“Maintaining an accurate process flow diagram and water balance are key to mine water planning,” says WSP senior hydrology associate Karen King.
The accurate measurement of the volumes and qualities of water sources, water movement and storage within, and water discharged from the mine site are significantly important. Moreover, conditions associated with mine-water treatment during the construction and operational phases of a mine will need to be specified in the application for the mine’s water-use licence (WUL).
“This licence needs to be issued before a new mine can be commissioned,” adds King.
She explains that these conditions, as stipulated by a mine’s WUL, will include details pertaining to water quality standards for storage and discharge.
A mine also needs a closure plan, which includes details about the funds that need to be allocated to closure, including funding for any water treatment, before it can be commissioned. These funds are kept in an interest-bearing account that the mine owners and managers cannot access until mine closure begins.
“A lot of the water-quality problems facing mine-affected regions, especially those involving acid mine drainage (AMD), were generated decades before mines were required to have WULs or closure plans. Finding the funding to treat these problems is difficult, as many of those who benefited from the existence of these mines have died or are no longer traceable”.
King adds that there are not enough large mining companies that are currently operational in the AMD-affected Witwatersrand areas to pay for water treatment.
“The South African government did prioritise this spending at one point, but sufficient treatment was not carried through,” she notes.
Depending on the mine closure plan, excess water on mines that have reached their end-of-life can be pumped, treated and discharged. It can also be used for irrigation, depending on the quality of the water.
King adds that there is a new approach to drive efficiencies in water use at mine sites, with mine operations aiming for “zero-water” or “dry-mining” operations.
“Waterless mining describes a situation in which technologies are used to source, use and discharge as little water as possible, and reuse as much water as possible,” she explains.
There are a range of options where water may be reclaimed and reused in the mining water cycle, depending on factors such as the age of the mine and finances.
“Some water-reducing options are cleaning that involves pressurised air instead of water, using dust-reduction or -supressing agents instead of water and adopting dryer methods for the transport of slurry. Additionally, reusing water instead of discharging water is key,” concludes King.
This article first appeared in Mining Weekly.