitation, is also defined. It was shown that the hydraulic shear rate can be useful for developing better hydraulic designs because it provides a second view, which, added to the shear rate curve over treatment time and effective shear rate, allows a more complete judgment of the performance of the designs.

Although roping in hydrocyclones is a problem that has been studied by many researchers, we do not yet have a theory that relates all the variables involved. Several experimental works with different approaches such as mechanical energy balance, work on hydrocyclones with water only and hydrocyclone air core measurements with different instruments in the laboratory and plant have attempted to explain the roping phenomenon. They have addressed design variables such as apex to vortex diameters and different cone angles as well as operating variables such as inlet solid concentration, particle size, pressure and overflow and underflow flow rates and concentrations in order to understand their effect on the roping condition. In this paper we intend to verify some of the conclusions of these studies and establish inlet pressure and particle diameter as the variables that, in combination, lead from spray to roping. We present a computational model using Computational Fluid Dynamics (CFD) to study a 75-mm laboratory hydrocyclone operating at a variable flow rate and with three different particle diameters. The Reynolds Stress Model and Eulerian multiphase model were used to model the turbulence and interaction of phases, respectively. The solid particles are described with the kinetic theory of granular flows (KTGF). Physical coherence and accuracy were compared with experimental data, where errors are within the expected range for an engineering prediction. The results indicate that transition from spray to roping generates an increase in the inlet flow pressure and/or particle diameter at a constant solid concentration in the feed flow. For 20-mu m-diameter particles an increase results in a decrease in the discharge angle, although it always has a spray shape, for 34-mu m diameters increasing the inlet pressure generates a semi-rope discharge and for 70-mu m diameter particles a small increase in the inlet pressure generates a roping condition. Transition to roping is characterized by a decrease in the air core diameter and discharge angle due to slow rotational velocity when particle diameter increases or higher accumulation of the solid fraction in the apex when inlet pressure increases. The passage from spray to roping occurs with a change in the frequency spectrum of the pressure oscillations in the walls of the hydrocyclone, with high amplitudes at low frequencies for spray discharge and noisy signals in all spectrums and damped low frequencies for roping.

A theory of sedimentation-consolidation evolved in the last decades of the 20th century and is accepted today by researchers worldwide. This theory provides a reliable method of thickener design, simulation and control. However, a process model, simple or sophisticated, empirical or phenomenological, is useful only if it is possible to determine, in an objective way, its experimental parameters. Although it is important for a mineral processing plant to perform periodical laboratory test to determine thickening parameters, and adjust the operation in this way, laboratory tests not always represent the behavior of the material in a thickener. Research workers at the University of Concepción developed new instrumentation, algorithms and software to determine the material properties of the thickener feed, such as settling velocity of the suspension and the compressibility of the sediment produced. Work was made in a major Chilean copper mineral processing plant to test the new instrumentation. In this paper, the auditing of one molybdenum thickener and a tailings thickener are presented using the two new online instrument.

The effect of various seawater electrolytes on the zeta potential and viscosity of silica suspensions has been studied as a function of electrolyte concentration, pH, flocculant and shear rate. Salts were alkali and alkaline-earth metal chlorides. The magnitude of the negative zeta potential of silica as a function of pH for monovalent cations follows Li+ > Na+ > K+ > Cs+ implying that adsorption follows Cs+ > K+ > Na+ > Li+. In the presence of divalent cations, the magnitude of the negative zeta potential as a function of pH decreases greatly following Mg2+ > Ca2+, implying that adsorption follows Ca2+ > Mg2+. Regarding the flocculant in solution, molecular simulations indicate that repulsion between anionic acrylate units causes the polymer to adopt expanded tertiary conformations, however with cations this repulsion is shielded causing the polymer to fold into balled-up conformations. The adsorption of cations on anionic flocculant chains follows inverse series than silica, i.e., Li+ > Na+ > K+ > Cs+ and Mg2+ < Ca2+. The different ability of silica and flocculant to adsorb cations leads to force fields that create three-dimensional networks of particles with resistance depending on the cation. The viscosity of silica suspensions formulated at 0.5 M salt and pH 7 in anionic flocculant follows KI > KCl > NaCl > MgCl2 > water, and in cationic flocculant follows KI < KCl < NaCl < MgCl2 < water. In anionic flocculant, the counterion is the same for silica and flocculant leading to strong particle-flocculant interaction and suspensions with high viscosity. The resistance of the particle networks formed are weakened only slightly as the shear stress increases In cationic flocculant, the cation is the counterion of silica while the anion is the counterion of flocculant, their ionic atmospheres are different giving rise to weak particle-flocculant interaction and low viscosity suspensions. The resistance of such networks is increasingly weakened as the shear rate increases. The higher the pH, the higher the repulsion, and the lower the viscosities of the suspensions formulated with either flocculant.