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Chapter
Bio Hydrometallurgical
Technology, Application and
Process Enhancement
Mulugeta SisayCheru
Abstract
The review is in general try to see some of the major microorganism involved in
bioleaching process and studied by different scholars, identify the mechanics and
techniques employed to bioleach minerals and factor that enhance or to inhibit the
leaching process of microorganism with major reaction taking while bioleaching. Here
the methodology and different leaching technique presented with their respected pros
and cons, which are commonly employed and reasons behind with justifiable evi-
dences were presented. The values and bioleaching sulfide mineral (copper), precious
metal (gold) and radioactive element (uranium) were discussed with some the known
producers in the world and finally some highlight given on industrial application of
bioleaching.
Keywords: bioleaching, leaching techniques, biooxidation, radioactive, pretreatment
. Introduction
Bioleaching is the extraction of metals from ores using the principal components
water, air and microorganism [1]. It is the extraction or mobilization of valuable
(target) metal from the ore, can also be defined as a process of recovering metals
from low grade ore [2, 3], with regard to solubility, bioleaching can be defined
as a process of recovering soluble one from insoluble impurities after dissolving
sulfide metal as soluble salt in a solution [4] that results toxics and heavy metals
removed. It is isolation of metals from their ores, concentrates and mineral wastes
under the influence of microorganisms leading to dissolution of metal solutions of
leach liquor containing metals [5], followed by solvent extraction, stripping, ion
exchange, electro wining to get pure metal.
Both bioleaching and biooxidation leads to recovery target mineral; but there is
technical difference between the two technologies. Bioleaching refers to the use of
bacteria, the common Thiobacillus Ferrooxidans and other bacterial as a leachant
to leach sulfide minerals where the target elements remains in the solution during
oxidation process, after the metal recovery the solid left behind regarded as residue
and in the contrary biooxodation discard the solution after having metal values
in solid phase [6, 7] microorganism also engaged in removal of radionuclides and
leaching of metal that are regarded as toxic in some cases and good for bioremedia-
tion of soil, the process stops radio nucleation that result the removal of stability of
target elements [7].
Biotechnology in Mining and Metallurgical Industry
Bioleaching has been used for a long period of time without regarded as microbial
leaching process; it has been used as early as 1000BC when a man from metal laden
recovered copper from a water, passes through copper ore deposit [8]. It was in 1556
at the mine located in Spain at Rio Tinto (Rd River) mine, slurry containing very high
concentration of ferric ions leached due to the action of microorganisms [4]. Copper
was precipitated from the solution obtained from this river, the very first bio miner-
alization process was copper dissolution, then the process continued to be developed
in countries like Norway, Germany and English at different era of time, in the year
1947 heap and dump leaching was practiced that leads to the development of bacte-
rial bioleaching process [9].
The gram-negative chemolithotroph bacterial, Thiobacillus Ferooxidans was
first cultured and isolated from mine water by Colmer and Hinkel [9]. Thiobacillus
Ferrooxidans is rod shaped ranging in diameter from 0.3 to 0.8 micrometers (μm),
in length from 0.9 to 2μm, 0.5μm in width in which its movement is due to a single
polar flagellum [10]. Since now this bacteria is the most studied. These bacteria were
able to oxidize sulfur to sulfuric acid and ferrous to ferric in acidic environment
where pH value is less than 5 [7, 10, 11]. From this point onwards the technology of
bioleaching has shown tremendous growth, especially industrial coppers produc-
tion, which makes annualized world copper production reach up 10% from 0.2%.
It was in Chile the first industrial scale copper bioleaching plant was established in
1980 using Thiobacillus bacteria [12] large-scale production begins and bioleaching
taken as main manufacturing process as any convection techniques in Chile 1984
[13]. Among the many microorganism involved, bacteria (autotrophic and hetero-
trophic), fungi and yeasts can be mentioned. The bacterium has these calcification
based on their species as Thiobacillus Ferrooxidans, Leptospirillum Ferrooxidans,
Thiobacillus Thiooxidans, Sulfolobus, but there are many classifications based on
different characteristics reveled by the organisms.
Acidophilic Thiobacillus species are used to leach refractory elements like gold,
they generally characterized as aerobic, acidophilic, and autotrophic used to leach
sulfide minerals (copper, nickel, zinc and soon). Most common bacteria involved
in bioleaching are Acidithiobacillus Ferrooxidans (Thiobacillus Ferrooxidans),
Acidithiobacillus Thiooxidans, Leptospirillum Ferrooxidans, Sulpholobus Spp,
Sulpholobus Thermosulphidoxidans and Sulpholobus Brierleyi. Acidithiobacillus
Ferrooxidans is most vital one, which was named and characterized in 1951.
Most common fungi are Aspergillus Niger and Penicillium Simplicissimum. The
efficiency of bioleaching depends up on physiological requirement and capability
of Thiobacillus to oxidize ferrous ion (Fe2+) and sulfur (S). There are five main
species of Thiobacillus, these are Thiobacillus Thioparus, Thiobacillus Dentrificans,
Thiobacillus Thiooxidans, Thiobacillus Intermedius, and Thiobacillus Ferrooxidans.
On the bases of pH values for growth genus Thiobacillus can be divided into two
groups, those that can grow only in neutral pH values are T. Thioparus and T.
Dentrificans. The second Thiobacillus species those grow at lower pH value are T.
