The processing of oilsands produces a significant volume of stable waste products that consist of a mixture of bitumen, clays, minerals, and water. Together these components form a mixture termed ‘sludge’. The compositions and structures of various particulate populations in the sludge may range from gelated aggregates, to finely divided suspensions which may be devoid of structure. However manner the aggregates are formed, the particulate populations in these structures are heterogeneous. The compositions of these populations may depend not only on the physical and chemical properties of the particles and the water but to a large extent also on the interparticle interactions.
There are many physical forces which interact to keep the particulates in a stable suspended state. These are electrical repulsive forces, steric forces, hydration forces and van der Waals attractive forces. Understanding the extent of and influence of some of these forces on the structure of the sludge requires knowledge of the physical and chemical character of its particulates.
The overall effort in these studies is aimed at finding components of the sludge which are most responsible for its stability. If this is possible} the properties of these components will be studied to determine which of these properties have the greatest influence on the sludge stability. In order to do this, we have selected a method of separation Which will have the least impact on the natural state of the components.
In this study, we have chosen one sample of sludge for study. To simplify the experimental design we separated the sludge into populations of particulates by ultracentrifugation, while at the same time maintaining the chemical environment of the particles as intact as possible. Since the populations of particulates making up the whole sludge are diverse, simplification by physical fractionation served only to reduce the populations into categories with common denominators. A common denominator at first was based on the physical property such as density. Later, after characterization, these involved surface functionalities and mineral compositions.
This paper specifically addresses the characteristics of the separated clays in the indigenous water (supernatant). Surface functionalities of each fraction are first examined. The reactivity of the surface functional groups and electrical properties derived from the charged groups at the surfaces are studied. Substantial emphasis is given to the effects of the particulates of each fraction as they form structures at high volume percent, under bulk conditions.
Sludge samples were obtained from one of the oilsands tailings ponds in northern Alberta. All chemicals (NaCl, KCl, NaoH, HCl and phosphate based buffers 4.0, 7.0, 10.0) were ACS grade and were obtained from Fisher Scientific.
Sludge separations was performed on an Beckman L-BO Ultracentrifuge using a Ti-19 and Ti-45 rotors. Separated layers were freeze dried using a Labconco freeze drier. Densities were determined on a Quantochrorne Micropycnometer. Size Distributions were conducted on a Microtrac full range analyser {FHA}. Electrophoretic mobility distributions (EMDS) were measured on a PENKEM system 3000 automatic electrokinetic analyser.
