Effect of suspension conductivity and fines concentration on coarse particle settling in oil sands tailings

Abstract

AbstractSedimentation of coarse particles in mature fine oil sands tailings (OST) was studied by varying the fines concentration and aqueous phase conductivity to determine under which conditions the coarser particles will settle and when they will not. An OST sample was desalinated, separated into finer and coarser fractions, then recombined for settling tests. The isolated finer fraction was predominately phyllosilicate clays (>87 wt%) while the coarser fraction was mostly quartz (<77 wt%). From optical backscattering (OBS) height scan measurements, complete sedimentation of the coarse particles was observed at low conductivity values and fines concentrations, but a sufficient increase in suspension conductivity or fines concentration caused a reduction in coarse particle settlement. Samples with lower fines concentration, 0.5 wt% and 2.4 wt%, exhibited coarse settlement over a wider range of conductivity values; whereas samples with higher fines concentration, 5.9 wt% and 8.2 wt%, exhibited decreased sedimentation even at low suspension conductivity values. At similar conductivity values and fines concentrations, increased sedimentation of pure quartz was observed compared to the coarse OST particles. This difference in settling behaviour was partially attributed to the presence of residual organics on the surface of the OST coarse particles. In addition to typical metallurgical assay methods (x‐ray diffraction and scanning electron microscopy), a synchrotron‐source computed tomography scan of the untreated OST sample was obtained to visualize the distribution of the fine, coarse, and fluid phases within the sample.