Bioleaching

Presentation on Bioleaching

1. Presentation on Bioleaching Submitted for self study evaluation for the course “Mass transfer - 2” Fifth Semester , Chemical Engineering - 2016 Submitted by : Sirajudheen K V Manikandan R 1RV13CH032 1RV15CH402

2. synopsis Definition of Bioleaching History Microorganisms used in bioleaching Features of organisms involved Chemistry of Bioleaching i.e., the reaction mechanisms Commercial process of bioleaching Case study : Copper leaching Main factors affecting bioleaching To conclude: Advantages and disadvantages of bioleaching

3. BIOLEACHING The ability of micro-organisms to solubilize metals from insoluble metals is known as ‘Bioleaching ’. (Bioleaching is the simple and effective technology for metal extraction from low grade ores and mineral concentrate by the use of micro organisms .) Successful commercial metal-leaching processes include the extraction of gold, copper, and uranium. It has been shown that micro-organisms can extract cobalt, nickel, cadmium, antimony, zinc, lead, gallium, indium, manganese, copper, and tin from sulphur -based ores. The basis of microbial extraction is that the metal sulphides , the principal component in many ores, are not soluble but when oxidized to sulphate become soluble so that the metal salt can be extracted.

4. HISTORY Copper recovery from mine waters in the Mediterranean area 3000 years ago. The role of bacteria in bioleaching was shown in 1947. In 1950´s copper dump leaching. In 1960´s the first industrial copper heap leaching operation. First industrial gold bioleaching plant in 1980´s

5. Microorganisms used in bioleaching The most commonly used microorganisms in bioleaching are ; * Thiobacillus thiooxidants * Thiobacillus ferrooxidants Thiobacillus thiooxidant and T. ferrooxidants have always been found to be present on the leaching dump .

6. Single celled organisms Chemosynthetic metabolism Derive carbon dioxide, oxygen from atmosphere Requires acidic PH Features of organisms involved

7. Chemistry of Bioleaching The reactions mechanisms are of two types, Direct bacterial leaching Indirect bacterial leaching

8. Direct bacterial leaching I n this process, a physical contact exist between bacteria, ores and oxidation of minerals takes place though enzymatically catalysed steps. In this process the microbes are not in direct contact with minerals, but leaching agents are produced by these microbes which oxidize the ores. Indirect bacterial leaching

9. An example f0r Direct bacterial leaching and indirect bacterial leaching : Extraction of uranium There are two possible processes. Direct leaching by T. ferrooxidants has been proposed in the following equation. 2UO2+ O2 + 2H2SO4 2UO2SO4 + 2H2O However, in conditions where oxygen is limited this cannot operate, and the indirect bioleaching process occurs: UO2 + Fe2(SO4)3 UO2SO4 + 2FeSO4 UO3 + H2SO4 UO2SO4 + H2O

10. Commercial process of bioleaching Naturally occur bioleaching process is very slow. For commercial extraction of metal by bioleaching the process is optimized by controlling the p H , temperature, humidity, O 2 and CO 2 concentrations. Some of the commercial process used in bioleaching: Heap leaching In situ leaching

11. Heap leaching Here the ore is dumped into large heaps called leach heaps Water containing inoculum of thiobacillus is continuously sprinkled over the ore Water is collected from the bottom and used to extract metal and generate bacteria in an oxidation pond

12. In situ bioleaching In this process the ore remains in its original position in earth. Surface blasting of earth is done to increase the permeability of water. Water containing thiobacillus is pumped through drilled passages to the ores. Acidic water seeps through the rock and collects at bottom. Again, water is pumped from bottom Mineral is extracted and water is reused after generation of bacteria

13. Copper leaching In 1991 the biological recovery of copper exceeded $1000 million and accounted for 25%of the world's copper production. The waste formed is generally that remaining after extraction of rock from a mine where the copper level is too low for it to be extracted economically (0.1-0.5%). The waste material is formed into terraced dumps 100 m wide and 5 m deep with an impermeable base. Dilute sulphuric acid is sprinkled or sprayed on to the dump so that as it percolates through the dump the pH is reduced to 2-3, which promotes the growth of T. ferrooxidans and other leaching microorganisms . The copper, upon oxidation to copper sulphate , is dissolved in the dilute acid and is collected at the bottom of the dump

14. Ores of copper from which copper is recovered are, Chalcocite(Cu2S) Chalcopyrite(CuFeS2) Covellite ( CuS )

15. Copper leaching is operated as simple heap leaching and in situ leaching process. Dilute sulphuric acid is percolated down through the pile. Liquid coming out of bottom of pile reach in mineral. Liquid is collected and transported to precipitation plant. Metal is precipitated and purified.

16. REACTIONS Chalcocite is oxidized to soluble form of copper Cu2S+O2+  CuS+Cu2+ + H2O Thereafter chemical reactions occur, i.e. CuS+8Fe +4H2O  Cu+8Fe+SO4+8H Copper is removed, FeO+Cu Cu+Fe2 +

17. Fe2 + is transferred to oxidation pond Fe+1/4(O2)+H+Fe3+ + 1/2(H2O) Fe3+ ions produced is an oxidation of ore It is pumped back to pile Sulphuric acid is added to maintain pH

18. Main factors affecting bioleaching Physicochemical Temperature, pH Microbiological Microbial diversity culture Population density affects leaching rate, microbial composition and activity needs to be low to obtain the fastest leaching rates and to keep ferric iron and metals in solution electron acceptor needed in chemical and biological oxidation mixed cultures tend to be more robust and efficient than pure high population density tends to increase the leaching rate

19. Benefits of bioleaching The extraction of metals using mechanical and chemical methods is difficult and expensive but biological methods are more cost-effective, use little energy, can function well at low concentration of metals, do not usually produce harmful emissions and reduce the pollution of metal-containing wastes .

20. Disadvantages Time consuming (Takes about 6-24 months or longer) Have a very low yield of mineral Requires a large open area for treatment May have no process control High risk of contamination Inconsistent yield because bacteria cannot grow uniformly.

21. References Article : Bioleaching : By , Sheama Farheen Savanur Article : Bio mining and Bioleaching by SARDAR HUSSAIN, Asst.ProfIn Biotechnology, GSc.CTA . Article ID : 1003 – 6326(2002) 02 – 0334 – 06; Bioleaching of refractory gold ore (III); Fluid leaching Jinya refractory gold concentrate by Thiobacillus ferrooxidants .

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