Cyclone Projects & Consulting T here are two inevitabilities about mining for certain types of minerals such as gold, platinum and chrome: they consume vast amounts of water and produce equally large quantities of waste. For example, one source reckons that for each kilogram of gold recovered, 240 kg of cyanide and 250,000 litres of water have been consumed and over 3,000 tonnes of solid waste and 25 tonnes of CO2 produced. It follows then that not only is tailing management an expensive part of the process, it's also one that needs to be handled with considerable responsibility. Environmentalists in the remotest parts of the world are there to pressurise mine operators. In the deserts of southern Africa, there is also the practical need to recover scarce water resources with the utmost efficiency. The mineral extraction process, in essence, requires rock to be crushed and ground small enough so that the minute ore particles can be extracted either by chemical or mechanical means. Depending on the particle size, the tailings left behind are referred to as slurry or slime: the former contains a proportion of grit where the grains can be as large as 1.6mm while the latter is predominantly composed of much smaller particles of less than 300 microns. Historically, tailings were simply discharged directly into streams and rivers. In the West this form of disposal has been outlawed since the 1930s but in some parts of the world it still continues, particularly where the terrain is diffi cult or the rainfall high. Such blatant disregard for the environment at mines in Papua New Guinea and Indonesia have gone a long way to creating hostility for the mining industry at large as well as burdening the community with enormous environmental liabilities and costs to remedy the situation. More efficient extraction techniques are now allowing lower grade ores to be mined, creating greater quantities of waste in the process. Tens or even hundreds of thousands of tonnes of tailings a month are not untypical and if storage can only be done on the surface, they call for huge dams to be employed that can stretch several hundred hectares with walls rising to 30 metres or more in order to store them. As the tailings have no commercial value, they are a burden to the mine operator, but they do have the potential to cause problems so their management is not something that can be taken lightly. The exact nature of the dam design and construction depends to a large extent on the geography in question, but since 1998, Cyclone Projects & Consulting [ CP& C] of Krugersdorp in the Gauteng province of South Africa has been offering a process of dam construction known as cycloning. The business was established by a South African engineer, G. J. van Ryssen, who had a quarter of a century July 09 www. bus- ex. com 47 Often the ancillary elements of a larger system provide some of the more interesting engineering solutions, as Dan Bailey discovers when investigating mining in southern Africa Constructive cyclones
footprints, which can be both expensive and impractical in many situations. At the same time, it extracts more water from the tailings for reuse. Van Ryssen identified the need to construct tailings dams by utilising cycloned slimes/ tailings disposal techniques on minerals other than just phosphate. Over the intervening years it has been responsible for much development work in perfecting the cycloning techniques for various types of ore. In fact, since CP& C was established it has carried out the majority of contracts in the design, supply and commissioning of cyclone systems for cycloned dams in Africa. A cyclone works on the principle that in a centrifuge the heavier particles suspended in a slurry will gravitate to the outside of the flow while the lighter material- the water- remains on the centreline through the vortex finder of the cyclone. As a result, tailings pumped through a cyclone will be separated and the solid particles can be " discharged" directly to where they are needed as the building material for a tailings dam wall, while more of the slurry bearing water is discharged in the basin of the dam with water being recovered in the process. In reality, it's not always that simple. Some materials don't lend themselves to dam wall construction. They lack the fundamental stability necessary to build a safe structure without the need for uneconomically wide wall zones. In the past, haphazard design has been a costly exercise for the industry. As such, CP& C recommends that on- site cyclone test work be conducted on the tailings before a custom- built cycloned system is designed. Often initial trials are carried out on the company's in- house cyclone test rig before on- site tests are conducted. CP& C utilises a mobile test rig to determine the geotechnical properties of the different cyclone streams, creating data which can then be used for dam capacity calculations, the required drain design for that specific tailings product and the design of the cyclone system suitable for the material. Providing the cyclones is only a small part of the turnkey service CP& C provides. First there needs to be a thorough assessment of the proposal, evaluating the feasibility of building what the client wants. Once the system has been designed to ensure the best cyclone underflow, material is utilised for a safe and stable wall zone and the individual units produced. CP& C sources the entire package of pipe work, valves and instrumentation before completing installation and commissioning of the final system and handing over to the of experience in dam and tailings management across a wide range of minerals such as phosphate/ copper, gold, platinum, magnetite, chrome, manganese, gypsum, fluorspar and kimberlite. Cycloning is a process that eliminates the need for large 48 www. bus- ex. com July 09 " Not only is tailing management an expensive part of the process, it's also one that needs to be handled with considerable responsibility"