Guided by circular economy principles, many mines are innovating ways of reducing water use, reusing and recycling it back into processing plants and, in many instances, even repurposing treated water for other applications.
The mining sector’s experience is setting the benchmark for responsible water stewardship, according to SRK Consulting South Africa (SA), which could be emulated by other industries and municipalities to better manage water.
“Water is crucial for socio-economic development, supporting human health and wellbeing and it is a critical resource for the sustainability of various industries, including mining,” said Steve Bartels, partner and principal civil engineering technologist at SRK Consulting SA. “Without water, mines cannot operate and, therefore, have to act responsibly in terms of how it uses this resource.”
This focus extends beyond managing water sourced from water service providers, said Bartels, noting that it also included the harvesting of water from surface catchment systems and from underground water ingress.
“This water is also often diverted into other applications to supplement losses in the system due to factors such as evaporation,” he said.
The efficient management of water movement within and beyond operations relies on mines’ sophisticated water balance systems.
“A mine’s water balance entails evaluating water entering the system, how much is available, the volume of water that various processes will consume, and how much of this can be recycled and then placed back into the system,” he explained.
Water scarcity
Bartels noted that this level of water stewardship was especially important in a water scarce country such as South Africa. The country experiences variable and below average rainfall of only about 464 mm, compared to the global average of about 850 mm. Alongside these levels are regular droughts in various areas of the country.
“Therefore, water recharge is not infinite, and we are running out of space to build deep and narrow dams that experience lower evaporation. Considering the pressure that a steadily increasing population is placing on existing water resources and the impact of climate change, we have to use every drop wisely,” he said.
Bartels said that mines had demonstrated the efficacy of water recycling in terms of ensuring security of supply.
Treating for re-use
“Municipalities in drought-stricken areas of the country would have possibly been able to better manage the crisis had they also been as efficient in terms of recycling limited available water. The water crisis in Cape Town during the worst drought in the history of the province, for example, would not have been as severe had accessible water in the system been recycled more efficiently,” he said.
While South Africa is yet to treat wastewater at a large scale, many international cities such as Singapore have been doing this for many years.
“Considering that the technologies to treat wastewater at a large scale are available, it is shortsighted not be evaluating their potential in a local context,” he said.
However, he noted that the high costs and energy-intensiveness of water reuse were obstacles in the way of greater implementation in the country.
To ensure feasibility of water reuse projects, mines will carefully consider the upfront capital costs and continued operational and maintenance expenses when evaluating water reuse as a strategy. The water reuse technology will be assessed, as well as the environmental trade-offs associated with various system types.
“There are always environmental trade-offs in water re-use in mining which can come at a high cost,” he said. “While these projects conserve water, treatment processes such as filtration, membrane procedures and chemical treatments, introduce new pollutants, which have to be effectively managed. The responsible disposal of brines and other treated wastewater may also be necessary.”
Improved efficiency, reduced impact
However, Bartels noted that newer technologies were enabling more cost-effective and efficient water re-use, while at the same time mitigating environmental impact.
An example of improved efficiency and reduced environmental impact in mine water recovery is tailings filtration, a newer technology that is still to be widely implemented internationally.
“In South Africa, the technology is still in its infancy with tailings filtration mainly being undertaken at a very small scale. However, it presents an opportunity for the industry to further improve the way in which it manages its water,” he said.
Bartels explained that traditional tailings management – where a slurry is pumped onto tailings dams – required a substantial amount of water. Water losses also occur due to evaporation, seepage and other processes and this has to be replenished, while the large dams required to store tailings are inherently water intensive.
“Produced by a filtration process, filtered tailings become a stackable material that can be transported mechanically as opposed to hydraulically,” he said. “In this way, water is removed from the tailings slurry before it is disposed of; this in turn allows for greater recovery and recycling back into mining processes.”
He added that, in addition to improved water management, the technology also eliminated the need for large, engineered tailings dams, which have failed in the past, and the dry stack facilities had a smaller footprint.
Robust legislation
Bartels noted that sound water stewardship in the industry was underpinned by robust legislation.
“To use surface water or groundwater, mines require a water use license. They enable the Department of Water & Sanitation to control the volumes of water that mines are allowed to extract, how and where it is stored, as well as the effluent quality that can be discharged into the environment. These parameters are determined by the National Water Act,” he explained.
Mines will also consult the National Environmental Management Act when assessing environmental impacts, and the Waste Act for waste classification and management, including administering the handling and storage of tailings.
“Mines understand that these regulations benefit the industry by safeguarding a resource that they need to continue operating and, by demonstrating responsible use of water, they also secure their social licenses to operate,” he concluded.
