Bioleaching ss.pptx
- 1. BIOLEACHING PRESENTED BY : J. JOYCE ANGEL II M.SC. APPLIED MICROBIOLOGY SACRED HEART COLLEGE TIRUPATTUR.
- 2. Synopsis Bioleaching Microorganisms in bioleaching Mechanisms involved in bioleaching Types Factors affecting bioleaching Advantages Disadvantages
- 3. Bioleaching Bioleaching /Metal Bioleaching / Biomining is a process in Mining and Biohydrometallurgy (process of interaction between microbes and minerals) Extracts valuable metals from a low-grade ore with the help of microorganisms such as Bacteria or Archaea Alternative to more traditional physical and chemical methods of mineral processing. One of the application of biohydrometallurgy. The modern era of bio mining began with the discovery of the bacterium Thiobacillus ferrooxidans Metals extracted from bioleaching: Antimony, Arsenic, Cobalt, Copper, Gold, Lead, Molybdenum, Nickel, Silver, Uranium, Zinc.
- 4. Microorganisms In Bioleaching a) Thiobacillus sp: Thiobacillus thiooxidans, T. ferrooxidans - mesophiles T. Prosperus (metal mobilizing bacteria) T. cuprinus (oxidizes metal ions) b) Leptospirillum sp: Leptospirillum ferrooxidans - acidophiles - oxidizes Fe c) Thermophilic bacteria Acidianus brierleyi Sulfobacillus thermosulfidooxidants d) Heterotrophic microorganism Saccharomyces cerevisiae, Rhizopus sp,Aspergillus & Penicillium simplicissium (fungi)
- 5. Mechanisms Involved In Bioleaching Thiobacillus thiooxidans and T. ferrooxidans have always been found to be present on the leaching dump. a) Direct Bioleaching or Contact Bioleaching: Physical contact exists between Microorganisms and Ores, and Oxidation of mineral takes place through enzymatically catalyzed steps. Example - Pyrite is oxidized to Ferric sulphate. b) Indirect Bioleaching: Microorganisms produce strong Oxidizing agent (Ferric ion & Sulfuric acid) which reacts with metals and extract them from the ores. Acidic environment is absolutely essential in order to keep Ferric iron and other metals in solution. Acidic environment maintained by oxidation of iron, sulfur, metal sulphides or by dissolution of carbonate ions. Example – Bioleaching of Uranium
- 6. Commercial Bioleaching Process Types: a) Slope Leaching or Dump Leaching b) Heap Leaching c) In situ Leaching a) Slope Leaching / Dump Leaching process: The Ores are first ground to get fine pieces then dumped into large Leaching dump. Water containing inoculum of Thiobacillus is continuously sprinkled over the ore. Water is collected from the bottom and used to extract metals and generate bacteria in an Oxidation pond.
- 7. b) Heap Leaching: 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 metals and generate bacteria in an Oxidation pond c) In situ Leaching: The ore remains in its original position in the earth. Surface blasting of earth is done to increase the permeability of water. Water containing Thiobacillus is pumped through drilled passage to the ores. Acidic water seeps through the rock and collects at the bottom. Again, water is pumped from bottom. Mineral is extracted and water is reused after generation of bacteria.
- 8. Factors Affecting Bioleaching Physico-chemical factors a) Temperature Affects leaching rate, microbial composition and activity. b) pH Needs to be low (Acidic) to obtain the fastest leaching rates and to keep ferric iron and metals in solution. c) Ferric oxygen reaction Electron acceptor needed in Chemical and Biological oxidation.
- 9. Microbiological factors: a) Microbial diversity culture Mixed cultures tend to be more robust and efficient than Pure culture. b) Population density High population density tends to increase the leaching rate. c) Metal Tolerance High metal concentrations may be toxic to microbes. d) Choice of Bacteria Suitable bacteria that can survive at High temperatures, Acid concentrations, High concentrations of heavy metals, remaining active under such circumstances
- 10. Mineral Factors a) Composition Provides electron donor and trace elements. b) Particle size Affects the available mineral/liquid contact area. c) Surface area Rate of oxidation by the bacteria increases with reduction in size of the ore and vice versa. d) Porosity Cracks and pores in the particles give rise to the internal area. e) Presence of other Metal sulfide Mineral having the lowest potential is generally oxidized first.
- 11. Advantages of bioleaching Simple process. Eco-friendly process. Inexpensive technique. Employed for collecting metals from waste and drainages. Use to extract refines and expensive metals which is not possible by other chemical processes. No poisonous sulfur dioxide emission as in smelter. No need of high pressure and temperature. Ideal for low grade Sulphide ores
- 12. Disadvantages of Bioleaching: Time consuming (takes 6 to 24 months or longer). Have a very low yield of minerals. Requires a large open area for treatment. May have no process control. High risk of contamination. Inconsistent yield because bacteria cannot grow uniformly.
- 13. THANK YOU