January 24, 2018

Water management for remote mines

Philip Wood, export sales director for leading manufacturer of plastic piping and water management systems Polypipe, discusses the challenges of meeting the water needs of remote mines, and the infrastructure that keeps mine water flowing.

Most easily accessible sources of minerals around the world have already been explored and exhausted, meaning companies must seek out increasingly isolated deposits without existing transport and power infrastructure.

The need to satisfy demand from emerging markets can often benefit nearby communities with jobs and development, but supplying the new site with the necessary utilities while avoiding damage to the local environment poses a considerable challenge.

Modern methods of sustainable power generation, including solar and wind energy, have made providing a remote mine site with electricity a more straightforward task, particularly in climates with little precipitation and long hours of daylight.

However, while these conditions are ideal for solar power, they generally also lead to a shortage of water sources in the local area. Mining operations will therefore be competing for a scarce resource with local communities and agriculture, and for this reason mines often choose to pump in water from further afield to satisfy demand.

Conversely, remote mines located in areas of high rainfall may need a complex water management infrastructure to prevent pit flooding and damaging tailings pond overflows.

The uses of water in mining operations are varied and substantial. In mineral processing, it is used to recover gold and copper from chemical solutions, to cool equipment such as rock cutters, and to wash minerals once extracted.

Ores can also be transported away from the site through pipelines in slurry, which can cut the costs associated with road or rail transport but increase the amount of water used by a mine.

Arid climates often lead to dusty conditions, particularly on service roads, and here water is used to damp down and control dust. Finally but no less importantly, high-quality water is also required to meet the drinking, cooking and washing needs of workers throughout the life of the mine.

As mining is one of the few industries that can use low-quality water – such as using seawater for some mineral processing or dust control – it can draw water from a variety of unconventional sources, which is useful for more remote operations.

Because of this it is also possible that, beyond simply minimising the impact of mining on the local environment, mines in remote areas can actually have a positive effect by assisting with the provision of safe, clean drinking water to nearby communities.

AREVA’s Trekkopje uranium mine in Namibia, for example, boasts a water desalination plant which supplies both the mine and local communities, while Anglo American’s eMalalheni Water Reclamation Plant in South Africa takes in contaminated water from various mines including its own, and delivers treated water into the municipality’s drinking water supply.

Remote mines, which will often need to treat their own contaminated water, could easily operate in a similar way with the addition of potable water piping systems channelling water away from the mine to local villages and farms.

Transporting water, whether fresh, saline or contaminated, over long distances and within the mine site itself, poses a challenge. Far from alternative sources of water or replacement pipes, the materials chosen need to be robust and durable, withstanding a variety of factors.

For example, pipelines must have a tough exterior which will not be perforated by rocks or damaged by slight land shifts above or beneath them. Pipes laid above ground will also need to withstand extremes of temperature and UV exposure.

The interior surfaces of pipes must be resistant to corrosion from slurries or rock fragments within processing water, as well as the chemicals, salts and acids used in extraction, while pipes used for potable water must resist bacterial growth.

Polyethylene (PE) pipes are an ideal solution for all aspects of mine water management and provide a lightweight, cost-effective and flexible alternative to traditional, heavy materials such as concrete and cast or ductile iron.

With significant inherent strength and impact resistance, they can be installed both above and below ground and can cope with temperatures in the range of -40ºC to +60ºC. This strength is achieved even in a very lightweight pipe, making PE pipes cheaper to transport, cutting fuel costs and the number of trips, and can be easily moved around site without heavy lifting equipment – key considerations when planning a water management system for a remote mine.

For the supply of potable water to a mine, PE significantly outperforms steel or concrete pipes as it is resistant to both galvanic corrosion and bacterium sediment build-up – unlike these traditional materials which can be badly damaged.

While the chemicals used in both mining and water treatment processes can have a corrosive effect on many traditional pipe materials, modern PE piping offers the resistance required to cope with even the most aggressive acids, bases and salts. Its inherent strength also offers protection against abrasion from metals or mineral particles, including rock fragments, meaning it can also be used to transport ore away from the site in slurry.

Ideal for extended pipelines over long distances, PE pressure pipes can be jointed using butt-welding or electro-fusion techniques to form a continuous homogenous pipeline with no risk of leakage. The extremely smooth bore of PE pipes offers reduced friction – meaning less drag and turbulence when large volumes of water are transported at high velocity.

In designing a water supply system for a remote mine, careful consideration must be given to the often harsh conditions in which pipelines may be laid, as well as the potentially damaging particles and substances which are likely to be suspended or dissolved in mine water – any pipework specified must be able to withstand these challenges.

Meanwhile, aspects of the water management solution must also be suitable for the provision of safe, clean drinking water. PE pipes fulfil all these requirements, with the added benefit of being incredibly lightweight and therefore easy (and less costly) to transport, install and reuse in future.

Polypipe’s solutions for mine dewatering pipework include PE100, a polyethylene system, and Ridgidrain, a high-density polyethylene (HDPE) solution, which offer the resistance to chemical corrosion and abrasive erosion required of a water treatment pipeline.

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