Submitted to: Dr.
Zahid Munir
Submitted by: SP21-BSO-055
Raja Suleman
BIOLEACHING: METAL EXTRACTION AND ITS PRACTICAL
APPLICATIONS
Introduction:
Bioleaching is a scientific process in which microorganisms, such as bacteria or fungi,
are utilized to extract valuable metals from ores, mineral concentrates, or other
metal-containing materials. It is a form of biotechnology that relies on the metabolic
activities of these microorganisms to solubilize and recover metals from their solid
mineral forms. The microorganisms involved in bioleaching interact with the mineral
substrate, often metal sulfides, and catalyze chemical reactions that result in the
release of metal ions into a liquid solution. These metal ions can then be recovered
through subsequent steps such as precipitation, solvent extraction, or electrochemical
processes. Bioleaching offers several advantages over traditional mining methods,
including lower energy consumption, reduced environmental impact, and the ability to
extract metals from low-grade or otherwise inaccessible mineral resources.
Microbial Bioleaching procedure:
Here are the microbiological details of how microbes bioleach metals:
1. Metal-Oxidizing Microorganisms:
• Key microorganisms involved in bioleaching belong to the group of
chemolithotrophic bacteria and archaea. They derive their energy from
the oxidation of inorganic compounds, such as metal sulfides present in
the ore.
• Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans are
commonly used bacteria in bioleaching. These microorganisms possess
enzymes and specialized organelles that enable them to oxidize metal
sulfides.
• Some archaea, such as Sulfolobus metallicus and Ferroplasma
acidiphilum, are also known to play a role in metal oxidation in extremely
acidic environments.
2. Attachment and Colonization:
The bioleaching microorganisms attach and colonize the mineral surfaces. They
produce extracellular polymeric substances (EPS), which form a biofilm matrix. The
biofilm allows the microorganisms to adhere to the mineral surfaces, creating a
favorable microenvironment for their growth and interactions with the metals. The EPS
also facilitates the accumulation and concentration of metal ions released during
bioleaching.
3. Bio-oxidation of Metal Sulfides:
• The primary mechanism by which microorganisms bioleaching metals is
through the oxidative breakdown of metal sulfides. This process involves
the following steps: a. Microorganisms, such as Acidithiobacillus species,
produce enzymes, including iron oxidases and sulfur oxygenases, which
catalyze the oxidation of metal sulfides. b. The microorganisms utilize the
energy obtained from the oxidation reactions for their metabolic
processes. c. Metal sulfides, such as iron pyrite (FeS2) and chalcopyrite
(CuFeS2), are converted into metal ions, such as Fe3+ and Cu2+,
respectively, along with the release of sulfur compounds. d. The bio-
oxidation of metal sulfides results in the solubilization and mobilization of
metal ions, making them available for further extraction.
4. Redox Reactions:
• Microbes involved in bioleaching mediate redox reactions between the
mineral surfaces and their metabolic processes.
• They transfer electrons from the mineral surfaces to their internal
metabolic pathways, facilitating the oxidation of metal sulfides and the
reduction of electron acceptors.
• Redox-active compounds and enzymes produced by the microorganisms, such
as iron- and sulfur-containing proteins, play a crucial role in these electron
transfer processes.
4FeSO4 + 2H2SO4 + O2 → 2Fe2(SO4)3 + 2H2O
2S° + 3O2 + 2H2O → 2H2SO4
2FeS2 + 7O2 + 2H2O
5. Acid Production:
• Bioleaching microorganisms often produce acids as by-products of their
metabolic activities. The acids contribute to the solubilization of metal
ions from the minerals.
• Acidithiobacillus species, for example, produce sulfuric acid (H2SO4)
through the oxidation of sulfur compounds, creating an acidic
environment that aids in metal dissolution.
6. Metal Resistance Mechanisms:
• To thrive in metal-rich environments, bioleaching microorganisms
possess various mechanisms to tolerate high levels of toxic metals.
• They may have metal efflux pumps and transporters that help them
manage and detoxify metal ions.
• Additionally, microorganisms in bioleaching consortia often exhibit
synergistic interactions, where different species contribute
complementary metal resistance mechanisms.
- Industrial Preparation of Biomining
Industrial bioleaching refers to the large-scale application of bioleaching processes in
commercial mining operations for the extraction of metals from low-grade ores. The
metals can be recovered by the microorganisms through two processes:
(1) Bioleaching and (2) Bio-Sorption
Microorganisms can be successfully used for the extraction of metals (e.g., copper,
zinc, cobalt, lead, uranium) from low-grade ores. Mining with microbes is both
economical and environmentally friendly.
