Bioleaching/Biocorrosion Metals/Biomining

Presented to: Dr. Michael Broaders

Presented by: Ms. Lisa Smith Ms. Marian Cummins Ms. Deborah Mc Auliffe

Presented on: 16th December 2005

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Table of Contents

1. Introduction………………………………………………………………………3

2. Biocorrosion………………………………………………………………...........6

3. Biooxidation…...………………………………………………………………....7

4. Bioleaching…...……………………………………………………………..……8

4.1 History of Bioleaching………………………………………………………..8

4.2 Why Bioleaching has Bioleaching become such an attractive alternative?.....10

4.3 General Properties of the

Microorganisms…………………………………...11

4.4 Specific Microorganisms…………………………………………………….11

4.5 Bioleaching Processes……………………………………………………….12

4.6 The Process…………………………………………………………………..13

4.7 Methods to increase biomining efficiencies and the impacts of Genetic

Engineering on Biomining…………………………………………………..16

4.8 Metal extraction operations………………………………………………….17

4.9 Examples of current Industrial Bioleaching Operations…………………….20

5. Case Studies……………………………………………………………………...22

6. Economics of Biomining………………………………………………………...30

7. Remediation of Metal-Contaminated Soil………………………………………33

8. Conclusion…………………………………………………………………….…35

References…………………………………………………………………….....37

Glossary…………………………………………………………………………40

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1. IntroductionBy Lisa Smith

Metal contamination of soil environments and the assessment of its potential risk to

terrestrial and aquatic environments and human health is one of the most challenging

tasks confronting scientists today.

While not all metals in soil, plant systems are inherently toxic, particularly in low

concentrations, there is an increasing incidence of metal pollution from aerial fallout,

spills, wastes and agricultural amendments including sewage sludge. Metal solubility and

availability in soil is influenced by fundamental chemical reactions between metal

constituents and soil components.

Heavy metal contamination of soil is a common problem encountered at many hazardous

waste sites. Lead ,chromium, cadmium, copper, zinc, and mercury are among the most

frequently observed metal contaminants. They are present at elevated concentrations at

many National Priorty List sites, are toxic to people, and threaten ground water supplies.

Gortmore, west of Silvermines in Co. Tipperary is an instance of how mining can affect a

community and the surroundings environment. In January 1999 the Environmental

Protection Agency (EPA) reported that a large tailings pond at Gortmore was “a

perpetual risk to human health and the (local) environment”. Firstly, it was an artificial

lake almost 150 acres covering nine million tonnes of tailings or ore waste (including

lead) piped into it from a nearby zinc mine. Once operations ceased after 25 years the

lake dried out and was covered to prevent any further dust blow and to control the escape

of possible contaminants. But local people could see could see discharges flowing into

the waterway. The area was officially termed a “tailings management facility”, few

agreed. Cattle died from lead poisoning, there is no significant evidence of transfer of

lead to humans, lead poisoning is not widespread and food production is generally safe in

the area. Nevertheless further evidence suggests the Gortmore tailings management

facility is not the only toxic site in the area. Urgent action was needed to resort

contaminated sites (ireland.com, 2000). In August 2005 the Minster for Communications,

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Marine and Natural Resources, Noel Dempsey announced funding by the state of €10.6

million for the remediation of toxic mining waste sites. Public consultation of proposed

remediation is to take place before the end of 2005 (ireland.com, 2005).

The sustainable development challenge facing the mineral and mining industry is to

provide the supply of minerals, metals and material required to sustain social and

economic growth without causing long term degradation of the environment.

Mining companies have become increasingly aware of the potential of microbiological

approaches for recovering base and precious metals from low-grade ores.

The mining industry uses microorganisms and their natural ability to digest, absorb and

change the quality of different chemicals and metals, to refine ores.

Biomining is the use of microorganisms to extract metals and minerals from ores in the

mining process. Ores of high quality are rapidly being depleted and biomining allows

environmentally friendly ways of extracting metals from low-grade ores.

Biomining uses naturally existing microorganisms to leach and oxidate. Biomining

includes two different processes biooxidation and bioleaching.

Biomining processes are usually done in heaps of ground ore. The low-grade ores are

ground into powder and piled in an irrigated outdoor facility. The heaps are then treated

with an acidic liquid that contains a fraction of the bacterial population required (some

naturally existing within the ore). The liquid with the metals extracted are then pumped

into another section where metal is recovered.

Bioleaching is a new technique used by the mining industry to extract minerals and

metals with the use of microorganisms. The process involves removing a soluble

substance from a solid structure by making it into a liquid form easy for extraction. In

this process low concentration of metals does not pose a problem for the bacteria as they

just ignore the waste which surrounds the metals, whereas with   traditional extraction

that of roasting and smelting these processes require sufficient concentration of elements

in the ores. So bacterial leaching is a process by which the metal of interest is extracted

from the ore by bacterial action, as in the case of bacterial leaching of copper

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Biooxidation also uses microorganisms, not to extract metals, but to make the metals

ready for extraction. Oxidation is the chemical reaction in which an element is changed

by the addition of oxygen and is mainly used for gold mining.

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2. BiocorrosionBy Lisa Smith

Physicochemical interactions between a metallic material and its environment can lead to

corrosion.

Corrosion is a “naturally occurring process by which materials fabricated of pure metals

and/or other mixtures undergo chemical oxidation from ground state to an ionized

species” (Beech, 2003). The process proceeds through a series of oxidation (anodic) and

reduction (cathodic) reactions of chemical species in direct contact with, or in close

proximity to, the metallic surface.

In natural habitats and man-made systems, surface-associated microbial growth, i.e.

biofilms, influence the physico-chemical interactions between metals and the

environment, frequently leading to deterioration of the metal. For example in a marine

environment the presence of a biofilm can accelerate corrosion rates of carbon steel by

several orders of magnitude. However, in contrast, certain types of biofilms produce a

protective barrier effect resulting in a significant decrease in corrosion rates of metals.

Deterioration of metal under a biological influence is termed biocorrosion or

microbiologically influenced corrosion (MIC).

“Biocorrosion is a result of interactions between metal surfaces and bacterial cells and

their metabolites” (Beech, Sunner, 2004).

The main types of bacteria associated with metals in terrestrial (and aquatic)

environments are sulfate-reducing bacteria (SRB), sulfur-oxidising bacteria, iron-

oxidising/reducing bacteria, manganese –oxidising bacteria and bacteria secreting organic

acids and slime. These organisms coexist in naturally occurring biofilms.

SRB are the main group of microorganisms and are generally anaerobic, however some

genra tolerate oxygen and even grow in its presence. They are distributed within two

domains: Archaea and Bacteria.

There is increasing recognition that microbes such as bacteria play an even larger role in

all forms of corrosion than previously thought. It is now reported that up to 70% of all

corrosion in water systems is caused or accelerated by microbes.

