Mining сэтгүүл-н 10-н сарын шинэ хэвлэл гарлаа та бүхэн доорх линкээр орж уншана уу ?
Link: http://issuu.com/miningglobal/docs/miningglobal-october-2015?e=12042171/30442800
Friday, October 16, 2015
TOP 10: Highest Paying Jobs in the Mining Industry
10.) Operators/ technicians/ miners
Salary: $150,000 to $165,000
From excavator operators to geological technicians, these positions are in constant demand. Underground miners have the ability to earn more than $150,000 a year compared to surface miners, whose annual salary ranges between $50,000 and $85,000. The salary for technicians can range anywhere from $50,000 to $150,000, with operators earning upwards of $165,000 per year.
9.) Surveyors
Salary: $165,000
Surveyors are a vital part of mining operations. They assist companies in measuring underground and open-cut mines, helping to maintain a proper mine plan by updating layouts and keeping records. The pay is also quite nice.
Senior level and chief surveyors can make anywhere from $80,000 to $160,000 per year, while entry level positions typically earn between $55,000 and $130,000 a year.
8.) Mine supervisors/ mill superintendents
Salary: $168,000
Like any supervisor position, these jobs offer great compensation. Annual salaries for Mine Supervisors (operations/maintenance) are $168,000 per year while underground and open pit supervisors rake in between $70,000 and $165,000 a year. A Mill Superintendent at a processing plant can make upwards of $168,000 a year.
7.) Occupational health safety and environmental professionals
Salary: $190,000
As two major components of the mining industry, health safety and environmental professionals get paid like it. An OHS officer is paid between $50,000 and $115,000 per year, while a top level OHS can earn upwards of $190,000.
6.) Geophysicists
Salary: $200,000
A Geophysicists studies the Earth using gravity, magnetic, electrical and seismic methods. Their role is paramount in the mining industry as they conduct surveys to locate minerals or ground water. A Senior Geophysicist can earn anywhere from $150,000 to $200,000 a year, putting it at number six on our list.
5.) Metallurgists
Salary: $220,000
The role of a Metallurgist is focused mainly in the extraction and processing of various metals. Just starting out, a Graduate Metallurgist can earn $50,000 to $90,000 per year whereas a Senior Metallurgist can make close to $220,000a year. The more experience you have, the more money mining companies will pay.
Top 10: Diamond Mines in the World
10.) Botuobinskaya (Russia)
Located in the Yakutia region of Russia, the Botuobinskaya diamond mine is estimated to contain roughly 70 million carats. The mine, which is scheduled to commence production in 2015, is owned and operated by Nyurba mining and processing division of ALROSA.
The company began the first phase of the stripping operation in late 2012. The operation will last three years with mining operations expected to begin in the fourth quarter of 2015. The Botuobinskaya mine will produce 1.5 million carats of diamonds annually for more than 40 years.
9.) Orapa (Africa)
As the world’s largest diamond mine by area, the Orapa diamond mine is located 240km west of Francistown city in Central Botswana. The open-pit mine is estimated to contain 85.7 million carats of diamond reserves.
Orapa commenced production in 1971 and underwent expansion in 1999 to double its previous capacity. Owned and operated by Debswana, a partnership betweenthe De Beers Company and the government of Botswana, the site is the oldest of the four diamond mines operated by Debswana.
8.) Jwaneng (Africa)
Another major diamond mine is Botswana is the Jwaneng site, which is located 160 miles south-west of Gaborone in south central Botswana. The mine, which has been in production since 1982, is another partnership owned and operated site by the De Beers Company and the Government of Botswana.
Regarded as the “richest” diamond mine in the world in terms of value, the Jwaneng mine is estimated to contain roughly 88 million carats of diamond reserves. Since 2010, the mine has undergone a major expansion (Cut-8) to extend the mine’s life cycle until 2025.
7.) Grib (Russia)
Located in the north-western part of Russia, Grib is an open-pit diamond mine estimated to contain over 98 million carats. The mine is expected to become the largest diamond mine in Russia in terms of size.
The Grib mine is owned and operated by Lukoil through its subsidiary Arkhangelskgeoldobycha (AGD). With production commencing in June 2013, the site is planned to go underground after 16 years of open-pit operation.
