Characterization of oil sands tailings containing a significant hydrocarbon content and a synthetic polymer

Courtney Dean, Sumi Siddiqua, Deborah Roberts, Greg Siemens

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Mining Geotechnics

ABSTRACT: Surface deposition of oil sands tailings thickened with polymer has recently been explored as a possible alternative for oil sands tailings disposal. This creates the potential for unsaturated conditions to develop, therefore the geotechnical properties and soil-water characteristic curve (SWCC) are required to understand the behavior of the tailings. A shrinkage curve was performed to determine the effect of shrinkage on the SWCC. The tailings in this study, which contain a significant hydrocarbon content and synthetic polymer, were classified as a silty sand, with a relatively low specific gravity of 2.04, and fines content of 58%. The results of the SWCC tests revealed that the shrinkage had little effect on the air entry values from various SWCC representations, and that these tailings are prone to cracking which may influence the SWCCs. This paper concentrates on the development of methods needed to test these complex tailings. RÉSUMÉ Surface dépôts de sables bitumineux des résidus épaissis avec polymère a récemment été explorées comme une alternative possible pour l'élimination de résidus de sables bitumineux. Cette crée le potentiel pour des conditions de développer, par conséquent les propriétés géotechniques et les caractéristiques de sol-eau courbe (SWCC) sont nécessaires pour comprendre le comportement des résidus. Une courbe de retrait a été effectuée pour déterminer l'effet du retrait sur la SWCC. Les résidus dans cette étude, qui contiennent un hydrocarbure significatif polymère synthétique et de contenu, ont été classés comme un sable limoneux, avec une specific gravity relativement faible de 2,04 et teneur en particules fines de 58 %. Les résultats des essais SWCC a révélé que le rétrécissement a peu d'effet sur les valeurs d'entrée air de diverses représentations SWCC, et que ces résidus sont sujettes à la fissuration qui peut-être influencer le lissage. Cet article se concentre sur le développement de méthodes pour tester ces résidus complexes. 1 INTRODUCTION Tailings produced from the extraction of bitumen in the northern Alberta oil sands are typically disposed of in tailings ponds. Due to environmental issues associated with this method of disposal and an initiative of the Alberta Energy Regulator (AER, formerly the Energy Resources Conservation Board, ERCB) to reduce fluid fine tailings produced in the oil sands (ERCB, 2009), technologies such as surface deposition are preferred. Surface deposition involves saturated deposition of slurried tailings and subsequent desaturation once the deposition site is at capacity. Because of this potential for unsaturated conditions, it is important to characterize the relationship between water content and soil suction. This relationship can be represented by a soil-water characteristic curve (SWCC) which gives the air entry value (AEV) for the material. Research has shown that if the material has shrinkage potential upon drying, that the shrinkage curve can be integrated into the SWCC to determine the true AEV (Fredlund and Rahardjo, 1993; Mbonimpa et al. 2006; Fredlund et al. 2011; Fredlund and Houston, 2013). Previous work on oil sands tailings show that this integration is best represented as the relationship between the degree of saturation and suction (Fredlund et al. 2011; Fredlund and Houston, 2013). The tailings under investigation are unique because they contain a high asphaltene content and a synthetic polymer (Masala et al. 2012). The synthetic polymer was added to prevent particle segregation within the tailings upon hydraulic surface deposition and desaturation (Masala et al. 2012). This paper explores the geotechnical characteristics of these unique tailings using methods previously described for oil sands tailings (Fredlund et al. 2011; Fredlund and Houston, 2013). This information is necessary for subsequent experimental design with this material for unsaturated contaminant transport studies. 2 METHODS A subsample of the tailings was made into a slurry by the addition of water treated by reverse osmosis (RO). To ensure initial saturation, the sample was placed on a vibrating table for 2 minutes to remove any air trapped in the voids (Péron, et al. 2006). Prior to the analyses, the slurry sample was stored at 4oC to slow any chemical reactions that may have been taking place. 2.1 Geotechnical Properties

RÉSUMÉ: cterization of oil sands tailings containing a significant hydrocarbon content and a

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Courtney Dean; Sumi Siddiqua; Deborah Roberts; Greg Siemens (2014) Characterization of oil sands tailings containing a significant hydrocarbon content and a synthetic polymer in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper224,author = Courtney Dean; Sumi Siddiqua; Deborah Roberts; Greg Siemens,title = Characterization of oil sands tailings containing a significant hydrocarbon content and a synthetic polymer ,year = 2014}