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4. BiooxidationBy Deborah Mc Auliffe

Many biotechnology-derived processes use microorganisms to help ease the usage of

harmful chemicals in various industrial processes. The mining industry uses

microorganisms and their natural ability to digest, absorb, and change the quality of

different chemicals and metals, to refine ores.

Biooxidation also uses microorganisms, not to extract metals, but to make the metals

ready for extraction. Oxidation is the chemical reaction in which an element is changed

by the addition of oxygen. Rust is an example of the oxidization of iron.

 

Biooxidation is mainly used in gold mining. Gold is often found in ores with gold

particles scattered throughout, called refractory ores, and the small particles of gold are

covered by insoluble minerals. These minerals make the extraction difficult. Therefore,

microorganisms that can "eat away" at the mineral coating are used to pre-treat the gold

ores before they can be extracted.

 

Bioleaching of copper, and biooxidation of refractory gold ores are the only well-

established large scale processes that are commercially carried out today.

 

Currently, 25 percent of all copper worldwide is produced through biomining. The

process is used on a variety of other metals such as gold and uranium. Biomining is not

yet a proven or profitable technology to apply to other metals such as zinc, nickel and

cobalt.

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4. BioleachingBy Marian Cummins

4.1 History of Bioleaching

Although mining is one of the oldest technologies known it has succeeded in escaping the

major technological advances seen in that of agriculture and medicine. Many minerals

and metals are mined today in exactly the same manner, as they were hundreds of years

previous. The crude ores are dug from the earth, crushed and the mineral is extracted by

either by extreme heat or due to the addition of toxic chemicals. But due to the

environmentally unfriendly aspect of these mining techniques new methods, which are

kinder and more environmentally friendly, are being used which uses microorganisms,

which leach out the metals- that of Bioleaching

One of the earliest recordings of bioleaching comes from Cyprus, reported by Galen, a

naturalist and physician AD166 who reported on the in situ leaching of copper. Surface

water was allowed to flow through permeable rock and as it percolated through the rock,

the copper minerals dissolved so the result was a high concentration of copper sulphate in

solution. This solution was allowed to evaporate with the resultant crystallation of copper

sulphate. Pliny (23-79 AD) reported the similar practice of copper extraction as copper

sulphate was widely used in Spain.

Prior to electrolysis, the recovery of the copper from copper sulphate was by

cementation (precipitation). It is thought that this process was known in Pliny time but no

written records of this have survived. Its is known that the Romans used to place scrap

iron into the river and over a period of a few months the copper precipated around the

iron. The pure copper was then recovered by smelting, but what the Romans didn’t

realize was microorganisms played a major biological contribution to this process by

generating the copper in the water. The Chinese were also aware of the process

(cementation) as documented by King Lui- An (177-122 BC). The Chinese implemented

the commercial production of copper from copper sulphate when the Chiangshan

cementation plant started operation in 1096 with an annual production of 190ton

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Cu/annum. Bioleaching and cementation were also described by Paracelsus the Great

(1493-1541). He noted the copper deposition onto iron at a spring in the Zifferbrunnen in

Hungary. Although he confused this deposition with that of transmutation, he assisted in

the use of bioleaching and by 1750 approx 200t/annum Cu were obtained in the

Zifferbrunnen area of Hungary using this process of bioleaching.

Even though these earlier bioleaching operations were difficult to document, it is

known that copper leaching was well established at the Rio Tinto mine in Spain by the

18th century. Rio Tinto literally means “coloured fiver”, a name given to the acidified

fiver that issues from the Sierra San Cristobol mountains on the fiver bed and on the

abundant microbial mats, the dense floating masses made up of different microorganisms

(reference 1). At Rio Tinto the process of heap leaching of copper sulphides was carried

out on an industrial scale in 1752. In this process the ore is heaped and crushed onto

open-air pads. The layers of ore were altered with beds of wood. Once the heap was

constructed the wood was ignited which resulted in the roasting of copper and iron

sulphides. Water was then added to the top of the heap. The addition of water caused the

copper and iron to dissolve which formed copper and iron sulphates. But due to the

significant environmental damage caused by the production of sulphuric acid in this

process, the process was stopped in 1888. This heap leaching process minus the roasting

step continued at Rio Tinto until the 1970’s.The reason for it’s success was unknown, but

it was thought to be due to “some obscure quality either of the Rio Tinto ore or the

Spanish climate’. But it is now widely accepted and known that it was in fact the

microorganism Thiobacillus ferroxidans that contributed to the success of Rio Tinto.

In the 1940’s in America, several million tons of sulphuric acid was discovered in the

Ohio River, this discharge was attributed to the weathering of subbitumous coal.

Naturally enough this pollution incident was unacceptable and it led to widespread

investigation by universities and several US government institutions, such as the US

Bureau of Mines as to the source of the pollution. The cause of the sulphuric acid was

due to the oxidation of pyrite, which is present in the subbitumuous coal, but it was also

noted that this oxidation occurred much more rapidly than could be contributed to by that

of inorganic chemistry. Also an important observation was that of the presence of sulphur

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oxidizing bacteria. And in 1950 a couple of years after the incident a new species was

identified that of Thiobacillus ferrooxidans. This organism is able to oxidize elemental

sulphur and ferrous ions at a much higher rate than that achieved by inorganic chemistry.

It is this catalysis of the oxidation of ferrous ions that makes Thiobacillus ferrooxidans

and other iron and sulphur oxidizing microorganisms such important catalysts in the

bioleaching process.

4.2 Why has Bioleaching become such an attractive alternative?

Bioleaching is a very attractive alternative to to the conventional mining techniques and it

is very desirable in today’s world due to the continued depletion of high grade reserves

and so it allows the more economically extraction of minerals by from low grade ores, it

also arise from the resulting tendency for mining to be extended deeper underground and

also it is a much more environmental friendly alternative to that of the conventional

mining methods to which there is a growing awareness of the environmental issues

associated with the smelting of sulphide minerals and the burning of sulphur rich fossil

fuels and of course there is the enormous energy costs that is associated with the

conventional methods. Bimining also improves recovery rates, reduces capital and

operating costs.

There has being a very widespread and rapid interest in the exploitation of biomining

especially in the copper industry, due to the fact that the copper in the low grade ore is

bound up in a sulfide matrix, it can be recovered by traditional smelting only at great

cost. In addition the world is running out of smelting capacity because of the depletion of

the high-grade ores means that more ore has to be smelted to produce the same amount of

copper. Oxidising bacteria can reduce the need for these expensive smelters. Whereas a

new smelter can cost 1 billion dollars the technology required for biomining I pretty

uncomplicated.

In order to understand the process of microbial mining or biomiining a number of

considerations must be understood and answered, such as what microorganisms are

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involved in the extraction of the metals from the rocks and where in nature do they

occur? What biochemical functions do these microorganisms perform and what do they

require in the need of nutrient and environmental conditions in order to maintain their

activity? What are the constraints of the commercial exploitation of such biological

techniques? And what impact will the new tools of genetic engineering have on the future

of biomining?

