**4. Parameters affecting colloidal stability in mineral processing**

Mineral processing is influenced in many ways by colloidal and surface forces (**Figure 4**).

**159**

*Application of Colloids and Its Relevance in Mineral Engineering*

Rheology is dominated by particle coagulation and thus affects the effectiveness of grinding. Selective homocoagulation/flocculation is advantageous by decreasing mechanical entrainment or dewatering for fine particle flotation of valuables. Flotation of fine particles also depends on the interaction of bubble-bubble and bubble-particle interaction. However, for thickening/dewatering, hetero-coagulation/ flocculation that is detrimental to selective flotation by slime coating is desirable.

The stability of colloidal system is mainly affected by interactions among the particles. The coagulation kinetics of multicomponent colloidal systems with regard

Many advancements have been made in the past several decades for accurate and direct measurements of forces acting between particles as a function of the surface separation. Although the findings were consistent with the colloidal forces doublelayer hypothesis, deviation was found at very short distances, mainly due to hydra-

The presence of cations in the aqueous process, which makes it possible to adsorb hydrated cations on the solid surface, is responsible for the resulting hydration force between the two mineral surfaces and is a significant flotation factor.

On the other hand, for predicting hetero-coagulation such as slime coating, zeta

No attraction, weak attraction, or strong attraction between different mineral

fines can be distinguished from the zeta potential measurements for a slurry

to the different electrical double layers for each dispersed species will vary. The reduction of diffuse layer potential by surfactant adsorption can result in coagulation. Another important factor affecting the coagulation of mineral particles is hydrophobicity and thus affecting the rheology of suspensions. This is particularly true when the particles are sufficiently hydrophobic, being able to counteract electrostatic repulsion through strong hydrophobic attractive forces. Colloidal interactions of slimes particles (<10 μm) requires careful attention, because it results in slime coating and hence diminishing the separation performance.

*DOI: http://dx.doi.org/10.5772/intechopen.95337*

**4.1 Colloidal stability**

*Colloidal chemistry in Mineral Processing.*

**Figure 4.**

*4.1.1 Methods to study colloidal stability*

tion forces or surface roughness.

potential calculation can be used.

mixture system containing various mineral fines.

*Application of Colloids and Its Relevance in Mineral Engineering DOI: http://dx.doi.org/10.5772/intechopen.95337*

*Colloids - Types, Preparation and Applications*

*Surface and Interfacial tensions for the molecules in bulk liquid.*

**2.1 Interfacial tension**

**Figure 3.**

presented in **Figure 3.**

Potential determining ions [H+

According to molecular theory, different crystal structures have different surface energy [9–11]. Interface is the boundary between two or more phases exist together. The properties of the molecules forming the interface are different from those in the bulk that these molecules are forming an interfacial phase. Several types of interface can exist depending on whether the two adjacent phases are in solid, liquid or gaseous state.

In the liquid state, the cohesive forces between adjacent molecules are well developed. There are various forces present between surface and interfaces molecules

Cohesive forces are present with the other molecules which are situated below or adjacent to them. Adhesive forces are being developed with the molecules of other phases in the interface. Surface tension (γ) is the force per unit length that must be applied parallel to the surface so as to counter balance the net inward pull. Interfacial tension is the force per unit length existing at the interface between two different phases.

**3. Methods for characterization of colloidal slurry phases**

and OH−

bottleneck in determining the absolute separation and the surface forces.

**4. Parameters affecting colloidal stability in mineral processing**

Mineral processing is influenced in many ways by colloidal and surface forces

in determining electrical charge at the surface in the colloidal system [12–15]. There are many diagnostic methods such as particle size analysis and turbidity measurements, surface force measurement with atomic force microscope (AFM) and surface force apparatus (SFA) are direct approaches for studying colloidal interactions, which could provide insights into molecular mechanisms of operating colloidal forces with high resolution [1]. After invention of these advanced techniques, these have become the most important tools in colloid and interface science to directly measure the interactions between particles and liquid substrates, and even the single molecular force involved in the rupture of a single chemical bond and the stretching of polymer chains. These are not only limited to hard or non-deformable surfaces, are also used to measure the forces between one solid particle and an air bubble or an oil drop. Although progress has been made in studying bubble-particle interactions using AFM in recent years, the deformation of the bubble by both the hydrodynamic and surface forces remains a

] at the interface plays a very important role

**158**

(**Figure 4**).

Rheology is dominated by particle coagulation and thus affects the effectiveness of grinding. Selective homocoagulation/flocculation is advantageous by decreasing mechanical entrainment or dewatering for fine particle flotation of valuables. Flotation of fine particles also depends on the interaction of bubble-bubble and bubble-particle interaction. However, for thickening/dewatering, hetero-coagulation/ flocculation that is detrimental to selective flotation by slime coating is desirable.

#### **4.1 Colloidal stability**

The stability of colloidal system is mainly affected by interactions among the particles. The coagulation kinetics of multicomponent colloidal systems with regard to the different electrical double layers for each dispersed species will vary.

The reduction of diffuse layer potential by surfactant adsorption can result in coagulation. Another important factor affecting the coagulation of mineral particles is hydrophobicity and thus affecting the rheology of suspensions. This is particularly true when the particles are sufficiently hydrophobic, being able to counteract electrostatic repulsion through strong hydrophobic attractive forces.

Colloidal interactions of slimes particles (<10 μm) requires careful attention, because it results in slime coating and hence diminishing the separation performance.

#### *4.1.1 Methods to study colloidal stability*

Many advancements have been made in the past several decades for accurate and direct measurements of forces acting between particles as a function of the surface separation. Although the findings were consistent with the colloidal forces doublelayer hypothesis, deviation was found at very short distances, mainly due to hydration forces or surface roughness.

