While Cape Town residents queue for water from springs as the city’s Day Zero approaches, mines have in recent years made significant strides toward self-sufficiency – not least so as not to compete with communities for increasingly scarce treated water from municipalities.
SRK Consulting principal hydrologist and partner, Peter Shepherd, has for some time highlighted the likely effects of more varied climatic conditions on the mining industry, and called for closer attention to be paid to mine water management plans.
“Monitoring and managing balance on mines is becoming more challenging as rainfall patterns become more varied – leading to heavier downpours between longer periods of dry weather,” says Shepherd.
“It is therefore more difficult to maintain optimal levels in storage and tailings dams – as possible over-topping in wet weather also brings a range of health, safety and environmental risks that must be avoided.”
The situation was simpler to manage when mines could simply top up their mine supplies whenever necessary from municipal sources.
Factors like population growth and urbanization – combined with the rising cost of treated water – have fundamentally altered the picture, he explains.
Mines now have a social and environmental responsibility to become as self-sufficient in supply as possible.
“This has led to huge improvements in water conservation in mining operations, and significant recycling of water – with positive spin-offs for the mines, the environment and the surrounding communities,” says Shepherd.
“Just ten years ago, most platinum mines managed to reuse – in their process plants – about 30% of the water it pumped to tailings dams; today, that figure is closer to 50% or 60%, and they plan to recycle still more than that in future.”
This trend has gone hand-in-hand with environmental efforts – often driven by stricter legislation – to prevent run-off from mining sites and to more effectively separate clean from dirty water.
“Mines are today very clear about the requirement that clean water run-off that flows towards the mine should be diverted into a river or stream,” says Shepherd.
“This allows the run-off to proceed into the watercourse without collecting any contaminants from a mining site – a key aspect of good mine water management.”
At the same time, the on-site water that has become polluted needs to be collected and channelled to a pollution dam – for re-use in an application, a washing plant for instance, that can accommodate its lower quality.
“Of course, it should be remembered that regulations demand that pollution dams must be capable of managing a one-in-50-year storm event, plus its operating water – so the design must take this into account,” states Shepherd.
Going beyond compliance, Shepherd suggested that excess dirty water can be treated and made available to other industries.
“It can even be treated to potable standard for local consumption,” says Shepherd.
A challenge that mines must regularly address is the siltation of its pollution dams, which reduces the capacity and results in more frequent spillage.
Silt traps are commonly required as part of an effective silt management strategy, and these must be regularly maintained.
The focus by many mines on a ‘water quality hierarchy’ has streamlined the amount of treatment required by more carefully channelling of different qualities to their best respective uses.
Potable water – requiring the most expensive levels of treatment – is limited to drinking and washing purposes.
Shepherd highlighted how SRK has been instrumental in developing ways of maximising the re-use on clients’ mining operations.
“Even before today’s stringent legislative requirements were introduced, we recommended that our clients install features that would collect water,” he said.
“These included groundwater barriers and collection facilities which allowed mines to minimise the surface area of their tailings storage facilities so they could reduce evaporation levels.”
Where appropriate, SRK was also able to recommend the idea of compartmentalised return water dams, which allowed the storage of different qualities within the same facilities – a strategy that supported the hierarchy objectives.
Keeping less water on tailings dams is certainly one of the aims of the new approach to management, and thickener technology is becoming more widely utilised – although it can be an expensive option.