What is the purpose of bioleaching?
low grade sulphide ores contain valuable. metals in low concentrations.
Bleaching is done to get valuable metals into solution phase, waste stays in solid phase for disposal
What is bioleaching?
the utilisation of metal-oxidising and/or acid generating microbes to extract metals from ores.
AMD done on purpose in a controlled manner
What sort of reactions are involved in bleaching?
Redox reactions.
Oxidative dissolution of heap to produce dissolved ions having the metals of interest.
What is dump bioleaching?
Acid is added to piles of waste, where indigenous bacteria proliferate.
Aids natural AMD by adding an acid.
is slow and inefficient - bacterial activity not optimised
What is heap bioleaching?
Finely crushed ores heaped to encourage aeration (more surface area –> more reactions).
- solutions recycled through the bioleaching process
- more controlled than the dump method
What are the 3 stages of heap bioleaching?
- spray heaps with sulphuric acid, bacteria and nutrient mixture (lixiviant)
- liquid treated in plant to precipitate and purify target metals
- Fe(II)-rich liquid then oxidised by microbes in ponds, then added to heaps
How is Cu precipitated out of solution in bioleaching?
- copper is undergoing a redox reaction with elemental iron (oxidation state 0) and then performs a redox reaction with Fe to get elemental Cu and Fe(II).
- Cu precipitates out of solution
- the Fe(II) its then oxidised to Fe(III).
What are some variables that affect the efficiency of bioleaching operations?
- Oxidants (Fe3+ required , physical addition not so economic so bacterial-mediated Fe2+ oxidation is key)
- pH - needs to be acidic for bacteria
- permeability - affects solution distribution, diffusion of O2
- nutrients - bacteria requirer N, P, K
- Temperature - acidiothiobacilluss ferrooxidans grow best as 20-35˚C
