Article

Understanding the water balance of potentially acide forming tailings deposited in a dry climate

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  • EMGA Mitchell McLennan
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... The key outcomes of the preliminary model are presented, along with a general description of the parameters required to develop similar models. Chapman et al. (2008) presented the preliminary results from the research project being carried out by the senior author under the supervision of Professor David J. Williams of UQ, and with support from Xstrata Nickel Australasia (Xstrata), the current owners of Cosmos Nickel Project (Cosmos). Chapman et al. (2008) focused on providing an overview of the challenges identified in relation to closure of the Cosmos TSF and presented preliminary outcomes of instrumentation installed within a trial TSF cell. ...
... Chapman et al. (2008) presented the preliminary results from the research project being carried out by the senior author under the supervision of Professor David J. Williams of UQ, and with support from Xstrata Nickel Australasia (Xstrata), the current owners of Cosmos Nickel Project (Cosmos). Chapman et al. (2008) focused on providing an overview of the challenges identified in relation to closure of the Cosmos TSF and presented preliminary outcomes of instrumentation installed within a trial TSF cell. The paper presented monitoring data collected to 31 December 2007. ...
... ? The majority of the considerable surplus water evaporates. Chapman et al. (2008) concluded that it is possible that, if the tailings are allowed to desiccate for a sufficiently long time period, rainfall events after closure will not recharge the tailings sufficiently to reform a hydraulic connection with the groundwater, thus resulting in negligible long-term seepage. The purpose of any cover would then be to limit dust generation, and promote some vegetation through storage of water, rather than to shed rainfall runoff, which would result in a poor vegetative cover and erosion. ...
... Under a hydraulic gradient of unity, these tailings under field conditions would pass water at a rate of about 10 -10 m/s (6 to 60 mm/year), not 10 -16 m/s as is implied by the laboratory-derived SWCC data. Chapman et al. (2008) described a field trial involving saline, Cosmos nickel sulfide tailings in Western Australia. In order to track the water cycle of the tailings deposition and desiccation cycles, towers fabricated from 25 mm box section were installed in advance of tailings deposition, on which piezometers, and series of 16 pairs of matric suction and Time Domain Reflectometry (TDR) volumetric water content sensors were fixed at 300 mm centres (Figures 28 and 29). Figure 30 shows the Cosmos tailings deposition and desiccation stages over a number of months, to a total height of about 4 m. Figure 31 shows the response of the matric suction sensors as they were progressively inundated by tailings, which were allowed to desiccate between deposition cycles. ...
... y functions derived using the method of Fredlund et al. (1994) from the laboratory and field SWCC data for Mt Keith tailings shown inFigure 26. Under a hydraulic gradient of unity, these tailings under field conditions would pass water at a rate of about 10 -10 m/s (6 to 60 mm/year), not 10 -16 m/s as is implied by the laboratory-derived SWCC data. Chapman et al. (2008) described a field trial involving saline, Cosmos nickel sulfide tailings in Western Australia. In order to track the water cycle of the tailings deposition and desiccation cycles, towers fabricated from 25 mm box section were installed in advance of tailings deposition, on which piezometers, and series of 16 pairs of matric suction and ...
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Unsaturated soil mechanics continues to play poor relation to saturated soil mechanics, although an unsaturated soil at a given density is stronger, less compressible and less permeable (i.e. performs better) than the same soil in a saturated state. There are many examples of unsaturated conditions in the mining field, including the wetting-up and drain-down of initially dry surface waste rock dumps; the irrigation and drain-down of heap leach materials; the drain-down, desiccation and rewetting of mine tailings; the dewatering of mineral products such as coal; the shear strength and compressibility of stored mine wastes; and the performance of geo-covers placed on mine wastes on rehabilitation. This paper highlights the key unsaturated soil mechanics parameters, overviews the nature of mining and processing wastes, and some products, and discusses the issues involved. Some applications of unsaturated soil mechanics addressing the shear strength, compressibility and permeability of mine wastes, and mineral products, are presented, together with data to highlight them.
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