Thiooxidans, T. intermedius, and T. Ferrooxidans.
Study of different scholars at the inceptions shows the capability of bacteria
(genus Thiobacillus) to oxidize sulfur compounds to sulfuric acid; it can oxidize also
range of sulfur compounds (S2−, S0, S2O4, S2O42−, SO42−) [11], followed by separation
process of the iron and the bacteria Acidithiobacillus Ferrooxidans (Thiobacillus
Ferrooxidans) from the solution. A. Ferrooxidans is found in drainage waters and it is
commonly identified as pyrite oxidizer [14]. The bacterial (acidophile) obtain energy
from inorganic sources, it grows in acidic medium that fixes carbon to the bacteria
itself. Most economically important metals like iron, copper, gold, and uranium can
be easily extracted by using acidophilic and chemo-litho-autotrophic microorganism.
Acidithiobacillus Ferrooxidans is chemoautotrophic microorganism or acidophilic.
Bio Hydrometallurgical Technology, Application and Process Enhancement
DOI: http://dx.doi.org/10.5772/intechopen.94206
Let see the ecology, physiology, availability and genetics of microorganism involved
in bioleaching. There are three basic principles for microorganism to leach and
mobilize target metals from ore concentrate – redox reaction, formation of organic
and inorganic acid and finally the excretion of complexing agent (Figure ) [4].
Here is a generalized reaction used to express biological oxidation of sulfide
mineral.
MS+2O2→MSO4, where M is bivalent metal and reaction below show a metal
sulfide directly oxidize by Acidithiobacillus Ferrooxidans to soluble metal sulfate
according to the reaction.
MS+2O2→M+2+SO4+2 [15].
. Mechanisms of bioleaching
The two majorly known mechanism in bacterial leaching are direct mechanism
(involves physical contact of the organism with the insoluble sulphide) or hypoth-
esized enzymatic reaction taking place between an attached cell and the underly-
ing mineral surface which is independent of indirect mechanisms and it is where
reduced sulfur dissolution takes place [16], it is only the direct attack of the bacteria
can lead to leaching. Check the following reactions.
222 424
2FeS 7O 2H O 2FeSO 2H SO .++ ® +
(1)
Indirect (involves the ferric-ferrous cycle) or it is a mechanism of sulfide oxida-
tion involves non-specific oxidation of surfaces by Fe3+ that is generated by micro-
organisms that oxidize iron or oxidation of mineral by ferric ions [16]. The attached
cells of bacterial oxidize the surface using either of the two mechanisms [9, 11, 14].
The reaction below shows oxidation of iron.
( )
0
2 24 4
3
FeS Fe SO 3FeSO 2S .+ ®+
(2)
Minerals are broken due to the attack to their constituents, that results energy
production for the microorganism. This energy production or oxidation passes
through intermediates reaction processes. Two mechanisms have been proposed for
the oxidation, viz. thiosulphate mechanism and polysulfide mechanism. Thiosulfate
mechanism includes acid-insoluble metal sulfides like pyrite (FeS2) and molybde-
nite (MoS2) and polysulfide mechanism includes acid-soluble metal sulfides like
chalcopyrite (CuFeS2) or galena (PbS) [15]. In thiosulfate mechanism, the attack of
ferric ion on acid insoluble metal sulfides brings about solubilization via thiosulfate
as an intermediate and sulfates as end product. The breaking reaction shown below.
Figure 1.
Image of bioleaching bacterial [4].
Biotechnology in Mining and Metallurgical Industry
3 22
2 2 23
FeS 6Fe 3H O S O 7Fe 6H .
+- ++
++® ++
(3)
23 22
23 2 4
S O 8Fe 5H O 2SO 8Fe 10H .
-+ -++
++® ++ (4)
In polysulfide mechanism, a combined attack of ferric ion and protons on acid-
soluble metal sulfides causes the solubilization with sulfur as an intermediate in its
elemental form which can be oxidized to sulfate by sulfur-oxidizing microbes that
the reaction is shown below [17].
( )
32 2
2
MS Fe H M 0.5 H Sn Fe n 2 .
++ + +
+ +® + + ³
(5)
32
28
0.5H Sn Fe 0.125S Fe H .
+ ++
+® ++
(6)
0.125S8+1.5O2+H2O→SO42−+2H+ the reaction show the production of
sulfuric acid results hydrogen (proton) for attacking mineral.
Fe (II) is re-oxidized to Fe (III) by iron oxidizing organisms (chemotrophic
bacteria), the role of microorganisms in solubilization.
2Fe2+ + 0.5O2+2H+→2Fe3+ + H2O this reaction keep iron in ferric state that
oxidize mineral.
The process of chemical attack takes place on a substrate or the mineral surface
where the bacteria forms a composite and attach itself as firm as possible in order to
increases maturity that finally detached and dispersed into the solution.
An important reaction mediated by Acidithiobacillus Ferrooxidans is:
( )
4 2 24 2 4 2
3
4FeSO O 2H SO 2Fe SO 2H O.
++ ® + (7)
Strong oxidizing agent, ferric sulfate that basically used to dissolve metal
sulfide minerals, and leaching brought about by ferric sulphate is termed indi-
rect leaching due to the absence of both oxygen and viable bacterial. Check the
following leaching mechanism of reaction on several minerals.