Ore Selection and Formulation:
Suitable ores for industrial bioleaching are those that contain metal sulfides, such as
chalcopyrite (CuFeS2), bornite (Cu5FeS4), and pyrite (FeS2), among others.
The ore is typically crushed and ground to increase the surface area available for
microbial interactions and subsequent metal extraction. Ore preparation may also
involve other steps, such as flotation or concentration, to enhance the ore's suitability
for bioleaching.
Microbial Strain Selection:
Industrial bioleaching operations utilize specific strains of microorganisms, often
Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans, due to their high
efficiency in metal oxidation. These strains may be naturally present in the ore or
introduced artificially as inoculants to ensure a robust microbial community capable of
efficiently extracting metals.
Bioleaching Reactors:
Large-scale bioleaching operations employ specially designed bioleaching reactors,
such as stirred tanks or heaps, to accommodate the high volumes of ore and microbial
culture. Stirred tank reactors provide controlled conditions, including temperature, pH,
and oxygen levels, to optimize microbial activity and metal extraction.
Heap leaching involves stacking the ore in large heaps and irrigating them with a
microbial culture and a leaching solution, allowing for bio-oxidation to occur naturally.
Process Monitoring and Optimization:
Industrial bioleaching processes require continuous monitoring and optimization to
ensure efficient metal extraction and minimize operational costs. Parameters such as
pH, temperature, nutrient availability, and oxygen supply are carefully controlled and
adjusted as needed. Sampling and analysis of the leachate are performed regularly to
monitor metal concentrations and assess the progress of the bioleaching process.
Refined Metal Collection:
Once the metal ions are solubilized in the leachate, they
are further processed to recover the desired metals.
Various techniques are employed for metal recovery,
including precipitation, solvent extraction,
electrowinning, and ion exchange, depending on the
specific metal and the desired purity of the final product.
These recovery techniques help separate the metal ions
from the leachate, allowing for the production of metal
concentrates suitable for further refining.
https://www.angloamerican.com/futuresmart/stories/our-industry/mining-
explained/mining-terms-explained-a-to-z/bioleaching-definition-and-
process
Applications of Bioleaching:
Bioleaching has found significant industrial and commercial applications in various
sectors. Some of the key areas where bioleaching is utilized are:
1. Mining Industry: The mining industry extensively utilizes bioleaching for the
extraction of metals from low-grade ores. It offers a cost-effective and
environmentally friendly alternative to traditional mining methods. Bioleaching
is commonly employed for the extraction of copper, gold, uranium, nickel, zinc,
and other metals.
2. Metal Recovery from E-Waste: Electronic waste (e-waste) contains a significant
amount of valuable metals. Bioleaching processes have been developed to
extract metals like gold, silver, copper, and palladium from e-waste. This helps
in resource recovery and reduces the environmental impact of e-waste
disposal.
3. Tailings Remediation: Mining operations generate large quantities of tailings,
which are waste materials containing residual metals. Bioleaching can be used
to remediate and recover valuable metals from these tailings, minimizing their
environmental impact and potentially generating additional revenue.
4. Industrial Effluent Treatment: Bioleaching processes have been applied for the
treatment of industrial effluents containing metal contaminants.
Microorganisms can bioleach the metals, thereby reducing their concentration
in the effluent and making it suitable for discharge or further treatment.
5. Precious Metal Refining: Bioleaching is used in the refining of precious metals,
such as gold and silver. It provides a more environmentally friendly alternative
to traditional chemical methods, minimizing the use of toxic chemicals and
reducing the generation of hazardous waste.
6. Phytomining: Phytomining is a specialized form of bioleaching that involves
growing plants in metal-rich soils. The plants absorb metals from the soil
through their roots, and then bioleaching processes are employed to extract the
metals from the plant biomass. Phytomining offers a sustainable and low-cost
method for metal recovery from areas with high metal concentrations.
Reference list:
https://www.biologydiscussion.com/biotechnology/metal-biotechnology/methods-of-metal-recovery-by-
microorganisms-2-methods/10446
https://www.angloamerican.com/futuresmart/stories/our-industry/mining-explained/mining-terms-explained-a-
to-z/bioleaching-definition-and-process
https://biotecharticles.com/Applications-Article/Bioleaching-Application-of-Biotechnology-in-Mining-Industry-
850.html
