55 no cabe duda sobre cuál es la dirección más conveniente; y temo que en este momento

In general, Schüler et al. (2011) mention the first stage of mining and ore crushing produces waste rocks that are placed in storage. The second stage, flotation, uses water, chemicals and energy. The input into flotation is the milled crude ore with low concentrations of rare earth oxide, ranging between 1–10 per cent, but the output possesses a higher concentration of REEs, around 30–70 per cent. The flotation process produces a huge waste stream, a mixture of water, chemicals and finely ground minerals called tailings. Lastly, the concentrate is further processed. Each process during production produces different effects and risks depending on the level of environmental protection systems.

The first problem associated with this method of mining relates to the tailings (Figure 2.1), which pose short and long term risks for workers, society and the environment. Tailings contain small particles, flotation chemicals and waste water that remain in the impoundment areas. Mostly, the elements in the tailings consist of radioactive materials, acids, sulphides, fluorides and heavy metals. The rare earth deposit per se contains uranium, thorium, some hazardous products and very few radioactive-free substances. They are exposed to rain water, and continued exposure pollutes ground water if the ground is not leak-proof. In addition, if the impoundment areas are unable to store this water after heavy rains, it will cause pollution in the surrounding water and soil as well. The worst case scenario might happen if the dam collapses (due to poor construction or overtopping from the heavy rainfall) and the toxic waste spreads to a wider area, leading to an ecological disaster.

The second problem is associated with waste rock stockpiles. These stockpiles are also exposed to rain water, and the toxic substances can be washed out into the surroundings unless proper water management and treatment processes are installed. However, the risk with these rocks is lower than in the case of tailings, as the former consists of coarse minerals while the latter consists of finely milled particles.

Thirdly, after the mine is abandoned, open pits might bring environmental harm. This poses similar dangers as it is exposed to the rainwater and may affect the environment in the same way as described above. Also, without proper measurement and monitoring processes, air emissions from mining operations, the milling, transportation and storage, waste rock stockpile or tailings can cause harm to employees and the neighbourhood.

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People will be exposed to wind-blown dust particles that contain toxic and radioactive substances.

Another environmental risk is related to the use of land during and after a mine closure. The land areas that are polluted include the mine, tailings, waste rock stockpiles and the surrounding areas. Moreover, the production process consumes water, which is also a problem. Furthermore, another grave concern is waste disposal. In most cases, the REEs contain thorium or/and uranium. Thus, REEs will pose a danger to the environment and neighbourhood if it is not properly stored and managed.

Figure 2.1 Potential risks of rare earth mining

Source: Schüler et al., 2011, p. 44.

In addition to the above-mentioned general problems associated with mining and processing, the magnitude of danger also depends on the specific type of mining method and the chemicals used in operations. According to the Massachusetts Institute of Technology (2010b), there are five types of mining methods: open-pit/open cast, underground, in situ leach (ISL), heap leaching and brine mining. Open pit mining is well known for its damaging effects on large areas of land. This is because rare earth minerals are available in small concentrations, so large amounts of ore need to be mined. In the crushing phase, hard rock releases radioactive elements, asbestos and metallic dust. Due

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to the low concentration of REEs, various chemicals need to be used to separate these elements (Burgueño, 2013), resulting in polluted tailings.

Underground mining faces the possibility of tunnel collapse, land subsidence and surface damage. The use of hydraulic pumps and suction dredges in operations can increase sedimentation in nearby rivers. In contrast, ISL involves minimal surface destruction, no tailings/waste rocks, no ore dust/direct exposure to the environment, as well as low water consumption. This is because this method simply dissolves the ore body and pumps it out. However, acids are used to dissolve the ore body and the fluids remaining after the leaching process pose a risk to ground and water resources.

With heap leaching mining, the concern is to ensure that the processed solutions remain within the heap leaching circuit. Having a water balance is important, as overflow of solutions containing toxic substances due to factors such as heavy rainfall or snow melting will affect the ecosystem. Sometimes, cyanide is used to extract metals from oxidized ores and the detrimental effect of cyanide on the environment is well documented. Meanwhile, brine mining poses a risk to the environment through its process of drilling, extracting and evaporating the brine solution to remove harmful elements or compounds. Casings, pipelines and storage tanks are vulnerable to corrosion due to high saline content in the solution, which may lead to water contamination.

In brief, it can be concluded that the safety of operations does not only depend on the high-technological machines employed in the production but also on proper management and monitoring from the authorities.

2.11 HEALTH EFFECTS ASSOCIATED WITH REEs PRODUCTION: THE