The presence of cations in the aqueous process, which makes it possible to adsorb hydrated cations on the solid surface, is responsible for the resulting hydration force between the two mineral surfaces and is a significant flotation factor.

On the other hand, for predicting hetero-coagulation such as slime coating, zeta potential calculation can be used.

No attraction, weak attraction, or strong attraction between different mineral fines can be distinguished from the zeta potential measurements for a slurry mixture system containing various mineral fines.

Zeta potential, electric double layer is first prescribed by Helmoltz [16]. The counter ions in an electrical double layer can exchange with ions of the same sign from the solution. In a similar way, the moment of counter ions occurs, with the application of electric field because of the concept of surface conductivity.

#### *4.1.1.1 Atomic Force Microscopic (AFM) analysis*

The bubble-particle attachment forces can be calculated by attaching a bubble to a stationary solid surface and a particle to an AFM cantilever. Strong long range attractive forces can be determined for a hydrophobic particle and an air bubble before any double-layer and van der Waals forces can be established, with the gas bubble acting like a hydrophobic surface.

The attractive hydrophobic attraction between the solid-water and the watergas interfaces is assumed to be the main driving force for film rupture and the attachment of air bubbles to hydrophobic mineral particles, taking into account the repulsive existence of electrostatic repulsion and van der Waals forces between particles and air bubbles encountered in flotation. The development of a dimple due to a hydrodynamic pressure greater than the internal bubble pressure is highly dependent on the velocity of the air bubble's approach. Although the higher bubble approach velocity leads to a more pronounced dimple, in order to evaluate the film thickness of the first dimple and the form of the film for hydrophobic solid surface systems, the surface hydrophobicity needs to be taken into account. By changing the reaction conditions such as electrochemical potential and solution pH, it is possible to maximise the alteration of hydrophobicity with/without collector.

#### *4.1.2 Effect of water chemistry*

As water is a polar liquid and moderate conductor of electricity, potential difference will not be observed in the absence of electric current. The chemistry of water has a great influence on the interaction forces in aqueous solution between solid surfaces. The colloidal stability of various slurry phases is influenced by various ions (monovalent, divalent, trivalent, etc.) present in the water. Cations function as a binder to bridge various charged surfaces in certain instances. If present in process water, reagents/surfactants bind with cations to minimise the amount of free cations in the liquid, are able to mitigate the undesirable effect of cations and thus promote the release of mineral particles. The water chemistry of the aqueous system where the attachment occurs is strongly influenced by bubble-particle attachment. Electrolytes in water compress the electrical double layer for the already hydrophobic particles and thus lower the energy barrier created during the collision between hydrophobic particles and air bubbles, which is advantageous for the bubble particle attachment. Knowledge about the surface properties and zeta potential is very important for flotation. The literature may define the ideal situation for different ores, but due to the presence of different interfering ions, the actual situation of different ores with varied mineralogy differs. Therefore, for flotation process effectiveness, the particle size distribution proportions of coarse and fine size groups, surface features of bulk and size fractions of different mineral species and their interactions with the reagents need to be understood and closely monitored.

#### *4.1.3 Effect of reagents*

Flotation reagents play the most important role in flotation, as the heterocoagulation that could contribute to the loss of liberated valuables in the tailings

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*Application of Colloids and Its Relevance in Mineral Engineering*

due to slime coating will affect less than the optimum quantity, while the optimum quantity helps to selectively homo-coagulate fine valuable particles, increasing the

Collectors are reagents which render minerals' surface hydrophobic by adsorption. The selection of an appropriate collector is critical for selective separation of valuable minerals from gangue minerals. Collectors can be classified into non-ionic, anionic and cationic depending on their ionic charge and

Frothers are organic compounds that dissociate into ions at the air-water interface and decrease the surface tension, thus stabilising the froth consisting of a multitude of mineral-laden air bubbles and inducing the mineralized surface

These are chemical compounds applied to the pulps of flotation to strengthen the collector-mineral Adsorption, that is, selectivity enhancement. This may be achieved by either (a) creating an environment or revitalizing the floatability of the desired mineral, (b) by suppressing the flotation activity of the undesired mineral (at a particular stage of flotation operation), (c) by removing the deleterious elements which hinder effective flotation of desired minerals or (d) by providing proper hydrophobicity for the selective adsorption between the mineral and collector.

Along with flotation, colloidal chemistry plays an important role in flocculation. Inorganic salts and synthetic high-molecular - weight polymers are commonly used in the treatment of mine waste and oil sands tailings to coagulate/flocculate the solid particles. Following its biomedical applications by settling experiments, the feasibility of using highly biocompatible glycopolymers in solid–liquid separation

Yield stress measurements are used in combination with electrophoretic and zero charge point measurements as a function of solution pH to detect the surface charge characteristics of particles that play a very important role in froth flotation. Although the coagulation peak, the isoelectric point and the zero charge point all converge at the same value for isotropic minerals, they spread across a wide range of anisotropic minerals, and with the addition of anionic polymer as a dispersant to

*DOI: http://dx.doi.org/10.5772/intechopen.95337*

There are different types of modifiers.

kinetics of fine particle recovery.

*4.1.3.1 Collector*

*4.1.3.2 Frothers*

buoyancy effect.

*4.1.3.3 Modifiers*

I. Activators

II. Depressants

III. Dispersants

IV. pH regulators

has been explored.

*4.1.4 Effect of surface charge*

active ion participation.

due to slime coating will affect less than the optimum quantity, while the optimum quantity helps to selectively homo-coagulate fine valuable particles, increasing the kinetics of fine particle recovery.
