Fine tailings from the Oil Sand Mining and Extraction Plant of Syncrude Canada, Ltd. were repeatedly extracted with distilled water and allowed to react for 24hours at each stage. The concentrations of major extractable ions were measuredand used in the geochemical computer program SOLMINEQ_88PC/Shell. Calcite wascalculated to be stable up the second extraction stage. Gypsum is not stable inthe initial liquid at either 25 or 60 ° C. Dissolved SiO2 is inequilibrium with quartz in the starting suspension, when the calculation isdone for 60 ° C. Sio2 remains high in subsequent extracts. Illitedissolution is insufficient to explain the K and Sio2 concentrationsin the extracts. A hypothetical phase such as analcime is also insufficient toexplain Na and Sio2 concentrations. The results suggest furtherinvestigation of amorphous and microcrystalline phases should be carried out.High HC03 - and SO42- concentrations cannot beexplained by mineral reactions, and may be associated with the oxidation oforganics associated with the solids during the extraction procedure. Volumereduction of fine tailings by recrystallization of colloids should be tested asa part of a study to characterize the kinetic response of the tailings tochanges in the chemical environment.
The problem of reducing the volume of sludge resulting from the processing ofoil sand via the hot-water process is a problem of coarsening or removing thefiner fraction of the tailings. The reason for investigating the mineralreactions in sludge is that thermodynamic arguments can be made that the sludgeis unstable and ought to recrystallize. This recrystallization can in principlebe controlled to yield crystalline materials with a sufficient grain size toallow their more rapid and convenient processing. Three driving forces forrecrystallization can be identified: Ostwald ripening, formation of new mineralphases of greater thermodynamic stability and changes in the chemicalenvironment, such as pH, resulting from the hot-water process.
The transformations of one clay mineral to another in response to changingenvironments have been known for quite some time. Clay minerals have also beensynthesized from seawater or amorphous gels of the appropriate compositionbelow 100 ° C over a period of days (Wollast et al., 1966; Harder, 1980) tomonths, (Harder, 1974).
Several factors limit the rate and extent of such recrystallization:
highactivation energies for dissolution and precipitation of minerals, especiallyaluminosilicates;
the presence of interfering substances such as humic-likeacids and metal soaps;
the small degree of disequilibrium.
In the absenceof "catalysts", the high activation energies mean that elevated temperatures, or extreme chemical conditions are required to obtain a reasonable rate,(Imasuen et al., 1989). Chemical substances such as humic acids and metal soapsreduce the active surface area of reacting minerals, and reduce ion transferrates, (Singer and Huang, 1990; Kotlyar et al., 1990).