( )
( )
2 4 44
3
CuFeS chalcopyrite 2Fe CuSO 5FeSO 2S.+ ®+ +SO
(8)
( )
( )
2 24 4
3
FeS Pyrite Fe SO 3FeSO 2S.+ ®+
(9)
( ) ( )
2 24 24 24 4
3 4–3
UO Fe SO 2H SO UO SO 2FeSO 4H .
+
+ +® ++
(10)
( )
Acidithiobacillus ferrooxidans
2 2 2 2 4 24
3
4FeS 15O H O 2Fe SO 2H SO .
++ + (11)
( )
Acidithiobacillus fer rooxidans
2 2 24 2 4 2
3
4CuFeS +17O +2H SO 4CuSO4 +2Fe SO + 2H O. (12)
Acidithiobacillus ferrooxidans
2 2 24 4 2
2Cu S 5O 2H 4CuSO 2H O.
++ +
SO
(13)
Acidithiobacillus ferrooxidans
24
2O CuSO .
+
CuS
(14)
Acidithiobacillus Ferrooxidans can convert elemental sulfur generated by
indirect leaching to sulfuric acid –.
Bio Hydrometallurgical Technology, Application and Process Enhancement
DOI: http://dx.doi.org/10.5772/intechopen.94206
Acidithiobacillus ferrooxidans
2 2 24
2SO 3O 2H O 2H SO .
++ (15)
This sulfuric acid maintains the pH value at levels, which is favorable to the
growth of bacteria and also helps for effective leaching of oxide minerals:
( )
24 4 2
CuO Tenorite 2H SO CuSO H O.+ ®+
(16)
( )
3 24 2 4 2
3
UO 3H SO UO SO H O 4H .
+
+ ® ++ (17)
Chemolithotrophic (uses carbon for the synthesis of new cell material) bacteria
can be categorized based on response to temperature as mesophiles, moderate
thermoacidophiles and extreme thermoacidophiles.
Mesophiles-grows at a temperature values ranges (28°C -37°C) where
Thiobacillus Ferrooxidans is able use the inorganic substrate to draw energy by
oxidizing Fe (II) to Fe (III) and sulfur to sulfide and sulfate. The other mesophiles
is Leptospirilium Ferrooxidans that use Thiobacillus Ferrooxidans to effect the oxi-
dization of sulfur to sulfate. Moderate thermoacidophie-temperature values ranges
(40–50°C), Sulfobacillus Thermosulfidooxidans is common one, which oxidize
both sulfur and iron from energy production. This category includes Archaea and
Eubacteria, and most of gram-positive microorganisms are included here. Extreme
thermoacidophiles-temperature ranges 60–80°C, genera Sulfolobus, Acidanus,
Metallosphaera and Sulfurococcus are in this category, [11, 18, 19]. Thermal value
some time extends above the limitation values, it is due to exothermal reaction
which is above the maximum growth temperature of microorganism, some micro-
organism genus like Archaea withstand thermal values up to 90° [19, 20].
This category is formed by closely related species that can act together with
a common name given Sulfolobus. Sulfolobusa Acidocaldarius, Sulfolobus
Sofataricus, Sulfolobus Brierley, and Sulfolobus Ambioalous that can oxidize Fe (II)
to Fe (III) and sulfur to sulfate. Aspergillus Niger and Penicillium Simplicissimum
are both used to leach sulfide minerals like copper with mobilization rate of
65% and aluminum, nickel, lead and zinc by more than 95% mobilization rate.
Thiobacillus and Leptospirillum are characterized by the oxidation of sulphide
minerals in acidic environment and temperature values less than 35°C, with regard
to area of application these two are mostly used in dump and tank leaching of metal
from sulphide based mixed ores [20, 21]. The other group of genus Sulphobacillus
used under the same areas of application but relatively higher temperature up
to 60°C, the temperature reaches up to 90°C in case of genera Sulpholobus and
Acidianus, Organotrophic microorganisms like yeast, fungi and algae which
destruct sulphide mineral and aluminum silicate, facilitate bio sorption of metals
that solubilize gold, these microorganism uses carbonate and silicate ore for the
extraction of metals and selective gold extraction from ore floatation and metal
solution.
. Autotrophic and heterotrophic leaching
The two bacterial leaching namely autotrophic and heterotrophic leaching
has their distinct characteristics while bioleaching process takes place, in case of
autotrophic bioleaching (effective on sulfide minerals) there are two proposed
mechanism of Acidithiobacillus Ferrooxidans action on sulfide minerals, first the
mechanism, that the bacterial oxidize ferrous ion to ferric ion in which the bulk
solution where the mineral is leached counted as indirect, this mechanism which is
Biotechnology in Mining and Metallurgical Industry
indirect oxidation of ferrous ions to ferric ions is exopolymeric process, both takes
place on the layer where the mineral is leached. The second proposed mechanism,
does not require ferrous or ferric ions, the bacteria directly oxidize the minerals
by biological means having direct contact mechanism of reaction. Autotrophic
leaching uses both Thiobacillus Ferooxidans and Thiobacillus Thiooxidans to leach
sulfide mineral and studies shows combining the two bacterial results an increase
in selectivity and rate of leaching efficiency while leaching of nickel sulfide. From
the heterotrophic genus of bacteria Thiobacillus and Pseudomonas are those used to
leach non-sulfide minerals and from the genus of fungi Penicillium and Aspergillus
(heterotrophic fungi) are those used in leaching process, a study shows 55–60%
leaching rate for nickel and cobalt, some other studies indicates that 95% and 92%
leaching rate achieved while using pretreated Aspergillus Niger by ultrasound for 14
and 20days respectively which increase its stability [4, 11, 20, 22] (Table ).
