Microbial Leaching

Microbial leaching, or bioleaching, uses microorganisms to extract metals from low-grade ores.

For example, in copper leaching, crushed ore containing copper sulfides and iron sulfide minerals is sprinkled with dilute sulfuric acid.

This process creates an acidic environment and releases ferrous iron in the ore.

The acidic conditions favor Acidithiobacillus ferrooxidans, which oxidizes ferrous iron to ferric iron.

Ferric iron reacts with copper sulfides, releasing copper ions in the ore.

A. ferrooxidans also oxidize the sulfur left behind, regenerating sulfuric acid and keeping conditions acidic.

The copper-rich liquid flowing down the ore, the leachate, is collected and treated with scrap iron in recovery tanks.

The scrap iron displaces the copper, which precipitates as metallic copper and releases ferrous iron into the solution.

Ferrous iron is pumped to an aerated pond, where bacteria A. ferrooxidans reoxidize it to ferric iron.

This ferric iron is pumped back to the heap, sustaining the iron cycle that enables continuous copper extraction.