Grib is the first new non-alluvial diamond mine to produce more than one million carats per year.
6.) Venetia (South Africa)
Owned and operated by De Beers, the Venetia diamond mine is estimated to contain more than 102 million carats. Located in the province of Limpopo in South Africa, the site is both an open-pit and underground mine producing roughly 3.066 million carats of diamonds in 2012.
With deposits consisting of 12 kimberlite pipes, the Venetia mine is the largest diamond producing mine in South Africa.
5.) Catoca (Africa)
Located in Angola, the Catoca is the fifth largest diamond mine in the world. Operated by Sociedade Mineira de Catoca, the mine is a joint venture with state-owned diamond company Endiama (32.8 percent), ALROSA (32.8 percent), China and state oil producer Sonangol (18 percent) and Odebrecht of Brazil (16.4 percent).
The mine is estimated to contain 130 million carats of mineable diamond. The Catoca mine accounted for 70 percent of Angola’s total diamond output.
Top 10 deep open-pit mines
Bingham Canyon
Bingham Canyon mine located south-west of Salt Lake City, Utah, US, is the deepest open pit mine in the world. The Bingham Canyon pit is more than 1.2km deep and approximately four kilometres wide.
The mine, which is owned and operated by Rio Tinto Kennecott, has been in production since 1906.
Also known as the Kennecott Copper Mine, Bingham Canyon produced about 179,317t of copper, 279,200 ounces of gold, 2.4 million ounces (Moz) of silver and 20 million pounds (Mlbs) of molybdenum in 2012.
The recoverable reserves at the open-pit exceeded 2.9Mt of copper, 2.8Moz of gold, 31Moz of silver and 240,000t of molybdenum as of December 2012.
Chuquicamata
Chuquicamata copper mine, situated 1,650km north of Santiago, Chile, is the second deepest open-pit mine in the world.
Chuquicamata, also known as the Chuqui open pit, is 4.3km long, three kilometres wide and more than 850m deep.
Chuquicamata copper mine has been in operation for more than a century. The mine is owned and operated by the Chilean state enterprise Codelco. The open-pit mine produced 443,000t of copper in 2011.
Feasibility study is underway to switch to underground production at Chuquicamata by the end of 2018. The ore reserve under the existing pit is estimated to be 1.7 billion tonnes grading at 0.7% copper. The underground development project is estimated to cost more than $4bn.
Escondida
Escondida copper mine located in the Atacama Desert, Chile, ranks as the third deepest open-pit operation. Escondida copper mining operation consists of two open-pit mines, namely Escondida pit and Escondida Norte pit. The Escondida pit is 3.9km long, 2.7km wide and 645m deep. The Escondida Norte pit is 525m deep.
BHP Billiton is the operator of the mine with 57.5% interest. Rio Tinto holds 30% stake in the mine. Escondida is currently the world's largest copper producing mine.
It produced 1.1Mt of copper in the financial year ending June 2013, which accounts for about five percent of global copper production. Escondida's recoverable copper reserve was estimated to be more than 32.6Mt as of December 2012.
Udachny
Udachny diamond mine located in the Eastern-Siberian Region of Russia is currently the fourth deepest open pit mine in the world. The Udachny pit is currently 630m deep. Mining at the Udachnaya kimberlite pipe has been going on since 1971.
The Udachny mine is owned and operated by Russia's state-owned company Alrosa. The mine produced ten million carats of diamond per year until 2011.
The probable contained diamond reserve at the open-pit was estimated to be 4.4 million carats as of July 2013.
The Udachny open pit operation is scheduled to close in 2014 with the opening of Udachny underground mine which is under construction. The contained diamond reserves for Udachny underground mining are estimated to be more than 108 million carats.
Muruntau
Muruntau mine in Uzbekistan, physically one of the largest open pit gold mines in the world, ranks as the fifth deepest open pit. The Muruntau open pit is 3.5km long and three kilometres wide. The depth of the mine has reached just more than 600m.
Muruntau was discovered in 1958. Mining operations started in 1967. Uzbekistan's Navoi Mining and Metallurgical Combinant own and operate the mine.
