Bioleaching

Question 1

What is bioleaching?

Answer 1

AMD done on purpose in a controlled manner.

The utilisation of metal-oxidisng and/or acid generating microorganisms to extract metals from ores.

Question 2

Why is bioleaching required?

Answer 2

Low-grade sulphide ores contain valuable metals in low concentrations.
Want to get into solution phase.

Question 3

What does dump bioleaching involve?

Answer 3

Passive method - cheap and easy but not optimised

• Acid added to waste piles
• Indigenous bacteria proliferate, helping natural AMD

Question 4

What does heap bioleaching involve?

Answer 4

• Crushed ores are heaped to encourage aeration
• Solutions re-cycled through bioleaching
• More controlled than dump bioleaching

Question 5

What are the three heap bioleaching strategies?

Answer 5

1. Spray heaps with H2SO4, bacteria and nutrients
2. Liquid is then treated in plant - aims to ppt. and purify target metals
3. Fe(II)-rich liquid is oxidised by microorganisms in ponds and re-added to heaps

Question 6

What are the five variables effecting bioleaching efficiency?

Answer 6

1. Oxidants
   - Fe3+ required
   - Bacterial mediated Fe2+ oxidation is key
2. pH
   - Acidic
3. Permeability
   - Effects O2 diffusion
4. Nutrients
   - Bacteria require K, N, P etc.
5. Temp
   - e.g. A. ferrooxidans require 20-30 degrees