Novel methodology for predicting the critical salt concentration of bubble coalescence inhibition

Bubble coalescence in some salt solutions can be inhibited if the salt concentration reaches a critical concentration Ccr. There are three models available for Ccr in the literature, but they fail to predict Ccr correctly. The first two models employ the van der Waals attraction power laws to establish Ccr from the discriminant of quadratic or cubic polynomials. To improve the two models, the third model uses the same momentum balance equation of the previous models but different intermolecular force generated by water hydration with exponential decaying. The third prediction for Ccr requires the experimental input for film rupture thickness and is incomplete. We show further in this paper that the third model is incorrect. We propose a novel methodology for determining C cr which resolves the mathematical uncertainties in modeling C cr and can explicitly predict it from any relevant intermolecular forces. The methodology is based on the discovery that Ccr occurs at the local maximum of the balance equation for the capillary pressure, disjoining pressure, and pressure of the Gibbs-Marangoni stress. The novel generic approach is successfully validated using nonlinear equations for complicated disjoining pressure

Packing of particles on the surface of bubbles

In this paper, geometrical packing models were derived to determine the coverage of particles on an air bubble. Nearly spherical glass beads of two size fractions and galena particles were used in the study. The coverage of air bubbles by glass beads was carried out in the concentration range 2.74 × 10⁻⁵–1.65 × 10⁻³ mM of CTAB. The results indicated that coverage at all concentrations could be approximated with a hexagonal model with monodispersed particles using the value of d[₄,₃]. This could be done with a relative deviation of the packing factor within 15%. The coverage of an air bubble by galena particles was carried out in a collectorless environment. The best models were found to be a hexagonal or square cell using the value of d[₁,₀]. Experimental observations on particle packing are given and implications for the froth phase of flotation are discussed

Bubble and Froth Stabilizing Agents in Froth Flotation

The mineral processing industry relies heavily on froth flotation to beneficiate complex minerals. The performance of the process depends on a multitude of chemical reagents affecting the solid mineral particles as well as the air bubbles used to collect the valuable mineral particles. In flotation, bubbles and froths are transiently stable by the use of a frothing agent or the presence of inorganic electrolytes in the process water. This review presents the primary stages characterizing bubble coalescence. The effect of flotation reagents and inorganic electrolytes on the stability of bubbles and the mechanisms which delay the coalescence of bubbles are discussed. Recently it had been proposed that solid particles external to the flotation system may be intentionally added to stabilize the froth phase, which has attracted attention from the flotation community. This gave rise to additional studies on the topic. The final section of the paper was therefore designed to capture the progress made on this particular subject. The use of solid flotation aids offers a promising future to increase the recovery of valuable particles as these external particles may be customized. The advantage of solid particles over soluble reagents is that they may be recovered and re-used making them environmentally and economically attractive

The influence of submicron particles and salt on the recovery of coarse particles

Coarse particles are more difficult to float. One of the factors that contributes to poor floatability is the stability of froth. The froth formed in industrial flotation cells is typically not strong enough to provide adequate support for coarse and dense particles. The present study investigates how the presence of hydrophobic submicron particles at low concentration increases the recovery of relatively coarse particles through improvement in the froth stability. Silica particles with d80 of approximately 230 μm were floated in a laboratory mechanical flotation cell in a collector-free environment in the presence of poly(propylene glycol) 425 as a frothing agent. The hydrophobicity of the feed particles was modified through an esterification process with different alcohols ranging from 3 to 8 hydrocarbon groups to form a coating of intermediate hydrophobicity. Hydrophobised silica submicron particles of 300 nm in size were added to the flotation cell at 0.01 and 0.1 wt% concentration. The effect of electrolyte, sodium chloride, in the concentration range 10⁻⁵–10⁻¹ M on the recovery of coarse particles was also investigated. For the feed employed, 1-butanol was found to provide relatively good flotation properties with a possibility for improvement by stabilising the froth phase. Both additives slightly stabilised the froth phase, which resulted in an increase in the maximum recovery of up to approximately 8%. It appeared that the additives had no significant effect on the first-order flotation rate constant

Foaming and gas dispersion properties of non-ionic surfactants in the presence of an inorganic electrolyte

