• Drop goal

    Mines in South Africa are employing increasingly sophisticated methods to address the twin issues of reducing water use and stopping pollution

    Drop goal

    Miners operating in South Africa, where scattered and erratic rainfall is increasingly the norm, describe water as the single-biggest environmental risk to their operations.

    This is unlikely to change. Population growth, economic development and climate change are adding to the water stress in some regions, according to the International Council on Mining and Metals.

    For example, Impala Platinum (Implats) says water is a particularly important issue in the Bojanala and Rustenburg areas, where its Impala Rustenburg shafts are situated. This is because of growth in the size of neighbouring communities, low rainfall and lack of new water capacity in the region. In addition, Anglo American says 70% of its global operations are in water-stressed areas.

    According to Department of Water Affairs and Sanitation (DWS) figures, in 2017 mining accounted for only 3% of South Africa’s water consumption. But mining effluent can have a severe effect on the quality of the country’s water resources. Mines can discharge water into the environment under carefully controlled conditions, but sometimes there are unplanned discharges, for example, seepage from dams or fracturing of a storage facility after an earthquake or high rainfall, which then releases polluted effluent into rivers and streams.

    According to SLR Consulting, mineral processing is the biggest water user on any mine site and while water can be recovered and reused, there is a problem with a build-up of chemicals. This creates issues such as a potentially highly toxic waste stream or sludge, which is difficult to dispose of. A better solution is to minimise water use in processing.

    Although water is important for many mining activities, including mineral processing (such as gold separation); as a coolant in pyrometallurgical processes (for instance, platinum smelting); for dust suppression on haul roads and waste dumps; and to transport minerals in a slurry through pipelines, it is often not necessary to use potable water. Processes such as dust suppression, for example, can use saline water instead.

    In its 2011 water efficiency guidelines, the DWS recommends various measures for mines to follow to conserve and manage their water use and prevent pollution of water systems. These include waterless processes; reducing water use by greater efficiencies and technology; reusing and recycling water as much as possible; disposing of wastewater in a way that does not damage the environment; and using feedback and adaptive management to become more efficient and cut water usage.

    In 2018 the DWS and the Minerals Council South Africa agreed to work together on devising water-saving measures, including developing benchmarks for each mineral to guide efficient water use, taking into account the different circumstances of each mine.

    Tamsyn Grewar of Mintek South Africa’s biotechnology division, in the Journal of the Southern African Institute of Mining and Metallurgy, examines the various options for treated mine water.

    According to Grewar, more than 90% of mine wastewater can be recycled using reverse osmosis and microfiltration. However, getting the water to an acceptable quality is not the only issue. The salts must be extracted so that when this water is eventually discharged it does not have to be diluted with potable water. She says the long-term DWS plan is to install desalination plants to treat highly saline-treated mine water to potable levels. However, this costs between ZAR12 and ZAR18 per cubic metre, a high price that may not be justifiable if greywater could be used for irrigation, flushing toilets or washing clothes. Grewar says that about 40% of the water consumed by South African households is used to flush toilets, with six to nine litres of drinking water being used for each flush.

    ‘Potable water is, however, not necessary for sanitation purposes and this represents a major mismanagement of our limited water resources,’ according to Grewar.

    At present, the lack of dual reticulation is a constraint but in future, ‘re-use of mine-impacted water in sanitation should be revisited once legislation is amended and infrastructure improved to allow for this option to be more widely utilised’.

    Grewar says there is a huge amount of water in the Mpumalanga coalfields. An estimated 360 megalitres (ML) a day of mine-impacted water would be generated if all those coal mines were to close. This could support about 6 000 ha of irrigated land.

    Treating mine water to irrigation standards would cut the costs considerably, says Grewar. A study conducted over eight years showed that crops such as sugar beans, wheat, maize and potatoes could be irrigated with mine water rich in calcium and sulphate, with no impact on soil, surface or groundwater.

