SURFACE AREA OF INTERSTRATIFIED PHYLLOSILICATES IN ATHABASCA OIL SANDS FROM SYNCHROTRON XRD, O.E. Omotoso, R.J. Mikula, P.W. Stephens, pp. 391-396

The surface area of the individual phyllosilicates (clay minerals) in Athabasca oil sands determined from XRD crystallite size measurements was found to be comparable to the bulk surface area measured by ethylene glycol monoethyl ether adsorption. The primary phyllosilicates are kaolin and illite but the large surface area is imparted by varying degrees of smectitic interstratifications in the primary phyllosilicates. The crystallite size information of each phyllosilicate was extracted from the 00l X-ray diffraction peaks using both the BertautWarren-Averbach (BWA) technique and Williamson-Hall (W-H) plots. The surface area was then determined from the aspect ratios that had been observed for the individual phyllosilicates. The ability to quantify the surface area contributions from individual phyllosilicates in the oil sands solid matrix is important for developing models to predict tailings behaviour and the release water chemistry. INTRODUCTION In the processing of oil sands, bitumen is removed with water at 50 to 80 oC at pH between 7 and 8.5. The tailings stream (which is mostly quartz with some clay minerals) is beached behind sand dykes where the sand settles out and the fine tails (mostly clay minerals) are impounded in recycle water ponds. The beach runoff in the settling pond typically settles to about 30 wt% solids after several years and these settled fine tails are referred to as mature fine tailings (MFT). Over 500 Mm of MFT have been impounded over decades of commercial operation in settling ponds that occupy about 35 km (1). Recent efforts to reclaim the ponds to a dry landscape depend on the ability to manipulate clay behaviour. Several studies have been conducted over the last 25 years to elucidate the clay mineralogy of the Athabasca oil sands solids. The predominant clay minerals are kaolin and illite. However, the source of the large surface area that has been observed in the fine tails cannot be attributed to kaolin and illite alone. Some invesitigators attributed the large surface area to discrete montmorillonite and mixed layered clays (2-4). Others have attributed the large surface are to the presence of ultrafine kaolin and illite particles (5-8). Some studies (9, 10) reported up to 90% amorphous Fe and Al oxides in a clay fraction. Over the years, several MFT samples from different locations in the ponds have shown similar settling and rheological behaviors (1). If the clay mineralogy of the MFT is responsible for its behavior, both the settling and rheological properties should vary significantly if the reported variations in mineralogy truly exist. Copyright (c)JCPDS-International Centre for Diffraction Data 2002, Advances in X-ray Analysis, Volume 45. 391