This document provides an overview of bioleaching and discusses its applications in extracting various metals. Bioleaching employs bacteria to convert insoluble metal sulfides into water-soluble metal sulfates. The key microorganisms involved are mesophilic and thermophilic bacteria that oxidize ferrous iron and sulfur. The bioleaching process involves providing bacteria with metal ores or concentrates, oxygen, nutrients, and maintaining optimal temperature and pH. Factors like mineral composition, surface area, and leaching method affect bioleaching. It allows extraction of metals from low-grade ores and has advantages of being cheaper and more environmentally friendly compared to conventional methods. Gold, uranium, and copper are some metals extracted via bio

1. Bioleaching
Submitted By,
Effat Jahan Tamanna

2. Objectives
After the end of the presentation we’ll know-
• Biohydrometallurgy and its applications
• Bioleaching
• Microorganisms involved in Bioleaching
• Bioleaching Process
• Factors and Parameters influencing Bioleaching
• Advantages and disadvantages of Bioleaching
• Bioleaching of Some Metals
– Gold
– Uranium
– Copper

3. Biohydrometallurgy
• Biohydrometallurgy is a method for obtaining metals from
their ores by using microorganisms.
• Interdisciplinary field involving processes that -
– make use of microbes (-bio)
– mainly take place in aqueous environment (–hydro)
– deal with metal production and treatment of metal containing materials
and solutions (–metallurgy)
• Bioleaching is one of the application of
Biohydrometallurgy.

5. Bioleaching
• “Bioleaching" or "bio-oxidation" employs the use of naturally
occurring bacteria, harmless to both humans and the environment,
to extract of metals from their ores.
• Conversion of insoluble metal sulfides into water-soluble metal
sulfates.
• It is mainly used to recover certain metals from sulfide ores. This is
much cleaner than the traditional leaching.
• Started around the late 1940s in South Africa. Since then it has
become a worldwide phenomena.
• Bioleaching is used to recover copper, zinc, lead, arsenic,
antimony, uranium, nickel, molybdenum, gold, silver and cobalt.
• Widely used in many counties such as Australia, Canada, Chile
China, Indonesia, United States, Zambia.

6. Microorganisms involved in Bioleaching
• Bacteria are classified according to temperature at
which they are active namely:
—Mesophiles (30 - 42 °C)
—Moderate thermophiles (45 - 50 °C)
—Extreme thermophiles (65 - 85 °C)
• The bacteria oxidise ferrous iron (𝐹𝑒2+) and sulphur (S)
to produce ferric iron (𝐹𝑒3+
) and sulphate (𝑆𝑂4
2−
)
• The 𝐹𝑒3+ in turn reacts with the sulphide minerals to
produce 𝐹𝑒2+
and S.

7. Bioleaching Process
1. The Inputs of Bioleaching:
• Metal ore or concentrate to provide energy for microbes.
• Proper air is supplied based on whether they are aerobic or anaerobic.
• 𝐶𝑂2, because bioleaching microbes need the macro-nutrient C; N, P, Ka, Mg
nutrients needed for bioleaching microbes.
• pH control is needed, optimum: 2.3-2.5.
• Bioleaching microbes cultivation for inoculation.
• Temperature control mechanisms, optimum: 30⁰C- 50⁰C.
• Distribution system, stirring, sprinklers, airflow, tubes allowing for the
circulation of microbes.
• Reaction catalysts if needed.

8. 2. The Bioleaching Process
• The microbial oxidation process occurs at the cell membrane of the
bacteria.
• The electrons pass into the cells and are used in biochemical processes
to produce energy for the bacteria while reducing oxygen to water.
• The critical reaction is the oxidation of sulfide by ferric iron.
• The main role of the bacterial step is the regeneration of this reactant.
• There are few types of bioleaching:
– In-situ Bioleaching
– Heap Bioleaching
– Vat Bioleaching
– Tank Bioleaching
– Autoclave Bioleaching

9. 3. Metal Recovery
• Metal is recovered from the leaching solution either by solvent
partitioning or by the use of scrap iron.
Reactions Involved is Bioleaching:
1. Disulfide is spontaneously oxidized to thiosulfate by ferric ion
(Fe3+), which in turn is reduced to give ferrous ion (Fe2+).
2. The ferrous ion is then oxidized by bacteria using oxygen.
3. Thiosulfate is also oxidized by bacteria to give sulfate.
4. The ligand-metal complex is extracted from the solution using an
organic solvent.
5. The metal can also be concentrated and separated by displacing
the metal with iron from scrap iron.