4.3 General Properties of the Microorganisms

The bacteria involved in biomining are among the most remarkable life forms known.

They are described as chemolithotrophic, which basically means rock eating, that is they

obtain their energy from the oxidation of inorganic substances. Many of them are also

autotrophic that is they utilize carbon dioxide in the atmosphere as the carbon source.

These microorganisms live in very inhospitable environments, which other microbes

would find it impossible to survive or tolerate; for example the sulphuric acid and soluble

metals concentrations are often very high. Some thermophilic microorganisms require

temperatures above 50 degree Celsius (122 degree Fahrenheit), and a few strains have

been found at temperatures close to that of the boiling point of water.

4.4 Specific Microorganisms

For many years the general impression was that Thiobacillus ferrooxidans was the only

microorganism responsible for the leaching proceeds. As previously stated this

microorganism wasn’t discovered until 1957 in the acidic water draining coal mines,

where it was then determined the relationship between the existence of this

microorganism and the dissolution of metals in copper- leaching operations. Since its

discovery in the Rio Tinto Mine in Spain a wealth of information has be collected

regarding its characteristics and also more importantly on the role it plays in bioleaching

of the metals.

T. ferrooxidans is rod shaped (usually single or in pairs), non- spore forming, gram

negative, and single pole flagellated ( HORAN, 1999;KELLY and HARRISON, 1984;

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LEDUC and FERRONI, 1994; MURR, 1980). T. ferrooxidans is also acidophilic; it tends

to be found in hot springs, volcanic fissures and in sulfide ores deposits that have high

sulphuric acid concentrations. It is also moderately thermophilic, thriving in temperatures

between 20 and 35 degree C. It obtains its energy for growth from the oxidation of either

iron or sulphur. The iron must be in the ferrous or bivalent form (Fe2+), and it is converted

by the action of T. ferrooxidans to the ferric or trivalent form (Fe3+). The nitrogen source

utilized is that of ammonium. T. ferrooxidans obtains carbon autotrophically from the

atmosphere as carbon dioxide. Although T. ferrooxidans has been characterized as being

a strictly aerobic organism, it can also grow on elemental sulphur or metal sulphides

under anoxic conditions using ferric iron as an electron acceptor. (Donti et al., 1997;

Pronk et al., 1992). It is generally found in environment with a Ph OF 2.0.

As important and all T. ferrooxidans is in the leaching process another important

microorganism taking part ii that of T. thioxidans, this is also a rod shaped bacteria, very

similar to T. ferrooxidans but it can’t oxidized Fe3+ it is also gram negative Its maximum

growth rate is at 35 degrees C, and it is the dominant microbe found at low Ph

environments. It has being found that mixed cultures of bacteria are responsible for the

extraction of metals from their ores such as is the case with the combined effects of T

ferrooxidans and T. thiooxidans are more effective in leaching certain ores together than

as an individual organism. Also Leptospirillium ferrooxidans and T. organaparus can

degrade pyrite (FeS2) and chalopyrite (CuFeS2), a feat, which neither species can do

alone.

4.5 Bioleaching Processes

The process of bioleaching falls under 2 methods that of direct leaching and indirect

leaching. Direct leaching is the process where the bacteria attack the minerals which are

susceptible to leaching by enzymes. By obtaining the energy from the inorganic material

the bacteria aid in the transferring of electrons from iron or sulphur to oxygen. The more

oxidized product is generally the more soluble the product. The inorganic material never

enter the bacterial cell, the electrons released by the oxidation reaction are transported

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through the cell membrane (and in aerobic organisms) to oxygen atoms forming water.

ATP (adenosine triphosphate) is produced when the transferred electrons give up their

energy.

Indirect leaching, in cons tract does not occur by the bacteria attacking the minerals.

The bacteria produce ferric iron (Fe3+) by oxidizing soluble ferrous iron (Fe2+) which is a

powerful oxidizing agent that reacts with the other metals, and transforms them into a

soluble oxidisable form in a sulphuric acid solution. In this way the ferrous iron is

produced again and is rapidly oxidized by the bacteria thus it is a continuous cycle. This

indirect leaching is generally known as bacterial assisted leaching. T. ferrooxidans can

speed up the oxidation of iron by a factor of more than a million than without the bacteria

being present in the solution.

4.6 The Process

In the case of the extraction of copper from its ore the aforementioned bacteria

T.ferrooxidans and T. thiooxidans are involved in this process, which is a 2-stage process

that of direct and indirect as previously discussed.

In stage 1, the bacteria break down the mineral arsenopyrite (FeAsS) by oxidizing the

sulphur ant the metal (arsenic ions) to a higher oxidation state whilst reducing dioxygen

by H2 and Fe3+ This allows the soluble products to dissolve as such

FeAsS(s) -> Fe2+(aq) + As3+

(aq) + S6+(aq)

This process of direct leaching as described previously occurs at the cell membrane of

the bacteria. The electrons pass into the cells and are used in biochemical processes to

produce energy for the bacteria to reduce oxygen molecules to water.

In stage 2, that of indirect leaching the bacteria oxidise Fe2+ to Fe3+ (whilst reducing O2).

Fe2+ -> Fe3+

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They then oxidise the metal to a higher positive oxidation state. With the electrons gained

from that, they reduce Fe3+ to Fe2+ to continue the cycle. This stage involves both ditect

and indirect leaching.

M3+ -> M5+

The gold is now separated from the ore and in solution.

The process for copper is very similar. The mineral chalcopyrite (CuFeS2) follows the

two stages of being dissolved and then further oxidised, with Cu2+ ions being left.

In the process of extracting copper (Cu2+) from a mixture, the copper ions are removed by

solvent extraction, which leaves the other ions in solution. The copper is removed by

bonding to a ligand, which is essentially a large molecule consisting of a number of

smaller groups each processing a lone pair. The ligand is then dissolved in kerosene

(organic solvent) and shaken with the resultant reaction:

Cu2+(aq) + 2LH(organic) -> CuL2(organic) + 2H+

(aq)

Electrons are donated to the copper, producing a complex, copper bonded to 2 molecules

of the ligand. As this complex has no charge as as it is no longer attracted to the polar

water molecules it dissolves in the kerosene and is then seperated from solution.This

initail reaction is reversible as so is pH dependent. The copper ions go back into an

aqueoeus solution by adding concentrated acid.

To increase the purity of the copper an electric current is added to the copper ions as it

passes through an electro-winning process. The copper ions which have a 2+ charge are

attracted to the negative electrode and thus collected.

