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Mehwish nazeer, Kanza saleem, Nazish mehmood
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:
Moderately thermophilic bacteria
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
First industrial gold bioleaching plant in 1980´s
Nowadays about 40 plants in industrial use for copper,
gold, zinc, cobalt, uranium.
Features of organisms
Single celled organisms
Derive carbon dioxide, oxygen from atmosphere
Requires acidic PH
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+
In second step Microorganisms catalyze the oxidation of
ferrous iron and sulphur, to produce ferric iron and
+ 1/4O2 + H+
+ 1/2 H2O
• S + 3/2O2 + H2O ---> H2SO4
Thiosulfate is also oxidized by bacteria to give
+2O2+H2O 2⟶ SO4
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+
The net products of the reaction are soluble
ferrous sulfate and sulfuric acid.
Mechanism involves in
Two processes are used in bioleaching:
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.
In direct bioleaching minerals which are
susceptible to oxidation undergoes direct
enzymatic attack by the microorganisms.
Commercial process of
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
These processes are:
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.
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.
Main factors affecting bioleaching
Temperature pH and to keep ferric
Microbial diversity culture
• 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
Benefits of bioleaching
Employed for collecting metals from waste and
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
(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