Silver is recovery by using an electrolytic process. Basically, silver based alloys higher than 80% silver are treated by this process. The electrolytic process of silver in acid silver nitrate solutions with simultaneous separation of gold as anodic mud has been practiced for more than fifty years. Impure silver is treated in a furnace to remove base metal compounds as impurities through oxidation and finally cast into anodes, which are placed into either Moebius Cells (vertical cells) or Balbach-Thum Cells (horizontal cells) for electrolysis.
Essentially, copper and silver are dissolved into the nitrate electrolyte and insoluble compounds such as gold are collected as slimes in anode bags. All aqueous electrolytes have a lower electrical resistance at higher temperatures, when the conductances of different ions tend to approach a common value under the same potential gradient. In this way, electrolysis is conducted at an elevated temperature, heat being provided from the power dissipated by the internal resistance of the cell. If the electrolyte were left to itself, a slow reduction of silver would result, due to silver and impurities are dissolving at the anode, while silver only is deposited on the cathodeThen, high purity silver crystals are deposited on stainless steel or titanium cathodes, which are periodically scraped manually or mechanically to extract the deposit. The deposit is removed, rinsed and dried before melting. The gold collected in the anode bag is sent to the gold refining process.
Copper is usually the main impurity and its concentration tends to growths in the electrolyte. Copper is eliminated from the solution by bleeding. Normally, in order to recover silver from the spent electrolyte, copper cementation is practiced followed by filtering, and washing of the precipitated. The refined crystals deposited at the cathodes content 99.99% Ag and are washed free of electrolyte, dried under vacuum and melted into 34 kg bars.