The uses of water in mining operations are substantial. Philip Wood looks at the facts behind the figures
Mining is the second largest industrial user of water in the world, with only power generation being responsible for higher water consumption. Globally, around 7-9 billion cubic metres of water are used for mining purposes each year, which is as much as a country such as Nigeria uses in total in a year1.
In Africa in particular, the responsible use and conservation of water used in mining operations is therefore vital to sustainability. According to a 2011 De Beers report2, arid lands cover around 60% of African land which, although it is home to around 15% of the world’s population, has only 9% of global renewable water resources.
Putting the spotlight on South Africa in particular, 2.5% of national water supplies are used to sustain mining activities in the country3, which may not seem a lot, but the 2004 National Water Resource Strategy4 puts this in perspective by contrasting South Africa’s annual average rainfall of 450mm with the world average of 860mm.
Recent evidence points to a 61% increase in mining projects in South Africa from 2005-13, placing additional pressure on a stretched resource5. The same study also looked at the common location of mines, finding there is often an overlap between mineral deposits and fertile agricultural land – for example platinum group metals are most concentrated in the Limpopo basin, in close proximity to cattle and crop lands – creating greater demand for South Africa’s most stressed and economically important groundwater source5.
The uses of water in mining operations are varied and substantial. It is employed to recover mineral ores 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.
While high-value minerals such as gold are fairly low in production volume, nevertheless large quantities of water are required to transport and process ore. For example, one tonne of gold uses 250,000 cubic metres of water6, whereas coal and other non-metal mines need less water per tonne of mineral produced.
As mines reach the end of their working life and exhaust supplies of high-quality ores, the remaining lower-quality ores begin to be extracted, which requires greater quantities of water in order to produce each tonne of metal. Coupled with increasing production, a reduction in ore quality means access to water becomes a business-critical issue7.
The mismanagement of water can disrupt production, as many extraction and washing processes depend upon clean water, as well as disrupting the transportation of minerals which is often run to a tight schedule. Where water is wasted and mismanaged, more water than is truly necessary is pumped on to the site, all at considerable cost – meaning properly managed water use can save money as well as optimise production and reduce downtime. Water mismanagement can also lead to damage to the wider environment through unintentional contamination, as well as a dangerous lack of fresh water available for workers. Only with the right pipework infrastructure in place to transport, store, supply and drain water, can this resource be properly managed on a mine site to reduce water stress, maintain high water quality, and prevent flooding or environmental damage.
Avoiding the wastage of water once used is equally as important as using it responsibly in the beginning and, whether available fresh water is plentiful or limited, it is clear that wastage can be more closely controlled. In a typical mining operation, only around 35% of water discharged to a tailings dam is reused in the process plant, making tailings ponds the biggest culprit in terms of water wastage. While a quarter of water remains in the dam, five per cent is lost to seepage and up to 35 per cent to evaporation6.
As seepage from pipes can account for up to 50,000 cubic metres lost per month in a mine using 1 million cubic metres in the same time period, robust yet flexible engineered pipework solutions are essential in minimising lost and wasted water.
For mine water management systems, polyethylene (PE) is the ideal choice for pipework. Well suited to the demands of mining operations, PE pipes offer inherent strength combined with the reduced weight and flexibility needed for transport to and installation in remote mining environments – unlike traditional metal or concrete pipes which are cumbersome to move. Plastic pipes are also much more adaptable than traditional materials, as bespoke lengths and angles can be designed to circumnavigate tailings ponds or fit around existing infrastructure.
Traditional materials, on the other hand, would generally be more difficult to handle and may require on-site fabrication, increasing the leakage risk. PE pressure pipes can be jointed using butt-welding or electro-fusion techniques to form a continuous, sealed pipeline which affords no risk of leakage. Additionally, the extremely smooth bore of PE pipes reduces the friction which is often a feature of traditional pipes – meaning less turbulence when water is transported at high velocity.
While the chemicals used in 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.
Suitable for use in tailings pipelines, mineral extraction and treatment applications, it can also be used to transport treated and potable water as it is resistant to both galvanic corrosion and bacterium sediment build-up – unlike steel or concrete pipes which can be badly damaged. Its inherent strength offers protection against abrasion from metals or mineral particles, including rock fragments, while its exterior surfaces are impact-resistant and suitable for underground installation if necessary. PE withstands both UV degradation temperatures in the range of -40˚C to +60˚C, ideal for mines at high altitudes where temperatures can drop well below freezing, and also for mines in arid, hot climates.
The interior surfaces of PE pipes resist bacterial growth, an attribute which is essential for the supply of drinking water to remote mines where no mains supply is available. Concrete and metal pipes, meanwhile, can be badly damaged by both bacterium sediment build-up and galvanic corrosion, to which PE is resistant.
Polypipe offers a number of product solutions for water management in mining applications from the supply and storage of potable and process water, to dewatering and treatment. These include PE100 pressure pipes, HDPE twin-wall gravity systems – Ridgidrain and RidgistormXL, and Polystorm cell units for water attenuation and re-use.
Philip Wood is with Polypipe, Doncaster, UK.
References: 1 Mining Magazine, October 2011; 2 De Beers Issue Brief #1, December 2011; 3 Thenewage.co.za – Conserving Water is Vital to South Africa’s Mining Sector, Mava Scott; 4 National Water Resource Strategy 1st Edition September 2004; 5 MSCI ESG Research October 2013; 6 Water in Mining and Industry – Ian Prosser, Leif Wolf & Anna Littleboy. CSIRO 2011; 7 Miningreview.com – November 27, 2008