Heterotrophic fungi Aspergillus and Penicillium species combined to leach
low-grade nickel-cobalt oxide ores, low-grade laterite ores and spudumene (alumi-
nosilicate), these aluminosilicate (spudumene) also leached by heterotrophic yeasts
(Rhodotorula rubra), Aspergillus Niger used to leach zinc and nickel silicate [11].
Bacterial leaching can be generalized in three mechanism redoxolysis, acidolysis,
complexolysis, and in case fungal leaching bioaccumulation is important mechanism.
To solubilize rock phosphorous, Aspergillus Niger has been used in many occasions
due to the production of organic acids with low molecular weight and phosphorous is
basically essential micronutrients for the growth of bio organism, these microorganism
convert insoluble phosphate to soluble, the two filamentous fungi used in phosphate
leaching are Aspergillus Niger and some Penicillium, the metabolic fungal reaction
produces organic acid that result the formation of acidolysis, complex and chelate [22].
The second group of bacterial genus is Leptospirillum, which is categorized in
moderate thermophilic bacteria that can only oxidize ferrous ions; it is dominate
iron oxidizer, which is referred as Leptospirillum Ferrooxidans (L. Ferrooxidans).
Oxidation process takes place under strong acidity and temperature up to 30°C,
L.Ferrooxidans has high affinity to Fe2+ and low affinity to Fe3+ which results
a working condition of high Fe3+/Fe2+ ratio, when redox potential is low, L.
Ferrooxidans has low growth rate at the initial stage of a mixed batch culture, a
native strain of Leptospirillum Ferrooxidans used to leach zinc from low grade
sulfide complex from La Silvita and La Resbalosa (Patagonia Argentina) [23]. The
leach liquor itself has been a place where microorganism found, higher amount of
Microorganism/ both autotrophic and heterotrophic Ore sample
Aspergillus Niger, Hyphomicrobium Flourapatite (phosphorus ore)
Pseudomonas Oryzihabitans Magnesite, Dolomite (magnesium ore)
Bacillus Licheniformis Silica
Thiobacillus Ferrooxidans, Acidianus Brierleyi, Sulfobacillus,
Thermosul Fidooxidans, Sulfolobus Rivotincti
Chalcopyrite (Low and high grade),
Pyrite, Covellite
Penicillium Simplicissimum, Penicillium Verruculosum,
Aspergillus Niger, Acidithiobacillus Ferrooxidans
Iron ore, Hematite, Zinc and nickel
Silicates
Thiobacillus Thiooxidans Pyrrhotite
Thiobacillus Caldus Arsenopyrite
Metallosphaera Sedula, Sulfolobus Metallicus (BC), Pyrite
Paenibacillus polymyxa Bauxite (low grade)
Table 1.
Some of microorganism and leachable ore [4, 11].
Bio Hydrometallurgical Technology, Application and Process Enhancement
DOI: http://dx.doi.org/10.5772/intechopen.94206
Leptospirillum Ferriphilum were in a leach liquor, in a study conducted to leach the
effect of pH on the bioleaching of a low-grade, black schist ore from Finland using
Acidithiobacillus Ferrooxidans and Leptospirillum Ferrooxidans as extractant [24].
The bacteria can relatively resist high concentration of uranium, molybdenum, and
silver, this is due to its affinity towards to ferrous ions or resistivity to refractory ele-
ments, but it cannot oxidize sulfur or any sulfur related compounds. By combing it
with other sulfur- oxidizing acidophiles, sulfur-oxidizing process can be achieved;
these are T. Caldus, T. Ferrooxidans, or T. Thiooxidans, to oxidize sulphidic gold
concentrate a mixed culture of Thiobacillus and Leptospirillum has been used [11].
The third group thermophic bacteria mainly characterized by oxidation of
iron to assure growth chemolithorophically, some are facultative autotrophs that
require synergetic effect of other microorganism to like yeasts extract, cysteine, or
glutathione. Among the microorganism in this group Sulfolobus species is the major
one, these organism categorized as moderate thermophilic at an average values of
temperature 40°C -60°C and the second group is extreme thermophilc at an average
values of temperature 65–85°C. One of the moderate thermophilic gram positive
bacteria, Sulfobacillus Thermosulfidooxidans is facultative autotrophs in which its
growth stimulated by yeasts extract, where the presence of CO2, weight and volume
ratio (w/v) are factor to facilitate and inhibit growth. From of extreme ther-
emophilic Sulfolobus Acidocaldarius and Acidianus Brierleyi are those in genera
Archaebacteria, among the other four genera Sulfolobus, Acidanus, Metallosphaera,
and Sulfurococcus act aerobically and categorized in extreme thermophilic aci-
dophilic bacterial which oxidizes ferrous and elemental sulfur and sulphide based
minerals. These bacteria grows under all conditions (auto, mixo, heterotrphic)
depending on the yeast extract ratio (w/v), found in facultative chemolithotrophic
species act in acidic medium and temperature value can be up to 90°C [11].
