Most mines both consume and produce water. Water is a critical component of mining operations, utilised in mining, downstream processing and product conveyance.
Water is often imported for operating purposes from remote locations or transferred as surplus mine water from within the mine to a treatment and/or discharge location. There’s a growing recognition that a high level, concerted approach to mine water management is not only an environmental responsibility but also contributes to the resilience and sustainability of mining operations.
Water demand is set to outstrip water supply by 40% by 2030. Sustainable mine water management is a global imperative. When successfully implemented using a water stewardship approach, it can mean the difference between operating at a profit or a loss. It’s challenging to get it right.
It’s incredibly important to mine responsibly – Jax Jocobsen, International Council on Mining & Metals
Emerging trends that impact water use and sustainability within the mining sector include:
- Future mining investment will be located in geographic locations where water is scarce
- Declining mineral grades will increase the intensity of mineral processing and therefore increase the use of water
- Older mines are extending their life of mine by mining deeper, thereby increasing the mine’s water reticulation requirements for ventilation, cooling and processing. These operations will increase the water demand.
- Increased regulations regarding the control and monitoring of water during the entire mine life cycle
These emerging trends present the mining sector with several risks:
- Water supply uncertainty resulting from environmental factors and climate variability contributes to the complexity of a sustainable mine water management system.
- For mines in dry climates, the key issue is a deficit in the water supply where water management should focus on conservation, such as collecting, storing and reusing contact water from the tailing’s storage facilities, seepage, open pit, and/or underground mine water.
- For wet regions, the greatest challenge is managing flood events and eliminating the risks of spilling, erosion and infrastructure failure. Mines in cold climate regions must consider the large quantity of water generated from snowmelt and ice thaw and manage the impacts of permafrost on drainage facilities. Each mine site requires a tailored and holistic mine water management solution.
- Risks influenced by local water resource management and governance effectiveness in dealing with factors such as increasing demand, increasing pollution being disposed into water bodies and increasing non-compliance of water quality
- Compliance issues related to downstream discharge impacts and increasing environmental regulations
- The immediate risk of non-availability of water supply by local water boards and utilities
- Challenges associated with local infrastructure adequacy
The development and implementation of a high-level mine water management framework, or stewardship, that minimises the mine’s dependency on the local water grid can fulfil several functions
It can provide the foundation for proactive planning and action to avoid work stoppages and incidents that could threaten operational continuity and mine viability and prevent liability to downstream water users.
A ‘circular’ mine water management framework
An effective mine water management framework provides an opportunity to implement a circular water economy within the environs of the mine. In contrast to the linear economy, a “take-make-dispose” model, the circular water economy promotes the reduction of water consumption, reuse of water and recovery of minerals from wastewater.
Platinum group metals (PGM) mines on the Eastern Limb of the Bushveld Complex in South Africa had a water balance where typically 1 000 litres of water was required per tonne of ore mined (2008). The ideal was to achieve 200 litres of water per tonne mined – not an easy feat.
In a typical mining operation, some 35%-45% of the water discharged to the tailings dam is reused in the process plant, while 25% of the water typically remains in the tailings dam. Some 5% of a mine’s total water usage is due to seepage losses from tailings dams and other process water infrastructure. In comparison, up to 35% of the mine’s water intake can be lost to evaporation.
Understanding the mine’s water balance and water-related risks provides opportunities for innovative mine water management strategies to transition the mine’s water reticulation to a circular water economy. Strategies may include:
1. Raw water pretreatment
This may incorporate a range of filtration technologies, from the basic removal of suspended solids to more specialised membrane filtration technologies that reduce total dissolved solids, including heavy metals. Raw water pretreatment optimises water stability minimising corrosion and scale, thereby protecting the mine water infrastructure. Disinfection may be required to maintain water safety.
2. Waste water treatment
Compliance with environmental regulations and protecting communities downstream from the mine requires flocculation and (frequently) pH adjustment to remove suspended solids and heavy metals such as nickel, uranium, lead and mercury. Acid mine drainage, a significant environmental risk, is typically treated this way before discharge to the natural waterways.
3. Water re-use
Excess surface and underground mine water and mine process water may be repurposed or recycled back into the mine water reticulation system after treatment through a multi-stage water plant to return the water to a quality that is fit for purpose.
Retreated mine water may be recycled to the cooling water system, returned for mine processing or treated to SANS and WHO quality potable drinking water for the local mining community. Re-using mine water reduces the mine’s water consumption and dependence on the public water reticulation system.
4. Mineral Recovery
A key component of the mine water reticulation system is (underground) settlers used to remove suspended solids originating from blasting, cleaning stopes, and backfill operations. The fines removed by settling are typically enriched with precious metals and are therefore a valuable product that needs to be delivered to the beneficiation plant.
The moisture content of the fines is too high to transfer directly from the settler to the beneficiation plant. Therefore, it is stored in underground and surface mud storage dams for further settling and mud dewatering. Unique, innovative integrated mine water management systems treat the water and fines from the settlers to improve the recovery of minerals and water quality. Such systems integrate high flow grit removal, automated flocculant treatment and high rate settling of the mine water.
The benefits of a sustainable mine water management plan outweigh the environmental, safety and operational risks and potential costs associated with water scarcity, water excess, water infrastructure failure and unsafe water quality.