Consolidation Behaviour of Coke-Capped Oil Sand Fluid Fine Tailings

Maki Ito, Shahid Azam

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

Session: Mining Geotechnics

ABSTRACT: Petroleum coke is a one candidate to improve dewatering of oil sand fluid fine tailings (FFT). The main purpose of this paper is to conceptually understand the consolidation behaviour of a 10 m high FFT coke capped deposit. Results of a numerical modeling indicated that a 0.5 m thick of coke layer over the FFT only improved overall interface height reduction by 0.2 m while the initial surcharge load increased. The capillarity within the coke layer accelerated the interface reduction especially within first two years. Identical properties for the no-capping scenario were found to be achievable after eight years of deposition. RÉSUMÉ Le coke de pétrole est un candidat pour améliorer la déshydratation des fluides de sables bitumineux dans les résidus fins. Le but principal de cet article est de comprendre conceptuellement le comportement de consolidation d'une couche de résidus de 10 m d'un dépôt de de coke. Les résultats d'une modélisation numérique indiquent qu'une épaisseur de seulement 0,5 m de la couche de coke sur la couche des fluides des résidus fins améliore la réduction globale de la hauteur de l'interface de 0,2 m et que la surcharge initiale a augmenté. La capillarité à l'intérieur de la couche de coke a accéléré la réduction de l'interface en particulier dans les deux premières années. Des propriétés identiques ont été jugées réalisables après huit ans pour le scénario de dépôt sans plafonnement 1 INTRODUCTION Fluid fine tailings (FFT) have low permeability and are placed at high rates of rise resulting in unconsolidated soft tailings deposits. The current amount discharged in tailings containment facilities sums up to 900 million m3 and the volume is expected to grow as the industry thrives (Hyndman, 2013). This poses significant challenge to managing tailings ponds during mine operation and closure since untreated FFT requires decades and centuries to consolidate. Delaying construction of final covers until the FFT deposits complete consolidating is virtually impractical. Several pre-depositional approaches, such as non-segregating tailings by flocculation (Scott et al., 1993), thickened tailings (Yuan and Lahaie, 2009), composite tailings production (Liu et al., 1997), in-line thickening (Jeeravipoolvarn et al., 2008), and centrifugation (Devenny, 2010) have been used to accelerate the FFT consolidation behaviour. Similarly, thin and thick layer deposition (Burns et al., 1993), freeze-thaw dewatering (Dawson et al., 1999), vegetation dewatering (Silva, 1999), and co-disposal (Benjamin et al., 2005) has been identified as dewatering enhancement methods in the containment facilities. A combination of the above technologies is crucial for timely FFT dewatering. Alternatively, petroleum coke has been introduced as a capping material of the FFT deposit. This non-sinking material can provide safe trafficable surfaces for construction personnel and heavy equipment. Prefabricated vertical drains as known as wick drains have been also installed in a coke capping (Abusaid et al., 2011). Classical Tazaghi's examples show that the rate of consolidation of a tailings deposit depends on the length of the drainage path. This can be achieved by the wick drains to reduce the drainage path length (Robertson et al., 1988). Whereas pilot and field scale projects have been initiated, the evaluation of long-term coke capping performance is still required. The main purpose of this paper is to understand the large-strain consolidation behaviour of FFT capped with coke. A quiescent one-dimensional large-strain consolidation model was developed by employing the governing equation formulated in terms of excess pore water pressure and using the FlexPDE software. The typical constitutive relationships of void ratio versus effective stress and void ratio versus hydraulic conductivity were used to obtain the fit parameters for the FFT. A 0.5 m coke layer and a 0.5 m water layer were imposed on the top surface of a 10 m high FFT column to analyze the effect of different types of capping. To evaluate the effectiveness of coke-capping over time, the modeling results were analyzed in terms of the dissipation of excess pore water pressure and the interface height reduction. 2 RESEARCH METHODOLOGY Figure 1 describes the large-strain consolidation modeling process. Tailings contained in a column with no horizontal discharge and homogeneous material properties throughout the column provided the rationale to develop a one-dimensional model. The model required four inputs related to tailings properties namely; volume compressibility (A and B), hydraulic conductivity (C and D), initial solids content, and specific gravity. The volume compressibility and

RÉSUMÉ: LIDATION BEHAVIOUR OF COKE-CAPPED OIL SAND FLUID FINE TAILINGS

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Cite this article:
Maki Ito; Shahid Azam (2014) Consolidation Behaviour of Coke-Capped Oil Sand Fluid Fine Tailings in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper143,author = Maki Ito; Shahid Azam,title = Consolidation Behaviour of Coke-Capped Oil Sand Fluid Fine Tailings,year = 2014}