Bio Leaching of Metal Ions Form Low Grade Metal Depositions

                         

  There are metal depositions in the world with low concentrations so they refer to as low grade metal depositions. Therefore it is non-effective to extract metal ions by using chemical extractions. Therefore metal ions from low grade depositions are extracted by using metabolic activates of bacteria.

Copper extraction: Low grade Copper depositions are known as low grade copper ore. Copper is available as Covelite (CuS). Covelite that is extracted from the underground deposition are pilled as heap. Concentrated sulfuric acid is added to the top the heap.  Usually Covelite are associated with pyrite (Fe2S).  Pyrite plays a major role of copper extraction process. Sulfur oxidizing bacteria such as Thiobacillus thioxidans use sulfide of the pyrite (Fe2S) as their substrate for their ATP synthesis. They oxidize sulfide into sulfate. This reaction releases ferrous ion from the mineral. Then these ferrous ion is used the substrate by Acidothiobacillus thioxidans. They oxidize ferrous ion into ferric ion. These ferric ions are collected and added to the top of heap. These ferric ions undergo a redox reaction with Covelite. Ferric is reduced back into ferrous. Sulfide of Covelite is oxidized into sulfate. These reaction releases cupric ion. A scarab metal is put to the tank to reduce the cupric ion into copper metal. Copper metal can be collected from the bottom of the tank. Ferrous ions are again oxidized into ferric by iron oxidizing bacteria.

Uranium extraction: In the environment, uranium depositions are found in the form of Uraninite (UO2) which water insoluble. Uraninite depositions are piled into heap. Pyrite also plays important role in Uranium extraction. Sulfur oxidizing bacteria such as Thiobacillus thioxidans use sulfide of the pyrite (Fe2S) as their substrate for their ATP synthesis. They oxidize sulfide into sulfate to take electron to run electron transport chain. This reaction releases ferrous ion from the pyrite (Fe2S). 

Then these ferrous ion is used the substrate by iron oxidizing bacteria such as Acidothiobacillus thioxidans. They oxidize ferrous ion into ferric ion. These ferric ions are collected and added to the top of the heap. These ferric ions undergo a redox reaction with Uraninite. Ferric is reduced into ferrous. Uraninite (IV) is oxidized into Pitchblende (VI) which less water soluble. Pitchblende can be collected from the bottom of the tank. Ferrous ions are again oxidized into ferric by iron oxidizing bacteria.