Inhibition of bubble coalescence: Effects of salt concentration and speed of approach

Castillo, Lorena A. Del; Ohnishi, Satomi; Horn, Roger G.

doi:10.1016/j.jcis.2010.12.057

Cited by 104 publications

(75 citation statements)

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“…Some other studies have also been conducted on the effect of salts on foam liquid films by using different techniques, with a focus on the effects of either salt type or concentration at an unquantified bubble approach speed or on the effects of bubble approach speed using a single salt [22][23][24][25][26]. Recently a systematic study considering the combined effects of salt concentration, interface approach speed and salt type on the lifetime, thinning rate (change of the film thickness) and growth rate (change of the radius) of the liquid films of salt solutions was reported [27].…”

Section: Effect Of Salts On Bubble Coalescencementioning

confidence: 99%

“…The effect of salts on bubble coalescence is characterised by measuring the rest time (before coalescence) of air bubbles at the air-liquid interface which significantly increases in the presence of inhibiting salts compared to pure water [34]. A slight variation of this technique was described by Del Castillo et al [24] in a study of the effect of bubble approach speed on the coalescence of bubbles in pure water and aqueous solutions of 0.1 and 0.5 M KCl. A schematic of the setup is shown in Figure 9.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

“…Purifying salts is challenging since specific techniques are required. Salt purification can be A C C E P T E D M A N U S C R I P T conducted through foam fractionation, roasting salts at temperatures below their melting points following crystallization, calcination or freeze-drying in liquid nitrogen under vacuum to remove excess moisture and possible trace organic contamination [17,24,45]. The TC95 of NaCl was plotted versus the reciprocal of the square root of bubble radius (R -1/2 ) in Figure 13.…”

Section: Comparison Of Transition Concentrations Of Saltsmentioning

confidence: 99%

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A quantitative review of the transition salt concentration for inhibiting bubble coalescence

Firouzi

Howes

Nguyen

2015

Advances in Colloid and Interface Science

113

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Some salts have been proven to inhibit bubble coalescence above a certain concentration called the transition concentration. The transition concentration of salts has been investigated and determined by using different techniques. Different mechanisms have also been proposed to explain the stabilising effect of salts on bubble coalescence. However, as yet there is no consensus on a mechanism which can explain the stabilizing effect of all inhibiting salts. This paper critically reviews the experimental techniques and mechanisms for the coalescence of bubbles in saline solutions. The transition concentrations of NaCl, as the most popularly used salt, determined by using different techniques such as bubble swarm, bubble pairs, thin liquid film micro-interferometry were analysed and compared. For a consistent comparison, the concept of TC95 was defined as a salt concentration at which the -percentage coalescence‖ of bubbles reduces by 95% relative to the highest (100% in pure water) and lowest (in high-salt concentration) levels. The results show a linear relationship between the TC95 of NaCl and the reciprocal of the square root of the bubble radius. This relationship holds despite different experimental techniques, salt purities and bubble approach speeds, and highlights the importance of the bubble size in bubble coalescence. The available theoretical models for inhibiting effect of salts have also been reviewed. The failure of these models in predicting the salt transition concentration commands further theoretical development for a better understanding of bubble coalescence in salt solutions.

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Section: Effect Of Salts On Bubble Coalescencementioning

confidence: 99%

Section: Accepted Manuscriptmentioning

confidence: 99%

Section: Comparison Of Transition Concentrations Of Saltsmentioning

confidence: 99%

See 1 more Smart Citation

A quantitative review of the transition salt concentration for inhibiting bubble coalescence

Firouzi

Howes

Nguyen

2015

Advances in Colloid and Interface Science

113

View full text Add to dashboard Cite

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“…Some other studies have also been conducted on the effect of salts on foam liquid films by using different techniques, with the focus on the effects of either salt type or concentration at an unquantified bubble approach speed, or on the effects of bubble approach speed using a single salt Del Castillo et al, 2011;Henry et al, 2009;Wang and Qu, 2012;. Recently a systematic study considering the combined effects of salt concentration, interface approach speed and salt type on the lifetime, thinning rate (change of the film thickness) and growth rate (change of the radius) of the liquid films of salt solutions was reported (Firouzi and Nguyen, 2014a of salts followed the reverse order of that for film lifetime, and it was shown that the transition concentration was independent of bubble approach speed in the investigated range of 10-300 µm/s.…”

Section: Effect Of Salts On Bubble Coalescencementioning

confidence: 99%

Drainage and stability of foam films during bubble coalescence in aqueous salt solutions

