Authors: Busani, B; Copeland, AM; Cooke, R; Keevy, M

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Busani, B, Copeland, AM, Cooke, R & Keevy, M 2006, 'A Holistic Approach to Optimise Process Water Retention and Residue Disposal for Orapa Mines', in R Jewell, S Lawson & P Newman (eds), Proceedings of the Ninth International Seminar on Paste and Thickened Tailings, Australian Centre for Geomechanics, Perth, pp. 147-156.

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Abstract:
Orapa Mine is situated 240 km west of Francistown, in Botswana’s arid central district. Water is a scarce non-renewable resource. It is currently supplied from an aquifer system around the mines that has negligible recharge. A combination of unfavourable factors including low rainfall, high evaporation rates and a flat topography contribute to this situation. Debswana is exploring various options to significantly reduce water consumption over the life of the mines. The Orapa mines are currently operating at an average raw water consumption of 0.5 m³/t of head feed for all the four treatment plants at Orapa, Letlhakane and Damtshaa. In order to extend the life of the existing aquifer, Orapa has an objective to reduce raw water consumption by 50% within the next decade. This will have the desired effect of increasing aquifer longevity at current consumption. However, Orapa is planning to replace one of its older plants with a new generation plant and will also build a dump treatment plant at Letlhakane Mine. These plants are likely to use more water as they will be designed to produce a finer product to enhance liberation of diamonds. Orapa Number No. 2 Plant, the newest treatment plant at Orapa uses high rate thickeners (Ultraseps) and consumes over 0.8 m3/t of raw water per head feed tonnage. The current disposal method comprises the pumping of combined thickened material to a slurry dam using cyclones for wall building. The mine is considering alternatives for future dewatering and disposal systems with a view to minimising water consumption, capital/operating costs and environmental impacts. The mine has investigated a number of options for future final residue dewatering and disposal. These include dewatering using conventional, high rate and paste thickeners with the associated disposal options. This study covers the complete supply chain from water supply, thickening, transportation and disposal including environmental and rehabilitation considerations. The study concludes that paste thickening of slimes only is not only more cost effective but also offers a known and tested technology solution. This paper presents the following aspects of the study: (i) Description of the various options investigated. (ii) Capital and operating cost comparison for each option, including net present cost (NPC) analysis. Paste2006–R.J.Jewell,S.Lawson,P.Newman(eds) ©2006AustralianCentreforGeomechanics,Perth,ISBN0-9756756-5-6 Paste2006,Limerick,Ireland 147



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