The copper can also be concentarted and recovered by using scrap iron which replaces

the copper in the reaction as thus:

Cu2+(aq) + Fe(s) -> Cu(s) + Fe2+

(aq)

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As described biomining has being extremely successful in the case of copper.But gold

can also be obtained in a similar manner. Up until recently the gold mining industry

depended on high grade ores near the surface og the earth.But by the 1980 and the

depletion of these ores forced miners to rely on the lower grade ores which were located

deeper in the mines. These low grade ores were more difficult to process in comparsion

to the high grade ores at the surface as they were naturally oxidized by bacteria, sunlight

and water. But the low grade ores are generally encased in sulphide minerals a and so

processing of these ores requires roasting or pressure oxidation and then treatment with

cyanide.Biomining means that the costly procedures of roasting and pressure oxidation

can be surpasssed by usinf T. ferrooxidans for the pretreatment of the gold ores. The first

mine to take advantage of this was Fairview mine in South Africa (owned by Gencor

(Pty) Ltd. )where most of the ore was the refractory sulphide type. By using biomining at

Fairview the recovery rate of the gold increased from 70 % to 95%.And due to this

success rate Gencor opened 4 more biomining sites, Harbour Lights, Tonkin Springs,

Wiluna and Younmi in Australia, San Bento in South America and the huge Ashanti

plant in Ghana which started in 1994 and by 1998 it was producing 800t/ day of gold

concentrate.

Although gold and copper are probably the most important and valuable metals and

undoubtedly this is what has pushed the huge interest there now is in biomining. But

biomining has also played a big part in the phosphates industry. Phosphates are definitely

not as valuable as the metals but their extraction is definitely plays a part in big time

mining. Phosphates for fertilisers is the world’s second largest agricultural chemical

(after nitrogen); about 5 .5 million tons are produced every year in the US alone. Another

1.1 million tons of higher quality phosphates are used as an additive in soft drinks and in

the manufacture of detergents, rubber, and industrial chemicals.

The traditional method of extracting phosphates from ores was by burning at high

temperatures with the resultant of solid phosphorus, or else by treatment with sulphuric

acid with phosphoric acid and huge amounts of useless low-grade gypsum being the

result. But with the process of biomining a much milder technique was available. This

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new technique used two bacteria that of Pseudomonas cepacia E-37 and Erwinia

herbicola, these bacteria were chosen from hundreds of bacteria as they have the unusual

ability: a direct oxidative pathway of converting glucose into gluconic and 2 ketogluconic

acids, which means that sulfuric acid doesn’t have to be used in the process and also this

milder technique it performed at room temperature and so it is a much more

environmentally friendly process.

4.7 Methods to increase biomining efficiencies and the impacts of Genetic Engineering on Biomining

As biomining is now at an all time high it the next challenge is to increase its efficiency.

At the present time it is only indigenous microorganisms that naturally occur in dumps or

mine run off that are used in the bioleaching process. So now the focus is on finding

microbial strains that are better suited to large scale industrial processing. One draw back

is that the bioleaching process releases large amounts of heat and

Can raise the temperature so much that the bacteria that are being in use are killed or

slowed down. To combat this work has being and is still currently being done on using

Archaebacteria for use in biomining. These primitive thermophiles, or heat loving

bacteria are so far poorly studied and they are found in deep-sea vents and in hot springs

such as in Yellowstone National Park, Iceland and in New Zealand. They thrive in

temperatures of up to 100 C or higher. They are currently being put to test at the

Younami mine in Western Australia.

Another challenge is to find or engineer strains that can stand up to the presence of heavy

metals such as mercury, arsenic, cadmium, these metals poison the microbes currently

being used in biomining and thus slow down biomining. Some steps have being taken

toward finding resistant strains to these poisons by showing that some microbes have

enzymes that can work in 2 ways that of protecting their basic activities from heavy

metals or by pumping the metals out of the bacteria. Also some work but not a lot has

being done on identifying genes that help the microbes deal with the heavy metals and

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these genes may be used to genetically engineer resistant strains. The genetically

engineering of bacteria to resist heavy metal poisoning is not an easy achievement.

As much less is known about the Thiobacillus species and the other microbes used in

biomining than is known for E. coli, which is of course a lab favourite? But hopefully this

genetically engineering of these microorganisms will take place at a much quicker pace

than the two millennia is took the Roman miners at Rio Tinto to become a major

improvement in biomining, but it is fairly safe to say that these developments will take

place sooner rather than later as biomining has become a worldwide accepted process

4.8 Metal extraction operations Insitu leaching is a promising alternative for the recovery of metals from low-grade ores,

which are in inaccessible places. Also this has the advantages as this technology has

minimal impact on the environment and it is currently used to extract residual minerals

from abandoned mines. The way this is performed is the leaching solution is applied

directly to the walls and the roof of the intact stope (an underground excavation from

which the ore has being removed) or else to the rubble of the fractured workings. Insitu

leaching has been successful to the recovery of copper and uranium,

Dump leaching is also a method employed for the extraction of metals but as in the case

for copper it is not a very fast or efficient process. The dumps often contain boulders and

large rocks which have a very low surface- to – volume ratio for the action of bacteria.

Also the interior of a large dump is low in oxygen, which is a requirement for the

oxidation of iron and sulphur compounds, and the temperature can also rise to over 50

degree C. because the oxidation process are exothermic. Also there is a significant

channeling of the acidified water as it percolates through the rocks, so the copper

solubiislation is restricted to only a minor portion of the dump. Despite these

disadvantages dump leaching is a low cost and a low-tech method or recovery.

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Heap leaching is the most popular metal extraction method used, in particular used for

copper. In this method the ore is heaped onto open air leach pads with a base of asphalt or

impervious plastic sheeting. The heaps are no more than a few meters high by a few

meters wide so as to allow the oxygen to diffuse to all parts of the heap and reduce the

build- up of heat from the leaching process. The heaps are sprayed with sulphuric acid

(for copper extraction) and with cyanide (for gold extraction) which contain a fraction of

the bacterial population, the rest being attached to the mineral, in a controlled manner and

the run off is collected on the plastic shheting.When the desired metal concentration is

obtained, the rich liquor is pumped to the solvent extraction section and then sent to the

electro winning, where the fine metal is recovered or where the purity can also be

increased as described earlier in the bioleaching process. The finely ground copper

concentrate provides a large surface to volume ratio and so promote bioleaching.

Nutrients such as phosphates can be added to promote growth if necessary. Heap leaching

is a more environmentally friendly option and is also more economic and it is especially

attractive for mines in remote areas or for small operations where only a small body of

ore is to be extracted. Although heap operation is simple and adequate to handle large

volumes of minerals, but their productivity and yields are limited due to the severe

difficult in maintaining an adequate process control.

Heap and dump leaching present a number of advantages such as simple operation,

low investment and operation costs and acceptable yields. On the other hand the

processes suffer from some serious limitations such as the piled material is very

heterogeneous and practically no close process control can be exerted, except for

intermittent pH adjustment and the addition of some nutrients. The rates of oxygen and

carbon dioxide transfer that can be obtained are low, and extended periods of operation

are required in order to achieve sufficient conversions (Acevedo and Gentina, 1989).

