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Tank leaching is a process used to extract trace metal from ore. In this technique, ground ore is mixed with a reagent inside a tank to form a slurry, allowing the metal to separate out so factories can recover it. The remaining materials in the tank may be recycled for more processing or disposed of, depending on policies at the facility and the chemicals involved. One concern with tank leaching is that it can generate large amounts of industrial pollutants that need to be handled responsibly to prevent environmental harm.
The first step in this process is preparation of the ore, which needs to be finely ground so it will make a uniform slurry. This increases the efficiency of the recovery process and can reduce the amount of chemicals the facility needs to use for the tank leaching. Once the ore is fully prepared, it can be added to the tank with a chemical agent like cyanide, which is used to process gold. Some tanks use a suspended slurry, while others are agitated; in both cases, a chemical reaction occurs to force the metal to separate from the rest of the ore.
Once trace metal is recovered from the load, there are several options for the remaining slurry. In some cases it can be filtered and processed so the chemicals can be used again, which cuts down on waste, expense, and environmental problems. Other remainders, called tailings, need to be discarded because they cannot be reused, in which case they are stored in a tailings facility until they can be treated. This is important, as the chemicals used can be harsh and they may need to be neutralized for safety.
Both continuous and batch leaching are available to suit the needs of different kinds of facilities. One advantage of leaching is that it can allow companies to recover usable metal from ore that would be expensive or impossible to process in other ways. As a mine reaches the end of its useful life, leaching may extend the usability of ores from the site so the company can extract as much usable material as possible. This also makes investment in sites with low yields more practical, as companies may consider leaching as an option for extracting the metal.
Environmental safety in the mining industry is a concern in a number of nations because mining is often very dirty work. Processes like tank leaching are subject to regulation by the government to ensure companies perform them safely, protecting workers and the environment. Violations can be punished with fines, including requirements to pay the costs for environmental cleanup if tank leaching causes contamination.