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Bioleaching/Biocorrosion
Metals/Biomining
Lisa Smith
Marian Cummins
Deborah Mc Auliffe
• Metal Contamination of soil environments
and the assessment of its potential risk to
terrestrial environments and human health
is one of the most challenging tasks
confronting scientists today.
• Challenge for mining companies
– Service-no long term impact on environment
• Increasing interest in microbial approaches
for recovery of base and precious metals
Biomining
• Use of microorganisms
– Ores of high quality rapidly being depleted
– Environmentally friendly alternative
Biomining
•
Naturally existing microorganisms leach
and oxidate
1. Bioleaching
2. Biooxidation
• Bioleaching
– Extraction of metals with the use of
microorganisms
• Biooxidation
– Microorganisms make metal ready for
extraction
General Properties
•
Chemolithotrophic - “ rock eating”
• Autotrophic
• Acidophilic ( acid loving)
• Use oxygen as the preferred electron acceptor
Specific Microorganisms
Most common:
• Thiobacillus ferrooxidans
• Thiobacillus thiooxidans
Thiobacillus ferrooxidans
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Rod shaped
Relatively quick growing
Gram negative
Strictly aerobic
Aerobic conditions uses Fe2+ or reduced S (S2-) as
electron acceptor
• Anoxic conditions use Fe3+ as electron acceptor
• Mod. Thermophilic, temperatures of 20-35 degree C and
pH of 2.0
Thiobacillus thioxidans
• Very similar to T. ferrooxidans
• Can’t oxidise Fe3+
The Process
• 2 Methods- Direct and indirect
• Direct- enzymatic attack and occurs at the
cell membrane
• Indirect- bacteria produce Fe3+ ( ferric iron)
by oxidizing Fe2+ (ferrous iron)
• Fe3+ is a powerful oxidizing agent that
reacts with the metals and so produces
Fe2+ in a continuous cycle.
Copper Process
• 25% Copper production is recovered by
biomining
• MS + 2O2
MSO4
• Metal sulphide is insoluble and metal sulphate is
usually water soluble
• Cu ore contains CuS and CuFeS2
• T. ferrooxidans brings about both direct and
indirect oxidation of CuS via the generation of
(Fe3+) ferric iron from (Fe2+) ferrous sulphate
• Cu is recovered by solvent extraction or by
using scrap iron where the iron replaces
the Cu
• CuSO4 + Fe
Cu + FeSO4
Other Application of Biomining
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Gold
Due to depletions by the 1980’s
Dependent on lower grade ore
Gold is encased in the sulphide minerals
T. ferrooxidans
Fairview mine in S. Africa
Recovery rate of 70% to 95%
Cont’d
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Phosphates industry
2nd largest agriculture chemical
5.5 million tons/ year in the US
Traditional method was burning at high temperatures
(solid phosphorus) or with H2 SO4(phosphoric acid and
gypsum)
• Pseudomonas cepacia E37 and Erwinia herbicola
• Glucose---- gluconic and 2 ketogluconic acid
• Environmentally friendly as no Hs SO4 required and it
occurs at room temperature.
Case Studies
+
Economics of Biomining
Microbes ‘TO TACKLE MINE
WASTE’
• Scientists are using microbes to clean up the
problem of corrosive acid pollution left over as
mining waste
• Some of the microbes being used were found in
America, Wales and the Caribbean island
• By discovering microbes which can survive in
this environment, will help address serious
environmental hazards at abandoned mines and
soil heaps
Industrial Biotechnology Biomining
• Commercial Capabilities
• Underpinning Existing Capabilities
• Emerging Capabilities
• Institutional Capabilities
• Knowledge / Skills
Chile Biomining Program
• Worlds first biggest producer of Copper
• In 1971 copper mines were nationalized
• But in 1990 Chile returned to democracy
• Started in 1990 with target @2.5m tons for the
year 2000
• This Figure was superseded in 1995 and
production exceeded 5m tons / late 1990’s
Economic Study of the Canadian
Biotechnology
• Canadian environmental & industrial
biotechnology firms
• Microorganisms in applications such as
bioremediation leaching, energy production
• Canadian Stakeholders with; U.S,
European, Japanese environmental
regulators
Biomining
“There’s GOLD in them thar’ Plants!”
• Gold rush miners might have been better
off using plants to find gold rather than
panning streams for precious metal
• Early prospectors in Europe used certain
weeds as indicator plants that signaled the
presence of metal ore
Remediation
• Response to human health effects
• Response to environmental effects
• Redevelopment
Bioremediation
• Destroys or renders harmless various
contaminants using microbial activity
• Bioremediation of metal-contaminated soil
– Soil Flushing
– Soil Washing
– Phytostabilization
– Phytoremediation
Phytostabilization
• Immobilization of a contaminant in soil
through
– Absorption & Accumulation
– Adsorption
– Precipitation
• Also use of plant & plant root to prevent
contaminant migration
• Soil is then farmed to improve growth and
reduce mobility and toxicity of contaminant
Phytoremediation
• Use of plants to remove contaminants
from soil
• Certain plant species-metal
hyperaccumulators
– extract metals, concentrate them in their
leaves
• Prevent recontamination-plants harvested
• Leaves accumulate
metals and are
harvested
• Roots take up metals
from contaminated
soil and transport to
the stem, leaves
Biomining
+Carried out insitu
+Less energy input
+No toxic/noxious gases produced
+No noise or dust problems
+Process is self generating
+Large or small scale operations
+Wide variety of metals (Cu, Ag, Pb, Au, Zn)
+Work on low grade ores
-Slow process
Traditional extraction causes
environmental problems and
degradation, biomining offers an
environmentally friendly alternative!!!!!!