Heap leaching can also be used for the recovery of gold. Most of the world’s gold

reserves contain the metal bound up in the small particles in the rocks. After grinding up

the rocks the gold is then recovered by gravity separation or by treatment with cyanide.

But more often theses techniques are proving to be ineffective in the recovery of the gold.

For example if the gold is found associated with pyrite, usually arsenopyrite, it can’t be

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recovered by gravity, while the cyanide reacts with the pyrite before it can complex with

the gold, making the process too expensive and environmentally hazardous due to the

large releases of cyanide. The gold in this case can be recovered by oxidizing the pyrite at

high pressure in an autoclave or by roasting, followed by recovery with cyanide. Both

techniques are very expensive and also pose a serious environmental risk as the liberated

gases contain arsenic.

Sometimes the gold can also be found as fine particles in carbonaceous sulphide

ores. By grinding the gold is liberating but it has a tendency to stick to the carbonaceous

compounds making it difficult to recover by conventional techniques.

It was discovered that microorganisms could oxidize the gold bearing pyrite and

arsenopyrite ores and also the carbonaceous ones. Also this process of using

microorganism’s means that the cyanide quantities needed is sufficiently reduced.

Commercial bacterial oxidation of refractory gold ores (those that were difficult to

recover by conventional methods) was first used at Gencor’s Fairview plant in South

Africa in 1986 (as previously mentioned). At that time the process used at Fairview was

that of oxidizing the gold by roasting, but wanted to expand its capacity by using the

bioleaching process and if improved successful to replace the traditional method with that

of bioleaching. By 1997 it was producing 40t/day of gold and the roasters had been

removed.

The technology used at Fairview is very different to that have the dump and heap

bioleaching processes used for copper. The finely ground gold arsenopyrite concentrate is

suspended and stirred in large tanks or bioreactors. Missing bacterial nutrients are added

and the pH is adjusted to 2. Oxygen is supplied and after about 5 days about 1/5 of the

arsenopyrite has been oxidized by the microorganisms and thus recovering up to 90% of

the gold. As previously stated the Fairview mine in South Africa was the first mine to

take advantage of the bioleaching process with recovery rates increasing from 70% to

95% and due to this success rate other mines followed suit.

Bioreactors also have their own drawbacks associated with their operation. The

choice of material for their construction is important and also the costs involved at

maintaining them at their correct temperature. The temperature inside the reactors can

rise rapidly to 50 degree C or higher, whereas the microorganisms predominantly prefer

19

temperatures of 20-40 degree C, so the reactors have d to be cooled to keep the

microorganisms alive. Although some plants are currently using extremely thermophilic

microorganisms which can grow at higher temperatures as is the case with the Youanmi

plant in Australia. This plant operates at 50 degree C. In all cases the bioreactors operate

at a pH of about 2 as previously stated and so associated with this is the problem of acid

corrosion.Severeal plants initially built rubber- lined metal bioreactors where this wasn’t

a problem but the more favored choice is that of stainless steel.

4.9 Examples of current Industrial Bioleaching Operations

■ Acid Mine Drainage

■ Rio Tinto, Spain

■ Dump Leaching

■ Bagdad, USA

■ Pinto Valley, USA

■ Sierrita, USA

■ Morenci, USA

■Heap Leaching

■ Cerro Colorado, Chile

■ Cananea, Mexico

■ Chuquicamata SBL, Chile

■ Collahuasi, Chile

■ Giilambone, Australia

■ Ivan Zar Chile

■ Morenci, USA

■ Punta del Cobre, Chile

■ Bioleaching of Gold Concentrates

■Ashanti, Ghana

■ Fairview, Zambia

■ Harbour Lights, Australia

20

■ Mount Leyshon, Australia

■ Sao Bento, Brazil

■ Wiluna, Australia

■ Youanmi, Australia

21

5. Case Studies

By Deborah Mc Auliffe

 

Microbes 'to tackle mine waste'

 

Toxic waste sign

Pollution left at industrial sites is an ongoing issue

Scientists are using microbes to clean up the problem of corrosive acid pollution left over

as mining waste.

 

Microbes are micro-organisms, especially bacteria which cause disease or fermentation.

 

Dr Barrie Johnson, from the University of Wales, Bangor, is leading research into their

use for cleaning up mine effluents.

 

Some of the microbes being used were found in the Caribbean and America.

 

Dr Johnson outlined his work at a conference of the Society for General Microbiology at

Heriot-Watt University, Edinburgh on Wednesday.

 

Microbes which break down minerals are already being used by miners to extract gold,

copper and other metals from their ores.

 

           

The challenge has been to find the strains which can be used to carry out this work

Bill Keevil, University of Southampton

 

By discovering microbes which can survive in this environment, Dr Johnson aims to

build on these developments to address serious environmental hazards at abandoned

mines and spoil heaps.

22

 

"We work with the mining industry to get metals from ores in more environmentally-

friendly ways," he said.

 

"We tend to work with micro-organisms which can clean up liquid wastes in mines,

which tend to be acidic."

 

Some of the microbes discovered have come from sites in Wales, America and the

Caribbean island of Montserrat. "We are using organisms that no-one has seen or worked

with before."

 

He said their techniques were different from others, because their microbes could

produce metals ready to be recycled, rather than metal-rich sludges, which he described

as "effectively toxic waste".

 

"Our ongoing research is focussing on extending the applications of biomining

technology, and on using newly-discovered extremophile bacteria to simultaneously

recover metals and clean up mine effluents from abandoned mines, streams that pass

through them and their waste tips," he said.

 

'Ideal'

 

Bill Keevil, professor of Environmental Healthcare at the University of Southampton,

said the potential for microbes to be used in this way had been known for some time.

 

"The challenge has been to find the strains which can be used to carry out this work," he

said.

 

He said the need was to find microbes which could survive at very high or very low pH

values (which express its acidity or alkalinity), and often high temperatures as well.

 

23

"The ideal would be a thermo tolerant bug that can survive at a low pH - you can then put

it in mine workings where it doesn't mind being...and clean up as they go."  (Ref: 1)

 

 

 Iniciativa Genoma Chile

The "Iniciativa Genoma Chile" (Chilean Genoma Initiative) was created in order to

integrate the country widely and systematically in the worldwide development of

genomics, proteomics and bioinformatics. It is focused on relevant areas of the national

economy, thus helping to trigger new developments and set up some efficient and

effective strategies for identifying and resolving problems as well as for keeping and

improving competitivity.

