Determining the significance of flotation variables on froth rheology using a central composite rotatable design

Froth performance in a flotation cell is expected to be affected by froth rheology due to change in the froth transportation rate. However, very little study has been performed to investigate how froth rheology responds to flotation variables. This paper presents an experimental program performed to study the effects of flotation variables (i.e. feed grade, feed particle size, froth height, superficial gas velocity and impeller speed) on the froth rheology. These conditions were varied using a central composite rotatable design (CCRD).Froth rheology was found to change significantly with a variation in flotation conditions and exhibited shear-thinning behaviour. Assuming the froth moving towards the flotation lip is an open channel flow, the shear rate in the froth was calculated to be less than 4s. Results of the CCRD experiments showed that the flotation variables have different effects on the froth rheology. The interactions between these flotation variables in determining froth rheology were also analysed. A shear rate specific empirical model was developed to relate froth rheology to the flotation variables and their interactions

Characterisation of kaolinite colloidal and flow behaviour via crystallinity measurements

This study evaluates the possibility of predicting colloidal and flow behaviour of kaolinite suspensions by measuring kaolinite crystallinity. The Hinckley index of different samples was calculated from XRD spectra as an indicator of the crystallinity. Kaolinite samples with a high Hinckley index showed a defined platy morphology with smooth surfaces of low surface area, whilst progressively roughened basal planes with prevalent broken edges were observed in kaolinite samples of lower Hinckley indices. Despite similarity in the elemental composition, the kaolinite samples present different surface charge properties, likely due to variations in exposed pH dependent edge sites. Poorly crystallised kaolinite samples were characterised by higher yield stresses and viscosities. This study highlights the importance of crystallinity characterisation towards predicting colloidal behaviour and flow characteristics of kaolinite suspensions

Effect of flotation conditions on froth rheology

Froth flotation has been widely used for separating and concentrating valuable minerals in an ore. Froth rheology is an important parameter that affects flotation performance by affecting froth transportation. This paper reports the results of an investigation into the effect of flotation conditions on the froth rheology, in particular the influence of frother dosage and feed grade. Atwo-factor factorial experiment program was performed in a 20 L continuously operated flotation cell. It was found that, within the boundaries of this work, varying the frother dosage has no significant influence on the froth rheology, while the feed grade exhibits a positive correlation with the froth viscosity. In line with the previous study, the froth rheology has a negative correlation with the bubble size, and a positive correlation with the fraction of the bubble lamellae covered by solid particles. The froth rheology model which has been previously developed by the authors (as a function of froth properties) was also validated in the current work

The temperature effect on electrokinetic properties of the silica–polyvinyl alcohol (PVA) system

The influence of polyvinyl alcohol (PVA) adsorption on the structure of the diffuse layer of silica (SiO2) in the temperature range 15–35 °C was examined. The microelectrophoresis method was used in the experiments to determine the zeta potential of the solid particles in the absence and presence of the polymer. The adsorption of PVA macromolecules causes the zeta potential decrease in all investigated SiO2 systems. Moreover this, decrease is the most pronounced at the highest examined temperature. Obtained results indicate that the conformational changes of adsorbed polymer chains are responsible for changes in electrokinetic properties of silica particles. Moreover, the structure of diffuse layer on the solid surface with adsorbed polymer results from the following effects: the presence of acetate groups in PVA chains, the blockade of silica surface groups by adsorbed polymer and the shift of slipping plane due to macromolecules adsorption

Detachment force of particles from fluid droplets

We calculate the deformation of a spherical droplet, resulting from the application of a pair of opposite forces to particles located diametrically opposite at the two ends of the droplet. The free-energy analysis is used to calculate the force–distance curves for the generated restoring forces, arising from the displacement of the particles relative to each other. While the logarithmic dependence of the “de Gennes–Hooke” constant on the particle to droplet size ratio, ν, is rather well known in the limit of very small ν, we find that for more realistic particle to droplet size ratios, i.e. ν = 0.001 to 0.01, the additional constant terms of O(1) constitute a significant correction to previously reported results. We derive the restoring force constant to be 2πγ[0.5 − ln(ν/2)]−1, in perfect agreement with the exact semi-numerical analysis of the same problem. The deviation from the linear force–displacement behaviour, occurring close to the point of detachment, is also investigated. A study of the energy dissipated shows it to be an increasingly dominant component of the work done during the detachment of the particles, as ν decreases. This indicates the existence of a significantly higher energy barrier to desorption of very small particles, compared to the one suggested by their adsorption energy alone. The influence of the line tension on the detachment force is also considered. It is shown that where line tension is important, the contact angle is no longer a constant but instead alters with the displacement of the particles from their equilibrium positions

Bulk and surface rheology of Aculyn™ 22 and Aculyn™ 33 polymeric solutions and kinetics of foam drainage

This paper was accepted for publication in the journal Colloids and Surfaces A: Physicochemical and Engineering Aspects and the definitive published version is available at http://dx.doi.org/10.1016/j.colsurfa.2013.05.072Experimental investigations of both bulk and surface rheology of solutions of commercially available polymers AculynTM 22 and AculynTM 33 in presence of sodium chloride are performed in a wide range of the polymer and salt concentrations. It is shown that the bulk viscosity and the surface viscoelastic modulus of solutions of both polymers increases with the increase of polymer concentration and the decrease of the salt concentration. Solutions of both polymers demonstrate very good foamability and form stable foams. Foam drainage is governed mainly by the bulk viscosity when the latter is in the range of 100-500 mPa·s

A review of polymeric dispersant stabilisation of titania pigment

A review of past and present published works examining the interaction of polymeric dispersants with titania pigment particles is presented. Titania is the most important white pigments currently used in the world and its suspension properties are very important for consumer industries such as paints, papermaking and plastics; if aggregates are present, the end-use properties including gloss, opacity and storage stability will be highly affected. As polymeric dispersants are generally used to disperse titania pigment particles, it is very important to understand the interactions between the pigment particles and polymeric dispersants of varying functionality. Although, in principle, the adsorption of polymers onto titania pigment and influences on pigment dispersion and stabilisation are fairly known, it is nevertheless hardly possible to forecast the behaviour of a given polymeric dispersant in advance, unless to have a broad knowledge of the interaction occurring between pigment and dispersants and effect of dispersant structure upon adsorption. While only titania pigment is discussed, the issues raised may also apply to other mineral oxides such as alumina or zirconia