Technology
MINE WATER
Accurate technology for AMD treatment The current acid mine drainage crisis contributes to the fact that clean natural resources in SA are becoming scarcer and legislation is forcing industry to take a closer look at the environmental impact of its processes. ccording to Daan Louw, Verder Pumps South Africa consultant, mines are forced to look at ways to optimise their process and recycle and treat water before reintroducing it to the environment. Although the government has known about the problem since the early 1970s, not much has been done about it and we have now reached the stage where damage is prevalent and a management programme is needed to attempt to maintain water levels at least below the relevant Environmental Critical Levels (ECLs). Rand Uranium started working on this when acid mine drainage (AMD) first became a problem at the mine s operation in Randfontein after the Western Basin flooded and started decanting onto the surface in September 2002, says Dr Basie van der Walt, who heads up the Rand Uranium Water Treatment Plant in Randfontein. We are currently treating 12 Mℓ of acid water per day, says Van der Walt. The water is pumped from 65 m below the surface at #8 Shaft. The problem is that with the recent rains the water level has risen to 41 m below surface and is now also overflowing at 17 and 18 Winze. The water flows into the Black Reef Incline Decant Dam, where it is pre-treated with limestone to protect the pumps and pipes right the way through the process, Van der Walt explains. The water is then pumped 4.2 km to the plant, where the
PERISTALTIC PUMPS FOR DOSING LIME According to Louw, mining is a tough, uncompromising process and the mining industry is equally demanding, being driven by the goals of mine profitability, plant efficiency, cost minimisation and yield maximisation. And now we have to add environmental and legal dimensions. Mining companies have to achieve their operational goals while fixing the problem and ensuring that future impact on the environment is kept to a minimum. In the case of Rand Uranium, Verder identified that two VF65s and one VF40 would be sufficient to deal with the duties the pumps are expected to perform. We also identified that training on the pumps would be necessary, which was made available to Rand Uranium staff at our premises in North Riding, says Louw. The nature of the medium being pumped is an important factor when considering pump selection for a specific
Pictures courtesy of Verder Pumps South Africa
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rest of the treatment occurs. At the set-off point of the process, the pH level of the water is approximately 3, and after treating the water by dosing limestone and lime, pH levels are at approximately 8. The water is also put through an aeration (oxidation) process to ensure that it complies with DWA specifications before it is pumped into the Crocodile River.
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application. When pumping lime, the high viscosity of the medium often causes pumps to clog up, resulting in a maintenance nightmare. When it comes to the treatment of AMD and the fact that we are working to catch up on the problem as well as trying to minimise current and potential negative impact on the environment, a process problem that will cause the plant to stop working is not an option, adds Louw. The Verderflex range of peristaltic pumps uses the process of peristalsis to pump products through a hose, in the same way blood, food and oxygen is pumped around the body, says Louw. The pulsation effect means that solids are kept in suspension and no build-up can take place. Build-up in the hoses is eliminated by using rubber Verderflex hoses that are designed to maximise life expectancy and performance. Verderflex hose pumps are designed to handle these tough operating conditions, ensuring optimal process flow. You only need two Allen keys to dismantle the pump on site, notes Louw. Correcting the pH is a very specific process and the pump used for dosing must be very accurate. Peristaltic pumps have a linear flow-speed characteristic and excellent repeatability, making it the most accurate solution available, Van der Walt concludes. BELOW Verderflex peristaltic pumps used for lime dosing LEFT Settling dams