Foams represent an important area of research due to their relevance in many industrial processes. Where there are geographical constraints, which can limit access to fresh water, there is an economic incentive in using recycled water, bore water and even seawater for industrial purposes. This creates a growing interest in determining the effect of inorganic electrolytes on foaming and gas dispersion properties of non-ionic surfactant solutions. The present study compares the foaming and gas dispersion properties of the non-ionic surfactants 1-pentanol, tri(propylene glycol) methyl ether, and poly(propylene glycol) 425. For all surfactants, the stabilisation mechanism was influenced by the concentration of surfactant and the presence of salt with PPG being affected to a lesser extent. Sodium chloride was observed to have a detrimental effect on foaming at higher surfactant concentrations but improved foaming at low surfactant concentrations. At low surfactant concentrations, the addition of salt improved foaminess by dampening the hydrophobic force. An increase in gas holdup with increasing surfactant concentration was observed and was attributed to a decrease in bubble size. For poly(propylene glycol) an initial decrease in gas holdup was observed at very low concentrations. Salt mainly affected gas dispersion properties at a higher concentration

Foaming and gas dispersion properties of non-ionic frothers in the presence of hydrophobized submicron particles

Foams represent an important area of research due to their relevance in many industrial processes. In many systems, particulates and surfactants co-exist and can largely define the stability of the foam. A typical example is froth flotation where hydrophobic particles and frothers are essential to maintain a stable froth. Grinding operations may yield a product containing submicron-size particles, which can affect the flotation process. The present study compares the foaming and gas dispersion properties of the non-ionic surfactants 1-pentanol, tri(propylene glycol) methyl ether, and poly(propylene glycol) 425 in the presence of hydrophobic colloidal silica particles in a column. In all cases, it has been found that the gas holdup increases proportionally with the increase in the concentration of particles in the system although an initial decrease may be observed. The effect of particles on the foaminess seems to be dependent upon the surfactant. With the 1-pentanol, the addition of particles systematically decreased the foaminess of the solutions. This is in contrast to poly(propylene glycol) solutions, which exhibited an increase. Interestingly, low concentrations of particles appeared to improve the foaminess of tri(propylene glycol) methyl ether; however, the froth became less stable with further increases in the number of particles in the column. Visual observation showed that the colloidal particles play a crucial role in defining the quality of the structure of the froth

An investigation of bubble coalescence and post-rupture oscillation in non-ionic surfactant solutions using high-speed cinematography

Most processes involving bubbling in a liquid require small bubbles to maximise mass/energy transfer. A common method to prevent bubbles from coalescing is by the addition of surfactants. In order to get an insight into the coalescence process, capillary bubbles were observed using a high speed cinematography. Experiments were performed in solutions of 1-pentanol, 4-methyl-2-pentanol, tri(propylene glycol) methyl ether, and poly(propylene glycol) for which information such as the coalescence time and the deformation of the resultant bubble upon coalescence was extracted. It is shown in this study that the coalescence time increases with surfactant concentration until the appearance of a plateau. The increase in coalescence time with surfactant concentration could not be attributed only to surface elasticity. The oscillation of the resultant bubble was characterised by the damping of the oscillation. The results suggested that a minimum elasticity is required to achieve an increased damping and considerable diffusion has a detrimental effect on the dynamic response of the bubble, thereby reducing the damping

Performance characterisation of new frothers for sulphide mineral flotation

The trend towards more complex and low grade ore bodies requires increasingly specialised flotation reagent suites to deliver the required separation efficiency of the valuable mineral from the gangue, and to maximize concentrate grade and recovery. A new range of frother formulations have been developed by BASF. These formulations have shown the ability to deliver improvements in grade and improved valuable recovery on synthetic sulphide/quartz mixtures when compared with commonly used frothers such as MIBC at comparable concentrations. Fundamental test work characterising foam stability, interfacial phenomena (e.g. coalescence time and bubble oscillation) and particle detachment in the froth phase were conducted and used to explain the improved performance trends observed

Analysis of a coal preparation plant. Part 1. Changes in water quality, coal seam, and plant performance

Coal preparation plants are under increasing pressure to reduce their consumption of fresh water leading to the use of recycle water. Recycled water generally contains a large quantity of dissolved inorganic electrolytes, which affect coal flotation. This paper reports the conductivity and pH measurements of water in the tailings stream of an industrial scale flotation cell covering a period of approximately two years. The different coal seams processed at the site were also compared and the influence the water quality on the overall yield of coal assessed. This study presents the large variation in inorganic content in recycled water observed for a wash plant and determines its possible effect on coal preparation. The maximum daily temperature was found to be an important factor controlling the amount of inorganic electrolytes in the water and, very significantly, the water management system implemented. The overall plant performance was somewhat affected by the use of water containing high concentrations of inorganic electrolytes. The effect of the quantity of ions in the water on the flotation process is explored in Part 2