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How does electrolytic refining purify copper?

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Diagram of a zinc-lead blast furnace system showing ore and coke entering through charge hoppers, with labeled furnace, air preheater, blower, taphole for slag and lead bullion, and a connected lead-splash condenser using rotors to separate and cool lead and zinc, with pathways for molten metals and off-gas. — metallurgy A zinc-lead blast furnace and lead-splash condenser. This technology is utilized mainly for producing zinc while managing both lead and zinc from raw materials, a technique that was highly influential in 20th-century smelting.

Electrolytic refining is the final stage in copper production, designed to achieve high-purity metal exceeding 99.9 percent. The process utilizes an electrolytic cell containing an aqueous solution of copper sulfate and sulfuric acid.12

In this setup, impure copper is cast into slabs that serve as the positively charged anodes, while pure copper sheets act as the negatively charged cathodes. When a direct current is applied, copper ions dissolve from the anode into the electrolyte and are subsequently deposited in a pure form onto the cathode.13

This method effectively separates copper from its impurities:
* Insoluble impurities: Elements such as precious metals do not dissolve and instead settle at the bottom of the cell as "anode slimes," which are collected for further processing and recovery.143
* Soluble impurities: Other metallic contaminants are managed through the chemistry of the electrolyte to ensure they do not deposit onto the cathode, resulting in a highly refined final product.15

This process is a cornerstone of extractive metallurgy, ensuring the efficient recovery of valuable by-products while producing high-purity copper.3