|An electrolytic cell used in the commercial refining of gold using the electro-chemical process.|
Monday, February 6, 2012
Refining Gold using Electrochemical Processes
This is a continuation of the previous article about the recovery of gold from concentrated stream heavies. In this article we will examine the WolhwillProcess that was originally invented in 1874 and is still in use today. This process is used to produce gold that is 99.999% pure. As an industrial-scale technique the Wohlwill process that was invented by Emil Wohlwill for refining gold using methods developed for electrochemistry.
The process makes use of a bar cast from impure gold that has been separated from concentrate like that in the first part of the process we explained in an earlier article. This is done by pouring the gold and other metals into a crucible, melting then and pouring them into a mold producing what is called a “dore” bar composed of gold, silver and PGM. If the amount of gold present in the dore bar is less then 95% it will be necessary to add enough pure gold to bring its content up to that level otherwise the other metals will be carried over in the finished product making the gold less then 99.999 fine. The Dore bar acts as an anode in the process.
The cathode in this reaction is made from thin sheets of 24k gold that are spaced on each side of the Dore bar that acts as the anode. Providing the anode is composed of more then 95% gold the remaining metals in the cathode will be deposited in the bottom of the electrolytical cell as anode sludge that can be recovered and the values of silver and PGM recovered in a later process.
The gold along with the other metals are dissolved at the anode when current is delivered to the cell with pure gold coming through the chloauric from ion transfer where it is plated as pure gold at the cathode. After the anode is completely dissolved the cathode is removed and melted down or processed for making the end product that is usually gold bullion pure gold like this is too soft for most other uses.
At 99.999 fine this gold is too soft for most purposes other then bullion so it must be alloyed with other metals most commonly silver although in some cases copper is also used. For making jewelry the most common karats used are 14 and 18 k. This is done by remelting the bullion and forming it into the shapes desired.
There are plenty of gold refiners that will refine the concentrate into pure gold, but they often keep the platinum values as part of the refining fee.