Generic modelling of desiccation for cyclic deposition of thickened tailings to maximise density and to minimise oxidation

Abstract

It has been shown in past publications by the authors' research group that desiccation and desaturation of surface deposited paste tailings can be reasonably predicted using unsaturated flow codes under both laboratory controlled conditions and at a relatively arid field site. Given the variability of climate site to site, and from day to day at any given site, can we make some general guidelines or principles using generic modelling to help guide deposition management? A suite of generic numerical analyses are undertaken in which climate, layer thickness, water retention properties and hydraulic conductivity of the tailings, and water content at deposition are varied. It is shown that considering a single layer in isolation can lead to severe underestimation of drying time required to achieve a given water content or density. The underlying previously desiccated tailings are shown to have a profound influence on the rate of drying of a freshly placed layer, and may indeed make it impossible to reach a given water content through desiccation alone. The use of capillary breaks to overcome this problem is briefly evaluated. https://papers.acg.uwa.edu.au/p/1063_25_Simms/ Generic modelling of desiccation for cyclic deposition of thickened tailings to maximise density P. Simms et al. and to minimise oxidation 294 Paste 2010, Toronto, Canada

Desiccation in dewatering and strength development of high-density hard rock tailings

“…Predictions of AE are quite reasonable, as the cumulative evaporation are somewhat under-predicted for Layer one and somewhat over-predicted for Layer five. The dewatering behaviour of Layer five conforms in principal to the predictions of Simms et al (2010), as the underlying tailings act as a reservoir for water during the later stages of dewatering, slowing down the rate of dewatering. As shown in Figure 9 in the model and in Figure 5 in the data, the underlying tailings do lose water to the top layer.…”

“…Note that the generic predictions for 0.5 m and 0.2 m layers are very close in their longterm behaviour. The measured data for Layer five dries faster than the predictions, but this is reasonable given the smaller amount of underlying tailings (<1 m) compared to the generic predictions that used five metres or larger (Simms et al, 2010).…”

“…Generic results using the same methodology and a range of likely parameters for hard rock tailings were presented in the proceeding of Paste 2010 (Simms et al, 2010). These results are compared with the drying box results and field measurements from two sites.…”

“…The Layer five drying results, along with two sets of field data, one from Bulyanhulu (Simms et al, 2007) and one from Musselwhite Mine (Kam et al, 2011), are compared with generic predictions made for dewatering of a 0.2 m layer deposited at 70% solids made in Simms et al (2010). The generic predictions are obtained directly from that paper.…”

Assessment of self-weight consolidation of flocculated fluid fine tailings under various environmental conditions

“…It is well understood and established that geotechnical engineering problems, such as high-volume change deposits (consolidation), stability of earthfill structures, and reclamation of tailings impoundments can best be analysed using fundamental principles of soil mechanics for both saturated and unsaturated soils. For example, unsaturated flow behaviour has been used to predict the dewaterability of thin and/or multilayer tailings deposits of high-density hard rock tailings as well as evaporation and drainage of tailings (Fisseha et al 2010;Qi et al 2016Qi et al , 2017aQi et al , 2017bSalfate et al 2010;Simms et al 2007Simms et al , 2010Simms et al , 2017. Large-strain consolidation properties and shear strength development for treated FFT was investigated under stress-controlled conditions (Fisseha et al 2017).…”