| Summary: | Eight oil sands ores were tested in order to quantify the levels of humic acids in these samples through the alkali extraction test originally developed to determine the oxidation of bituminous metallurgical coals. The test gives a concentration of humic acids released from ores, which in combination with the measurement of the total organic carbon content in the alkali extracts provides a measure of ore/bitumen weathering. It was found that poor ores exhibited the highest tendency to leach large amounts of humic acids per gram of bitumen in the samples which was quantified using the absorbance at 520 nm obtained from the UV/visible spectra.
The results of contact angle measurements of water on bitumen showed that bitumen became more hydrophilic as pH increased, and that the hydrophobicity of bitumen drastically decreased when the sample was artificially oxidized. Additionally, the results suggested that humic acids make bitumen hydrophilic only if they are part of the internal/surface bitumen structure.
Slurries of good ores displayed higher yield stresses than slurries of poor ores. This result is explained by the higher bitumen concentration existing in slurries of good ores which leads to more aggregation. Additionally, it was shown that bitumen oxidation/hydrophobicity also affected the rheology of oil sands slurries which also explains that slurries of poor ores displayed lower cohesion/aggregation than slurries of good ores. Yield stress data agreed with data obtained from power draw measurements that showed that good processing ores required more power for mixing. Extraction data obtained from flotation experiments indicated that the role of humic acids naturally present in the ores was basically that of a depressant of bitumen since poor ores contained the highest proportion of humic acids per gram of bitumen.
Overall, it is possible to assess the processability of oil sand ores by quantifying the occurrence of humic acids in the ores, and to correlate ore processability with the rheology of oil sands slurries. Although poor ores are characterized by lower viscosities and lower power requirements during mixing, the presence of humic acids in these ores and their depressing action also contribute to lower bitumen recoveries.
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