Why are silver and gold recovered during electrolytic copper refining?

During the electrolytic refining of copper, precious metals like silver and gold are recovered because they do not dissolve into the electrolyte along with the copper.1

When an electric current is passed through the electrolytic cell, the copper anode dissolves and deposits as pure copper on the cathode. Because silver and gold are less reactive than copper, they do not enter the solution. Instead, they settle at the bottom of the refining tank as insoluble impurities known as anode slimes.12

These slimes contain a significantly higher concentration of precious metals than the original ore concentrate. Once collected, these slimes undergo further processing—often involving smelting to create a metal mixture called doré—to separate and refine the silver, gold, and other platinum-group metals. This process is an essential economic component of copper production, as it allows for the efficient recovery of valuable by-products that would otherwise be lost.23