Water security is a key operational risk facing the mining industry. Many mines are in water-scarce regions. Mining operations use large amounts of water in mineral extraction, ventilation, and cooling activities.
The security of the water supply is critical to the continuity of mining as a business. This, along with the United Nations Sustainability Goal 6, has many mines placing water as a key pillar in their environmental sustainability strategy, set with clearly defined objectives and targets.
A deep-level PGM mine in the Limpopo water catchment area in South Africa has implemented several action plans to achieve the objectives and targets set out in its Environmental Sustainability Framework by improving the management of internal water sources available to the mine.
Laser focus on priorities for improved water security
The key priorities for this mine include further reduction of fresh, potable water and increased recycling of the mine’s excess overflow water, amounting to 3,4ML/day.
The incoming fresh water is potable water supplied by the local water board. The volume of water supplied is allocated within limits set by the water board.
Consequently, the makeup water supply to the condenser cooling towers was frequently constrained, and the system could not be bled to consistently maintain the cooling water conductivity and cycles within the range that ensured stable water. Scale and corrosion risks that could lead to condenser system failure were significant.
The ideal for the mine was to treat the mine’s overflow excess water to a quality that when blended with the cooling tower makeup water, will maintain a stable and consistent recirculating conductivity. This would ensure steady cycles in the cooling tower and reduce the risk of water-related fouling.
At the same time, repurposing the mine’s overflow excess water aligned with the mine’s environmental sustainability framework, and contributed to achieving the sustainability targets set in the framework.
A water treatment plant to decrease risks and enhance productivity
A water treatment plant incorporating membrane technology was required to reduce the conductivity and chlorides of the overflow excess water to provide a consistent source of additional makeup water that would ensure the optimal cooling of the condenser circuit.
Watercare Mining was commissioned to design, build, install, commission, operate and maintain a 2,3ML/day membrane plant, intercepting the mine process water line before the hot water dams.
The water treatment plant recovery is 70% – 75%, producing 1.6ML/day – 1,725ML/day of product water fed to the condenser cooling tower makeup line. The 25% – 30% rejection is lost in the CIP (cleaning in place), backwash and brine.
The chemical analyses of water samples taken before and after the treatment process showed that the membrane-treated product water quality was comparable to the board-reticulated potable water. The exceptions were nitrates and ammonia.
Even though nitrate and ammonia of the membrane-treated water were higher than the board water, the level of these elements was still within the SANS 241:2015 potable water specifications and will not pose a risk to the cooling circuits.
The key parameters (conductivity and chlorides) to manage the cycles of concentration of the condenser cooling circuit were present at significantly lower levels in Watercare Mining’s treated water than in the board water.
Watercare Mining supplies the product water at 28,6% less than the cost of board-reticulated water. More importantly, the improved water stability, consistent cycles of concentration, and better-managed bleed-off have significantly decreased the risk of condenser equipment failure caused by water fouling. Inadequate mine ventilation and insufficient water chilling have a direct impact on the mine’s productivity.
The repurposing of mine and fissure water to condenser cooling makeup water achieved:
1. Alignment with the mine’s Environmental Sustainability Framework
2. Alignment with the UN’s water and energy sustainability Goal 6
3. Improved control of the condenser cooling water circuit
4. Reduced dependence on reticulated board water
5. A cost saving on the condenser cooling circuit makeup water
We have proudly added this project as the 15th industrial water treatment plant that has made an impact on the water sustainability of our clients.