All the major concepts of bioleaching have been discussed, so what are factors
affecting rate of bioleaching and leaching efficiency, the major factors can be summa-
rized as microbiological, mineralogical and physiochemistry factors. A physiochemis-
try factor includes temperature, pH, redox potential, oxygen content, carbon dioxide
content which facilitate mineral oxidation required for cell growth, mass transfer,
light, surface tension which mean that the topography of mineral surface that indi-
cate the rate adsorption and crystal structure which has direct relation on the rate
of reaction. Microbiological factors includes microbial diversity that is the distinct
nature of micro organisms with regard to range of unicellular organisms, variety
of microorganism found in an environment suitable for bioleaching, these includes
bacteria, fungi, algae, flagellates, and those found in microbial biocenosis, the other
microbiological factors are population diversity, metal tolerance, spatial distribution
microorganism and adaptation ability of microorganism. The third major factor is the
nature of mineral processed, characteristics like grain size which affect rate of dis-
solution, porosity related to rate of chemical attack and digestion rate, hydrophobicity
is another physiochemistry factor to determine the rate leaching, hydrophobicity is
differentiating whether the elements are water hating or loving while floatation takes
place. Process is the other major factor affecting leaching efficiency, techniques where
bioleaching process takes place (heap, dump, in situ) which we will be discussed
below, pulp density is the variable which results variation on dissolution rate, a study
shows that dissolution metal increases while pulp density increases but it is based
on (w/v) ratio that is between 5 and 20%, the other factor is concentration of target
mineral, this can inhibit the growth of microorganism, that cause a limitation of pulp
density usage [25]. Stirring speed is also another factor affecting rate of dissolution
and geometry of the heap during heap leaching process, the other major factor is
the presence of fluoride released from the ore sample, which inhibits the process of
bioleaching, and when the release decreases the rate of inhibition eventually reduced.
Biotechnology in Mining and Metallurgical Industry
Besides leaching process microorganisms are used for bioremediation of mining
sites, treatment of gangue, tailing, and mineral wastes from the industry, contami-
nation of sediments due heavy metals and soil from toxicities, sewage sludge can
cured by microorganism in which the process is called bioremediation [26].
. Bacterial leaching techniques
The successful bioleaching process is characterize by the intimacy of microor-
ganisms to a mineral surface, strong attachment result high rate of oxidation and
dissolution on a substrate (mineral surface), this is achieved by the rate success of
bio film formation. In general leaching techniques are two – Percolation leaching – a
solution infiltrate through a fixed mineral location, and agitation leaching - min-
eral bearing ore stirred by a solution but while working in large scale, percolation
leaching is usually chosen [7]. The principal commercial methods are aerated
stirred-tanks, in situ, dump, heap, vat, bench scale, tank, column, reactor leaching
are among the many. It was dump bioleaching process taken as the first commercial
bioleaching in 1950 used to leach copper from sulfide minerals, since then bioleach-
ing bloomed by copper oxide heap leaching, industrial microbial leaching process
applied for sulfidic gold and bioheap commercial leaching of copper ore (chal-
cocite and covellite). The high production of bio heap leaching of copper in 1980
established at Lo Aguirre mine in Chile processing 16,000 tones ore/per year at the
inception [27], these wipe the way that led to Chile’s industrial bio copper produc-
tion in large scale especially from the year 1984 [28].
. Stirred-tank biooxidation
Aerated, stirred-tank bioreactors, used in mineral concentrate feeds, involve a
series of stages that can have lots of tanks connected in parallel depending on the
retention of the concentrate [7] a study conducted to check Na-chloride can possibly
enhances the chemical and bacterial leaching of chalcopyrite uses three bioreactors
engaged with inoculum of the bacteria [29]. Other tanks needed for value adding
purposes which are usually single tanks might be connected in series, since these tanks
subject to chemical attack, air, heat and sulfide mineral, they should be relatively resis-
tant to corrosion, chemical attack, and soon, in order to have these character tanks
can be lined with rubber, galvanized, or other corrosion protection method like using
sacrificial anode or using high grade material like stainless steel, aluminum or copper.
Temperature maintained at optimum level by cooling coil or some time tanks
are equipped with water jackets depending on the required temperature by the
bacteria, these values can be conditioned based of the mineral to be leached, and
sometimes the chemical used to enhance the leaching process [29]. Several tanks
can be continuously arranged, named as continuous stirred tank reactor (CSTR),
as per the above it can be followed by a series of small equal sized reactors [16].
Example of bioleaching of sulfidic gold concentrates, that the discharge from the
final stage is subjected to water washing and solid/liquid separation in thickeners.
Even though there is less power consumption basically used for agitator and blower,
it has linear relationship with the amount of sulfide -sulfure which is required to
oxidize and recover the target metal from the parent ore, rate of recovery depends
up on the metal grade also.
The main advantages of these tank over other conventional methods like pres-
sure autoclave, roasting, smelting, calcination and soon are; it has low capital and
operational cost, relatively less construction period, less complicated requiring less
skilled man power and most importantly it is environmental friendly. In general
Bio Hydrometallurgical Technology, Application and Process Enhancement
DOI: http://dx.doi.org/10.5772/intechopen.94206
Australia, Chile, USA, Brazil and South Africa are among those countries involved
in bio oxidation by stirred tank [7, 16].
. Dump leaching
Dump (run of mine) [18] leaching involves uncrushed waste rock and low grade
ore is piled up or changing a pit to dump by blasting it. Conventional methods
would be very expensive to process these type of ores samples, except dump leach-
ing, dump can be very huge, containing in excess of 10 million tons of waste rock,
up to 60m deep [7, 30].
