An innovative water-saving technology that uses fibre-optic sensing to measure water flows at a South African platinum mine won an award for the Best Use of Smart Technology for Sustainability at the Mines and Technology conference in November last year. The event is Europe’s largest mining investment gathering, and it forms part of Mines and Money London, which is now in its 16th year. It attracts delegates from 75 countries, among them senior executives of 150 mining houses.
The winning water-wise technology was successfully trialled at Anglo American Platinum’s Mogalakwena platinum mine near Mokopane (formerly Potgietersrust) in Limpopo. The miner expects that this accurate, real-time monitoring of all mine-wide water flows will yield significant water savings. ‘Developed with our technology partners, Silixa, it is the world’s first permanent installation using this type of distributed sensing technology,’ states the company.
‘Unlike traditional sensors that measure at discreet, predetermined points, this installation uses a single fibre-optic circuit, several kilometres long – enabling continuous real-time metering of mine water flows across multiple points throughout a region comparable in size to Lower Manhattan.’
According to the UK-headquartered Silixa, its metering system can be installed ‘on-the-fly, without disrupting process flow or requiring costly calibration. The system is compatible with liquid, gas, slurry, organic, reagent and multiphase flows’.
The mining major’s plan to automate the water-balance system at Mogalakwena is supported by its other FutureSmart Mining technologies such as evaporation measurement. The group says that the system will not only conserve water but ultimately improve metal recovery. ‘Because it uses no expensive sensing parts and no power, it is both cost efficient and environmentally sound – an important step towards our sustainable mining goals.’
Typical of mining operations, Anglo American operates the majority of its mines (approximately 75%) in geographic regions with high water risks. As mines increasingly compete with industry, agriculture and local communities for the precious resource, water-related issues have risen to the top of the sustainable mining agenda. Without water, there can be no mining. It’s a vital ingredient in mineral processing, dust suppression, slurry transport as well as in the drinking and hygiene requirements of a large mining workforce.
Accurate measurements and real-time water data are crucial in understanding the water flow across any mining operation, which is a prerequisite to conserving water by improving water-balance calculations and efficiencies.
‘Mines use a water-balance model to establish losses and determine how much make-up water is required, mainly to replace the evaporation and seepage from tailings facilities and return water dams,’ says Peter Shepherd, principal hydrologist and partner at SRK Consulting Johannesburg – a specialist consultancy of engineers and scientists whose services include mining exploration, feasibility, mine planning, production and mine closure.
‘The biggest water loss in mining happens from tailings dams,’ he says. ‘On average 35% of water is lost through evaporation; 20% to 25% of the water remains locked in the tailings slurry; and, in older dams, 5% is lost through seepage from the bottom of the dam.’
However, South African miners have made good progress over the past decade as they comply with (and go beyond) ever-more stringent water-conservation regulations. They are not only reducing the water loss from tailings dams, but also increasing the amount of water that is retreated for use in process plants. According to Shepherd, South Africa’s platinum industry now captures between 50% and 60% of water from tailings dams for reuse in their operations.
‘In the past, these dams only had a limited clay layer or some other type of impermeable material as a barrier that still allowed seepage. The new tailings storage facilities are lined with an impermeable layer including plastics,’ he says. ‘That’s an expensive capital outlay but it’s being done worldwide, even in African countries such as the DRC and Ghana, especially in gold and some copper tailings dams.’
Shepherd believes that the next big drive to prevent water loss will focus on reducing evaporation from the dams. Millions of cubic metres of water could be saved annually by reducing the area where the slurry is deposited onto a tailings dam. Less exposure to the sun will reduce the evaporation loss, he says. This can be done by designing deeper tailings with a smaller footprint, or by covering the surface of return water dams. There are ingenious – but costly – solutions, such as plastic shade balls that flood the surface of pollution-control dams and block out the sunlight, and floating solar panels that generate energy while limiting evaporation.