Geotechnics of nonsegregating oil sand tailings

Abstract

The present method of oil sands tailings disposal results in a tailings pond with a fine tailings zone that will take many decades to consolidate fully. The fine tailings accumulate as a result of the segregating characteristics of the tailings stream. Nonsegregating mixes of total tailings are desirable to prevent or greatly reduce the formation of a fine tailings zone. This study investigated the use of lime and sulphuric acid to prevent segregation of the tailings stream. Two batches of Syncrude tailings were tested. These averaged 48 and 55% solids and 17% fines (< 44 μm). The hindered settling and consolidation properties of nonsegregating mixes were determined using large-diameter standpipe and slurry consolidation cells. Nonsegregating mixes were achieved by adding 600–800 ppm CaO, based on total weight, or 7.5–10 mL/L of 10% H2SO4, based on the total volume of tailings. Predictions of field performance using a finite strain consolidation program indicate that a deposition rate of up to 20 m/year of treated total tailings is possible, depending upon the simultaneous degree of consolidation desired. The discovery of nonsegregating mixes with sufficient self-draining capability opens many options to address this important waste-management problem. Key words : oil sand tailings, nonsegregating, hindered settling, consolidation, permeability, laboratory.