Tailings
- Also known as
- mine tailings, tails, tailings storage facility
Tailings are the waste left after the valuable minerals have been extracted from ore: a slurry of finely ground rock, water and residual process chemicals. They are stored in engineered facilities, most often behind dams, and increasingly dewatered before storage.
What are tailings?
When ore is processed, only a small part of it is the valuable mineral. The rest, the gangue, has been crushed and ground, often to the consistency of sand or silt, and leaves the plant mixed with water as a slurry. That waste stream is tailings. It also carries residual chemicals from processing, and in some ores it contains sulfide minerals that can generate acid when exposed to air and water.
Because most of the ore ends up as tailings, mines produce them in very large volumes over their lives, and safe, long-term storage is one of the industry’s most important responsibilities.
How tailings are stored
- Tailings dams. The most common method stores slurry in a tailings storage facility behind an embankment. Dams are classified by how the embankment is raised over time: upstream, downstream or centerline construction. Upstream construction, which builds on previously deposited tailings, is the least costly but the most vulnerable to failure, and some jurisdictions have restricted or banned it.
- Thickened and paste tailings. Removing more water before deposition produces a denser material that is stored with less free water.
- Filtered, or dry-stacked, tailings. Tailings are filtered to a moist cake that can be stacked and compacted, greatly reducing the risk of a flowing failure and recovering more water.
- In-pit disposal and backfill. Tailings placed in mined-out pits, or mixed with cement and returned underground as backfill.
Tailings safety
Catastrophic failures of tailings dams, including the collapse at Brumadinho, Brazil, in 2019, have caused loss of life and severe environmental damage. In response, the International Council on Mining and Metals, the United Nations Environment Programme and the Principles for Responsible Investment published the Global Industry Standard on Tailings Management in 2020, which sets requirements for the design, construction, monitoring, governance and closure of tailings facilities.
Why tailings dewatering matters
Tailings are mostly water when they leave the plant. Recovering that water:
- Reduces fresh water use, which is critical in dry regions where mines compete for water.
- Improves stability, because less free water in storage reduces failure risk.
- Reduces the size of storage facilities.
- Returns process water to the plant, although recycled water can carry reagents and dissolved ions that affect processing.
Dewatering usually begins in a thickener, where flocculants help fine particles settle so that clear water can overflow for reuse. The clarity of that overflow is measured as turbidity. Filtration may follow for dry stacking.
Tailings and Locus biosurfactants
Locus Mining describes its biosurfactant reagents as improving flocculation, particle settling and water recovery in tailings and dewatering circuits, including thickener underflow density and overflow clarity.
Frequently asked questions
Finely ground rock, mostly the gangue minerals of the ore, mixed with water and small amounts of residual process chemicals. Their exact composition depends on the ore and the process.
They can be. Risks include failure of the storage facility, acid generation from sulfide minerals, and release of metals or process chemicals. Well-designed, monitored and closed facilities manage these risks.
Waste rock is rock mined to reach the ore but never processed; it is coarse and dry. Tailings are what remains after ore has been ground and processed; they are fine and wet.
Sources
- Global Industry Standard on Tailings Management, ICMM, UNEP and PRI, 2020
- Wills' Mineral Processing Technology, 8th edition, B. A. Wills and J. A. Finch, Butterworth-Heinemann, 2016
- Mining waste resources, U.S. Environmental Protection Agency