Hans Emil Wohlwill, a German engineer, invented the Wohlwill Process in 1874. Unlike the Miller Process, which is known among refineries as a relatively cheap and easy way to produce high-purity gold (in the 99.95% purity range), the Wohlwill Process is complex and expensive. But when done correctly, it can produce gold samples of 99.999% purity.
The Wohlwill Process has three main components:
- The anode – an electrode through which electric current flows into a polarized electrical device
- The cathode – an electrode through which electric current flows out of a polarized electrical device
- The electrolyte – an electrically conductive substance (standing in for a polarized electrical device)
Each of these components contains gold. The anode is made of somewhat impure gold – about 95% purity or higher (lower purity will reduce the efficiency of the procedure). The cathode is made out of pressed 24k gold sheets. The electrolyte is pure chloroauric acid, made by dissolving gold in a powerful acid called aqua regia.
With these components properly set up, an electric current is applied. Electricity travels from the anode, through the conductive electrolyte, and into the cathode. When this occurs, the gold in the impure anode dissolves and its ions travel though the chloroauric acid, then electroplate or “stick” to the 24k gold cathode. This continues until the anode completely dissolves. The ultra-pure gold that collected on the cathode is melted down to whatever specification the application demands.
This is a very expensive procedure – especially because it takes gold to make gold. To perform the Wohlwill Process, a refiner must have enough gold for anodes and cathodes. They also must have large amounts of gold on hand to convert to chloroauric acid (fortunately, this process is reversible). Because of the complexity and cost of the Wohlwill Process, it’s used only for specific applications. Instead, most refiners prefer to use the Miller Process to create high-purity gold.