In order to digest some of unwanted minerals like silicate and to promote the
growth of acidophilic microorganism, acid water solution is spread on the top
surface, the acid water solution percolate through the dump, the more acidic the
environment the more growth of microorganisms that oxidize minerals to be
recovered. The pregnant leach liquor or acid run-off is collected at the bottom of the
dump, from where it is pumped to a recovery station. After collection the process
followed by solvent extraction, electro wining for the metal production but dump
aeration is vital for the microorganism to growth, tailing from solvent extraction
recycled on the top of dump. Escondida mine found Chile is the biggest bio dump
leach in world [26, 30].
. Heap leaching
Heap leaching (crushed and agglomerated) [18] is composed of air, acid and
microorganism where commutation takes place on rock samples to turn it to smaller
particles which increases the surface area for acid digestions and conditioning it
to microorganisms, particle should not be very fine and should be piled allowing a
simplifies aeration pipe placed to facilitate air flow. To improve drainage of the min-
eral containing solution from the bottom of the ore, conditioned ore is spread on
specially engineered pads (lined with high-density polyethylene (HDPE)), which
consist of perforated plastic drain lines and air also supplied to optimize the growth
of microorganism [7]. Heap can be large up to kilometer long, but commonly less
than 500m wide and 10m long, the size and height of a heap depends up on air (for
bacterial to grow) water, acid, heat generated due to the process and its dissipation
[31]. Heap surface should be permeable enough for the sulfuric acid to infiltrate and
dissolves iron to ferric solution producing ferric ion that react with copper sulfide
results ferrous ion and copper solutions. Acidithiobacillus Ferrooxidans oxidize
iron where the bacterial can be inoculated and works by attaching itself to ore, with
having free movement. After collecting PLS (pregnant leach solution), then solvent
extraction is followed where the target mineral recovered and formed into cathodes.
This aerobic bacteria works only in the presence of oxygen in the heap, those
bacteria consume it from the solution where oxygen is in liquid phase. This process
enhances the conversion of ferrous to ferric ions as per the reaction below.
23
22
Fe 0.25O H Fe 0.5H O.
+ ++
+ +® +
(18)
Heap some time can be crushed 19mm with rotating drum with acidified water
[29] aeration can be conducted using low pressure fans those directing air through
piping on the pad [26]. It is clear that heap leaching requires the preparation of the
ore, primarily size reduction, so as to maximize mineral-lixiviant interaction and
lay of an impermeable base to prevent lixiviant loss and pollution of water bodies.
Heap leaching basically used to leach low-grade ore of copper and zinc, even in
the case of copper grade level can be (0.2–2%). To have an effective heap leaching
Biotechnology in Mining and Metallurgical Industry
process a mathematical model has been developed by taking heat, mass transfer,
liquid, gas flow and chemical process in to consideration [31]. Heap also employed
to bioleach silicate mineral, in a study where two microorganism were tested
‘Ferroplasma acidarmanus or the common Acidithiobacillus ferrooxidans against
the amenity of silicate minerals. Beside oxidation process energy was generated
from flat plate solar energy collectors where heap is designed by HeapSim, heap
bioleach simulation tool was used to simulate the heap and process occurring in the
heap, even calculating the copper output [32].
. In situ bioleaching
In situ leaching requires making the ore permeable for a solution and air to be
circulated through the ore body. It does not require metal containing material to be
removed from the ground [18]. It employs a method of recovering target minerals
from the leach solution. The acid solution percolates until it reaches to imperme-
able layer. In situ includes recovery of minerals from the intact ore. The resulting
metal-enriched solutions are recovered through wells drilled below the ore body.
In case of in situ leaching the main concern is pollution of ground water, with this
regard there are three types of ore bodies generally considered for in situ leaching:
surface deposits above the water table, surface deposits below the water table and
deep deposits below the water table. It is burden materials, establish permeability
allowing air to pass in which metal bearing solution collected in the sumps [7]. It is
combined with mineral recovery operation time and again to pull out the minerals
from recovered fluid or pregnant solution or leachant. Acidified leach solutions,
applied to the top surface of the entire ore zone, infiltrate through the fragmented
ore due to the blast. The leaching bacteria become established and facilitate metal
extraction. Metal-rich solutions or large volume of solution is circulated with the
aid of gravity flow and pumped and recovered in sumps then again pumped to
the surface for metal recovery, the returning fluids to the extraction operation are
known as “barren solution”. Metal recovery depends on two major things first the
bacteria used (Acidithiobacillus Ferrooxidans) and permeability of the ore-body,
which can be increased by fragmenting of ores in place, called “rubblizing”. Due to
the ground water pollution this leaching process becomes less used and less popular
[18] on the contrary it has been said that it is a best substitute for open pit and shaft
mining operation, basically when in situ leaching is applied, no gangue or tailing is
byproduct, it also called green mining or mine of the future [33].
