Bio mining methods

3.  INTRODUCTION :
 Biomining is an application of biotechnology in recovery of various minerals
from ore.
 Biomining is defined as extracting mineral ores or enhancing the mineral
recovery from mines using microorganisms instead of traditional mining
methods.
 Copper was the first metal extracted using microorganisms in the ancient past
in the Mediterranean region.
 The efficiency of biomining can be increased either by finding suitable strains
of microorganisms or by genetically modifying existing microorganisms, made
possible due to rapid advances in the field of biotechnology and microbiology.
 Biomining includes two different chemical processes called bioleaching and
bio oxidation. Thus, bio mining is an application of biotechnology and is also
known as microbial leaching or alternately, bio oxidation.

4. Method
There are different types of bacteria present in nature
that oxidize metal sulphides and solubilise minerals,
thus, helping in their extraction from the ores.
It is very important to select suitable microorganisms
to ensure the success of biomining,

5. CHARACTERISTICS OF BACTERIA USED IN BIO MINING
 Mineral extraction involves the production of high
temperatures so the bacteria should be able to survive
the heat, hence, they should be thermophilic.
 Bio-mining involves using strong acids and alkalis,
hence, bacteria should be chemophilic.
 Bacteria should produce energy from inorganic
compounds, hence, should also be autotrophic
(characteristic of an organism capable of making
nutritive organic molecules from inorganic sources via
photosynthesis i.e., involving light energy or
chemosynthesis i.e., involving chemical energy).
 The bacteria should be able to adhere to the solid
surfaces or have the ability to form biofilms.

6. IDENTIFICATION OF BACTERIA
There are some techniques to identify the bacteria:-
1) Immunofluorescence :- This technique is generally used
to identify specific antibodies or antigens present in
biological fluids. Fluorescent antibodies are used to
identify bio-mining bacteria.
2) Dot Immunoassay :- This technique is used to identify
ore-adhering bacteria like T.ferrooxidans and
T.thiooxidans.
The bacteria are applied in the form of dots on a
nitrocellulose film. Antigen-antibody reaction is carried
out on the film and then treated with a secondary
antibody to make the reaction visible by producing a
colour. The sample can be approximated by comparison
of the test sample with that of a known sample.

7. 3) Dot-blot Hybridization:-This is a DNA based technique
to identify biomining bacteria such as T.ferrooxidans.
The bacteria are isolated from samples of ores and soil
treated with sodium dodecyl sulfate (SDS). The cells are
disrupted to extract DNA and the extracted DNA is then
purified. The DNA obtained from ore sample is fixed on
nitrocellulose membrane using southern blotting
technique. Genetic probes are used to identify and
distinguish various biomining bacteria used in this
procedure. The DNA fragments on the membrane are
treated with standard probes.

8. GENERALLY USED BACTERIA:-
 Thiobacillus ferrooxidans is a chemophilic, moderately
thermophilic bacteria which can produce energy from
oxidation of inorganic compounds like sulfur and iron. It is
the most commonly used bacteria in biomining.
 Thermothrix thiopara is an extremely thermophilic bacteria
that can survive very high temperatures between 60-75C
and is used in extraction of sulfur.
 Several other bacteria such as T.thioxidans, Thermothrix
thiopara, Sulfolobus acidocaldarius and S. brierleyi are also
widely used to extract various minerals.
Techniques like genetic engineering and
conjugation are used to produce bacteria with desired
characteristics.

9. RECOVERY OF MINERAL
Minerals are recovered from ores by the microorganisms
mainly by two mechanisms:
(a)Oxidation and
(b) Reduction.
(A)OXIDATION:-
Micro-organisms (like T.ferroxidans) oxidize ferrous iron
to ferric iron.
4Fe++ + O2 + 4H+ → Fe+++ + 2H2O
The bacteria attach to the surface of the ore and
oxidize by a direct and indirect method.

10. DIRECT METHOD:-
In this method the ore is oxidized by the microorganisms
due to the direct contact with the compound.
2FeS2 + 7O2 + 2H2O → 2FeSO4 + 2H2SO4
INDIRECT METHOD:-
In this method the mineral is indirectly oxidized by an agent
that is produced by direct oxidation.
For example, the ferric ion produced by the above
reaction is a powerful oxidizing agent and can release sulfur
from the metal sulfides. Thus production of ferric ion
indirectly causes oxidation of metal sulfide resulting in the
breaking of the crystal lattice of the heavy metal sulfide
and separating the heavy metal and sulfur.
CuS + Fe+++ → Cu+ + S + Fe++

11. (B)REDUCTION:-
Bacteria like Desulfovibro desulfuricans play an active
role in reduction of sulfates which results in the
formation of hydrogen sulfides.
4H2 + H2SO4 → H2S + 4H2O

12. TYPES OF BIO MINING
There are 3 types.
1)Stirred tank Biomining
2)Bioheaps
3)Insitu Bioleaching

13. STIRRED TANK BIOMINING
 Used for leaching from substrates with high mineral
concentration.
 Expensive and time consuming.
 Used for Copper and refractory gold.

