this is about how we extract metal from microorganisms

1. Bio leaching
Group members
Mehwish nazeer, Kanza saleem, Nazish mehmood
m.Ishaq javaid
m.adil

2. Introduction
 Bioleaching is the simple and effective technology for
metal extraction from low grade ores and mineral
concentrate by the use of micro organisms.
 Commonly used microorganisms are:
 Mesophiles
 Moderately thermophilic bacteria
 extremophiles

4. History
 Copper recovery from mine waters in the Mediterranean
area 3000 years ago.
 The role of bacteria in bioleaching was shown in 1947.
 In 1950´s copper dump leaching.
 In 1960´s the first industrial copper heap leaching
operation.
 First industrial gold bioleaching plant in 1980´s
 Nowadays about 40 plants in industrial use for copper,
gold, zinc, cobalt, uranium.

5. Features of organisms
involved
Single celled organisms
Chemosynthetic metabolism
Derive carbon dioxide, oxygen from atmosphere
Requires acidic PH

6. Procedure
Bacteria perform the key reaction of regenerating the major
ore oxidizer, mostly ferric ion. This reaction takes place
in the cell membrane of bacteria.
 In the first step, disulfide is spontaneously oxidized to
thiosulfate by ferric iron (Fe3+
), which in turn is reduced to
give ferrous iron (Fe2+
):
• FeS2+6 Fe3+
+3 H2O 7⟶ Fe2+
+S2O3
2-
+6 H+
spontaneous
 In second step Microorganisms catalyze the oxidation of
ferrous iron and sulphur, to produce ferric iron and
sulphuric acid:
• Fe2+
+ 1/4O2 + H+
---> Fe3+
+ 1/2 H2O
• S + 3/2O2 + H2O ---> H2SO4

7. Thiosulfate is also oxidized by bacteria to give
sulfate:
• S2O3
2-
+2O2+H2O 2⟶ SO4
2-
+2 H+
(sulfur oxidizers)
The ferric iron produced in reaction (2) oxidized
more sulfide as in reaction (1), closing the cycle
and given the net reaction
• 2 FeS2+7O2+2 H2O 2⟶ Fe2+
+4SO4
2
+4H+
The net products of the reaction are soluble
ferrous sulfate and sulfuric acid.

8. Mechanism involves in
bioleaching
Two processes are used in bioleaching:
 Direct bioleaching
 Indirect bioleaching

9. In direct bioleaching
In indirect method of bioleaching of
minerals bacteria produce strong oxidizing
agent which reacts with metals and extract
them from the ores.

10. In direct bioleaching minerals which are
susceptible to oxidation undergoes direct
enzymatic attack by the microorganisms.
Direct bioleaching

11. A: In direct mechanism
B: Direct mechanism

12. Commercial process of
bioleaching
Naturally occur bioleaching process is very slow.
For commercial extraction of metal by
bioleaching the process is optimized by
controlling the PH, temperature, humidity, o2 and
co2 concentrations.
These processes are:
 Slope leaching
 In-situ leaching
 Heap leaching

13. Slope leaching
In slope leaching the ore is finely ground and kept in large pile in a
slope which is subjected to continuous sprinkling of aqueous solution
of microorganisms. The leach liquor collected at the bottom of the ore
is processed further for metal recovery.
In situ leaching
In in situ leaching ore is subjected to bioleaching in its natural
occurrence, aqueous solution of microorganisms is pumped through
drilled passages with in the ore. The leach liquid collected at the
bottom of the ore used for metal extraction.
Heap leaching
In heap leaching ore is arranged in heap and goes through the
same procedure as in slope leaching. The aqueous solution
containing microorganism works on the heap of ore and produces the
leach liquor. The leach liquor is used for metal recovery.

14. Main factors affecting bioleaching
FACTOR
Physicochemical
Temperature pH and to keep ferric
Oxygen reactions
Microbiological
Microbial diversity culture
Population density
Metal tolerance
EFFECT
• affects leaching rate, microbial
composition and activity
• needs to be low to obtain the
fastest leaching rates and to keep
ferric iron and metals in solution
•electron acceptor needed in
chemical and biological oxidation
•mixed cultures tend to be more
robust and efficient than pure
•high population density tends to
increase the leaching rate
•high metal concentrations may be
toxic to meta

15. Benefits of bioleaching
 Simple
 Inexpensive
 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 emissions as in smelters
 no need for hi pressure or temperature
 ideal for low-grade sulfide ores
 Environment friendly process

16. Disadvantages
Time consuming
(takes about 6-24 months or longer)
Have a very low yield of mineral
Requires a large open area for treatment
May have no process control
High risk of contamination
Inconsistent yield because bacteria cannot grow
uniformly