unit 4&5

• Biomining


  Using microorganisms to extract minerals from ores
• Traditional mining techniques have been deleterious to the environment and health
• Microorganisms used in biomining

  • They leach out minerals from ores in a more efficient and environmentally friendly way compared to traditional mining
• Biomining process


  1. Microorganisms oxidize inorganic materials like copper sulfide minerals

  2. This releases acid and an oxidizing solution of ferric ions

  3. Metals are washed out from the crude ore
• Approximately 25% of all copper mined worldwide is now obtained from leaching processes
• Acidophilic archaea


  Microorganisms that tolerate up to 4% of copper and have been exploited for mineral biomining
• Between 40 and 60% copper extraction was achieved in primary reactors and more than 90% extraction in secondary reactors with overall residence times of about 6 days
• Challenges in biomining

  • Bioprocessing releases a great deal of heat, which can slow down or kill the bacteria currently being used
  • Microbes need to be resistant to heavy metals like mercury, cadmium, and arsenic which can poison them and slow down bioprocessing
• Thermophilic bacteria found in hot springs and around oceanic vents can function in high temperature oxidative environments and solve the heat problem
• Microbes with enzymes that protect their basic activities from heavy metals or pump them out can be engineered to be resistant
• Biomining is now at the top of mining technology, and future development of the technology appears promising
• Oxidation of ferrous ion (Fe2+) to ferric ion (Fe3+)

  1. Energy producing reaction for some microorganisms

  2. Fe3+ forms insoluble Fe(OH)3 precipitate in H2O

  3. Many Fe2+ oxidizing microorganisms also oxidize sulfur and are obligate acidophiles that further acidify the environment by producing H2SO4
• Acidithiobacillus ferrooxidans

  Best studied Fe2+ oxidizing bacterium, an acidophilic chemolithotroph
• Oxidation of pyrite (FeS2)

  1. Slow chemical process with O2 as electron acceptor initiates oxidation

  2. Acidithiobacillus ferrooxidans grows rapidly in the acidic environment and further acidifies it

  3. Fe3+ reacts spontaneously with pyrite, producing more Fe2+ which can be used by the microorganisms, initiating a cascade reaction
• Industrial microbial leaching process

  1. Low grade ore is dumped in a large pile (leach dump)

  2. Dilute sulfuric acid solution (pH 2) is percolated down through the pile

  3. Liquid rich in the mineral is collected at the bottom and transported to a precipitation plant

  4. Liquid is then pumped back to the top of the pile and the cycle is repeated
• Copper extraction in biomining

  1. Acidithiobacillus ferrooxidans oxidizes Cu in chalcocite (Cu2S) to Cu2+, forming covellite (CuS)

  2. Covellite can then be oxidized, releasing soluble Cu2+

  3. Chemical oxidation of copper ore with ferric (Fe3+) ions formed by microbial oxidation of ferrous ions is the most important mechanism
• Uranium leaching in biomining

  1. Acidithiobacillus ferrooxidans can oxidize U4+ to U6+ with O2 as electron acceptor

  2. Uranium leaching process likely depends more on chemical oxidation of uranium by Fe3+, with A. ferrooxidans contributing through reoxidation of Fe2+ to Fe3+
• Gold extraction in biomining

  Acidithiobacillus ferrooxidans and relatives are able to attack and solubilize arsenopyrite minerals, releasing the trapped gold
• Gold and silver are also recovered from ores using cyanide leaching
• Biomining has a key role to play in increasing copper production to meet future demand
• Future developments in biomining

  • Microbes could potentially be used for processing of oxide ores through reductive bioleaching
  • Ore pre-treatment methods like bioflotation and bioleaching of impurities are under development to utilise more complex ores
  • Application of bioleaching to recover metals from various metal-containing waste materials is being explored to make the overall lifecycle of mineral resources more sustainable
• Biofuel


  Fuel derived from biological materials, such as plants and animals
• Automobile fuels by 2020 are likely to consist mainly of gasoline, methanol from coal, diesel oil, and liquefied petroleum gas, with only a small percentage of ethanol derived from biomass
• Alcohol production process


  1. Reduction of material to water-soluble sugars

  2. Fermentation to produce alcohol

  3. Distillation by boiling to separate alcohol from water
• Alcon Biotechnology developed a continuous-fermentation process for producing fuel alcohol that could be housed in a standard shipping container
• The continuous-fermentation process may revive if oil prices rise significantly
• Social science research went into alcohol development as an alternative source of energy
• Brazil and other countries actually became committed to full-scale production, with mixed results
• For a number of reasons, the energy crisis abated by the 2000s, and the avenue of alternative fuels was de-emphasized in the U.S.
• Alcon Biotechnology, a joint venture between John Brown Engineers and Allied Breweries, developed a continuous-fermentation process that could be housed in a standard shipping container
• The process appealed to and gained approval in countries such as the Philippines, which had been trying to produce more fuel alcohol to offset growing oil import bills
• Although significant sales of the new process did not materialize, the process may revive if oil prices rise significantly
• Biofuel


  A fuel that is derived from biological materials, such as plants and animals
• Biomass


  Recently living organisms, most often referring to plants or plant-derived materials
• Biomass conversion


  1. Thermal conversion

  2. Chemical conversion

  3. Biochemical conversion
• Biomass conversion can result in fuel in solid, liquid, or gas form
• Biofuels have increased in popularity because of rising oil prices and the need for energy security
• Anaerobic digestion


  Organic matter is converted, by bacterial action, into a useful mixture of methane and carbon dioxide in the absence of air
• The first commercial bioenergy plant was built in Ashford, Kent, England, by RHM, and was followed by a second facility in Bordeaux, France
• As part of a continuing development program, five mobile plants have been sited at industrial locations in the United Kingdom