10. Here,
M= a
Bivalent
Metal

14. Factors and Parameters Influencing Bioleaching
Factors Parameters
Physiological Temperature, pH, light, pressure
Redox and water potential
Oxygen and Carbon dioxide Content
Microbiological
Parameters
Microbial diversity
Population Diversity
Microbial Activities
Properties of Minerals Mineral type, composition
Grain size, porosity
Surface area
Processing Leaching mode
pulp density
Stirring Rate

15. Advantages of Bioleaching
• Bioleaching is simpler, cheaper to operate and maintain.
• The process is more environmentally friendly than
traditional extraction methods.
• Bioleaching if used for all processing could drastically
reduce the amount of greenhouse gases in our
atmosphere.
• Bioleaching can be used extract metals from ores that are
too poor for other technologies.

16. Disadvantages of bioleaching
• The bacterial leaching process is very slow .
• that the heat created from the dissolving process can kill
the bacteria.
• Toxic chemicals are sometimes produced in the process.
• Unlike other methods, once started, bioleaching cannot
be quickly stopped.

17. Bioleaching
of
Some Metals

18. Bioleaching of Gold
• Gold ores: calaverite (𝐴𝑢𝑇𝑒2), sylvanite 𝐴𝑔. 𝐴𝑢 𝑇𝑒2, petzite (𝐴𝑔3 𝐴𝑢𝑇𝑒2)
• From low-grade sulfidic ores, gold cannot be extracted.
• Gold ores need to be pretreated by roasting or by pressure oxidation to free
the gold prior to cyanide leaching.
• These pretreatment is costly. After this,70-95% of the gold in the ore can be
recovered by cyanide leaching process.
• Sodium cyanide leaching process converts gold to a soluble cyanide complex.
4Au + 8NaCN + 2H2O + O2  4Na[Au(CN)2]+ 4NaOH
2Na[Au(CN)2] + Zn  Na2[Zn(CN)4] + 2Au
• Bioleaching occurs in reactors or heap leaching process using Thiobacillus
ferrooxidans.
• After leaching ,it converts the porous ore of exposed gold for cyanide leaching.

20. Bioleaching of Uranium
• Uranium ores: uraninite or pitchblende (𝑈𝑂2), Brannerite
(𝑈𝑇𝑖2 𝑂6)
• Uranium ores occurs in low grade ores and is insoluble. It can be
converted to the leachable form by oxidation with ferric ion.
• Reaction Involved :
UO2
2- tetravalent uranium, insoluble oxide
UO2SO4
2- hexavalent uranium, soluble sulfate
𝑈𝑂2 + 2𝐹𝑒3+
+ 𝑆𝑂4
2−
→ 𝑈𝑂2 𝑆𝑂4 + 2𝐹𝑒2+
(𝑈4+
+ 2𝐹𝑒3+
→ 𝑈6+
+ 2𝐹𝑒2+
)
• Fe2+ is reoxidized by Acidithiobacillus ferroxidans.
• Ferrus ions produced during uranium oxidation are converted back
to Fe3+ by chemical oxidants, such as chlorate, Manganese dioxide
or hydrogen peroxide.

21. • This ion in turn acts as an oxidant to convert UO2
chemically to the leachable UO2SO4.

22. Bioleaching of Copper
• Copper Ores: Calcopyrite (𝐶𝑢𝐹𝑒𝑆2), Chalcocite 𝐶𝑢2 𝑆 , Covellite CuS
• Copper ore is a low grade ore.
• In bioleaching of Copper, the action of Acidithiobacillus involves the
oxidation of 𝐶𝑢𝐹𝑒𝑆2 via generation of ferric ions.

24. References
• Microbial Ecology
―Atlas and Bartha
• Introduction to Environmental Biotechnology
―AK Chatterjee
• Wikipedia

25. Thank You