    ‘The potential for linking mining with agriculture has been recognised by some in the industry, although it will need widespread adoption to make a significant impact on the status quo,’ she says. Implats aims to recycle 40% of water across the group and prioritises the use of greywater. It pays particular attention to Impala Rustenburg, which accounts for 51% of the group’s water consumption. The mine uses just 60% of its water allocation, and its controls include monitoring water usage; daily dashboard reporting; water recycling and using alternative water sources. It also uses scavenger boreholes, which recover the dirty groundwater that accumulates around tailings dams.

    Another mine operating in the dry Rustenburg region, Lonmin’s (now Sibanye-Stillwater’s) Marikana, put an integrated water-management plan in place in 2012, encompassing various areas. These include improving the lining of existing pollution control dams and building new ones; using berms to divert clean stormwater flow away from dirty water areas; using scavenger boreholes; and strategically placing water-treatment plants so water can be reused, such as for dust suppression. In addition, it has implemented more innovative methods, such as aquifer storage and recovery, where surface water is stored underground to minimise evaporation and can be used for domestic, agricultural and environmental purposes.

    Petra Diamonds, which has mines in South Africa and Tanzania (and an exploration programme in Botswana), operates in dry areas, and its operations are water intensive. In its 2019 financial year, it cut clean water usage across all its operations by 14%, compared with 2018, although its total water usage (clean and grey) increased by 49%. All its new projects substitute potable or raw water with recycled water from various sources, including internal as well as effluent from municipal wastewater plants. For the past four years (2019), the percentage of recycled water it has used has remained above 50%.

    One of the premier examples of sustainable water use is the US$100 million eMalahleni Water Reclamation Plant commissioned in 2007 as a joint operation between Anglo American and BHP Billiton South Africa (of which the present South32 is a spin-off). It initially treated water from four coal mines and its capacity has subsequently been expanded to be able to treat water from six coal mines.

    The treatment plant supplies about 12% of the daily water needs of the eMalahleni Municipality and has the capacity to produce about 50 ML a day of potable water from mine wastewater. It also produces a gypsum by-product that can be used as a construction material for affordable housing.

    ‘The eMalahleni Water Reclamation Plant is a shining example of how an environmental liability – mine water – can be transformed into an asset with extensive benefits for the local community, the environment and our own operations,’ said then CEO of Anglo American’s thermal coal business, Godfrey Gomwe, in 2013.

    It is in mining groups’ own interests to reconsider how they use water in their operations, from ore processing to dust suppression

    The treatment is based on high-recovery precipitating reverse osmosis technology, and the water that emerges complies with SANS 241, a potable water standard (except on turbidity).

    Optimum Coal established a plant nearby using the same model, producing 4 million to 5 million litres of water a day for the towns of Hendrina and KwaZamokuhle. However, when the Gupta family took over Optimum Coal, the plant’s supply of water became erratic and there were issues with payment of contractors. The mine has only recently been discharged from business rescue.

    Anglo American, as part of its FutureSmart mining technology project, is researching waterless mining, among other strategies to cut its water consumption.

    Waterless mining would include a closed-loop approach, to minimise water losses by reusing the same water repeatedly. The group is exploring ways to minimise evaporation from storage dams, which accounts for 10% to 25% of a mine’s water losses and costs Anglo American about US$200 million a year to replace. Another innovation is Concentrating the Mine, a low-cost initiative to minimise the amount of water sent to tailings dams, with the goal of producing dry, stackable tailings. For ultra-fine particles, which are difficult to remove, it is researching the use of chemical additives in copper tailings that separate subterranean water from fine metal particles.

    Apart from dry processing, Anglo American is also exploring dry separation, an alternative way to crush and separate ore to the required particle size using less water than with traditional methods. It is also testing non-aqueous processing using a bespoke polymer.

    While pollution of water sources from mines is still a reality in South Africa, it is evident that many mines are seriously trying to tackle the issue, in their own interests as well as in response to pressures from shareholders and civil society.

    By Charlotte Mathews
    Images: Anglo American