Factors affecting the aeration of small bitumen droplets

Abstract

n the processing of Athabasca oil sands, bitumen' is recovered from the slurried ore via water-based flotation methods, as first developed I by Clark and Pasternack (1932). As the densities of bitumen and water are virtually identical at processing temperatures (Liu, 1989; Pandit et al., 1995;Basu et al., 1996, Shaw et al., 1996, it is essential that a density difference between the two phases be created through aeration of the liberated bitumen drops. In the subsequent flotation step, the aerated bitumen/water/sand slurry is transferred to a quiescent flotation vessel to allow the coarse sand particles to settle and the aerated bitumen droplets to rise to the top, forming a bitumen-rich froth layer which is then collected for further processing. To lower production costs, continual efforts are also made to conduct bitumen extraction a t progressively lower temperatures (Mankowski et al., 1998).Although the importance of air in oil sands extraction process is undeniable, the fundamentals of bitumen aeration has received very little attention. In this area, Drelich and coworkers (1 994, 1995, 1996) have conducted studies on the spreading of diluted bitumen films on millimetresized air bubbles. These studies suggest that the aeration of diluted bitumen occurs spontaneously via encapsulation and is controlled by the bitumen-water interfacial tension. Our present focus, by contrast, will be on the aeration of small bitumen drops that are approximately 10 to 40 pm i.d.; the bitumen in this study is not diluted by any solvent. Such small droplets are an important consideration as they represent the difficult-to-recover portion of the total hydrocarbon in an oil sand slurry. Shaw et al. (1996) noted that, as the characteristic size of the bitumen droplets falls to about 10 to 40 pm, colloidal forces, such as those resulting from electrostatic interactions, may become increasingly important in determining the aeration of the droplets. In this study, the spreading of small (-25 pm) bitumen droplets onto air surfaces is examined-both from a surface energetic perspective as well as from direct observations. Such experiments are conducted using novel micromanipulation techniques which will be described in the next section.Based on principles of surface thermodynamics, the spreading of a fluid onto a substrate can be predicted by the so-called spreading coefficient 5: a positive 5 implies spontaneous spreading of the liquid while a negative value suggests 'beading' on the surface (Adamson, 1976). For the spreading of bitumen on air bubbles, the appropriate expression for 5 is:where ow and ob are, respectively, the surface tensions of water and bitumen, and obw is the bitumen-water interfacial tension (IFT). In order to predict the spreading phenomenon (by estimating the sign of 3, it is Small bitumen droplets, roughly 10 to 40 pm in diameter, constitute a significant fraction of the total hydrocarbon in an oil sands flotation process. In this study, the aeration of such droplets is examinedboth from a surface energetic pe...

Effect of hydrolyzable metal cations on the coagulation between hexadecane and mineral particles

“…Using a micromechanical device, Moran et al [11] observed that bitumen did not make contact with an air bubble surface when kaolinite was present in the solution. The tests of Moran et al [11] were conducted in simulated process water that contained many different electrolytes, including 0.3 mmol/L CaCl 2 and 0.3 mmol/L MgCl 2 .…”

Understanding Water‐Based Bitumen Extraction from Athabasca Oil Sands

“…The efficiency of their attachment would therefore depend on the hydrodynamic and water chemistry environment of the system. In terms of the effect of bitumen droplet size on bitumen-bubble attachment, a recent study using a micropipette technique by Moran et al (2000b) and Yeung and Moran (2000b) indicated that smaller bitumen droplets in the micron size range were much more difficult to attach to an air bubble than the droplets in the millimeter size range. Although a positive spreading coefficient exists in bitumen-air bubble systems, the aeration of bitumen droplets appears not always guaranteed.…”

Adsorption isotherms of associating asphaltenes at oil/water interfaces based on the dependence of interfacial tension on solvent activity

“…The interfacial tensions between LM-Ath-C7 asphaltenes dissolved in toluene and distilled water were measured with a micropipette apparatus [57] using the maximum bubble pressure method [58].…”