- Title
- Stabilisation of bubbles and froths with colloidal particles and inorganic electrolytes
- Creator
- Bournival, Ghislain
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2015
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Froth flotation is a widely used separation technique in the mineral processing industry. It consists of capturing valuable, hydrophobic particles with air bubbles, which rise to the surface. The bubbles segregate at the surface to form a froth zone. Valuable particles are recovered by the overflowing/skimming of the froth phase. The froth phase plays a crucial role in upgrading the concentrate by draining out non-valuable particles. The stability of the froth phase is partly controlled by chemical factors (e.g. surfactants) and physical factors (e.g. particles) among others. Inherent to the process, froth stabilising particles are depleted, which compromises the stability of the froth phase in subsequent flotation cells. This thesis details the stabilisation of flotation froth by the addition of hydrophobic silica nanoparticles and salt to improve flotation performances in the presence of non-ionic frothers. With this objective in mind, a system of nanoparticle, non-ionic surfactants, and inorganic electrolytes were characterised by their performance in a binary coalescence apparatus and a bubble column before being tested in flotation. The effect of the chemical reagents on the coalescence of bubbles was determined using the bubble-pair technique developed by Ata. The four non-ionic surfactants (i.e. 1-pentanol, 4-metyl-2-pentanol, tri(propylene glycol) methyl ether, and poly(propylene glycol) 425) were characterised using bubbles of 2 mm in diameter. Among the selected surfactants, the polyglycols were found to provide greater resistance to coalescence. It was also found that a minimum concentration is required to have any effect on the coalescence time. This is opposite to the results with alcohols, which showed a smoother transition from coalescing to non-coalescing. The oscillation of the projected area of the resultant bubble was quantified using the damping coefficient of the oscillation. It was noticed that an elasticity of approximately 1 mN m-1 was needed to immobilise the surface. Too much surfactant could reduce the stability of the bubbles and the surface due to a fast relaxation of the surface. Some inorganic electrolytes are known to prevent bubble coalescence. Chloride and sulphate electrolytes were tested. There appeared to be two regions; a low and a high concentration region. At low concentrations, the resistance to coalescence was in the order of milliseconds whereas coalescence was prevented for seconds at higher concentrations. The two regions observed could be the result of a transition affected by the relative speed of approach of the capillary bubbles. Using sodium chloride as a typical inorganic electrolyte, the oscillation of the resultant bubble showed no significant variation with increasing concentration. The dynamic foaming and gas dispersion properties of 1-pentanol, tri(propylene glycol) methyl ether, poly(propylene glycol), sodium chloride, and octanol-esterified nanoparticles were investigated by sparging N2 gas in solutions contained in a bubble column of 40 mm in diameter. The gas holdup was found to initially slightly decrease upon addition of NaCl from 10-5 to 10-3 M, but increased at a concentration of 10-1 M. Accordingly, the bubble mean diameters (d10 and d32) decreased only at 10-1 M NaCl. A sufficient concentration of non-ionic surfactant increased the gas holdup. In the case of poly(propylene glycol), the lowest concentrations tested in the study slightly decreased the gas holdup, which then sharply increased. In general, an increase in gas holdup could be explained by the ability of the surfactant to reduce the size of the bubbles. A bi-modal bubble size distribution was observed under some experimental conditions. Interestingly, the results were somewhat related to those obtained from the coalescence of capillary bubble pairs. Bi-modal bubble size distributions were associated with a coalescing environment (i.e. short coalescence time) and low resistance to the expansion and compression motion of the surface upon coalescence (i.e. low damping constant). The 300 nm octanol-esterified silica nanoparticles increased the gas holdup. The effect of particles was mostly believed to be the outcome of changing the fluid properties such as the density and the viscosity. While mixed with surfactant, a small concentration of nanoparticles resulted in an increase in the gas holdup by preventing bubble coalescence. The foams were evaluated using the unit of foaminess defined by Bikerman. Although the hydrodynamic and surface excess concentrations were different, the surfactants followed a trend similar to that found for the coalescence of capillary bubble pairs. That is, the polyglycols were more persistent than the 1-pentanol. It was shown that surface elasticity could mostly, although not solely, dictate the drainage and rupture of foam films of dilute concentration or surfactant solutions. On the other hand, elasticity could allow enough stability to the film for surface forces to be active at higher surfactant concentrations. The presence of sodium chloride was found to either increase or decrease the foaminess of surfactant solutions depending on the concentration of surfactant. This was attributed to the effect of surface forces. When used in conjunction to nanoparticles, sodium chloride improved the foaminess of the colloidal dispersions in the concentration range where the particles have tendency to coagulate. The effect of silica nanoparticles on the foaminess of surfactant solutions seemed to be dependent on the concentration of surfactant and particles. The nanoparticles somewhat improved the foaminess of polyglycol solutions. At 0.01 wt% of particle, the foaminess of tri(propylene glycol) methyl ether solutions was enhanced. However, the foaminess decreased with further addition of particles. In the case of poly(propylene glycol), the foaminess increased with the concentration of particles over the concentration range tested. The nanoparticles were also observed to affect the structure of the foam by preventing coalescence within the foam. Lastly, flotation of coarse silica was performed in the presence of nanoparticles and salt. Poly(propylene glycol) was chosen as a frother due to the positive impact found in the bubble column with the addition of nanoparticles. The presence of additives improved the properties of the froth, which resulted in a higher overall recovery. This confirms the possibility of using nanoparticles to enhance froth stability and improve the performance of flotation cells.
- Subject
- flotation; froth; foam; bubble; nanoparticle; frother; inorganic electrolyte
- Identifier
- http://hdl.handle.net/1959.13/1059806
- Identifier
- uon:16700
- Rights
- Copyright 2015 Ghislain Bournival
- Language
- eng
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