Improved Water Consumption at the Sishen Tailings Storage Facility Complex

Abstract

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.