Tailings
Because of this comminution, tailings consist of a slurry of fine particles, ranging from the size of a grain of sand to a few micrometres.
[4] These tailings contain large amounts of pyrite (FeS2) and Iron(II) sulfide (FeS), which are rejected from the sought-after ores of copper and nickel, as well as coal.
Although harmless underground, these minerals are reactive toward air in the presence of microorganisms, which if not properly managed lead to acid mine drainage.
[5] In addition to being useless and abundant, phosphogypsum is radioactive due to the presence of naturally occurring uranium, thorium, and their daughter isotopes.
Making provision for the approximately 70 million tonnes (150 billion pounds) that is produced annually is one of the most significant problems for the aluminium mining industry.
As a result, significant effort is being invested in finding better methods for safe storage and dealing with it such as waste valorization in order to create useful materials for cement and concrete.
Piles of coal refuse can have significant negative environmental consequences, including the leaching of iron, manganese, and aluminum residues into waterways and acid mine drainage.
[13][14] Early mining operations often did not take adequate steps to make tailings areas environmentally safe after closure.
For example, the Province of Quebec, Canada, requires not only the submission of a closure plan before the start of mining activity, but also the deposit of a financial guarantee equal to 100% of the estimated rehabilitation costs.
[20] The rejected minerals and rocks liberated through mining and processing have the potential to damage the environment by releasing toxic metals (arsenic and mercury being two major culprits), by acid drainage (usually by microbial action on sulfide ores), or by damaging aquatic wildlife that rely on clear water (vs suspensions).
[22] Other disasters caused by tailings dam failures are, the 2000 Baia Mare cyanide spill and the Ajka alumina plant accident.
In 2015, the iron ore tailings dam failure at the Germano mine complex in Minas Gerais, Brazil, was the country's biggest environmental disaster.
The dam breach caused the death of 19 people due to flooding of tailings slime downstream and affected some 400 km of the Doce river system with toxic effluence and out into the Atlantic Ocean.
[18] The ponded water is of some benefit as it minimizes fine tailings from being transported by wind into populated areas where the toxic chemicals could be potentially hazardous to human health; however, it is also harmful to the environment.
Tailings ponds are used to store the waste made from separating minerals from rocks, or the slurry produced from tar sands mining.
Tailings are sometimes mixed with other materials such as bentonite to form a thicker slurry that slows the release of impacted water to the environment.
Paste tailings are used in several locations around the world including Sunrise Dam in Western Australia and Bulyanhulu Gold Mine in Tanzania.
A common modern approach is to mix a certain quantity of tailings with waste aggregate and cement, creating a product that can be used to backfill underground voids and stopes.
HDPF is a more expensive method of tailings disposal than pond storage, however it has many other benefits as it can significantly increase the stability of underground excavations by providing a means for ground stress to be transmitted across voids – rather than having to pass around them – which can cause mining induced seismic events like that suffered previously at the Beaconsfield Mine Disaster.
When STD is used, the depth of discharge is often comparatively shallow, and extensive damage to the seafloor can result due to covering by the tailings product.
[22] Phytostabilisation is a form of phytoremediation that uses hyperaccumulator plants for long-term stabilisation and containment of tailings, by sequestering pollutants in soil near the roots.
Foght et al (1985) estimated that there are 103 anaerobic heterotrophs and 104 sulfate-reducing prokaryotes per milliliter in the tailings pond, based on conventional most probable number methods.
[30] Siddique (2006, 2007) states that methanogens in the tailings pond live and reproduce by anaerobic degradation, which will lower the molecular weight from naphtha to aliphatic, aromatic hydrocarbons, carbon dioxide and methane.
Moreover, these methanogens change the structure of the tailings pond and help the pore water efflux to be reused for processing oil sands.
[33] The UN and business communities developed an international standard for tailings management in 2020 after the critical failure of the Brumadinho dam disaster.
[3] The program was convened by United Nations Environment Programme (UNEP), International Council on Mining and Metals (ICMM) and the Principles for Responsible Investment.
