Authors: Rozina, E; Mizani, S; Malek, M; Sanchez-Sardon, M; Simms, P

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Rozina, E, Mizani, S, Malek, M, Sanchez-Sardon, M & Simms, P 2015, 'Dewatering in a laboratory simulation of a multilayer deposit of inline flocculated mature fine tailings', in R Jewell & AB Fourie (eds), Proceedings of the 18th International Seminar on Paste and Thickened Tailings, Australian Centre for Geomechanics, Perth, pp. 81-93.

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Abstract:
This paper examines the dewatering behaviour of in-line flocculated oil sand mature fine tailings. Tailings used in this study had an initial solids concentration of 36% and were dosed at 650 g/t, using laboratory procedures that have previously been shown to represent field mixing conditions. Three layers of initial thicknesses of 0.3 to 0.35 m were successively placed in an instrumented box 0.7 by 1 m in plan, mounted on scales and equipped with a drainage system. Water content sensors and porewater pressure sensors were placed at various heights. Volume change was tracked by non-contact displacement sensors and by time-lapse imaging and hand measurement of crack development. Increases in evaporation were found to be strongly correlated with the appearance of cracks. The actual evaporation rate exceeded the potential evaporation rate as long as crack development continued to occur. This is the first documented case of evaporation exceeding the potential rate in any controlled laboratory study. Despite substantial drainage, supernatant water formed on top of the tailings, and remained there longer than the initial consolidation phase of dewatering. Consolidation alone was able to increase solids concentration of the tailings to about 53%. For these tailings, which show a relatively high shear strength (achieving the directive 74 requirement between 55 and 60% solids, if porewater pressure is near zero or negative), not much drying is required to bring the tailings to regulatory compliance; even less is required if the tailings consolidate further when buried by new layers. Conservatively extrapolating the results of this test, it is estimated that a rate of rise of 2.2 m per year would still allow for the regulatory shear strength of 5 kPa to be achieved. This rate of rise is comparable to that proposed by field studies on similar tailings in thin lifts.

References:
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