The final pit depth under the current mine plan is reported to be 650m, after which the mine will switch to underground operation.
Muruntau's contained gold reserves and resource including the historical production is reportedly estimated at 170Moz. The mine is known for its production capacity of about 2Moz of gold per year with averaging ore grade of 2.4g/t gold.
Fimiston Open Pit (Super Pit)
The Fimiston Open pit, also known as the Super Pit, located on south-east edge of Kalgoorlie, Western Australia, is the sixth deepest open-pit mine in the world. The gold producing open pit mine is 3.8km long, 1.5km wide and up to 600m deep.
The mine is owned and operated by Kalgoorlie Consolidated Gold Mines (KCGM), a 50-50 joint venture company comprised of Barrick Gold and Newmont Mining.
The mine produced 296,000oz of gold during the first half of 2013. The proven and probable reserves at Filmiston open pit as of December 2012 was estimated to be more than 8Moz.
Grasberg
Grasberg mine located in the Papua province of Indonesia currently ranks as the world's seventh deepest open pit operation. The miming operation at Grasberg consists of both open pit and underground mines. The Grasberg open pit is more than 550m deep. Grasberg is the largest gold mine in the world.
The mine also produces copper and silver. The Grasberg open pit operation started in 1990 and expected to continue up to 2016. The mine is operated by Freeport Indonesia (PTFI), a subsidiary of Freeport-McMoRan Copper & Gold (FCX) which owns 90.64% of the Grasberg mining operation.
The mine produced 862,000 ounces of gold and 695Mlbs of copper in 2012. The proven and probable ore reserve at Grasberg (open pit + underground) as of December 2012 was estimated at 2.424Mt grading 0.83g/t gold, 4.24g/t silver and one percent copper.
World's top 10 gold deposits
#6 | OYU TOLGOI | 46,340,000 Oz Gold
Location: South Gobi Desert, MONGOLIA
#10 | Obuasi | 29,830,000 Oz Gold
Location: GHANA, western Africa
In the #10 spot is Obuasi, owned by major gold producer AngloGold Ashanti. It is primarily a high-grade underground mine with periodic open-pit operations during its long history. It is located in the Ashanti region of southwest Ghana in western Africa; a prolific gold producing region for centuries. The underground operation extends to a depth of 1,500 meters or 4,900 feet (almost a mile). Mining began at Obuasi more than 110 years ago, in 1897 when it was originally known as the Ashanti Mine.
#9 | CADIA EAST | 37,600,000 Oz Gold
Location: New South Wales, AUSTRALIA
In the #9 spot is Cadia East, owned by Australian major Newcrest. The large underground mining operation is part of a trio of gold mines, in close proximity to one another, known collectively as Newcrest's Cadia Valley Operations, roughly 250 kilometers west of Sydney. The other two mines are Cadia Hill and Ridgeway. Cadia Hill is a large open-pit mine nearing the end of its useful life just as the newly developed Cadia East recently began its expected 30 year mine life. Gold was first discovered in the gold and copper bearing Cadia region in 1851 and Cadia East was discovered in 1994.
#8 | MPONENG | 39,557,000 Oz Gold
Location: Near Johannesburg, SOUTH AFRICA
In the #8 spot is Mponeng, owned by South African major AngloGold Ashanti. It is located just 65km west of Johannesburg in one of the world's most prolific mining regions known as the Witwatersrand. In addition to being one of the largest, Mponeng is also one of the world's deepest underground mines. It extends over 2 miles below the surface and it takes over an hour to reach the bottom. The rocks at this depth reach a temperature of 150 degrees farenheit requiring slurry ice be pumped underground to cool the environment down to a bearable 85 degrees.
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#7 | PUEBLO VIEJO | 40,085,000 Oz Gold
Location: DOMINICAN REPUBLIC
Coming in at #7 is Pueblo Viejo, owned jointly by majors Barrick (60%) and Goldcorp (40%). This large deposit is located in the Dominican Republic, roughly 100km northwest of the capital of Santo Domingo. It might surprise some that this small island nation is rich in mineral reserves. The open pit mine is very new and began production in January 2013. It also has large silver and copper reserves to complement its gold deposit. As it ramps up to full production, it will also be one of the largest producers in the world, but we'll save production figures for a separate Top 10 List.
