Influence of humic acids on oil sand processing. Part I: Detection and quantification of humic acids in oil sand ores and their effect on bitumen wettability

摘要

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 (TOC) content in the alkali extracts provides a measure of ore/bitumen weathering. It was found that poor ores (low bitumen and high fines contents) exhibited the highest tendency to leach large amounts of humic acids per gram of bitumen in the samples. It was also shown that the absorbance at 520 nm obtained from the UV/visible spectra of the alkali extracted solutions correlated very well with the quality of the ores, with the highest absorbance obtained from the extracts produced by the poor ores. A comparison between the UV/Visible spectra of solutions obtained from the alkali-extraction tests and spectra of solutions of commercial humic acids also indicated that the total organic carbon content of the extracts of good ores primarily originated from compounds other than humic acids while the organic matter released by poor ores was dominated by humic acids. The results of contact angle measurements on fresh and oxidized bitumen samples indicated that contact angles decreased and bitumen became more hydrophilic as pH increased. It was also shown that the hydrophobicity of bitumen drastically decreased when the sample was artificially oxidized, although the amount of humic acids generated in bitumen during the oxidation process was small. Additionally, the effect of added humic acids on the wettability of bitumen was also evaluated. It was found that the contact angle of bitumen significantly decreased in the presence of humic acids at pH 3, but the effect of humic acids was not significant at higher pH values (7 and 10). At pH 7 the effect of humic acids on bitumen wettability was minor compared to the effect of artificial oxidation of bitumen. These results suggest that humic acids make bitumen hydrophilic if they are part of internal/surface bitumen structure. However, if they are added as free chemicals their effect is minor, particularly under neutral and alkaline pH conditions, which also indicates that adsorption of humic acids from solution onto bitumen is low.