Bioleaching

“Bioleaching" or "bio-oxidation" employs the use of naturally occurring bacteria, harmless to both humans and the environment, to extract of metals from their ores.
Conversion of insoluble metal sulfides into water-soluble metal sulfates.
It is mainly used to recover certain metals from sulfide ores. This is much cleaner than the traditional leaching.

1. Bioleaching Submitted By , Effat Jahan Tamanna

2. Objectives After the end of the presentation we’ll know- Biohydrometallurgy and its applications Bioleaching Microorganisms involved in Bioleaching Bioleaching Process Factors and Parameters influencing Bioleaching Advantages and disadvantages of Bioleaching Bioleaching of Some Metals Gold Uranium Copper

3. Biohydrometallurgy Biohydrometallurgy is a method for obtaining metals from their ores by using microorganisms. Interdisciplinary field involving processes that - make use of microbes (- bio) mainly take place in aqueous environment (– hydro) deal with metal production and treatment of metal containing materials and solutions (– metallurgy) Bioleaching is one of the application of Biohydrometallurgy.

4. Bioleaching “ Bioleaching " or "bio-oxidation " employs the use of naturally occurring bacteria , harmless to both humans and the environment, to extract of metals from their ores. Conversion of insoluble metal sulfides into water-soluble metal sulfates. It is mainly used to recover certain metals from sulfide ores. This is much cleaner than the traditional leaching. S tarted around the late 1940s in South Africa . Since then it has become a worldwide phenomena. Bioleaching is used to recover copper, zinc, lead, arsenic, antimony , uranium, nickel, molybdenum, gold, silver and cobalt . Widely used in many counties such as Australia, Canada, Chile China, Indonesia, United States, Zambia.

5. Microorganisms involved in Bioleaching Bacteria are classified according to temperature at which they are active namely: Mesophiles (30 - 42 °C) Moderate thermophiles (45 - 50 °C) Extreme thermophiles (65 - 85 °C) The bacteria oxidise ferrous iron ( ) and sulphur (S) to produce ferric iron ( ) and sulphate ( ) The in turn reacts with the sulphide minerals to produce and S.  

6. Bioleaching Process 1. The Inputs of Bioleaching: Metal ore or concentrate to provide energy for microbes. Proper air is supplied based on whether they are aerobic or anaerobic. because bioleaching microbes need the macro-nutrient C; N, P, Ka , Mg nutrients needed for bioleaching microbes. pH control is needed, optimum: 2.3-2.5. Bioleaching microbes cultivation for inoculation. Temperature control mechanisms, optimum: 30⁰C- 50⁰C. Distribution system, stirring, sprinklers, airflow, tubes allowing for the circulation of microbes. Reaction catalysts if needed.  

7. 2. The Bioleaching Process The microbial oxidation process occurs at the cell membrane of the bacteria. The electrons pass into the cells and are used in biochemical processes to produce energy for the bacteria while reducing oxygen to water. The critical reaction is the oxidation of sulfide by ferric iron. The main role of the bacterial step is the regeneration of this reactant . There are few types of bioleaching: In-situ Bioleaching Heap Bioleaching Vat Bioleaching Tank Bioleaching Autoclave Bioleaching

8. 3. Metal Recovery Metal is recovered from the leaching solution either by solvent partitioning or by the use of scrap iron. Reactions Involved is Bioleaching: Disulfide is spontaneously oxidized to thiosulfate by ferric ion (Fe 3+ ) , which in turn is reduced to give ferrous ion (Fe 2 + ). The ferrous ion is then oxidized by bacteria using oxygen. Thiosulfate is also oxidized by bacteria to give sulfate. The ligand-metal complex is extracted from the solution using an organic solvent . The metal can also be concentrated and separated by displacing the metal with iron from scrap iron .

9. Here, M= a Bivalent Metal

10. Factors and Parameters Influencing Bioleaching Factors Parameters Physiological Temperature, pH, light, pressure Redox and water potential Oxygen and Carbon dioxide Content Microbiological Parameters Microbial diversity Population Diversity Microbial Activities Properties of Minerals Mineral type, composition Grain size, porosity Surface area Processing Leaching mode pulp density Stirring Rate

11. Advantages of Bioleaching Bioleaching is simpler, cheaper to operate and maintain. The process is more environmentally friendly than traditional extraction methods. Bioleaching if used for all processing could drastically reduce the amount of greenhouse gases in our atmosphere. Bioleaching can be used extract metals from ores that are too poor for other technologies .

12. Disadvantages of bioleaching The bacterial leaching process is very slow . that the heat created from the dissolving process can kill the bacteria. Toxic chemicals are sometimes produced in the process. Unlike other methods, once started, bioleaching cannot be quickly stopped.

13. Bioleaching of Some Metals

14. Bioleaching of Gold Gold ores: calaverite , sylvanite , petzite ( From low-grade sulfidic ores, gold cannot be extracted. G old ores need to be pretreated by roasting or by pressure oxidation to free the gold prior to cyanide leaching. These pretreatment is costly . After this,70-95 % of the gold in the ore can be recovered by cyanide leaching process . Sodium cyanide leaching process converts gold to a soluble cyanide complex. 4Au + 8NaCN + 2H 2 O + O 2  4Na[Au(CN) 2 ]+ 4NaOH 2Na[Au(CN) 2 ] + Zn  Na 2 [Zn(CN) 4 ] + 2Au Bioleaching occurs in reactors or heap leaching process using Thiobacillus ferrooxidans. After leaching ,it converts the porous ore of exposed gold for cyanide leaching.  

15. Bioleaching of Uranium Uranium ores: uraninite or pitchblende ( ), Brannerite Uranium ores occurs in low grade ores and is insoluble. It can be converted to the leachable form by oxidation with ferric ion. Reaction Involved : UO 2 2- tetravalent uranium, insoluble oxide UO 2 SO 4 2- hexavalent uranium, soluble sulfate ( ) Fe 2+ is reoxidized by Acidithiobacillus ferroxidans . Ferrus ions produced during uranium oxidation are converted back to Fe 3+ by chemical oxidants, such as chlorate, Manganese dioxide or hydrogen peroxide .  

16. This ion in turn acts as an oxidant to convert UO 2 chemically to the leachable UO 2 SO 4.

17. Bioleaching of Copper Copper Ores: Calcopyrite ( ), Chalcocite , Covellite CuS Copper ore is a low grade ore. In bioleaching of Copper, the action of Acidithi o bacillus involves the oxidation of via generation of ferric ions.  

18. References Microbial Ecology Atlas and Bartha Introduction to Environmental Biotechnology AK Chatterjee Wikipedia

19. Thank You