14. PROCESS:-

15.  Stirred tank bioreactors lined with rubber or corrosion
resistant steel and insulated with cooling pipes or
cooling jackets are used.
 Thiobacillus is the commonly used bacteria. Since it is
aerobic the bioreactor is provided with an abundant
supply of oxygen throughout the process provided by
aerators, pumps and blowers.
 This is a multi step process consisting of-
large no. of bio reactors connected to each other in
series.
 Runoff from one tank serves as raw material for the
next.

16.  The substrate moves from one reactor to another and in the
final stage it is washed with water and treated with a variety
of chemicals to recover the mineral.
 In this way, the reactor can operate in continuous flow
mode, with fresh ore being added to the first tank while the
runoff from the final tank is removed and treated.
 The ore to be processed is generally crushed to a very small
particle size, to ensure that the solids remain suspended in
the liquid medium.
 Mineral nutrients in the form of (NH4)2SO4 and KH2PO4
are also added to the tanks to ensure maximal microbial
density is maintained.

17. Limitations:-
 Due to the extremely high cost of stirred tank reactors,
they are only used for highly valuable materials.
 Expensive and time consuming.
Ex:- for gold, the ore body must contain high conc. of
Arsenopyrite (AsFeS).

18. BIOHEAPS
 Bioheaps are large amounts of low grade ore and effluents from extraction
processes that contain trace amounts of minerals.
 Such effluents are usually stacked in large open space heaps and treated with
microorganisms to extract the minerals.
 Bioheaps are also called biopiles, biomounds and biocells.
 The low grade ores like refractory sulfide gold ore and chalocite ore (copper)
are crushed first to reduce the size then treated with acid to promote growth
and multiplication of chemophilic bacteria.
 The crushed and acid-treated ore is then agglomerated so that the finer
particles get attached to the coarser ones, and then treated with water or other
effluent liquid.
 This is done to optimize moisture content in the ore bacteria that is inoculated
along with the liquid.
 The ore is then stacked in large heaps of 2-10 feet high with aerating tubes to
provide air supply to the bacteria thus promoting biooxidation.

19. ADVANTAGES:-
Bio-heaps are:
(a) cost effective,
(b) of simple design and easy to implement, and
(c) very effective in extracting from low concentration ores.
DISADVANTAGES:-
Bio-heaps
(i) are time consuming (takes about 6-24 months),
(ii) have a very low yield of mineral, require a large open area
for treatment, have no process control,
(iii) are at high risk of contamination,
(iv) have inconsistent yields because bacteria may not grow
uniformly in the heap.

20. INSITU-BIO LEACHING
 In-situ bio-mining is usually done to extract trace amounts
of minerals present in the ores after a conventional
extraction process is completed.
 In this method the mineral is extracted directly from the
mine instead of collecting the ore and transferring to an
extracting facility away from the site of the mine.
 The mine is blasted to reduce the ore size and to increase
permeability and is then treated with water and acid
solution with bacterial inoculum.
 Air supply is provided using pipes or shafts.
 Biooxidation takes place in-situ due to growing bacteria
and results in the extraction of mineral from the ore.

21. FACTORS EFFECTING BIOMINING
(a) Choice of Bacteria - Suitable bacteria that can survive
at high temp., acid concentrations, high conc. of heavy
metals and remain active under such circumstances are
to be selected to ensure successful bioleaching.
(b) Crystal Lattice Energy - This determines the
mechanical stability and degree of solubility of the
sulfides. The sulfide ores with lower crystal lattice energy
have higher solubility, hence, are easily extracted into
solution by the action of bacteria.

22. (c) Surface Area - Rate of oxidation by the bacteria
increases with reduction in size of the ore and vice-versa.
(d) Ore Composition - Composition of ore such as
concentration of sulfides, amount of mineral present, and
the extent of contamination, has direct effect on the rate of
biooxidation.
(e) Acidity - Biooxidation requires a pH of 2.5-3 for
maximum results.
The rate of biooxidation decreases significantly if the
Ph is not in this range since the activity of acidophilic
bacteria is reduced.

23. (f) Temperature - Optimum temperature is required for
biooxidation to proceed at a fast rate.
Optimum temp range =25-35° C depending on the type of
ore being selected.
The rate of biooxidation is reduced significantly if the
temperature is above or below the optimum temperature.
(g) Aeration - The bacteria used in biomining are aerobic
thus require an abundant supply of oxygen for survival and
growth. Oxygen can be provided by aerators and pipes.
Mechanical agitation is also an effective method to provide
continuous air supply uniformly and also to mix the
contents.

24. (h) Solid-liquid Ratio - The ratio of ore/sulfide to the
leach solution (water + acid solution + bacteria inoculum)
should be maintained at optimum level to ensure that
biooxidation proceeds at maximum speed. The leach
solution containing leached minerals should be removed
periodically and replaced with new solution.
(i) Surfactants - Adding small amounts of surfactants like
Tween 20 to the leaching process increases the rate of
biooxidation .
The surfactants decrease the surface tension of the
leach solution, thus, wetting the ore and resulting in
increased bacterial contact which ultimately increases the
rate of biooxidation.

25. ADVANTAGES OF BIO-MINING
1)Biomining is becoming popular because it is cheap,
reliable, efficient, safe, and environmentally friendly,
unlike traditional mining methods.
2)Ores of high quality are rapidly being depleted and
3)biomining allows environmentally friendly ways of
extracting metals from low-grade ores
(ores that have small amounts of valuable metals
scattered throughout).

26. THANK YOU