This document discusses the process of bioleaching, which uses microorganisms like bacteria and archaea to extract valuable metals from low-grade ores. It involves two main mechanisms - direct contact between microbes and ores, or indirect leaching using acids and oxidizing agents produced by microbes. Key microbes used are Thiobacillus species and Leptospirillum ferrooxidans. Commercial bioleaching includes methods like dump, heap, and in situ leaching. Factors like temperature, pH, microbial culture composition affect the process. Though inexpensive and eco-friendly, bioleaching is also time-consuming and has low and inconsistent metal yields.

1. BIOLEACHING
PRESENTED BY :
J. JOYCE ANGEL
II M.SC. APPLIED MICROBIOLOGY
SACRED HEART COLLEGE
TIRUPATTUR.

2. Synopsis
 Bioleaching
 Microorganisms in bioleaching
 Mechanisms involved in bioleaching
 Types
 Factors affecting bioleaching
 Advantages
 Disadvantages

3. Bioleaching
 Bioleaching /Metal Bioleaching / Biomining is a process in Mining and
Biohydrometallurgy (process of interaction between microbes and minerals)
 Extracts valuable metals from a low-grade ore with the help of microorganisms such as
Bacteria or Archaea
 Alternative to more traditional physical and chemical methods of mineral processing.
 One of the application of biohydrometallurgy.
 The modern era of bio mining began with the discovery of the bacterium Thiobacillus
ferrooxidans
Metals extracted from bioleaching:
Antimony, Arsenic, Cobalt, Copper, Gold, Lead, Molybdenum, Nickel, Silver, Uranium, Zinc.

4. Microorganisms In Bioleaching
a) Thiobacillus sp:
 Thiobacillus thiooxidans, T. ferrooxidans - mesophiles
 T. Prosperus (metal mobilizing bacteria)
 T. cuprinus (oxidizes metal ions)
b) Leptospirillum sp:
 Leptospirillum ferrooxidans - acidophiles - oxidizes Fe
c) Thermophilic bacteria
 Acidianus brierleyi
 Sulfobacillus thermosulfidooxidants
d) Heterotrophic microorganism
 Saccharomyces cerevisiae, Rhizopus sp,Aspergillus & Penicillium simplicissium
(fungi)

5. Mechanisms Involved In Bioleaching
 Thiobacillus thiooxidans and T. ferrooxidans have always been found to be
present on the leaching dump.
a) Direct Bioleaching or Contact Bioleaching:
 Physical contact exists between Microorganisms and Ores, and Oxidation of mineral takes
place through enzymatically catalyzed steps.
Example - Pyrite is oxidized to Ferric sulphate.
b) Indirect Bioleaching:
 Microorganisms produce strong Oxidizing agent (Ferric ion & Sulfuric acid) which reacts
with metals and extract them from the ores.
 Acidic environment is absolutely essential in order to keep Ferric iron and other metals in
solution. Acidic environment maintained by oxidation of iron, sulfur, metal sulphides or by
dissolution of carbonate ions.
Example – Bioleaching of Uranium

6. Commercial Bioleaching Process
Types:
a) Slope Leaching or Dump Leaching
b) Heap Leaching
c) In situ Leaching
a) Slope Leaching / Dump Leaching process:
 The Ores are first ground to get fine pieces then dumped into large Leaching dump.
 Water containing inoculum of Thiobacillus is continuously sprinkled over the ore.
 Water is collected from the bottom and used to extract metals and generate bacteria
in an Oxidation pond.

7. b) Heap Leaching:
 The ore is dumped into large Heaps called Leach heaps.
 Water containing inoculum of Thiobacillus is continuously sprinkled over the ore.
 Water is collected from the bottom and used to extract metals and generate bacteria in
an Oxidation pond
c) In situ Leaching:
 The ore remains in its original position in the earth.
 Surface blasting of earth is done to increase the permeability of water.
 Water containing Thiobacillus is pumped through drilled passage to the ores.
 Acidic water seeps through the rock and collects at the bottom. Again, water is pumped
from bottom.
 Mineral is extracted and water is reused after generation of bacteria.

8. Factors Affecting Bioleaching
Physico-chemical factors
a) Temperature
 Affects leaching rate, microbial composition and activity.
b) pH
 Needs to be low (Acidic) to obtain the fastest leaching rates and to keep ferric iron
and metals in solution.
c) Ferric oxygen reaction
 Electron acceptor needed in Chemical and Biological oxidation.

9. Microbiological factors:
a) Microbial diversity culture
 Mixed cultures tend to be more robust and efficient than Pure culture.
b) Population density
 High population density tends to increase the leaching rate.
c) Metal Tolerance
 High metal concentrations may be toxic to microbes.
d) Choice of Bacteria
 Suitable bacteria that can survive at High temperatures, Acid concentrations,
High concentrations of heavy metals, remaining active under such
circumstances

10. Mineral Factors
a) Composition
 Provides electron donor and trace elements.
b) Particle size
 Affects the available mineral/liquid contact area.
c) Surface area
 Rate of oxidation by the bacteria increases with reduction in size of the ore
and vice versa.
d) Porosity
 Cracks and pores in the particles give rise to the internal area.
e) Presence of other Metal sulfide
 Mineral having the lowest potential is generally oxidized first.

11. Advantages of bioleaching
 Simple process.
 Eco-friendly process.
 Inexpensive technique.
 Employed for collecting metals from waste and drainages.
 Use to extract refines and expensive metals which is not possible by other chemical
processes.
 No poisonous sulfur dioxide emission as in smelter.
 No need of high pressure and temperature.
 Ideal for low grade Sulphide ores

12. Disadvantages of Bioleaching:
 Time consuming (takes 6 to 24 months or longer).
 Have a very low yield of minerals.
 Requires a large open area for treatment.
 May have no process control.
 High risk of contamination.
 Inconsistent yield because bacteria cannot grow uniformly.

13. THANK YOU