14. Based on published literature, critically analyze various heap bioleaching models.

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1 Assignments 1. What do you mean by biogenesis? With respect to sulfur cycle in nature, explain the role of acidophilic microorganisms and anaerobic sulfate reducers in the formation, dissolution and precipitation of sulfide minerals? 2. (a) Critically analyze the role of native microorganisms in the formation of ocean ferromanganese nodules? (b) Assess the utility of manganese and iron reducing organisms in the bioprocessing of ocean nodules to recover copper, nickel and cobalt. 3. (a) With respect to a typical growth curve, discuss the growth rate of Acidithiobacillus ferrooxidans under different ph and temperature conditions. (b) What is generation period? (c) Derive a relationship to determine generation time with respect to number of generations. (d) What is the generation time for a bacterial population that increases from 10 4 cells to 10 6 cells in five hours? (e) Can you estimate the number of generations? 4. For the following reaction related to growth of At.ferrooxidans 2FeSO 4 + ½ O 2 + H 2 SO 4 = Fe 2 (SO 4 ) 3 + H 2 O Derive a relationship between specific rate (K 1 ) and concentration of FeSO 4, using Monod equation, showing dependence on acid concentration and temperature. Make all suitable assumptions. 5. (a) Derive a simple relationship for bacterial growth kinetics based on Monod equation. (b) What are the relationships that could be used to explain bacterial oxidation of sulfide minerals. (c) Propose suitable models to explain bioleaching of sphalerite and chalcopyrite. (d) What are the factors limiting biooxidation of chalcopyrite. (e) How do shrinking core models fit in with the above bioleaching systems. 6. Differentiate clearly between (a) In situ leaching and heap leaching. (b) Show diagrammatic representations to bring out major features in each. 7. (a) Illustrate with appropriate equations, various bioleaching mechanisms in the presence of Acidithiobacillus ferrooxidans. (b) What is the role of bacterial adhesion in sulfide mineral oxidation? (c) What are the possible mechanisms behind sulfide mineral adhesion of At.ferrooxidans? 1

2 8. (a) What is metal toxicity in relation to growth of At.ferrooxidans? (b) How would you assess and quantify metal-toxicity with respect to different ions such as copper, iron, zinc, uranium and molybdenum? (c) What are adapted strains? In what manner adapted strains influence bioleaching rates? 9. (a) Comment on bioenergetics with respect to ferrous iron and sulfide oxidation by Acidithiobacillus ferrooxidans. (b) What are the mechanisms governing ferrous iron and sulfide biooxidation. (c) How is the iron oxidation machinery affected if Acidithiobacillus ferrooxidans are exclusively grown in the presence of only sulfide substrates? 10. (a) Differentiate between direct, indirect and contact mechanisms in bioleaching. (b) Can bioleaching of sulfide minerals such as ZnS and CuS be efficiently undertaken in the absence of ferrous iron using At.ferrooxidans? 11. Clearly differentrate among the following: (a) Mesophiles and thermophiles (b) Aerobes and anaerobes (c) Direct and indirect biooxidation mechanisms (d) Heap, dump and insitu leaching (e) Iron oxidation rate and iron oxidation index with respect to growth of At.ferrooxidans. 12. (a) Taking appropriate examples, discuss the various microorganisms useful in bioleaching with respect to mesophiles, moderate and extreme thermophiles. (b) Plot a qualitative curve depicting bioleaching efficiency in the presence of mesophiles and thermophiles as a function of temperature. (Take chalcopyrite bioleaching as an example). 13. (a) Critically discuss various factors influencing microbial growth and biooxidation of sulfide minerals, taking At.ferrooxidans and sphalerite mineral as examples. (b) What are the various types of bioleaching with respect to commercial applicability? In what way, they are different with respect to types of minerals, mineralogy and particle size? 14. Based on published literature, critically analyze various heap bioleaching models. 15. Can heterotrophic microorganisms (both bacteria and fungi) be used in bioleaching of nonferrous mineral containing ores? Discuss a few possible examples. 2

3 16. (a) What are biomaterials? Discuss with examples from some naturally formed materials. (b) What do you mean by biomimetics? (c) What are the principles and stages governing biomimetic materials processing? (d) Discuss experimental approaches to prepare gold and silver nanoparticles through bioreduction. 17. Discuss technical features of the following bioleaching processes with appropriate examples. (a) GEOCOAT TM process (b) BioCop TM process (c) BIOX TM process to treat refractory gold concentrates (d) Stick Bugs TM process (e) Stope bioleaching for uranium 18. Discuss biotechnological applications in gold processing in relation to the following aspects: (a) Biogenesis of gold occurrence in nature (b) Microbial precipitation of gold nanoparticles (c) Biooxidation of refractory sulfidic gold concentrates (d) Cyanide free biodissolution (e) Heap bioleaching of lean ores and waste tailings. 19. With respect to nickel extraction discusses the following: (a) Bioprocessing of nickel containing laterites (b) Heap bioleaching of polymetallic nickel ores associated with black schist. 20. Based on published literature, critically discuss use of bioleaching in the processing of various types of industrial wastes (electronic scrap, spent catalysts, metallurgical slags and tailings, fly ash and tannery wasters). 21. Critically analyze various electrochemical factors with respect to bioleaching of multimineral sulfides. 22. (a) How does applied DC potentials (or currents) influence growth and activity of Acidithiobacillus ferrooxidaus? (b) Bring out the role of electrolytic growth conditions on the activity and growth of At.ferrooxidans (c) Illustrate the principles and operating conditions in electrochemical bioreactors for At.ferrooxidans 3