This initiative is part of the Chilean government's Program of Development and

Technological Innovation (2001-2004). Through three sub-programs : Information

Technology, Biotechnology in forestry, agriculture and aquaculture, and clean

technologies. It is partly financed by the IADB, and directed by a comitee whose

members are representatives of: the Ministery of Economy, Corfo (FDI), the Ministery of

Agriculture and CONICYT who manages the program.

The Iniciativa Genoma Chile was born in 2001 to improve and increase human and

scientific capabilities already existing in the national system of science. The orientation is

towards the improvement of competitivity in relevant areas of the chilean economy such

as the ones whose production can gain value through state-of-the-art technologies.

The scientific relevance and the formation of scientists.

This program is relevant since it will allow us to enter the top scientific achievements and

then apply these innovations in the mid term, finally creating economic rewards. The

program first considers agriculture and biomining, since they are key areas of the national

economy.

The program is considering, in these two areas already mentioned, the formation and

specialization of young scientists who are members of the projects who belongs to the

program. It will train in the use of scientific strategies and techniques which were not

available before in our country.

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The offer

The Genoma Initiative will finance public contests and research projects through its two

main programs : Biomining and Renewable natural ressources.

 

a. Genoma program in renewable natural ressources

The goal is to get solutions to social and economical problems in the forestry area,

agriculture, aquaculture and the other ones related to natural ressources.

 The first call for proposals in vegetal health and post-harvest was closed on May 2002.

This joint project, has as one of its goals not only to generate new links between

institutions and companies but also to integrate scientists, entrepreneurs and technologists

through its development.

The winning initiatives of the First Convocatory were granted with M US$3.5, and they

form the first Chilean network of Vegetal Genomics working on functional genomics of

nectarines and studying the viral infection and development of diagnostics systems, as

well as post-harvesting problems in grapes.

The total budget for this first call for proposals reach M US$ 6.3 adding the institutional

and private contributions. The projects were selected according to their impact, the

economical benefits and the potential improvement of the international positionning of

the products thanks to the developments financed by the initiative.

The Network in vegetal Genomics is promoting collaborative work at two different

levels. The first one at the management of the Genome Program in Renewable Natural

Resources through its board conformed bymembers of the Ministry of Economy, the

Agrarian Innovation Funds (Ministry of Agriculture), CORFO and CONICY.The second

level is conformed for the three groups of scientists participating in the network.

With this effort, this national initiative takes shape putting together the most important

national academic institutions and scientists in the country aiming to develop projects

which will study relevant problems on nectarines and grapes, which are of social and

economical importance to Chile.

25

Approved projects

Scientific Director: Dr. Ariel Orellana Lpez

Title: Functional Genomics in nectarines : platform to strenghten Chilean competitivity in

fruit exportation.

Main institution: Universidad de Chile.

Asociated institutions: INIA, Fundacin Chile, Asociacin de Exportadores de Chile,

Fundacin para el desarrollo Frutcola.

** Total budget: M$ 1.227.905

 

Scientific Director: Dr. Hugo Pea Corts

Title: Scientific and technological platform for the development of the Vegetal Genomics

in Chile. 1st stage : Functionnal genomics in grapevine.

Main institution: Universidad Tcnica Federico Santa Mara.

Asociated Institutions: Universidades: de Chile, Santiago y de Talca, INIA, Asociacin de

Exportadores de Chile, Fundacin para el Desarrollo Frutcola, Fundacin Chile. .

** Total budget: M$1.751.796

Scientific Director: Dr. Patricio Arce Johnson

Title : Genomic studies and genetic expression in grapes : answer to viral infection and

development of diagnostic systems.

Main Institution: Pontificia Universidad Catlica de Chile.

Asociated Institutions: Universidad de Chile, Fundacin de Ciencia para la Vida, Bios-

Chile Ingeniera Gentica S.A.

** Total Budget: M$ 1.096.396

**Including Institutional and Private Funds.

Institutional Elegibility .

To the funds of the Program can apply Chilean citizens, among others, public or private

universities, technological companies with profit aims, technological institutes,

26

foundations, corporations and others, that fulfill the requirements. These institutions can

apply associated or forming a legal partnership with Chilean citizens as well as associated

to foreign citizens or institutions.

b . Biomining program

The Biomining Program of the Genoma Initiative started in 2001, in order to improve the

bacterial lixiviation process and the development of new mining technologies thanks to

genomics, bioinformatics and proteomics.

The chilean government (Ministery of Economy, CORFO and CONICYT) and

CODELCO (National Corporation of Copper) agreed on the constitution of a consortium

made by investors such as mining and technological companies who bring ressources and

themes of research and development.

BioSigma SA is a consortium formed by CODELCO-Chile and Nippon Mining & Metal

Co. Ltda in July 2002. With a first capital of 3 M US$, it will be focused on technological

development in biomining. CODELCO holds 66.6% of the capital, while the Japanese

firm holds 33.3%. Besides its own capital, the firm will manage M US$ 2 from the R&D

oriented funds from CORFO and CONICYT. In the R&D activities of BioSigma

international research centres, companies and university laboratorieswill be participating.

The goal is to develop biotechnologies for mining using genomics, proteomics and

bioinformatics. By working with national and international scientists, the improvement of

the competitivity in the national mining ressources and the opening of new opportunities

for industrial development will be achieved. The products will range from the

improvement of processes such as bacterial lixiviation to genes technology, in order to

get microorganisms to be used in the present and future natural ressources. They will be

especially focused on the comercial application and the environmental sustainability.

This program finance its projects through a public call for proposals. Due to the

importance for the national economy and the degree of knowledge existing in our country

in this area, we chose to improve the processes of bacterial lixiviation of minerals, thanks

to new technologies using bioinformatics and genomics.

Necessary conditions for applying :

For applicants with Chilean legal personality

27

Institutional capability for R&D.

Institutional capability for project management.

For applicants with Foreign legal personality

Institutional capability for R&D.

Institutional capability for project management.

It is compulsory to involve a Chilean entity or to be settle in Chile.

Groups of people can apply, if they engage themselves in forming an enterprise once they

are selected.

For groups of people which are applying, they must have:

Team capability for R&D.

Team capability for project management.  (Ref. 5)

 

Biomining: There's Gold In Them Thar Plants

April 19, 2005 09:37 AM -

Gold rush miners might have been better off using plants to find gold rather than panning

streams for the precious metal. Early prospectors in Europe used certain weeds as

indicator plants that signaled the presence of metal ore. These weeds are the only plants

that can thrive on soils with a high content of heavy metals. One such plant is alpine

pennycress, Thlaspi caerulescens, a wild perennial herb found on zinc- and nickel-rich

soils in many countries. This plant occurs in alpine areas of Central Europe as well as in

the Rocky Mountains. Most varieties grow only 8 to 12 inches high and have small, white

flowers.

Biomining is the use of plants to mine valuable heavy metal minerals from contaminated

or mineralized soils. In fact, 25% of all copper is mined this way, amounting to $1 billion

in revenue annually. This ranks it as one of the most important applications of

biotechnology today. Bioprocessing is also being used to economically extract gold from

very low grade, sulfidic gold ores, once thought to be worthless.

