Owing to the current acid mine drainage (AMD) crisis in South Africa, which is contributing to the country’s clean natural resources becoming scarcer, mines are being forced to look at ways to enhance their processes and to recycle and treat their water before reintroducing it into the environment, says pumps specialist Verder Pumps South Africa consultant Daan Louw.

He adds that legislation is forcing industry to take a closer look at the impact of its processes on the environment, adding that, while government has known about the problem since the early 1970s, not much has been done about it.

He says South Africa has now reached the stage where damage is prevalent and that a management programme is needed to attempt to maintain water levels at least below the relevant environmental critical levels.

Louw emphasises that mining is a tough, uncompromising process and the industry is equally demanding – driven by the goals of mine profitability, plant efficiency, cost minimisation and yield optimisation.

“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. “Mining companies cannot achieve this on their own,” he says.

He highlights that Verder recognises and strives to support its customers by providing pumping solutions.

“We source the best possible solution to suit the application, providing customers with the best products, solutions and support available,” he adds.

Case Study: Rand Uranium
AMD first became a problem for uranium miner Rand Uranium about a decade ago, when the Western basin flooded at the mine’s Randfontein operation and the company started decanting onto the surface in September 2002, says Rand Uranium head Dr Basie van der Walt.

“We are currently treating 12 megalitres of acid water a day,” he says.

The water is pumped from 65 m below the surface at Shaft No 8. Further, with the recent rains, the water level has risen to 41 m below surface and is now also overflowing at 17 and 18 Winze.

Van der Walt explains that the water flows into the Black Reef Incline decant dam, where it is pretreated with limestone to protect the pumps and pipes throughout the process. The water is then pumped 4.2 km to the plant, where the rest of the water treatment occurs.

At the start of the process, the pH level of the water is about 3 and, after treating the water with limestone and lime, pH levels are at about 8.

The water is also put through an aeration, or oxidation, process to ensure that it complies with DWA specifications before it is pumped into the Crocodile river.

In the case of Rand Uranium, Verder identified that two VF65s and one VF40 would be sufficient to deal with the miner’s AMD demands.

“We also identified that training on the pumps would be necessary, and we made this available to Rand Uranium staff at our premises in North Riding,” says Louw.

Meanwhile, he explains that the nature of the medium being pumped is an important factor when considering pump selection for a specific application. When pumping lime, for instance, 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 on decreasing the potential negative impact on the environment, a process problem that will cause the plant to stop working is not an option,” says Louw.

He highlights that 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 are conveyed through the body.

The pulsation effect means that solids are kept in suspension to ensure that there is no build-up, which is also eliminated with rubber Verderflex hoses that are designed to increase life expectancy and performance.

Verderflex hose pumps are designed to handle these tough operating conditions, ensuring optimal process flow.

Meanwhile, Van der Walt highlights that correcting the pH of mine water is a specific process and the pump used for dosing must, therefore, be accurate. “Peristaltic pumps have a linear flow-speed characteristic and excellent repeatability, making it the most accurate solution available,” he says.

Central to resolving South Africa’s AMD problem are water treatment plants, which Van der Walt believes are possibly the most important infrastructural requirement, relying solely on the design and quality of the equipment installed.

“We can see the damaging impact that AMD already has on the environment and we are working on a long-term viable solution to this problem,” he concludes.