Bioleaching of iron, copper, gold. uranium

MICROBIOLOGY

1. BIOLEACHING OF IRON , COPPER, GOLD, URANIUM PRESENTED BY: Mousami Jaria St. Geeorge College of Management and Science MSc Microbiology Semester 2

2. BIOLEACHING It is the extraction of metal from sulfide ores or concentrates using materials found native to the environment namely water, air, microorganisms. It is the leaching of sulfide minerals that distinguishes bioleaching from conventional acid leaching wherein only oxidized minerals are leached. Biooxidation is an associated process,it is the oxidation of sulfide minerals associated with but not necessarily part of the mineral to be extracted.

3. Bioleaching is used to process ores of copper, nickel, cobalt, zinc, uranoum whereas biooxidation is used in gold processing . Widely used in countries like Australia, Canada, Chile, China, Indonesia,US , Zambia. Started around 1940s.

4. OVERVIEW OF BIOLEACHING PLANT

5. MICROORGANISMS INVOLVED The commonly used microorganisms in bioleaching are: Thiobacillus thiooxidans Thiobacillus ferrooxxidans FUNGI: Aspergillus niger , P enicillium simplicissimum Others involved are : Bacillus licheniformis , B . luteus , Pseudomonas fluorescence , Sulfolobus acidocaldarius etc.

6. Cadmium sulfide Thiobacillus

7. MECHANISM DIRECT BIOLEACHING : In this bioleaching , bacteria directly oxidize minerals and solubilize metals. A physical contact exists between bacteria and ores and oxidation of minerals takes place through enzymatically catalysed steps Eg : pyrite oxidised to ferric sulphate 2FeS 2 +7O 2 2FeSO 4 + 2H2SO 4

8. 2 . INDIRECT BIOLEACHING : In this type , bacteria produces the strong oxidizing agent such as ferric ion and sulphuric acid on oxidation of soluble iron or soluble sulfur respectively. Acidic environment is absolutely essential in order to keep ferric iron and other metals in solution. Acidic environment is maintained by oxidation of iron, sulfur, metal sufides or by dissolution of carbonate ions Eg : bioleaching of uranium UO 2 + Fe(SO 4 ) UO 2 SO 4 +2FeSO 4

9. COMMERCIAL BIOMINING PROCESS SLOPE LEACHING : Fine ore is kept in large slope shaped dump. A water solution made of inoculum is continuously sprayed over the ore. After that , the leach liquor is gathered at the bottom and processed for supplemental metal recovery.

10. 2. HEAP LEACHING: The ore is arranged in large heaps . An aqueous mixture of microorganisms is sprinkled over the leach pile. Then solution is collected to help recover even more metal. 3 . IN–SITU LEACHING : Ore remains in natural state while leaching process takes place.

11. Water that contain Thiobacillus is pushed through drilled passageways within the ore The leach fluid is then stored untill its time for metal recovery.

12. ADVANTAGES Simple Inexpensive Recovery of metals from low grade ore To extract expensive metals. Ideal for low grade sulfide ores. Environment friendly process. Employed for collecting metals from waste and drainages.

13. DISADVANTAGES Low yield of minerals Time consuming ,6-24 months or longer. Requires large open area for treatment. Heat generated from dissolving process can kill bacteria. High risk of contamination.

14. BIOLEACHING OF COPPER Chalcopyrite(CuFeS 2 ), Covellite ( CuS ), Chalcolite (Cu2S) are ores of copper from which copper is recovered. Carried out by heap leaching or Insitu leaching. Action of acidithiobacillus involves the oxidation of CuFeS 2. CuFeS 2 + 4O 2 Cu 2 + Fe 2 + 2SO4 2 - Sulphuric acid is the byproduct of this reaction . It maintains necessary acidic environment for extraction.

15. BIOLEACHING OF IRON Iron ores: Hematite(FeO3), Magnetite(Fe3O4), Limonite(2FeO3.3H2O), Siderite(FeCO3). The oxygen must be removed from the iron (Fe3) oxide in order to leave the iron behind. Acidithiobacillus ferrooxidans are used as bacterial agents. Maximum extraction occurs at pH 1.3 Fe 2 O 3 +3CO 2Fe+3CO 2

16. BIOLEACHING OF GOLD Gold ores: Calaverite ( AuTe 2 ), S ylvanite ( Ag.Au )Te 2 , Petzite ( Ag 3 AuTe 2 ). Gold cannot be extracted from low grade sulfide ores. Iron and Sulfur acidophillic bacteria are able to oxidize certain sulphidic ores. Thiobacillus ferrooxidans is used in process Gold ore is first pretreated by roasting or pressure oxidation.

17. 4 Au+8NaCN + 2H 2 O+O 2 4Na(Au(CN) 2 )+ 4 NaOH . 2Na (Au(CN) 2 )+ Zn Na(Zn(CN) 4 )+2Au Heap leaching technology is used.

18. BIOLEACHING OF URANIUM Uranium ores : Uraninite or Pitchblende (UO 2 ), Brannerite (UTi 2 O 6 ). Uranium ores occur in low grade ores and is insoluble, converted to leachable form by oxidation of ferric ion. Insitu bioleaching technique used. UO 2 +Fe(SO 4 ) 3 UO 2 SO 4 +2FeSO 4 In this process T. ferroxidants acts on iron oxidant and not directly on uranium.

19. It acts on pyrite (FeS2) in uranium ore and produces ferric sulphate and sulphuric acid The soluble form of uranium is in leach liquor is extracted in organic solvents like trimethyl phosphate, precipitated and recovered.

20. THANK YOU