Bioleaching of copper, gold and uranium

1. Bioleaching
Dr. Aswartha Harinath Reddy M.Sc, Ph.D
Department of Life Sciences
Srikrishnadevaraya University
Anantapur –A.P. India

2.  Bioleaching is the extraction of metals from their ores through the
use of living organisms.
 Bioleaching is used to recover copper, zinc, nickel, molybdenum,
gold, silver, and cobalt.

3. Bioleaching of Copper (Cu)

4. Bioleaching of Copper:
 Copper has been one of mankind's most important metal
resources since the beginning of civilization.
 it holds and important role in the functioning of modern
society. It's main uses include piping, coinage, electronics, and
even antibiotics.

5. Microbes Involved in Bioleaching:
 The bacteria which are naturally involved in growing up among
rocks are most suitable and applicable ones for bioleaching.
 The most commonly used microorganisms for copper
bioleaching are
 Thiobacillus ferrooxidans,
 Leptospirillum ferrooxidans
 Thiobacillus thiooxidans.

6.  Other microorganisms which may also be used are;
 Bacillus licheniformis, B. luteus, B megaterium, B leptospirillum
ferrooxidants, Pseudomonas flurescens, Sulfolobus acidocaldarius,
etc;
 Fungi have not shown a broad area of examples in the field of
bioleaching.
 Some of the fungi associated with bioleaching are Aspergillus niger
and Aspergillus oryzae.

7. Advantages of Bioleaching :
 Extraction of metals form low grade ores
 Very economical process
 Employed for collecting metals from wastes or drainages
 Environment friendly process
 Used to extract refined and ex pensive metals which is not possible
by other chemical processes.
Disadvantages of Bioleaching:
 Very slow process
 Dependency on several atmospheric conditions decreases the
efficiency of the process.

8. Forms of Copper
 Copper sulfides (Cu2S) (e.g. chalcopyrite and chalcocite)
 Copper oxides (e.g. cuprite (Cu2O)
 Copper carbonates (CuCO3) (e.g. azurite and malachite)
Azurite Cuprite Chalcopyrite Malachite Chalcocite

9. Copper Leaching:
 For removal of copper Chalcocite (Cu2S), Covellite (CuS) ores
commonly used.
 Chalcocite is oxidized to soluble form of Copper (Cu2+) and
Covellite by T. ferrooxidans.
Cu2S + O2 CuS + Cu2+ + H2O
 Covellite is oxidized to copper sulphate by bacteria or chemicals.
2CuFeS2 + 8½ O2 + H2SO4 2CuSO4 + Fe2(SO4)3 + H20

10. Bioleaching of Iron (Fe)

11. Iron (Fe):
 It is by mass the most common element on Earth, forming
much of Earth's outer and inner core.
 Iron plays an important role in biology, forming complexes
with molecular oxygen in hemoglobin and myoglobin.
There are four unpaired electrons in the 3d subshell of iron.
Explanation:
The ground state configuration of Fe is [Ar]4s23d6

12. Microorganisms used in the bioleaching of Iron:
 Thiobacillus ferrooxidans is a gram negative, rod-shaped,
motile, non-spore forming bacterium.
 It derives the energy of the growth from the oxidation of iron
or sulphur in ore.
 This microorganism oxidises ferrous ions (Fe2+) to ferric
ions (Fe3+) and converts sulphur (S) to sulphate (SO4).

13.  Thiobacillus thiooxidans has similar functions and it grows mostly
on Iron and sulphur ores.
 Leptospirillum ferrooxidans and Thiobacillus organoparpus work
in a combination to extract iron and copper from pyrite and
chalcopyrite.

14.  One of the most common form of iron and sulphur in nature is
pyrite FeS2. (Iron Disulphide crystal systems)
 In bioleaching of pyrite the Thiobacillus ferrooxidans oxidize Iron
disulphide in to Ferric sulphate and sulphuric acid.
 The overall summary reaction of pyrite oxidation is as follows:
Thiobacillus ferrooxidans
4FeS2 + 15O2 + 2H20 2Fe2(SO4)3 + 2H2SO4
Pyrite + Oxygen + Water Ferric sulfate+ Sulfuric acid

15. Uranium (U) microbial leaching
atomic number 92 and 6 are valence electrons.

16.  Uranium leaching is more important than copper,
although less amount of uranium is obtained than
copper.
 For getting one tonne of uranium, a thousand tonne of
uranium ore must be handled.
 The most visible civilian use of uranium is as the thermal
power source used in nuclear power plants and nuclear
weapons.

17.  Chemical process:
 Insoluble tetravalent Uranium is oxidized with a hot
H2SO4/Fe3+ (Ferric sulfate hydrate) solution to make soluble
hexavalent Uranium sulfate at pH 1.5-3.5 and temperature 35°C.
UO2 + Fe2(SO4)3 UO2SO4 + 2FeSO4

18.  Bioleaching of Uranium is indirect process.
 T. ferrooxidans does not directly attack on uranium ore, but on
the iron oxidant.
 Fe3+ (Ferric ions) is used as an oxidant in the leaching of
Uranium from Uraninite (UO2).
 The pyrite reaction is used for the initial production of
Fe3+ leach solution.

19.  Ferric iron is then regenerated by the bacteria to complete the
cycle:
Giving the overall reaction:
4Fe2+ + O2 + 4H+ → 4Fe3+ + 2H20
2UO2 + 4Fe3+ → 2UO2
2+ + 4Fe2+
T. ferrooxidans
ferrous ions (Fe2+) to ferric ions (Fe3+)
Uraninite+ ferric ions Uranium + Ferrous

20.  Some bacteria like Pseudomonas aeruginosa can also be used
to extract high value metal like uranium from low quality
uranium ore containing around 0.02% uranium.
 Rhizopus arrhizus is another bacterium that can extract
uranium from low grade uranium ores….

21. Bioleaching of Gold (Au)

22.  Gold is a chemical element with symbol Au and atomic number 79.
 In its purest form bright and yellow colour.
 It is one of the least reactive chemical elements, electrically inert
metal and is solid under standard conditions.
 As a precious metal, gold has been used for coinage and jewelry.
Gold:

23. Microbes Involved in Bioleaching:
Bacteria:
 Thiobacillus ferrooxidans
 Acidithiobacillus ferrooxidans
 Acidiphilium cryptum.
 Chromobacterium violaceum
Fungi:
 Aspergillus niger
 Penicillium simplicissimum

24.  Furthermore, some studies have found that the presence of
trace amounts of Au ions does not affect the growth of
microorganisms.
 Because Au ions are often deposited in cell walls and
periplasmic membranes of microorganims.

25. Chemical method:
 Principally, gold is embedded in arsenopyrite, and pyrrhotite.
 A key step in gold extraction is conversion of the solid metal
into a soluble cyanide complex:
 Straight cyanidation (Chemical methods) of the gold ores
yields poor recoveries.
2Au + 4NaCN + O2 + 2H2O → 2NaAu(CN)2 + 2NaOH + 2H2O2

26.  Bacterial oxidation is an interesting, low capital cost method
alternative method with high potential for the liberation of
finely dispersed gold from pyrite.
 The bacteria gradually breakdown the sulphides and release
gold.

27. And
ALL THE BEST………..