How Gold is Separated from Impurities
When mining for gold, it is fairly common to find that the gold is mixed in with silver deposits. When both are joined in the ore, a process known as gold parting must be carried out to separate the precious metals. In centuries past salt cementation was used to achieve this result. As the name suggests, this gold refining process involved the use of common salt. It helped to create the necessary hydrochloric acid and chlorine that would react with the silver in the ore. The resulting silver chloride would be removed leaving behind purer gold. Today however chemicals such as sulphur are used. Gold does not react with sulphur, but silver does, creating a sulphide. This option tended to produce faster results and high concentrations of pure gold.
Another option was acid parting. Nitric acid was the typical choice and upon distillation to increase its strength, could dissolve silver leaving behind solid gold. It would however require that the ore be broken down to fine particles for the best result. The aqua regia process involved the use of a combination of hydrochloric and nitric acid. Gold would react and turn into a soluble chloride, while silver an insoluble chloride. Filtration was used to separate the two precious metals.
The miller process is a more modern option in gold parting that uses chlorine gas to turn impurities in the ore into soluble salts that are skimmed off the surface of the mixture. A more recent process involves the use of electroparting. Here an electrolytic cell is use to melt all the metals in the ore except gold and platinum. It is a faster process that yields the highest purity of gold at a very fast rate. Another highly efficient process is the wohlwill process that uses cathodes and acids. The dissolved gold plates itself of the cathode while impurities like silver form an insoluble chloride.
When mining for gold, it is fairly common to find that the gold is mixed in with silver deposits. When both are joined in the ore, a process known as gold parting must be carried out to separate the precious metals. In centuries past salt cementation was used to achieve this result. As the name suggests, this gold refining process involved the use of common salt. It helped to create the necessary hydrochloric acid and chlorine that would react with the silver in the ore. The resulting silver chloride would be removed leaving behind purer gold. Today however chemicals such as sulphur are used. Gold does not react with sulphur, but silver does, creating a sulphide. This option tended to produce faster results and high concentrations of pure gold.
Another option was acid parting. Nitric acid was the typical choice and upon distillation to increase its strength, could dissolve silver leaving behind solid gold. It would however require that the ore be broken down to fine particles for the best result. The aqua regia process involved the use of a combination of hydrochloric and nitric acid. Gold would react and turn into a soluble chloride, while silver an insoluble chloride. Filtration was used to separate the two precious metals.
The miller process is a more modern option in gold parting that uses chlorine gas to turn impurities in the ore into soluble salts that are skimmed off the surface of the mixture. A more recent process involves the use of electroparting. Here an electrolytic cell is use to melt all the metals in the ore except gold and platinum. It is a faster process that yields the highest purity of gold at a very fast rate. Another highly efficient process is the wohlwill process that uses cathodes and acids. The dissolved gold plates itself of the cathode while impurities like silver form an insoluble chloride.