Gold does not exist in nature in the same form that it is in jewellery that we buy. It often occurs as grains, flakes, masses or veinlets in rocks. After gold ores are excavated from the surface of the earth, they are ground to extract the metal. But the metal, at this stage, is not yet in its pure form as it still contains a variety of impurities, including copper, zinc, iron and silver. To eliminate these impurities, gold should undergo the purification process.
There are various methods used to purify or refine gold and they can be categorized into three: through the use of acid, use of fire, and use of electricity. These methods, however, vary in terms of complexity of the process, level of purification, and the costs involved.
Gold Purification Using Acid
Using acid for purifying gold is the most common and simplest approach to removing any impurities from this precious metal.
Two common types of acid used for refining gold are hydrochloric acid and nitric acid. These two acids are mixed in a beaker to create the purifying solution. Then, they are filtered before gold is added into the mixture. Upon contact with the solution, any other substances present in the ore and some other impurities are removed.
Gold Purification Using Fire
The use of fire or subjecting gold in a heating process is another common method of refining gold.
This process will require a clay crucible, filter, and burning furnace that can produce a heat of up to 2,000 degrees Fahrenheit. Gold, then, must be placed in borax that is able to withstand the heat level. Gold must be heated until it is smooth before it is transferred onto another container to cool. After the metal has cooled, the resulting product is free of any impurities or other metal substances.
Gold Purification Using Electricity
The use of electricity is one of the latest methods used for purifying gold. This process is commonly referred to as the Wohlwill process. Using this method, the impure gold is placed in a solution made up of gold chloride and hydrochloric acid. Then, electric current is passed through that solution to remove the impurities from the gold. The impurities will then settle onto the bottom of the container.
Among all the methods of purifying gold, the Wohlwill process is considered to be the best as it produces 99.99 percent of pure gold compared to that of the other methods that is only 99.5 percent gold. The only drawback to this method is that it usually comes with a huge cost.