Iron Cycle Flashcards
What are the 2 oxidation states iron cycles between in nature?
Fe2+ and Fe3+
What is Fe2+?
Ferrous
What is Fe3+?
Ferric iron
Where does biological Fe reduction take place (location)?
- waterlogged soils, lake sediments
What organisms use Fe as an electron acceptor?
- facultative anaerobes and obligate anaerobes
When does Fe oxidation take place?
in presence of O2 from water
Give a specific example of an iron oxidizer at a natural pH
Gallionella
Give an example of an iron oxidizer at a low pH
Thiobacillus (strict acidophile)
What is the iron reduction equation
Fe3+ –> Fe2+
What is the iron oxidation equation
Fe2+ –> Fe3+
Define pyrite
- FeS2 - IRON AND SULFUR
- natural form of iron in coal and ore
What conditions are easier for metal extraction from ore?
low pH because metals are more mobile in acidic positions
How does thiobacillus keep inner pH stable?
- high energy for efflux pump of H+
What happens when thiobacillus is taken from acidic conditions?
they continue to pump and kill themselves
What is the importance of Pyrite?
- Iron and sulfur cycles coming together
Why must pyrite be kept watered?
- makes it highly mobile –> releases iron from ore and generates sulfate
What happens once Fe2+ is stabilized from pyrite?
it keeps the pH down and favours metabolism via thiobacillus
How is acidity of pyrite maintained?
due to amount of H+ released
What happens to ferrous iron once it is mobilized?
it continues cycling (propagation cycle)
Where is microbial leaching practiced?
where chemical concentration of metal is not economically feasible (not readily oxidized)
Explain the process of microbial leaching
- Sprinkle acidic solution(Fe2+ and H2O) on CuS to make it more mobile and separate from ore (low pH on pile)
- Water is added to CuS and ferric iron to make Cu2+ (soluble) as well as ferrous iron and sulfate with H+ (acidic)
- Addition of liquid copper to Cu2+ to remove metal from scrap pile
- added to oxidation pond (acidic ferrous rich)
- propagation transformation (Fe2+ –> Fe3+ via thiobacillus)
What does acid dumping help with?
- keeping pH low for thiobacillus
- increases mobilization
What is the importance of free copper, sulfate and ferrous iron?
they keep acid content where it needs to be
What happens when you dump liquid copper on soluble copper?
- they swap electrons and take copper metal out of scrap
When Fe2+ is transformed into Fe3+, what does it release?
free copper
What is the equation after acid is added to CuS during microbial leaching
CuS + Fe3(+) + H2O —> Cu2(+) + Fe2+ +So4 + H+
