Unusable but not Useless
The term tailings refers to the residue that’s left after the usable materials have been recovered. It’s impossible, in a practical sense, to remove every single molecule of metal from ore. So, tailings contain remnants with such a low concentration of metal that they’re currently not cost effective to process further. However, improved extraction processes or increased market value of the metal in question has, over time, often reverted this “waste” to a valuable commodity. Especially as virgin mineral deposits are depleted or are found deeper and deeper underground and are increasingly difficult to extract. Therefore, the potential future value must inform decisions on how tailings are best handled and managed.
Depending on the type of ore and the extraction processes that are applied, tailings will be some combination of coarse or finely ground clay, sand and silt. Tailings that have been mixed with water to make a slurry are typically stored in ponds. Tailings can also be dewatered to form dry stacks or thickened to form a substance similar in consistency to toothpaste. Both of these options are suited to their own specific storage practices. There are risks and benefits to each storage method and the ideal solution often depends on a careful weighing of local conditions. It’s worth noting, however, that about 50% of tailings produced today are stored in ponds.
Are Tailings Bad?
Aside from minute amounts of remaining ore, tailings contain residual elements from the extraction processes which can include sulfuric acid, ammonia, cyanide, and naphthenic acids. In addition, some ores contain toxic heavy metals such as arsenic, mercury, lead, or selenium. Other risks come from radioactive uranium tailings and taconite tailings, which are known to contain asbestos fibers. It’s important to recognize that, while the natural state of most of these ores generally present little concern, the process of extracting the ore and concentrating the waste can significantly magnify the toxicity. Clearly, mobilization of any of these potent toxins into the surrounding environment can do significant damage to aquatic life, wildlife, ground and surface water, and even human populations in the area.
Because of their deadly potential, tailings are stored in ponds, stacks or other structures that are expected to safely contain highly toxic materials, often in perpetuity. Since no technology currently exists to eliminate the toxicity of mine tailings, it’s clear that the refuse generated by mining activities presents an enduring threat to soil, water supplies, wildlife and human populations.