Existing topography at an operational lateritic nickel facility is such that if the tailings beach slope could be increased to 1-2% for approximately one year, significant costs related to wall building could be deferred. As additional thickening capacity would require significant capital expenditure, polymer treatment technologies have instead been investigated. As part of the trial process for polymer treatment, the stability of the potential steepened beach was assessed. While beach slopes of the range targeted here would, for many materials, be unlikely to produce an unstable landform, lateritic nickel tailings develop very low dry densities, consolidate slowly, and contain hypersaline pore fluid. This combination results in a lower resistance to slope instability, all else being equal. Further, polymer treatment technologies, while providing benefits through rapid dewatering and beach slope development, have been shown to result in an increased brittleness for some materials. Laboratory characterisation of the polymer treated material was first undertaken, by means of (i) monotonic, cyclic and post-cyclic simple shear testing, to assess the potential for strength loss of the material, (ii) laboratory-scale shear vane testing, to estimate residual shear strength, and, (iii) settling and consolidation tests, to provide input to consolidation modelling. A consolidation model of the proposed steepened beach was then developed. Outputs from this model were used as the basis for infinite slope stability analyses on a variety of scenarios. It was found that over the one year planned deposition period, beach slopes of 1.5% or less are likely to result in a satisfactory factor of safety (FS) for the steepened beach. 2 Previous relevant studies 2.1 Steepened beach stability A number of previous studies have been undertaken to assess the expected stability of proposed unconstrained tailings beaches, most of which were developed from thickened tailings deposition. Each of

A pilot plant paste thickening campaign was conducted at the Anglo Platinum Limited Mogalakwena South Concentrator plant in South Africa in order to determine the water saving capability of paste and thickened tailings (P&TT) technology. In the process a simple water consumption model was developed for estimating the overall water consumption of the mine. The model indicates that for the Mogalakwena tailings, significant water savings are achieved by discharging thickened tailing directly to the TSF but only at densities where free water release at the TSF is close to zero.

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Tailings material from the existing Sishen plant is currently being deposited on four individual tailings dams. The solids concentration of the tailings can not be increased by means of thickening as the current process can not deal with flocculant. Decant water from each tailings dam is transferred into two seepage sumps via gravity penstock decant systems from where the water is returned back to the Sishen plant. The water balance and water recovery for the current Sishen tailings disposal system is not optimised and the dams are used on a random basis for the storage of storm rainfall and excess process water. The deposition cycle on the dams in terms of layer thicknesses and cycle times was not optimised. Significant evaporational losses therefore occur which is not ideal for an operation in such an arid climate.The Sishen Expansion Project (SEP) involves the establishment of a separate process plant. Tailings material from the SEP plant will be disposed off in the cross area in between the current four individual tailings dams. One leg of the cross area will be closed off at a time and filled with SEP tailings materials. It is planned to fill the four legs of the cross area over a period of approximately 10 to 12 years. The SEP will increase the current water consumption and has prompted the optimisation of the tailings dam complex water balance.Once the cross area is filled up to the same level of the four individual tailings dams, the four dams and the filled cross area will be consolidated into one single dam with four operating paddocks. The principle of operating four paddocks with optimised deposition strategies and small pool areas contributes towards improved water recoveries. The method of tailings disposal and dam operation also remains the same as per the current operations.A return water dam (RWD) will be constructed as part of the SEP. The RWD will consist of an operating compartment capable of containing five days operational storage. Any run-off water from a 1:50 year 24 hour rainfall event on top of the tailings dams will be contained on top of the tailings dams and decanted in the shortest period of time possible. This paper will discuss how the water consumption of the Sishen tailings dam complex was improved by conventional means other than thickened tailings. The improved water consumption over the life of mine will also be discussed.