#6 | OYU TOLGOI | 46,340,000 Oz Gold
Location: South Gobi Desert, MONGOLIA
At #6 on our list is Oyu Tolgoi, owned jointly by Rio Tinto (34%), Turquoise Hill (32%) and Mongolia (34%). This is another newly developed mammoth deposit located in the remote southern reaches of Mongolia. The mine cost the princely sum of US$6.6B to develop and went into production in January 2013. In addition to its 46Moz+ of gold, it also contains over 40 billion pounds of copper worth US$140B. It's really a copper mine masquerading as a gold mine. It will also be one of the largest gold and copper producers on earth as it ramps up to full production.
#5 | OLYMPIADA | 47,500,000 Oz Gold
Elements of Open-Pit Mining – Ил уурхайн элементүүд
Benches
Benches are possibly the most distinguishing feature of an open pit. Benches can be divided in into working benches and inactive benches. Working benches are in the process of being excavated, whereas inactive benches are the remnants of working benches left in place to maintain pit slope stability.
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Догол
Догол нь ил уурхайн хамгийн онцлог шинж тэмдэг юм. Догол нь ажлын ба ажлын бус догол гэж хуваагддаг. Ажлын догол нь ухаж ачигдаж байдаг бол ажлын бус догол нь уурхайн хажуугийн тогтворжилтыг хангах зорилгоор үлдээсэн ажлын доголыг үлдээц билээ.
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Between main benches, catch benches are left in place to prevent cascading material from compromising safety in active areas of an operation. Dozers or front end loaders can be used to aid the main excavator to maintaining good floor conditions. Furthermore, they can increase main excavator efficiency by reshaping the muck pile to increase bucket fill factors, and possibly aid in the selective mining of ore and barren rock.
Haul roads
Haul roads constitute a key element of an open –pit mine, providing the main haulage route for ore and overburden from active excavating areas to the pit rim or beyond.
The selection and application of a suitable wearing course, combined with regularapplication of water and chemical suppressants, are most feasible and effective options for dust suppression measures. In addition to the measures discussed previously, avoiding spillage also plays an important role in fugitive dust suppression and, possibly more importantly, prolonging tire life.
Some of the main contributes to a high rolling resistance and bad haul road performance are inadequate wearing course construction application as well as haul road defects such as potholing, rutting, loose material (dust and stones), corrugations (commonly referred as washboards), surface cracking, and insufficient drainage.
Overburden disposal
Overburden forms, by far, the largest volume of material produced by most open – pit mines. Overburden is deposited either top – down or bottom up. End dumping (or top – down dumping) of overburden involves dumping the material over an advancing face. During operation of the dump, only limited reworking of material by dozers is required. Recontouring starts after the end of the dump life. In paddock dumping (also knowing as bottom – up dumping), the layers of overburden are stacked by dumping on top of the dump, followed with spreading by bulldozers to form relatively thin layers.
Pit Expansion
Expansion of an open – pit mine is done in a series of phases, often referred to as pushbacks or cut backs.
Pushbacks can be either conventional or sequential. Essentially, both methods push back a pit shell the same distance horizontally; however, sequential pushback does this through a number of smaller, active benches pushed simultaneously at several levels, whereas a conventional pushback mines the whole horizontal extent of push back level before progressing to the next level. Different zones of sequential pushbacks are divided by haulroads.
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Идэвхитэй үйл ажиллагаа явагдаж байгаа хэсэгт аюулгүй ажиллагааг хангах материал унахаас урьдчилан сэргийлжүндсэн доголуудын хооронд барих доголуудыг үлдээдэг. Улны нөхцөлийг сайтар хангахын тулд үндсэн экскаваторт тусалж бульдозер болон утгуурт ачигч ашиглаж болно. Үүнээс гадна тэдгээрийг нурлыг хэлбэршүүлж шанага дүүргэлтийг нэмэгдүүлэх замаар үндсэн экскаваторын ашигт ажиллагааг нэмэгдүүлэх, хүдэр ба хоосон чулуулгийг ялгаж ачих зэрэгт ашиглаж болно.