To increase the efficiency of biomining, the search is on for bacterial strains that are

better suited to large-scale operations. Bioprocessing releases a great deal of heat, and

this can slow down or kill the bacteria currently being used. Researchers are turning to

28

heat-loving thermophilic bacteria found in hot springs and around oceanic vents to solve

this problem. These bacteria thrive in temperatures up to 100 degrees Celsius or higher

and could function in a high temperature oxidative environment.

More about biomining from the Canadian government.

[by Justin Thomas] (Ref. 6)

29

6. Economics of BiominingBy Deborah Mc Auliffe

Biomining is a form of mining (mineral processing) that utilises microorganisms to

degrade metal sulfides for the enhanced recovery of metals with economic value.

Biomining has developed into one of the most successful and important areas of

biotechnology; the estimated 1999 global value of the process was about $10 billion.

There are many advantages to using bioleaching for the extraction of metals in terms of

cost-efficiency, simplicity, robustness, high performance and environmentally friendly

alternative to conventional mineral processing methods.

1) Bioleaching of pyrite by defined mixed cultures of moderately thermophilic

acidophiles

Leaching of pyrite (FeS2) concentrate and ground rock pyrite has been investigated using

defined pure cultures and consortia of four moderately thermophilic bacteria: (i) a

thermotolerant Leptospirillum isolate (strain MT6); (ii) Acidithiobacillus caldus (strain

KU); (iii) a novel Gram-positive bacterium `Caldibacillus ferrivorus' (strain GSM); (iv) a

Sulfobacillus isolate (strain NC). Parameters measured included total iron released from

pyrite, Fe2+ and Fe3+ concentrations, dissolved organic carbon , pH, Eh and numbers of

different bacterial species. Pure cultures of both strain MT6 andstrain KU did not

accelerate the pyrite concentrate dissolution, while both strain GSM and strain NC were

able to do so, albeit at relatively slow rates and at low redox potentials. The most

effective dissolution of pyrite was observed in mixed cultures that included strain MT6,

all of which maintained high redox potentials. The data indicate that strain MT6 was the

most significant in the consortia and that At. caldus, although active in generating acidity

and numerically the dominant acidophile present in mixed cultures, contributed nothing

either directly or indirectly to pyrite oxidation.

30

2) Exploitation of important iron-metabolising microorganisms and development of

RFLP method for their differentiation

Research on the biooxidation of sulfide minerals has tended to be heavily biased towards

Gram-negative bacteria, such as Leptospirillum ferrooxidans and Acidithiobacillus

ferrooxidans. However, the research team at the UWB has been finding significant

biodiversity which has potential important role in biomining. We have isolated and

characterised a number of phylogenetically distinct Gram-positive iron-metabolising

bacteria, some of which are novel genus. Also, we have isolated gram-negative bacteria,

such as L. ferrooxidnas and At. ferrooxidans, which, in contrast to other recognised

species, have unique characteristics. Development of a rapid, simple and convenient

method to differentiate such microbes would have significant importance in the quick

examination of biodiversity in industrial samples. To this end, a RFLP (Restriction

Fragment Length Polymorphism) protocol is being currently developed.

European Topic Centre on Terrestrial Environment

Topic Centre of European Environment Agency

Local soil contamination

Contaminated sites are the legacy of a long period of industrialisation involving

unconsidered production and handling of hazardous substances and unregulated dumping

of wastes. The expansion of industry and subsequent increase in the amounts of industrial

wastes have led to considerable environmental problems in all industrialised countries.

Additionally, mining activities and former military sites, the latter resulting mainly from

the former Soviet army presence in Central and Eastern European countries, are giving

rise to severe contamination problems.

seriously considerably endanger human health and the environment. Pollution of drinking

water, uptake of pollutants in plants, exposure to contaminated soil due to direct contact,

inhalation and ingestion are major threats. Provision of public and private money for

remediation, as well as restrictions onn land use and the use of groundwater and surface

water for waste-related activities, are particularly important responses.

The foundation for dealing with local soil contamination was laid by the former European

Topic Centre on Soil (ETC/S), which began its work in 1996. ETC/Soil addressed this

31

issue by developing a relevant network and initiating a data collection process.

Development of policy relevant indicators has been of major interest for the EEA within

the Topic Centre. The Centres first steps were to provide a basis for future work by

reviewing land management practices and the state-of-play in various countries. The

problems which have to be dealt with were discovered to be the following:

differing approaches for contaminated site management in EEA countries

different levels of progress in contaminated sites management

different definitions of "contaminated site"

differing legal requirements.

So far, three indicators for soil contamination have been developed and published in

several reports:

Soil polluting activities from localised sources

Expenditures for cleaning-up contaminated sites

Progress in the management of contaminates sites

The main objective within the European Topic Centre on Terrestrial Environment is to

contribute to the further development of policy-relevant indicators on local soil

contamination, the collection and assessment of data related to those indicators that have

been developed, and the provision of aggregated data in published reports, proceedings

and electronic form. The Centre seeks to ensure the close involvement of EEA country

representatives, for example,in the form of workshops with a strong focus on the

integration of new member States. Work on local soil contamination is also intended to

develop into close consideration of EU regulations (recent and future policy aspects, link

with reporting obligations, ...).  (Ref: 3)

 

32

7. Remediation of Metal-Contaminated SitesBy Lisa Smith

It is now widely recognised that contaminated soil is a potential treat to human health,

and its continual discovery over recent years as led to international efforts to remedy

many of these sites, either as a response to the risk of adverse health effects of

environmental effects caused by contamination or to enable a site to be redeveloped for

use.

Soil Flushing; Soil flushing is a developing insitu technology where a solution is injected

in the ground in order to move contaminants to an area where they may be extracted from

the ground and treated.

Soil Washing; Soil washing is an exsitu remediation process where the contaminated soil

is excavated and washed with water to remove contaminants. Additives may be added to

the water to enhance removal and the soil may have to go through several remediation

cycles to remove the contaminants.

Stabilization/Solidification; Can be an insitu or exsitu remediation technique using

cement, concrete, chemical fixation to stabilize or physically bind contaminants. The

solid mass limits the solubility of mobility of the contaminants but does not destroy them.

Bioremediation is an option that offers the possibility to destroy or render harmless

various contaminants using natural biological activity.

Phytostabilization; Phytostabilization is the immobilisation of a contaminant in soil

through absorption and accumulation by roots, adsorption onto roots, of precipitation

within the root zone of plants and the use of plants to prevent contaminant migration via

wind and water erosion, leaching and soil dispersion.

