Tailings (or slurry) is the collected waste materials produced after the extraction of minerals and metals from mined ore. It’s a substance that consists largely of powdered rock and water.
From the mill, the tailings is often pumped to surface storage facilities which are commonly constructed using earth dams. These range in size from a swimming-pool to areas over 1,000 hectares. As the sandy residue of tailings gradually drains and becomes compact and dry, grass and other vegetation is planted to stabilise the environment. This is called the reclamation process.
Before the water in the tailings can be used again, or discharged into the local drainage system, it must be treated to remove harmful substances that would pollute the environment or risk the health and safety of local communities near the facility.
If not managed properly, tailings can have a damaging impact on the environment and human health and safety, with pollution from effluent and dust emissions being potentially toxic to humans, animals or plants. This harm is multiplied many times over should a tailings storage facility physically fail. Flooding from tailings materials can greatly damage the surrounding environment and even lead to loss of human life.
Mine closure and post-closure
The management of tailings, both during and after mining, is the responsibility of mining companies and is subject to advanced regulatory regimes. This means that tailings management needs to be effective throughout the life of an operation, from initial feasibility through to closure and post-closure.
The type of after-care can vary greatly depending on the nature of the tailings. In cases where tailings doesn’t contain harmful substances, water is drained from the tailings storage facility to safeguard its physical stability, and then re-shaped, covered with soil and vegetated. In other instances, longer-term measures may need to be put in place to safeguard the physical stability, chemical stability and subsequent land use of the tailings storage facilities.
Critical control management
The mining and metals industry is working towards the elimination of fatalities and catastrophic events. The sound management of tailings storage facilities is therefore an integral part of company operational and risk management strategies.
Critical control management has been identified as an approach to managing low probability, high impact events such as catastrophic failures of tailings storage facilities. Find out more about critical control management.
ICMM commitment on tailings management
Catastrophic tailings dam failures at Mount Polley (Canada) in 2014, Samarco (Brazil) in 2015 and Brumadinho (Brazil) in 2019 have shown that risk management cannot be taken for granted.
ICMM undertook a review on tailings storage facility management in 2016. The review was global in scope and looked at how best to effectively maintain the safety of tailings dams. The review found that a greater focus on governance is needed to assure that the extensive existing technical and management guidance is effectively applied.
ICMM concluded that a position statement, with full CEO commitment is the most effective way it can collectively address tailings dam safety. The position statement, issued in December 2016 commits members to minimise the risk of catastrophic failures of tailings dams by adopting six key elements of management and governance.