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What Is Electrowinning?

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  • Written By: Emma G.
  • Edited By: Melissa Wiley
  • Last Modified Date: 19 August 2014
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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 the metal ions onto a cathode. 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 electrowinning unit consists of a large tank known as a reaction chamber. This chamber houses at least one set 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 metals in the solution to plate onto the cathode in a process similar to electroplating.

The electrolysis process used in electrowinning allows the elemental metal to be recovered. This sets electrowinning apart from other recovery technologies, such as evaporation and ion exchange, which result in little more than a more concentrated metal-bearing solution. Despite this, the metal recovered is usually still not pure enough to be used in plating if left unprocessed. As a result, it is often sold as scrap. Some companies use this recovery technique as a way of creating extra income by selling the scrap metals.

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The efficiency of the electrowinning process depends on the concentration of metal in the solution. It becomes progressively less efficient as more metal is removed. The surface area of the cathode also affects efficiency. The greater the surface area, the greater the efficiency, which is why electrowinning units have been designed that use large rectangular plates or mesh grids as cathodes.

The final variable that affects efficiency is the type of metal being recovered. Metals most commonly recovered by electrowinning include copper, silver, and gold. Cadmium, zinc, and even nickel can also be recovered using this process. Nickel is least common because the solution must be carefully ph-controlled throughout the process in order for it to be effective.

Although electrowinning is a useful process, it does have some drawbacks. It becomes very inefficient if the solution has less than 1,000 mg of metal ions per liter. Also, it cannot be used in solutions that contain chlorine ions, such as hydrochloric acid, because electrolysis of chlorine ions can result in chlorine gas, which is extremely hazardous.

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anon286931
Post 4

Can you please tell me where electrowinning is used, and what the chemical equation is, for that use?

David09
Post 2

@NathanG - I agree. This is strictly an industrial process, not for the do-it-yourselfer looking to find gold.

I’m thinking that it’s got to be a very large scale industrial process as well. If the end result of all of this electrorefining is to sell the stuff as scrap metal, then they are going to be filtering through massive volumes of liquid solution in order to get what they want.

I suppose they run tests first to determine the concentration levels of the metals in the solution, so that they can have a fair idea if the process is even worthwhile.

NathanG
Post 1

I’ve heard of people panning for gold, but I don’t suppose that gold electrowinning is for the average gold hunter. It appears from the explanation given here that this is a very detailed process involving technical equipment, and very small amounts of metal recovered in the process.

I can see how companies would do this but not anyone else. The rest of us will have to dip in the water and reach for stuff that can be felt with our bare hands – or stuff that can be detected with a metal detector at the very least.

Still, I like the electrowinning process because it seems that it filters out precious metals that perhaps could not be retrieved any other way.

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