Electrowinning is a process that removes metal ions from liquid solutions, often used to recover precious metals. It relies on an electronic current to plate metal ions onto a cathode. The efficiency depends on metal concentration, cathode surface area, and metal type. It cannot be used in solutions with less than 1,000 mg of metal ions per litre or chlorine ions.
Electrowinning is a process used to remove metal ions from liquid solutions such as rinse water, plating baths and used process solutions. Most often used to recover precious metals, it relies on an electronic current to plate metal ions onto a cathode. The recovered metals can then be sold for scrap or processed for use in plating. The solution can also be recycled with less stress on water treatment systems.
An electrolytic extraction unit consists of a large tank known as a reaction chamber. This chamber houses at least a number of cathodes, which are negatively charged electrodes, and anodes, which are positively charged electrodes. When the unit is turned on, direct current (DC) flows from the cathode to the anode through the liquid solution. The flow of electricity causes the metals in the solution to electroplate on the cathode in a process similar to electroplating.
The electrolysis process used in electron mining allows the elemental metal to be recovered. This distinguishes electrowin from other recovery technologies, such as evaporation and ion exchange, which result in little more than a more concentrated metal-containing solution. Despite this, the recovered metal is usually not yet pure enough to be used in plating if it is not processed. As a result, it is often sold for scrap. Some companies use this salvage technique as a way to create extra income by selling the scrap metal.
The efficiency of the electrowinning process depends on the metal concentration in the solution. It becomes progressively less efficient as more metal is removed. The surface area of the cathode also affects the efficiency. The larger the surface area, the higher the efficiency, which is why electrolytic extraction units have been designed that use large rectangular plates or mesh grids as cathodes.
The last variable affecting efficiency is the type of metal being recovered. The metals most commonly recovered from electronic mining include copper, silver and gold. Cadmium, zinc and even nickel can also be recovered using this process. Nickel is less common because the solution must be carefully controlled by pH throughout the process for it to be effective.
While electrowinning is a useful process, it has some drawbacks. It becomes very inefficient if the solution has less than 1,000 mg of metal ions per litre. It also cannot be used in solutions that contain chlorine ions, such as hydrochloric acid, because the electrolysis of chlorine ions can cause chlorine gas, which is extremely dangerous.
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