Silver Refining Methods

The Parkes Process

• The Parkes Process is used to extract silver from lead concentrates. In the Parkes Process, lead concentrates are roasted and smelted to obtain a lead juice. Zinc is added to the lead mixture, which quickly reacts with valuable metals such as gold and silver, forming insoluble compounds that float on top of the mixture. The zinc is then extracted by vacuum resorting, and the remaining lead mixture goes through another process called "cupellation" to extract remaining silver and gold content.

Cupellation

• The mixture of lead and silver is put together into a cupel, and introduced into an oven, where it is heated to 1,200 degrees Celsius. Heat causes the lead to solidify into a glassy "calx", which dissolves all the imperfect metals, and pure silver results. Cupellation can also be used for mixtures of lead with other valuable metals, but the valuable metals will be composite, and will need to be separated from each other through additional processes.

Silver Refining from Zinc Compounds

• Zinc concentrates need to go through two phases for silver to be extracted. They are roasted, then leached with sulfuric acid, which dissolves most of the zinc content. The result is a lead concentration of lead, silver and a small concentration of zinc. The whole mixture is melted, and powdered coal is blown over it, vaporizing the zinc from the mixture. The Parkes Process or cupellation is then used to extract pure silver from the mixture.

Electro-Refining Method

• Pure silver can be also extracted from sulfated copper slime by using electricity. The process regulates the concentration of sulfate ions which contains the silver, separating it. This method is more modern and required sophisticated laboratory technologies to be carried out properly.