Background
Alberta’s Athabasca Oil Sands Region (AOSR) is a high-profile oil producing area within Canada. Exploration began in the 1920s, with pilot plants starting in the mid 1940s, and production commencing in earnest in 1967.
As the name suggests, the oil sands consist of bitumen interbedded with sand at varying depths, but most operations are surface mines. Processing mined ore is labour intensive, and results in a byproduct called tailings, which is a mix of sand, hydrocarbons and metals that were not extracted during processing, and water. Water is used in the extraction process, and thus ends up in the waste stream. Tailings are stored in large facilities (tailings storage facilities [TSFs]), which contain tens of millions of cubic metres of tailings slurry. hundreds of thousands of cubic metres are added per day to these ponds, and this has been going on since the onset of production. To date, approximately 1.4 Bn m3 are stored across the AOSR..
Why Are Tailings Stored?
As mentioned, tailings are a byproduct of oil sands mining, but they are not unique to the oil sands. Simply, tailings is ore that’s been crushed to roughly sand sized fragments for the purpose of extracting metals, oil, or other valuable products contained in the rock.
In the oil sands, Crushed oil sands are mixed with warm water so they can be pumped through hydrotransport pipelines from the mine/crusher to the extraction plant. Hot water is then used to separate the bitumen from the sand. Once liberated, the hydrophobic bitumen attaches to air bubbles and floats, while the much denser sand settles. The bitumen forms a froth at the surface that can be recovered. After bitumen recovery, you’ve now got a massive quantity of water + sand + silt/clay + residual bitumen that has to go somewhere. Much of the water is subsequently recovered from the tailings system and recycled back into extraction, but some water is still retained in the tailings to allow for transportation to the TSF.
https://www.cbc.ca/news/canada/north/tailings-release-health-1.7635669