Bioleaching/Biocorrosion

 Metals/Biomining

  

Presented to: Dr. Michael Broaders

Presented by:  Ms. Lisa Smith

                       Ms. Marian Cummins

                       Ms. Deborah Mc Auliffe

Presented on: 16^th December 2005

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

1.     Introduction

By 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, 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

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.

2.     Biocorrosion

By 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.

4. Biooxidation

By 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.

4. Bioleaching

By 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 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 18^th 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 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 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; 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 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⁺

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)

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 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 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.

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 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 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

             ■ Mount Leyshon, Australia

             ■    Sao Bento, Brazil

             ■ Wiluna, Australia

             ■ Youanmi, Australia

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.

"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.

"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.

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.

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. 1^st 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, 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

• 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 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)

6. Economics of Biomining

By 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.

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 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)

7. Remediation of Metal-Contaminated Sites

By 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.

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.

8. Conclusion

Traditional extraction caused environmental hazards and degradation, biomining offers many advantages including;

v  It is carried out insitu,

v  Less energy output,

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

v  No noise or dust problems,

v  Process is self generating,

v  Can be carried out in large or small scale operations,

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

v  Is used to remove impurities of mixtures

v  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 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.

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)

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

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

Glossary

By 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

 by:G.Byambasvren