Firouzi¹

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Bubble coalescence and thin liquid films (TLFs) between bubbles known as foam films, are central to many daily activities, both natural and industrial. They govern a number of important processes such as foam fractionation, oil recovery from tar sands and mineral recovery by flotation using air bubbles. TLFs are known to be stabilized by some salts and bubble coalescence in saline water can be inhibited at salt concentrations above a critical (transition) concentration. However, the mechanisms of the inhibiting effect of these salts are as yet contentious. The aim of this work is to characterise the behaviour of saline liquid films both experimentally and theoretically to better understand the mechanisms.The effect of sodium halide and alkali metal salts including NaF, NaBr, NaI, NaCl, KCl and LiCl on the stability of a foam film was investigated by applying the TLF interferometry method. To mimic realistic conditions of bubble coalescence in separation processes, the drainage and stability of TLFs were studied under non-zero bubble (air-liquid interface) approach speeds (10-300 µm/s) utilizing a nano-pump. For each of the salts studied, a critical concentration (Ccr) above which liquid films lasted for up to 50 s depending on the salt type, concentration and the interface approach speed, was determined. For concentrations below Ccr, the saline liquid films either ruptured instantly or lasted for less than 0.2 s. Ccr follows the order NaF

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“…Further investigations were resumed in 2015 which were reported in Chapter 5 and 6. During that period, few investigations had been made by other researcher which focused on evaporation and impurities (Yaminsky et al, 2010b), bubble speed and single salt at low concentration (Castillo et al, 2011;Firouzi et al, 2014;Yaminsky et al, 2010a). The key finding is that speed of liquid films or bubbles promotes film rupture or bubble coalescence.…”

Section: Resultsmentioning

confidence: 99%

Stability and coalescence of bubbles in salt solutions in a bubble column and thin liquid films

Nguyen¹

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Salts are known to inhibit bubble coalescence at the concentration greater than a critical (transition) concentration. The phenomenon of bubble coalescence governs the size distribution of bubbles, which is vital to many natural and industrial processes including mass transfer in the ocean, multiphase reactors and mineral recovery in froth flotation. Despite intensive studies over nearly a century resulting in multiple hypotheses, mechanisms of the coalescence inhibition are still unclear.Researchers have greatly agreed that it is the liquid films between bubbles that control the coalescence and must be firstly understood. Surprisingly, most studies have just focused on the bubble tests, but there was a lack of comprehensive studies about the liquid films in a surfactant-free salt system. This thesis aims to provide experimental evidence and extend the current understanding of the liquid film stability and coalescence in salt solutions.Firstly, the effect of superficial gas velocity (3.5, 10, and 18 mm/s), salt type (NaCl, NaI and CsCl) and concentration (0.001M to 3M) on bubble coalescence and gas holdup in a small bubble column were studied. For the first time, it was found that the transition concentration for coalescence inhibition is not a unique entity of salts as reported but it decreases with increasing gas velocity, which highlights the importance of hydrodynamic conditions. The results also confirmed the ion specific responses of investigated salts to transition concentration and gas holdup.To understand the coalescence, liquid films of the simplest subject, deionised water (DI), were studies using the micro-interferometry method with the Sheludko cell. It was showed that films of DI water drained very fast and ruptured instantly when two bubbles were first brought into contact.However, the film drainage rate and rupture thickness sharply decreased and the film lifetime steeply increased with increasing contact time up to 10 min, but then they levelled off. It was argued that the phenomenon was due to the migration of inherently dissolved gases which act as the long-range hydrophobic attraction. The JC Erickson et al.' theory of the hydrophobic attraction and the extended Stefan-Reynolds models to include the air/water surface mobility were also employed. The liquid film study was then extended for salts without a presence of surfactants. Drainage and stability of liquid films in different salts (LiCl, NaCl, KCl, CsCl, KNO3, NaClO3, CaCl2, and MgSO4) over a wider range of concentration (0.001M -3M) were studied in the close (saturation) Sheludko cell with the strictly controlled saturation level and surface contact time. Films of all salts drained slower and lasted longer with increasing salt concentration. Also, the so-called non-inhibiting ii salt, NaClO3, indeed inhibits coalescence at high concentrations (greater than 1M). The effect of the DLVO forces was totally ruled out. Based on the correlation between the experimental results and the data of oxygen solubility and solution viscosity, i...

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Inhibition of bubble coalescence: Effects of salt concentration and speed of approach

Cited by 104 publications

References 86 publications

A quantitative review of the transition salt concentration for inhibiting bubble coalescence

A quantitative review of the transition salt concentration for inhibiting bubble coalescence

Drainage and stability of foam films during bubble coalescence in aqueous salt solutions

Stability and coalescence of bubbles in salt solutions in a bubble column and thin liquid films

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