A water-driven approach

Mining in South Africa has faced a significant downturn in recent years. Focusing on water efficiency may help secure savings for mines while also preserving a limited resource. By Danielle Petterson

South Africa, although technically a water-scarce country, is fortunate to have sufficient water resources available to support large-scale mining operations. However, the relatively wide availability of water may have led to complacency around the use of water in mining operations, says Stephen Rose, director advisory group: Industry, Royal HaskoningDHV.

“Optimising your water efficiency has a direct impact on optimising the performance of your mine. When we are undertaking feasibility or economic assessments for mines, we often find that water is a key deciding factor in determining whether the mine will be viable or not,” he says. This is fundamentally linked to the availability of water on the mine site and the cost of importing water.

Mines use a vast amount of water in their operations. On average, in South Africa, coal mines use 0.8 m 3 water per run of mine (RoM) tonne, gold mines use 2.5 m 3 per RoM tonne, and platinum 1.7 m 3 per RoM tonne.

However, a massive disparity exists in water use at different mining operations. “There is data to indicate that certain mines are doing far better at water conservation and reuse than others. On some gold mines, water use drops to as low as 1.1 m 3 per RoM tonne. On mines that don’t perform as well, it goes up to 3.5 m 3 per RoM tonne,” says Rose.

While some mines are performing better than others, current legislation – which Rose describes as prescriptive and forwardlooking – enforces compliance in many areas. However, enforcement of the law can be a challenge.

Water efficiency “Mining is extremely water intensive and it is absolutely critical that the mine’s operations are geared up to be as efficient as possible to minimise the use of fresh water. We should adopt a water-driven mining approach with water-sensitive practices at the core of mining,” says Sheilla de Carvalho, director business unit: Industry & Smart Asset Management, Royal HaskoningDHV.

When it comes to optimising water usage to make a more profitable mine, there are two metrics to focus on: consumptive water use and total water use throughout operations. Optimising your water use per tonne not only increases the chances of having your water-use licence application approved but also creates a more sustainable business. “The less water you use, the less you have to pump, the less you pay in electricity charges, the smaller equipment you will require and, consequently, the less your maintenance costs are likely to be,” explains Rose.

Many mines in South Africa are waterpositive – meaning they generate more water than they use. When discharging into the environment, water must be

treated to potable standards, or higher. Reusing water within the mine can therefore sometimes be the cheaper option. Extensive opportunities exist for the reuse of excess water generated from the mine within operations and, in the case of heavily water-positive mines, to boost potable water supplies for surrounding communities.

Water pumped out of the mine can be reused as process water, for dust suppression, or to feed supporting mining infrastructure such as offices and change houses. Progressive technologies are also creating a shift towards dry tailings methodologies in which water is pressed out of the final product and reused within the mine or the process. Further opportunities exist to extract valuable by-products from mine water, although this often requires economies of scale.

In some instances, water can be treated for use outside the mine, often for agriculture or potable consumption. The Optimum Coal plant in Mpumalanga, for example, supplies much of Hendrina’s potable water. The Sishen mine in the Northern Cape, operated by Kumba Iron Ore, discharges its excess groundwater into the Vaal Gamagara Regional Water Supply Scheme.

“It is not only technically feasible, but it should become the responsible way to treat your excess water in the mining industry,” says Rose.

The right technology Using the right technology is key. Royal HaskoningDHV’s Crystalactor® technology, for example, uses a crystallisation process to purify water,

harvesting high-purity pellets that are reusable and can be sold in some cases. According to Rose, it is typically used when there are heavy metals, phosphates and carbonates in the water, as is typical in mining operations.

Provided the feedwater is of sufficient quality, Crystalactor can largely be used as a stand-alone technology, thereby reducing costs. The process also creates very dry solids, which vastly reduces disposal costs.

“The Crystalactor can also be used to treat some of the components of acid mine drainage. Some of the high-level benefits include the generation of high-purity crystals, which can be sold as by-products, extremely low energy consumption and low chemical consumption,” explains Rose.

Crystalactor technology is currently being used at one of South Africa’s gold mines on a dewatering circuit for underground fissure water. Here, it

softens the water and removes uranium and nickel.

“The important thing is to think holistically about where the water is being generated and the surrounding communities and potential impacts and/or benefits thereof. We should not only be looking at mine water treatment technologies for the mine itself, but also potential biological treatment technologies within these communities and harnessing the combined opportunities for reuse,” says De Carvalho.

She highlights Nereda®, a biological treatment process, which can be coupled with other technologies and offers many benefits including high energy efficiency and a small footprint. Nereda purifies water using the unique features of aerobic granular biomass. Contrary to conventional processes, the purifying bacteria concentrate naturally in compact granules, with superb settling

properties. As a result of the large variety of biological processes that simultaneously take place in the granular biomass, Nereda can produce excellent effluent quality.

“You need to know what you are dealing with and employ the best combination of technologies, taking into account the final use of the water. The economics need to make sense,” adds Rose.

De Carvalho also highlights the importance of digital technologies that allow mines to make more informed decisions. “We are seeing a lot more attention being paid to the optimisation of mine operations, including water systems. You are now able to perform functions based on real, measured data and therefore reduce the use of chemicals, input energy costs and water wastage due to process inefficiencies.”

An example of this is AquaSuite, which Royal HaskoningDHV developed together with other partners. AquaSuite allows for better monitoring, operation and control of your water system. The software uses accurate machine-learnt artificial intelligence prediction, based on good data, to tell you how to operate your system most efficiently and effectively, and, if desired, automate operations and support predictive maintenance.

“Data-informed decisions are critical,” stresses De Carvalho. “I’m pleasantly surprised to see that many of the mining houses in South Africa are aware of technologies around improved operations and maintenance, as well as data science. The awareness is there, the next step is for the private sector to join hands to implement these technologies faster and show the clear benefits not only on their mines but to the benefit of society at large.”

Improve awareness “One of the biggest drawbacks in South Africa is the level of education, awareness and training around the sustainable use of water. That often means that people are hesitant to employ more advanced technologies in remote places where they may be the best fit,” says Rose.

De Carvalho elaborates that while the need for water and its use within the mine is top of mind, the economic value of

water, both from a mining and societal perspective, is not always very apparent. “We must find a way to attribute more value to water and move away from policy to day-to-day discourse. We need to think about water-sensitive mining the same way we think about water-sensitive cities.”

She adds that without this approach, water may become a limiting factor for mining operations as well as development in general. Rose concurs that a holistic view of the mine and the context in which it exists and operates is important; the mine should become an asset to the community.

“The sustainable use of water should be carried across the mining industry, government and regulatory bodies, together with communities and private companies. It should be everyone’s responsibility. The mining houses have a huge role to play, but the value of public-private partnerships is immense, and they will lead to more sustainable, holistic and forward-looking views on the management of our precious and limited water resources,” concludes Rose.