IRON CYCLE

IRON CYCLE

• Iron (Fe) is one of the most abundant elements in Earth’s crust.
• The Iron cycle (Fe) is the Biogeochemical cycle of Iron through the Atmosphere, Hydrosphere, Biosphere and Lithosphere.

STEPS INVOLVED IN IRON CYCLE

• On the surface of earth, Iron exists naturally in Two oxidation states, (i) Ferrous [Fe²⁺ or Fe(II)] and (iii) Ferric [Fe³⁺ or Fe(III)]. A third oxidation state, Fe⁰ is abundant in Earth’s core and is also a major product of human activities from the smelting of Iron ores to form Cast iron.
• Iron cycle has two steps. They are

1.  Ferrous iron oxidation
2. Ferric iron reduction

Iron cycle (Oxidation – Yellow; Reduction – Red)

1) Ferrous Iron Oxidation

• In Ferrous iron oxidation, the Ferric iron (Fe³⁺) is reduced to the Iron ore (Fe⁰) and then oxidized to Ferrous iron (Fe²⁺). This reaction is a Chemical oxidation process.
• The oxidized Ferrous iron (Fe²⁺) is again reduced to Iron ore (Fe⁰).
• The Ferrous iron (Fe²⁺) undergoes Ferrous iron oxidation by the Bacterial or Chemical oxidation process and results in formation of Ferric iron (Fe³⁺).
• Microorganisms involved in Ferrous iron oxidation process are Gallionella sp., Thiobacillus ferrooxidans, Sulfolobus sp., Iron bacteria (Sphaerotilus sp. & Leptothrix sp.) and Dechlorosoma suillum.

2) Ferric Iron Reduction

• The oxidized Ferric iron (Fe³⁺) is reduced to Ferrous iron (Fe²⁺) by the Bacterial or Chemical reduction process.
• Ferric Iron Reduction is a Two steps process.

ü  Step - I: Ferric iron (Fe³⁺) is reduced to Ferric hydroxide (FeOH₃)

ü  Step - II: Ferric hydroxide (FeOH₃) is reduced to Ferrous iron (Fe²⁺)

• Microorganisms involved in Ferric iron reduction process are Geobacter metallireducens, Geobacter sulfurreducens, Ferribacterium limneticum, Shewanella putrefaciens and Aquaspirillum magnetotaticum.