Stabilisation of bubbles and froths with colloidal particles and inorganic electrolytes

by Ghislain Bournival

Institution: University of Newcastle
Degree: PhD
Year: 2015
Keywords: flotation; froth; foam; bubble; nanoparticle; frother; inorganic electrolyte
Record ID: 1057002
Full text PDF: http://hdl.handle.net/1959.13/1059806


Research Doctorate - Doctor of Philosophy (PhD) 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…