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Bioleaching
Some bacteria can live by using the energy of the bond between sulfur
and copper. This separates the metal from the ore and is called bioleaching.
It has the advantage that it is very energy efficient
typically using only 30% to 50 % of the traditional method.
It has the disadvantage that it is very slow.
http://www.gcsescience.com/ex23.htm
Longman AQA GCSE book
What is Bio-leaching Technology?
Bio-leaching is a hydro-metallurgical process that extracts value-bearing metals from their ores
through the use of bacteria. In recent years, demand for copper has risen dramatically. On this basis,
the effective application of lowgrade copper ore, which was previously discarded as tailings, has
become an increasingly pressing issue. Since 1990, bioleaching technology has been employed to
extract copper from low-grade secondary copper sulfide ore at certain mines. Focusing not only on
secondary copper sulfide ore, BioSigma is working to further harness the potential of the bacteria
found in nature to develop a technology that will efficiently leach and refine copper from primary
copper sulfide ore, long thought to be a difficult process.
Under the bio-leaching process, bacteria perform the action of oxidizing iron and sulfur. In order to
procure the energy required to spur bacterial growth, both iron and sulfur oxidizing bacteria draw on
electrons found in the iron and sulfur, respectively. As a result, the iron and sulfur oxidize. Copper,
with which bacteria cannot be used, remains unoxidized. That is to say, copper is a by-product of the
bioleaching process. Previously discarded tailings serve as a resource while the bio-leaching
technology also contributes to improved economic benefits by accelerating the speed of leaching in
the hydro-metallurgical process.
Copper Recovery Process utilizing Bio-leaching Technology
http://www.nmm.jx-group.co.jp/english/sustainability/theme/environment-conscious/index.html
Figure 1. Irrigation style bioleaching. Crushed copper ore is piled and dilute H2SO4 is trickled through
the pile. Bacteria oxidize the sulphide, producing acid. As the matrix containing the metal is
destroyed the metal dissolves in the acidic solution to produce the ‘leach liquor’. This liquid is then
subjected to electroplating to remove the metal ions from solution.
http://www.scq.ubc.ca/the-little-workers-of-the-mining-industry/
Bioleaching
Bioleaching uses bacterial microorganisms to extract precious metals, such as gold, from ore in
which it is embedded. As an alternative to smelting or roasting, miners use bioleaching when there
are lower concentrations of metal in ore and they need an efficient, environmentally responsible
method. The bacteria feeds on nutrients in minerals, thereby separating the metal that leaves the
organism's system; then the metal can be collected in a solution.
Bioleaching works because of how special microorganisms act on mineral deposits. They are a
catalyst to speed up natural processes inside ore. The bacteria uses a chemical reaction called
oxidation to turn metal sulphide crystals into sulfates and pure metals. These constituent parts of
ore are separated into valuable metal and leftover sulphur and other acidic chemicals. Eventually,
enough material builds up in the waste solution to filter and concentrate it into metal.
For some types of metal, such as copper, bioleaching is not always economically feasible or fast
enough, even with its low cost. However, in certain areas of the world or with other metals, this
simple, effective, and low cost method offers a smart choice. For example, developing countries
often do not have the infrastructure or capital investment to begin smelting, yet their land contains
enough ore that its extraction can significantly improve their national economy. One day we may use
bioleaching to mine other metals, such as zinc and nickel, on the Moon.
http://www.wisegeek.com/what-is-bioleaching.htm
AQA textbook
Phytomining.
Some plants absorb metal compounds (including copper) when they grow.
The plants can then be burned and the metal is extracted from the ash.
The process is called phytomining and it can also be used to extract metals
from contaminated land. Brassicas (the cabbage family)
can extract metals including cadmium, cobalt and nickel.
http://www.gcsescience.com/ex23.htm
Phytomining
http://pangeacrafts.com/phytomining-of-copper
Phytoextraction (Phytoaccumulation)
Phytoextraction is the name given to the process where plant roots uptake metal contaminants from
the soil and translocate them to their above soil tissues. As different plant have different abilities to
uptake and withstand high levels of pollutants many different plants may be used. This is of particular
importance on sites that have been polluted with more than one type of metal contaminant.
Hyperaccumulator plant species (species which absorb higher amounts of pollutants than most other
species) are used on may sites due to their tolerance of relatively extreme levels of pollution.
Once the plants have grown and absorbed the metal pollutants they are harvested and disposed of
safely. This process is repeated several times to reduce contamination to acceptable levels. In some
cases it is possible to recycle the metals through a process known as phytomining, though this is
usually reserved for use with precious metals. Metal compounds that have been successfully
phytoextracted include zinc, copper, and nickel, but there is promising research being completed on
lead and chromium absorbing plants.
http://arabidopsis.info/students/dom/mainpage.html
Phytomining cleans soil, generates revenue - Science Update - Brief Article
Studies have now shown that using certain plants to extract metals from soil is commercially feasible.
These specially selected plants--called hyperaccumulators--are known for their ability to take up and
store particular metals. Now a team of scientists has developed a nickel hyperaccumulator plant for
commercial use. After evaluating several hundred strains of Alyssum plants for favorable genetic
characteristics, they have developed the first commercial crop capable of hyperaccumulating nickel
and cobalt. This haylike crop would be burned after harvest to create a biomass energy byproduct,
with nickel and cobalt recovered from the ash.
This approach to cleansing contaminated soils is a win-win strategy because using it doesn't cost
much and the recovered nickel is valuable. While establishing a low-grade pasture or woodlot on
contaminated land or nickel-rich serpentine soils might yield about $50 to $100 per hectare annually,
producing the nickel phytomining crop could yield about 400 kilograms of nickel, worth over $2,000. If
you count the sale of energy produced by burning the plant to get the metal-rich ash, the value rises
to more than $2,500 netted from that same hectare. And the plants can extract nickel from mining
wastes and mineralized soils for which conventional mining techniques are not economic.
http://findarticles.com/p/articles/mi_m3741/is_8_50/ai_90873347/
AQA textbook
http://www.hoddereducation.co.uk/SiteImages/fd/fd2a4d44-7a04-4a21-a918-68f2736b81fb.pdf