Tailings are the waste materials left after the target mineral is extracted from ore. They consist of:
- Crushed rock
- Trace quantities of metals such as copper, mercury, cadmium, zinc, etc.
- Additives used in processing, such as petroleum byproducts, sulfuric acid and cyanide.
Types of tailings disposal
Tailings, often in the form of a wet slurry, are typically stored in impoundments behind earthen dams, but disposal methods vary, including:
- Backfilling – the tailings are usually combined with a binder like cement, then used to fill voids in the underground operation. This is widely considered the safest form of tailings disposal.
- Dry stacking – the tailings are dewatered, or “filtered”, after mill processing. The resulting tailings are mostly dry and can be stacked in piles and compacted.
As of 2013, the National Inventory of Dams listed 839 tailings dams in the U.S. and a 2010 study reported more than 18,400.
Tailings impoundment failures are increasing in frequency and severity
In August 2014, a tailings dam breach at the Mount Polley Mine in British Columbia released 5 million cubic meters of toxic waste into nearby creeks and a lake. The failure was so violent that it ripped mature trees from the forests and sent them miles downriver into Quesnel Lake.
The following year, in Brazil the Samarco Mine’s tailings dam failed catastrophically, killing 19 people downstream and sending mine waste down the Rio Doce river over 300 miles to the Atlantic Ocean.
Unfortunately, these two recent failures are not aberrations. Research of all serious tailings failures since 1915 shows:
- The rate of serious tailings dam failures is increasing.Half (33 of 67) of serious tailings dam failures in the last 70 years occurred in the 20 years between 1990 and 2009.
- The increasing rate of tailings dam failures is propelled by, not in spite of, modern mining practices.The increasing rate of tailings dam failures is directly related to the increasing number of TSFs larger than 5 million cubic meter capacity necessitated to allow the economic extraction of lower grades of ore.
- 11 catastrophic failures are predicted globally from 2010 to 2019.Predicted total cost of these 11 failures is approximately $6 billion.
Wet tailings disposal is inherently risky
After the Mount Polley failure, the mining industry-friendly British Columbia provincial government commissioned an independent investigation panel comprised of industry consultants/academics. The panel shocked the mining industry world by recommending industry stop using wet tailings disposal — the industry standard method — because it inherently risks tailings impoundment failures.
To date, no government, including British Columbia’s, has acted on the expert panel’s recommendations to end wet tailings disposal.
Aqueous tailings dumping is not the solution
In some cases, companies dump tailings into rivers, lakes and oceans. This type of disposal should be banned because:
- Tailings can contaminate aquatic life with toxic heavy metals and milling chemicals
- Some metals, particularly mercury, may bioaccumulate up the food chain, ultimately harming humans.
- It causes turbidity (murkiness from suspended particles) and reduces oxygen levels which directly impacts aquatic life.
- We simply don’t understand mine waste’s impacts on aquatic ecosystems, and it’s more difficult to control the release of contaminants.
In 2012, Earthworks and MiningWatch Canada released a report, Troubled Waters, which found that each year, mining companies dump over 180 million tonnes of these hazardous mine wastes into water bodies — more than 1.5 times the amount of waste that US cities send to landfills each year.
Emphasis should be placed on reducing, recycling, and re-using metals rather than risky and irresponsible types of mine waste disposal.