4 23. (a) What is electrobioleaching and how it is different from general bioleaching? (b) Discuss various mechanisms involved in the electrobioleaching of sphalerite, pyrite and chalcopyrite with respect to applied DC potentials. 24. (a) What is biobeneficiation and how is it different from bioleaching? (b) Discuss the various consequences of microbe-mineral interactions relevant to biobeneficiation based on microbially-induced flotation and flocculation. (c) How does cell wall architecture of bacterial cells influence their mineral adsorption behavior? 25. Critically discuss the following: (a) Bacterial cell surface hydrophobicity. (b) Origin of surface charge on bacterial cells (c) Electrical double layer at mineral-solution interfaces in the presence of bacterial cells. (d) Biopolymers and bioenzymes as bioreagents in mineral beneficiation. 26. Discuss the applicability of microbially-induced flotation and flocculation for the following mineral separation processes. (a) Galena sphalerite (b) Removal of iron oxides from kaolin clays (c) Removal of silica and alumina from iron ores (d) Removal of arsenopyrite from pyrite and chalcopyrite. 27. (a) Differentrate between biofouling, biocorrosion and biodeterioration. (b) What are the major microorganisms involved in microbially-influenced corrosion (MIC) of metals and alloys? (c) What are biofilms? How does biofilms influence metallic corrosion? 28. Discuss the major types and characteristics of (a) Sulfate reducing bacteria (SRB) involved in microbially-influenced corrosion. (b) Critically analyze various proposed mechanisms in anaerobic corrosion in the presence of SRB. 29. (a) What are the materials commonly used as human body implants? (b) Discuss their corrosion behavior with respect to different body locations. 4

5 30. (a) Define acid mine drainage (AMD) (b) What are the factors that influence AMD formation? (c) What are the major microorganisms and biochemical reactions involved in AMD? (d) How would you establish acid production capacity of sulfide ores in the laboratory? (e) Briefly discuss a few prevention and remediation strategies for AMD. 31. With respect to occurrence, dissolution, speciation and detoxification of arsenic discuss the following: (a) Native microorganisms inhabiting arsenic-contaminated mine wastes and tailings. (b) Microbiological mechanisms in arsenic dissolution from arsenic containing sulfide minerals. (c) Arsenic tolerance in mining bacteria. (d) Biological strategies in arsenic detoxification through oxidation of arsenite, precipitation using SRB, biosorption and use of Acidithiobacillus ferrooxidans. 32. In relation to bioremediation discuss the following: (a) Constructed wetlands for acid mine drainage (b) In situ remediation of uranium-contaminated sites (c) Biological cyanide degradation (d) Biosurfactant facilitated remediation of chromium contaminated soils. 33. At the Malanjkhand copper mines, lean grade chalcopyrite ore burden is dumped at site and over the years millions of tonnes of such ore burden containing approximately 0.4% Cu (chalcopyrite + pyrite) have accumulated. Can you propose a suitable bioleaching approach to recover copper from such overburden economically? Write a research proposal containing justification and experimental plan of action based on previous work on similar ores. 34. Uraninite ores occur either associated with pyrite or in absence of any sulfide mineralization. Can you propose suitable bioprocessing methodology under both the above conditions, for the two types of ores; (a) One containing pyrite in sufficient quantities. (b) Nonsulfidic, carbonate based uranium ores? 35. Flotation tailings from a lead-zinc mine, contain 2-3% zinc as sphalerite. Can a bioleaching approach be recommended to recover the zinc from waste tailings in a cost- effective fashion? Justify you recommendations with respect to mineralogy, microbial load of the tailings and the proposed biotechnological route in detail. 5

6 36. In a uranium hydrometallurgical plant using acid leaching, waste tailings containing unrecovered uranium are impounded. Considering the nature of the radioactive waste, can you propose an environmentally acceptable detoxification and uranium recovery strategy? 37. Discuss the applicability of the following bioremediation methods with respect to mining of coal and nonferrous minerals. (a) Phytoremediation (b) Biosorption (c) Use of aerobic and anaerobic bacteria in an active hybrid reactor set-up (d) Constructed wetlands (passive) 38. (a) Arrange the following sulfide minerals as a galvanic series in a bioleaching environment. Pyrite Chalcopyrite Galena Sphalerite Pentlandite Pyrrhotite Arsenopyrite (b) A multisulfide ore contains pyrite, chalcopyrite, galena and sphalerite. Propose a galvanic interaction model which can explain the leaching behavior of the above ore in a bioleaching medium. 39. Even though, Acidithiobacillus ferrooxidans is the most widely implicated organism in the bioleaching of various sulfide minerals, its wider acceptability is limited due to slow growth and difficulties associated with harvesting larger amounts of biomass. Critically discuss various microbiological and engineering strategies to overcome the above problem. 40. Based on published literature, write a critical review on the genetic engineering of At.ferrooxidans. Bring out salient molecular biological aspects of this organism, relevant to bioleaching. 6