. Bioleaching of some elements
. Bioleaching of uranium
Recent study shows that elements like uranium, copper, gold, zinc and other
elements are commercial focus of bioleaching and biooxidation [34]. Many studies
indicate microbial leaching is more important in low-grade ore, ore sample collected
from Mianhuakeng uranium mine located in northern Guangdong province in
China, leached by heap, by mixed microorganism of Acidithiobacillus Ferrooxidans
and Leptospirillum Ferriphilum with 88.3% leaching efficiency [35]. Uranium leach-
ing takes places by indirect mechanism, as Acidithiobacillus Ferrooxidans does not
directly interact with uranium minerals. The role of Acidithiobacillus Ferrooxidans
in uranium leaching is the best example of the indirect mechanism. Bacterial activ-
ity is limited to oxidation of pyrite and ferrous iron. The process involves periodic
spraying or flooding of worked-out stops and tunnels of underground mines with
Bio Hydrometallurgical Technology, Application and Process Enhancement
DOI: http://dx.doi.org/10.5772/intechopen.94206
lixiviant [4]. The pH of lixiviant was optimized during the bioleaching of uranium
from low grade Indian silicate-apatite ore with 0.024% of U3O8. This study uses
Acidithiobacillus Ferrooxidans for leaching and biochemically generated ferric ions
as an oxidant, optimizing particle, pulp density and redox potential results 98%
uranium bioleaching. In this indirect bioleaching of uranium, the bacteria generate
ferric sulfate and pyrite is oxidized by a lixiviant, within acidic environment the
oxidations of ferrous ion to ferric ions process executed by the bacteria is fasters
than chemical oxidation [36]. In case of uranium bioleaching the main drawback
is to oxidize uranium (IV) since it insoluble but on this bioleaching process when
ferrous sulfate produced in the process, then re-oxidized to ferric sulfate which
enzymatically oxidize uranium (IV) to uranium (VI) by the energy produced by this
reaction. A case study in India at Jaduguda mines proofs that use of biogenic ferric
sulfate produced by the strain which was then used for efficient uranium extraction
and cause no harm to the environment, while extracting uranium, use of reduced
MnO2 in Bacfox process to generate biogenic ferric sulfate, results passed air satu-
rated ferrous sulfate solution over Acidithiobacillus Ferrooxidans which is absorbed
on solid surface [36]. Since the permeability of the ore surface is a factor, the above
study uses a process called “rubblizing” that increase fragmenting of ore in place
which can be applied in the extraction of sulfide mineral, gold and uranium. While
isolating the bacteria from mine water, the isolation media and H2SO4 consumption
during isolation, pH variation and temperature were determinate factors, the micro-
bial cell count and the growth of (A. Ferrooxidans) determines by rate of oxidation
of iron from Fe2+ to Fe3+, so while leaching if the amount of Fe2+ decrease means
the bacteria is using it as energy source to convert it to Fe3+, uranium bioleaching
depends on the synergic effects Fe3+ and proton produced by the bacterial [37] that
process uses either of the two energy sources to growth iron or sulfur. The reaction
of making insoluble uranium to soluble form is as follows [38].
( )
2 2 4 24 4
3
UO Fe SO UO SO 2FeSO .+ ®+
(19)
Studies indicate that microbial cell count and pulp density ranges 5–30% (w/v),
particle size <75μm has brought an optimum ore leaching but it should be clear that
each ore has its own distinct behavior and no size fits all, meaning results indicated
here might be different for another ore sample due to ore elemental composition,
crystal structure, grade, topography and surface tension.
. Bioleaching of copper
The ore is loaded on a water-resistant surface or ore is piled on an imperme-
able surface until a dump of suitable dimension forms. After leveling the top, then
spraying a leach solution onto the dump is followed [4]. These dump is a habitat of
heterogeneous microorganism. Dump can have variety particles sizes, where the
bacterial annexation, which is anaerobic (microaerophilic), thermophilic begins
from the top.
Dump leaching used to pretreat low-grade, refractory- sulfidic gold ores and to
leach copper from chalcocite ores while ore grade is low with values ranges between
0.1–0.5%. Copper can be obtained from ore rocks from the mound then washed
with dilute H2SO4 to facilitate the oxidation process of mineral by acidophiles,
which is followed by cementation process where copper is precipitated from the
drainage with scrap iron since it primary iron oxidizing process [39]. Check the
leaching process of copper sulfide chalcocite (Cu2S), which occurs with pyrite
(FeS2), leaching is due to ferric ion reacts with copper sulfide mineral processes
ferrous and copper ions in solution.
Biotechnology in Mining and Metallurgical Industry
32 2
2
Cu S 4Fe 4F 2Cu S.
++ +
+ ®+ +
(20)
3 22
22 4
Fe 8H O 14Fe 15Fe 2SO 16H .S+ + -+
++ ® + + (21)
In these regions indirect leaching by ferric sulphate also prevails. The exterior of
the dump is at ambient temperature and undergoes changes in temperature reflect-
ing seasonal and diurnal fluctuations. Many different microorganisms have been
isolated from copper dumps, some of which have been studied in the laboratory.
