Consolidation of Syncrude Oil Sands Fine Tailings1

Abstract

Abstract A novel process has been developed whereby oily sludges produced as an undesirable by-product of bitumen extraction from oil sands can be treated to recover residual organics, heavy metal minerals, and amorphous solids for potential commercial exploitation followed by consolidation of the coarser solids to form wet aggregates. These aggregates may be suitable as fertilizer for fertilizing farmland, making a fertile base for landscaping, or as a natural fertilizer. Introduction The extraction of bitumen from the Athabasca oil sands using the Hot Water Extraction Process results in the accumulation of large volumes of fluid wastes called fine tailings(1, 2). A general description of fine tailings would be a complex system of clays, minerals, and organics. According to Camp(3), fine tailings show little tendency to dewater, even when subjected to mechanical dewatering procedures. These clay tailings are acutely toxic to aquatic organisms and are currently being stored in large tailings ponds. The buildup of these partially settled clay tailings presents not only an environment problem but also a significant repository for non-recyclable water, which eventually must be reclaimed. The reason for the intractability of the clay tailings has been a subject of several studies(4–7). Based on the results of published work, it is generally believed that a combination of residual organics and fine clay particles contribute to the stability of fine tailings. Yong and Sethi(2) have attributed the high water holding capacity of fine tailings to the presence of amorphous minerals such as iron oxide and clays. Our group at NRC has been actively involved in research dealing with various aspects of fine tailings(5–7, 8–14). As a result, we have developed a number of fractionation schemes to separate fine tailings into various components. Recently, we have reported the isolation and characterization of amorphous solids from Syncrude fine tailings(15). In this investigation, we have studied the settling characteristics of fine tailings solids after various treatments. Materials and Methods Materials Aqueous tailings samples used in this investigation were from the Syncrude tailings pond. The physico-chemical properties, handling procedures, and the procedure for the removal of residual bitumen and hydrophobic solids have been reported previously(7). Process Description A flow diagram for the process is shown in Figure 1. The sample is first treated to remove residual bitumen(7, 8). The clean tailings were then divided into two portions. One portion was used to study the consolidation behaviour without removing amorphous solids and the other portion was mixed with one of the reagents to dissolve or disperse amorphous solids(15–17). The contents were agitated until the amorphous solids dissolved producing a dark brown suspension layer. At the end of agitation, the contents were centrifuged for fractionation into a dark brown suspension layer and a sediment layer. The dark brown suspension was carefully decanted from the sediment. This fraction was then treated using the gelation process to precipitate the amorphous solids for potential commercial applications(15). The precipitation of amorphous solids also results in the release of clear water that can be recycled.