Water worries

From the late 1990s it became clear that water would become a major issue for mining in the 21st Century. Competing demands and growing populations will limit access to fresh water and in many places, climate change will reduce the water available. Extreme weather events will overtop dams.

Although mining accounts for only one percent of water consumption in the USA for example, social and political pressure on miners is growing. Governments are limiting access to water and demanding that discharges are cleaned up. In extreme cases, water is the lubricant for catastrophic tailings dam failures. There have been many spills and leakages in recent years. It seems that engineering knowledge, management practices, or both, are not up to the task.

Kinross Gold’s Maricunga gold mine in Chile was shut down last August. A court upheld the regulator’s decision to shut down the water system, and Kinross said it would lay off approximately 300 employees. Many other mines, including Chilean copper mines, are building desalination and reverse osmosis plants. These will make new water sources available and clean up discharges that would otherwise enter waterways or the water table. Some plants elsewhere, built as insurance against unpredictable mine inflows, have never been turned on.

The final cost of the Samarco tailings dam failure in November 2015 is still unknown. We do not know whether the mine can be restarted. This will depend on stakeholders and the Brazilian regulators. Vale has announced that by 2025 it will change many mines to dry processing. It will reduce both the use of dams and the amount of tailings it creates by 700 million metric tons. It expects a large net gain, approximately $2 billion, from this strategy. If this is true, how many other mines could benefit?

Initiatives such as selective mining and ore sorting can greatly reduce the need to deposit wet tailings. Some processing methods are much more water-efficient than others. Some processes can be tuned to use saline groundwater or seawater. The Argyle diamond mine in northern Australia reduced its water consumption substantially by capturing and recycling water used by the processing plant, capturing seepage from tailings and maximizing use of mine drainage water. Vale’s S11D iron ore project in Brazil uses the humidity in the ore itself to remove impurities, reducing water consumption by 93%. Minera Esperanza’s copper and gold mine in Chile uses untreated seawater. A supply pipe transports seawater 145 km from the Pacific coast to the mine site.

A growing public demand for better water management will bring about changes. Whether these come at a cost, or bring an economic benefit to mining companies, will depend on their ability to innovate. Innovation should begin at the feasibility study and continue through to mine closure.