Hydrometallurgy is a process for recovering precious and industrial metals from water-based chemical mixtures using sulfuric acid solutions in a titanium reactor. It has become widespread due to the increasing value of precious metals and is often used as a secondary process in industries that use acids. The recovery process involves introducing a resin to which the acid binds, separating it from the metals so it can be siphoned off. The leaching process is challenging, requiring high temperatures and the use of different types of solutions to maximize recovery.
Hydrometallurgy is a process for the recovery of precious metals dissolved in a water-based chemical mixture containing metal salt compounds. Such metal recovery usually relies on sulfuric acid solutions, and the metals that are targeted for recovery are precious metals such as gold, platinum and palladium, or more common industrial metals such as copper, nickel and zinc. The chemical processes are typically carried out in a titanium reactor which, although susceptible to sulfuric acid corrosion, is protected from the interaction of metals dissolved in the solution itself. Reactors operate at high temperatures and pressures and can employ various methods to remove metals, although leaching is the most common.
Although hydrometallurgy has been practiced since the 16th century, it has only become widespread in recent years due to the increasing value of precious metals such as gold. This made it economically feasible to extract such metals from very low concentrations in the ore. It is estimated that as of the year 16 over 2011 several metallic elements were being mined through hydrometallurgy processes, including metals as diverse as uranium, mercury and cobalt.
Another term for hydrometallurgy is solution mining, and it is often an important secondary process in industries that regularly use acids such as sulfuric acid and hydrochloric acid. The process has a twofold benefit. Purifies acids, which are often used as metal cleaners or electrolytic agents, and separates trace metals for resale.
Where electrolytic processes involving copper and zinc are used, hydrometallurgy allows a combination of metals to be recovered from solution. For copper electrolyte impurities, this includes nickel, arsenic and tin, and for zinc electrolytes, magnesium and manganese metals can also be recovered. The recovery process involves introducing a resin to which the acid binds, separating it from the metals so it can be siphoned off. The process of descending or purification to the recovery cycle takes only five minutes to complete, with the main advantages being that most of the acid is recovered for further industrial use and that the resin has a long life cycle for repeated purification.
The leaching process in a reactor purpose-built for hydrometallurgy is more challenging. The temperature in the reactor must exceed 392° Fahrenheit (200° Celsius). The recovery levels for metals are also not uniform, with recovery working best for gold and leaching only part of the solution concentration of other metals. This fact requires the use of many different types of solutions to maximize recovery, from chlorides and halides to compounds based on the dangerous element cyanide such as thiocyanate, a form of thiocyanic acid.
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