Bioleaching uses iron- and sulfur-oxidising bacteria to regenerate ferric iron and sulfuric acid, which in turn oxidise and dissolve sulfide minerals. It operates at ambient temperature and pressure, so it suits low-grade ores and concentrates where smelting is uneconomic. Rates are far slower than chemical leaching, so residence times are measured in days rather than hours.
Why it matters in practice
Its economics rest entirely on being cheap rather than fast, which means agitation, aeration and temperature control become the dominant costs. Because the bacteria are living systems, bioleaching reactors behave more like bioprocess plant than like chemical reactors.
How it is measured or specified
Bench evaluation runs in shaken flasks first, then in aerated columns at 5 to 15 per cent solids, pH 1.5 to 2.0 and 30 to 45 °C for mesophilic cultures, or 45 to 55 °C for thermophiles. The numbers that reach the flowsheet are the ferric-to-ferrous ratio, the sulphide oxidation rate in kg per cubic metre per day, and the air demand, typically 0.5 to 1.0 vvm in a stirred tank. Heap irrigation rates of 5 to 15 L per square metre per hour are established in columns rather than on the pad.
Equipment referenced in this entry
Related terms
Where this appears on this site
Reference entry GL-BIOLEACHING. Source slug bioleaching · segment leaching. Definitions on this page describe engineering practice in hydrometallurgical process design; they are not a substitute for test work on your own material.
Working with Bioleaching? Send the feed material, the throughput and the medium — an engineer replies with a preliminary configuration and the sizing reasoning attached.