33

Phytostabilization occurs through contaminants accumulation in plant tissue and in the

soil around the roots, changes in chemistry of the contaminant cause it become insoluble

and/or immobile in the soil (i.e. less toxic). After investigating the contaminant chemistry

in soil, soil is farmed, fertilisers or other products might be used to improve soil

conditions for plant growth, to reduce chemical mobility and plant toxicity of the

contaminant. Plant species are selected based on local conditions, native flora, soil

composition and the plants tolerance to the contaminants in question. Irrigation is

provided if necessary, as well as supplement fertilisation and/or soil amendment.

Plants immobilise metals and radionuclide in the soil minimising their mobility in water

or wind. Success achieved when a stable vegetation cover develops and contaminants and

portions of metals decrease to non-toxic or background levels.

Phytoremediation; Phytoremediation is an emerging bioremediation technology that uses

plants to remove contaminants from soil. “Phytoremediation is cost-effective “green”

technology whereby plants vacuum heavy metals from the soil through their roots”

(www.agclassroom.org). Certain plant species known as metal hyperaccumulators, have

the ability to extract elements from the soil and concentrate them in their stems, shoots

and leaves. The plants possess genes that regulate the amount of metals taken up from the

soil by the roots, the metals enter the plant’s vascular system and are transported to other

parts of the plant finally deposited in the leaf cells. The metals are removed from soil by

harvesting the plant’s shoot and extracting the metal preventing soil recontamination.

The plant Thlaspi caerulescens, commonly known as alpine pennycress, is a member of

the broccoli and cabbage family and thrives on soils having high levels of zinc and

cadmium.

34

8. Conclusion

Traditional extraction caused environmental hazards and degradation, biomining offers

many advantages including;

It is carried out insitu,

Less energy output,

No toxic or noxious gases produced, SO2 is produced from traditional mining

methods,

No noise or dust problems,

Process is self generating,

Can be carried out in large or small scale operations,

Can be used for a wide variety of metals, Cu, Ag, Ni, Co, Pb, Se, Au, Zn,

Is used to remove impurities of mixtures

Works on low grade ores

The main disadvantage of biomining is that it is a slow process.

Biomining contributes to sustainable development in the same way all microorganism-

mediated process do: it uses existing organisms and mechanisms in nature.

Due to the fact that the over that the overall process of biomining is a more

environmentally friendly alternative than that of conventional mining methods, it also

improves recovery rates, reduces capital and operating costs and probably one of the most

significant factors that has lead to it’s universally accepted acceptance is the fact that it

permits economical extraction of minerals from low grade ores, which are being used

more and more as highgrade ores are being depleted. Due to these advantages of

biomining it is a realistic safe bet that genetically engineering a bacterium to resist heavy

metal poisoning, which may not be an easy task, but that it will occur sooner rather than

later and it is for definite that it will not take the two millennia that it took for the curious

35

phenomenon noticed by the Roman miners at Rio Tinto to become a major improvement

in copper mining.

Biomining is an environmentally friendly alternative to conventional mining processes.

36

References

Acevedo, Fernando. "The use of reactors in biomining processes." Electronic Journal of Biotechnology, Nature Biotechnology. Vol.3 No. 3, Issue of December 15, 2000. 

Barrett, Jack & Hughes, Martin. A Golden Opportunity - Chemistry in Britain, June 1997

Beech, B. Iwona. (2003). Sulfate-reducing bacteria in biofilms on metallic materials and corrosion, Microbiology Today, 30, 115-117.

Beech, B. Iwona, Sunner, Jan. (2004). Biocorrosion: towards understanding interactions between biofilms and metals. Current opinion in Biotechnology, 15, 181-186.

Biomining. Access Excellence at the National Health Museum. www.accessexcellence.org/AB/BA/biomining.html

Biotechnology Applications in the Mining Industry: Bioleaching. NRCan Biotechnology, Factsheets. www.nrcan.gc.ca/cfs/bio/fact2.shtml

Biotechnology in gold extraction. The Hindu. www.hinuonnet.com/thehindu...02/21/stories/20020221000060300.htm

Brock - Biology of Micro-organisms

Canada's Biotechnology Regulations: Who's mining the store? NRCan Biotechnology, Factsheets. www.nrcan.gc.ca/cfs/bio/fact9.shtml

Environment Consultation Document. CBS Online. www.strategis.gc.ca/cgi-bin/...%20(product%20contains%20)%20 5 June 2002. (Ref: 2) 

37

Harrison, R. - Nuffield Advanced Science Book of Data

Hill, G.C. & Holman, J.S. - Chemistry in Context, Pages 316-317

http://www.agclassroom.org/teen/ars_pdf/9earth/2000/06phytoremedation.pdf

http://www.biobasics.gc.ca

http://www.copper.org/innovations/2004/May

http://www.ejbiotehnology.info

http://en.wikipedia.org/wiki/Bioleaching

http://www.evvirotools.org/factsheet/remeditech.shtml

http://www.ireland.com/newspaper/ireland/2000/0628/archive.00062800012.html

http:// www.ireland.com/newspaper/ireland/2005/1116/3458522606HM2TIPPERARY.html

http://www._mining-technology.com

http://www.pamp.com

http://www.spaceship-earth.org/REM/BRIERLEY.htm

http://web.tiscali.it/biomining/history.htm

Marx, Jean L. A Revolution in Biotechnology, Pages 83-92

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Metals and minerals. The Biotechnology Gateway. www.strategis.gc.ca/bio 

Minerals & Metallurgical Processing - Biotechnology Special Issue, Commercialisation of Bioleaching for Base-Metal Extraction

Minerals and Metals Sector. NRCan Biotechnology, FAQ. www.nrcan.gc.ca/cfs/bio/faq3.shtml

Sector Overviews: Mining and Energy. CBS Online. www.strategis.ic.gc.ca/ssg/bh00175e.html 11 June 2002 

Shriver & Atkins - Inorganic Chemistry

Taylor, Jane. Micro-organisms and Biotechnology, Pages 113-115

    Winter, Mark. - d-Block Chemistry

      

39

GlossaryBy Deborah Mc Auliffe

* Acidophilic autotrophs - Organisms that are able to live solely on sulphides and in acid

conditions

    * Biohydrometallurgy, biomining, bioleaching - A method of mining and extracting

metals from ores by using micro-organisms

    * Centrifugal extractor - A method of solvent extraction that uses the principle of

centrifugal forces

    * Electrowinning - The final method of extracting the metal, by using an

electrochemical cell

    * Extract - The organic liquid that holds the useful product after solvent extraction

    * Leaching solution - A solution that is used for solubilisation and removal of metals

from an ore by microbes attack

    * Ligand exchange solvent extraction - A method of extracting a mtal from a solution

by using ligands

    * Raffinate - The aqueous solution that is taken off after solvent extraction

    * Thiobacillus ferroxidans - Micro-organisms that they can get all their energy from

oxidising Fe2+ to Fe3+ and are able to live solely on sulphides and in acid conditions

 

40