Уурхайн автозам
Уурхайн автозам нь ил уурхайнчухал элемент бөгөөд ухаж ачих идэвхтэй бүсээс хөрс болон хүдрийг уурхайн хүрээ болон түүнээс гадагш тээвэрлэх боломжийг хангадаг.
Замын хучилтыг зөв сонгож усан болон химийн тоос дарагчийг тогтмол хэрэглэх ньхамгийн дөт ба үр дүнтэй тоос дарах арга юм. Асгацаас зайлсхийх нь өмнө дурдсан арга хэрэгсэлүүд дээр нэмээд тоос дэгдэлтийг дарахаас гадна түүнээс илүү чухал байж болох дугуйны насжилтыг уртасгах чухал ач хобогдолтой. Өнхрөлтийнөндөр эсэргүүцэл болон автозамын бүрэн бус ашиглалтанд хүргэх зарим гол шалтгаан нь тохироогүй замын хучилт болон нүх хонхорхой, мөр, сийрэг материал(тоос ба чулуу), дэржигнүүр (нийтэд угаалгын нидрүүлэг), гадаргуугийн хагарал,хангалттай бус ус таталт зэрэгтэй холбоотой автозамын эвдрэл багтдаг.
Хөрсний овоолго
Өнөөг хүртэл хөрсний овоолго нь ихэнхи ил уурхайн үйлдвэрлэлийн бүтээгдэхүүний хамгийн их хэмжээг эзэлсээр ирсэн. Хөрс нь дээрээс доош,болон доороос дээшээ байдлаар байршуулагдаж болдог. Хөрсийг босоо ахилттай (дээрээсээ доошоо) овоолох үедматериалыг ахилтын мөргөцөгийг давуулж буулгадаг. Овоолгын проссын явцад зөвхөн бага хэмжээний материалыг бульдозероор дахин шүлжүүлэх шаардлага гардаг. Овоолгын гүйцсэний дараа дахинхэлбэршүүлэх ажил эхэлдэг. Хэвтээ ахилттай овоолох (мөн доороосоо дээшээ овоолох гэж ярьдаг) үед хөрсний давхаргыг овоолгын дээгүүр буулгаж бульдозероор харьцангуй нимгэн үе үүсгэж тараадаг.
Уурхайн тэлэлт
Ил уурхайн тэлэлт нь ахилт буюу орол гэх дараалсан хэд хэдэн үе шатуудаар хэрэгждэг. Ахилт нь энгийн ба цуварсан байж болно. Үндсэндээ хоёр арга уурхайн хүрээг хэвтээ; гэвч цуварсан ахилтын үед хэд хэдэн түвшинд нэгэн зэрэг жижиг ажлын доголуудаар хэрэгждэг бол энгийн ахилтаар ахилтын түвшин дэх бүх хэвтээ тэлэлт нөгөө түвшинд шилжихийн өмнө бүрэн ашиглагддаг. Цуварсан ахилтын өөр өөр бүсүүд хоорондоо автозамаар тусгаарлагддаг.
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| Figure 15.1 Bench elements |
1. pothole
n. 1. хадны хонхорхой. 2. замын нүх/ хонхорхой.
n. (British) exploring of caves or pits
2. corrugation
үрчлээ,атираа,хуниас
3. rut
n. 1. дугуйны мөр. 2. хэвшил, зуршил. 3. нэг хэвийн байдал. 4. ороо. rutted adj. дугуйны мөр гарсан. rutting adj. орооны (үе), ороо орсон.
мөр,харгуй,заншил,отоо,ороо,зуршил,хэвшил,мөр,шан
n. annual period of sexual excitement in some animals (esp. deer); groove, furrow; routine, habitual procedure or course of action
4. corrugation
сущ.
3) тех. сморщивание; рифление; волнистость
5. simultaneously
нэг зэрэг,зэрэгцээгээр
adv. concurrently, at the same time
Maintenance and repair / Үйлчилгээ ба засвар
Thursday, October 15, 2015
Bioleaching/Biocorrosion
Metals/Biomining
Presented to: Dr. Michael Broaders
1. 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.
2. 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.
3. Bioleaching
By Marian Cummins
3.1 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 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
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
In the 1940’s in America 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.
3.2
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?
3.3 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
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.
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