These include a variety of mesophilic, aerobic iron and sulfur oxidizing microor-
ganisms; thermophilic iron and sulfur oxidizing microorganisms; and anaerobic
sulphate reducing bacteria. In copper leaching the concentration of target metal
by itself is an important variable, copper concentration (100–300mM range) is
values cause difficulty for the microorganism to operate, selecting the microorgan-
ism is one of the mechanisms of copper resistant, Acidithiobacillus Ferrooxidans
can resist copper concentration and strong acidic environment [40]. Thiobacillus
Ferrooxidans was the main product observed after a culture study, from an ore or
leach solution for the identification of composition of bacterial population and
incase of low ferrous ions, it was Leptospirillum Ferrooxidan was observed, the
study shows that utilization of ferrous iron as energy source is dominated by the
previous bacteria as the culture shows. Pseudomonas aeruginosa, where heterotro-
phic bacteria produce various organic acids in an appropriate culture medium is
used in copper leaching [41]. The addition of salt in bioleaching of copper resulted
process enhancement, after designing the bioreactor the bioleaching of copper was
enhanced in both stirred tank or shack flask by adding sodium chloride in leach
solution, increasing the dissolution of Fe3+ that eventually reduces precipitation
[29] addition of some elements might result inhibition of bioleaching process, fluo-
rine in solution increase the viscosity of leach liquor that result inhibition of biole-
aching [42]. It is important to understand the microbiology, which is responsible or
identify a means to study bulk activity of microorganism, these features are oxygen
uptake in solid and liquid samples, redox potential, pH, ferrous iron concentration
and temperature. Microbial leaching has also direct relation with enrichment and
culture from solution of ores. Acidithiobacillus Thiooxidans, Acidithiobacillus
Ferrooxidans, and Leptospirillum Ferrooxidans have been cultured where the
process run at an ambient temperature and the strain of bacterial related to the
microorganism mentioned here [27, 43]. Leach solutions enriched with copper
exit at the base of the dump and are conveyed to a central recovery facility. In most
large-scale operations the leach solution, copper-bearing solution pumped into
large cementation units containing iron scrapings for cementation and then elec-
trolysis followed [4]. It was in Chile and Australia the commercial bio heap leaching
of copper started mass production. And the first bioleach heap copper extraction
plant is in China [44]. The copper extracted percentage can be calculated as,
E=Copper content in the solution/copper content in the sample X 100% [41].
. Bioleaching of gold
Acidophilic bacteria are able to oxidize gold containing sulphidic ore, such a
process can be ameliorated by conventional process of cyanidation, these basi-
cally reduces the complexation by increasing the capability of microorganisms to
reach to the target metal. Certain sulphidic ores containing encapsulated particles
of elemental gold, resulting in improved accessibility of gold to complexation by
leaching agents such as cyanide. Relative to other conventional process and pre-
treatments like roasting, smelting and pressure oxidation, bio-oxidation demands
Bio Hydrometallurgical Technology, Application and Process Enhancement
DOI: http://dx.doi.org/10.5772/intechopen.94206
less cost and no harm to nature [7]. Though it is under study a commercial bio-
oxidation and bio heap leaching of gold prior cyanide extraction. It is the bacteria,
Acidithiobacillus Ferrooxidans used to oxidize the sulphide matrix for gold recov-
ery. Prior to extraction, gold ore must be bio-oxidize by the bacteria. In this process
refractory sulphidic gold ores contain mainly two types of sulphides: pyrite and
arsenopyrite where silver ion was used as a catalyst in acidic environment. Since
gold is usually finely disseminated in the sulphide matrix, the objective of biooxida-
tion of refractory gold ores is to break the sulphide matrix by dissolution of pyrite
and arsenopyrite and extract 95% of iron and arsenic, the residue of both filtered
through a vacuum pump. The consumption of cynide is much higher while biooxi-
dation, the study suggested that using thiourea instead of cyanide is much less toxic
but since the process require high consumption of thiourea cost increase steadily,
consumption of thiourea reduced by using different agents like SO2, bisulfite,
cystine, cystine with oxygen during extraction process [45].
. Industrial application
The mesophilic tank leaching is the most common bioleaching process in the
world; thermophilc tank is favored while the temperature is high, among such tanks
BioCop™ well known, In order to have effective thermophilc tank the following are
basic requirements, microbial catalyzed reaction which is needed to facilitate metal
dissolution by microbial oxidizing of ferrous iron to ferric iron, initial solublization
of ferrous ion takes place using acid solution, oxidation of mineral sulfide takes
place by the combination effects of ferric iron and acid solution followed by oxidi-
zation of reduced sulfur to sulfate by microorganisms. Reactor configuration is the
other factor where the six equal size continuous reactor, three arranged in parallel
considered as primary reactors, and the other three arranged in series considered
as secondary reactors, in this case reactors are considers as a large continues stirred
tank supplied with aeration and agitation. The other factors are oxygen, carbon
dioxide, pulp density and finally even though the operational cost is much less
plant location, construction material, blower or compressor to supply oxygen to the
microbes, high power agitator in case of oxygen plant for oxygen dispersal in the
reactor. Growth of industries results the demand of metals in very high quantity
and likely go further in the years to come. This brings diminution of high grade ore
with effluents and solid wastes that needs to be treated to recover the important
elements and protect the environment.
Regarding to environment biohydrometallurgy is vital process, the fact that bio-
process is conducted without the presence of toxic chemical and relatively required
low cost makes it most needed. The direct implication of microorganisms in the
reduction of uranium is of considerable interest because of its potential application
in bio remediating of contaminated sites, in pretreating radioactive wastes, biole-
aching is becoming a promising technology.
Biotechnology in Mining and Metallurgical Industry
Author details
Mulugeta SisayCheru
Institution- Jimma Institute of Technology, Jimma, Ethiopia
*Address all correspondence to: mulugetajimma07@gmail.com
© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms
of the Creative Commons Attribution License (http://creativecommons.org/licenses/
by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,
provided the original work is properly cited.
Bio Hydrometallurgical Technology, Application and Process Enhancement
DOI: http://dx.doi.org/10.5772/intechopen.94206
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