2MICROBIAL DESULPHURIZATION OF COAL PRESENTED BY:TARHUB ASGHARBIOL 473
3IntroductionAlong with many contents coal contains high amount of sulphur content.Sulphur dioxide emits when coal burnt causing air pollution.For the removal of this pollutant we can used many method through which we can remove sulphur dioxide.One possible method is flue gas desulphurization.
4Flue gas desulphurization It is a set of technologies used to remove sulfur dioxide (SO2) from exhaust flue gases of fossil-fuel power plants, and from the emissions of other sulfur oxide emitting processes.Installation of this equipment in developing countries is often expensive.So that is why low cost technologies are used to removed SO2.
5Microbial desulphurization During coal combustion heat is released to produce steam in boilers.After combustion process sulphur in the form of pyrite FeS2 is transformed into gas phase.Bioleaching support a use of bacteria for the removal of pyritic sulphur from coal.Acidithiobacillius ferrooxidians and sulfolobus acidocaldarius were well known to be effective and removing pyritic sulphur from coal.
6Biological CleaningBioleaching – Two different mechanisms for biologically catalyzed oxidation of pyrite (sulfur combined with iron)DirectIndirect
7Direct Bioleaching 2 FeS2 + 7 O2 + 2 H2O → 2 FeSO4 + 2 H2SO4 Requires direct contact between the bacterium and the pyrite.Generally not favored as with some coals the microorganisms are too large to fit inside the coal pores.Reaction:2 FeS2 + 7 O2 + 2 H2O → 2 FeSO4 + 2 H2SO4
8FeS2 + 14 Fe3+ + 8 H2O → 15 Fe2+ + 16 H+ + 2 SO4 Indirect BioleachingThe indirect method is more prominent due to the limiting size of the coal pores compared to the size of the microorganism.ReactionsFeS Fe H2O → 15 Fe H+ + 2 SO42 Fe H+ + O2 → 2 Fe3+ + H2O
10microbial desulfurization process(microbial floatation separation method) Recent years have seen increased burning of pulverized coal and the development of a liquid fuel called CWD, which combines coal with water. For this reason, much attention is being focused on microbial desulfurization processes."floatation separation method" is a process in which the ash is removed from coal.
11Process A suspension made with pulverized coal mixed with water is put into a separation tank. From the bottom of the tank, air bubbles are blown in, to which the particles of coal adhere and float.The particles of ash are hydrophilic, so do not adhere to the air bubbles and sink of their own dead weight.pyrite particles have the same surface properties as coal and would float along with the coal, not allowing any separation to take place.
12ProcessIron bacteria added to the suspension selectively adheres to the pyrite particles, making them become hydrophilic. The pyrite particles then sink, enabling desulfurization while floatation separation is taking place.
13Presented by: Amra M Qadir Roll number: 13-10034 BiominingPresented by: Amra M QadirRoll number:
14Biomining:The use of micro-organisms to facilitate the extraction of metals from sulphide or iron-containing ores .The metal solublization process is due to a combination of :ChemistryMicrobiology
15Bioleaching:Metals is exctracted into the water this process is known as bio-leaching.Bio-oxidation : it is used in gold recovery where the metal remains in the mineral .Metals for which this techniue is employed includes: copper , nickle, cobbalt, zinc and uranium.For recovery of gold and silver , the activity of leaching bacteria is applied only to remove interfering metal sulfides from ores.
16Common microganisms:Thiobacillus.Lepto spirillum.These are mesophill, acidophile and chemoithoautotrophes. They obtain energy from oxidation of either ferrous ion to ferric or reduction of sulphur compounds to sulphuric acid.
17Mechanism:Microorganism enhance metal sulfides oxidation and leaching kinetics is still controversial.One school of thought.Other school of thought.Recent research has demonstrated that glycocalyx in Acidithiobacillus Ferrooxidans and Leptospirillum ferrooxidans consists of a weak exopolysaccharides layer to form a bridge between the bacterium and the crystal surface. It creates a microenvironment where most of the bioleaching processes takes place.
18The most efficient leaching reaction takes place within the exoploysaccharide layer that surrounds the microbial cells.Bioleaching process take place in three phase systems:Aqueous phase.Solid phase.Gaseous phase.
19Types of biomining: Irrigation type( CU): Crushed ore is stacked in columns, dumps or heaps.Leaching solution percolate through the ore.Irrigation may also be conducted in-situ.Minimizes expense of operation.Maximizes quantity of material that can be processed.
20Stirred tank reactor: Continuously operated, highly aerated. Process is highly controlled.Maximizes the decomposition rate.To perform bioleaching process the adequate suspension aeration and mixing is necessary.Selection of a suitable reactor for a biomining process and design should be based in the physical , chemical and biological characteristics of the system.
21Bioleaching and biooxidation are best performed in a continuos mode of operation in which volumetric productivity is high and reactor volumes can be kept low.In biomining the mineral species involved are usually recalcitrant to microbial action.and affinity is quite low.It improves the yield and efficiency of bioleahing processes.
22Heap and dump leaching: Best known operation is Kennecott mine in Bingham canyon, Utah.Numerous dumps having upto billion tones low grade ore.Run of mine ore is pilled upto 350m.Irrigated with a iron and sulphate rich waste water stream( raffinate).Raffinate is devoid of CU.Microorganisms solubilize sulfide into sulfate.Copper sulfate rich is removed from the bottom, the CU removed then the CU free liquid recycled to dump.Takes years to recover metal from an ore.
23Advantages: Simple equipment. Low investment and operation costs. Acceptable yields for the treatment of lower grade ores.
24Disadvantages: Plied material is very heterogenous. No close process control can be exerted.Rates of oxygen and carbon dioxide transfer can be obtained are low.
25Gold:AU is finely divided in pyrite ores. These recalcitrant ores in which Au can’t be readily solublized by cyanidation and which normally require roasting at 700F in oxygen.The ore is first concentrated then microbially treat to decompose the arsenopyrite which makes the AU more accessible to cyanidation. This is called as biooxidation because the Au is not solubilized by micro-organisms.
26Biox Process:Ground gold containing concentrate is fed with phosphate, ammonium and water into a series of continuous reactors.Solid content in vessel is 10-18%.Residence time in reaction is 3 days.Process operate at about 40c and PH is 1.5
27Advantages of bio-oxidation Au: Portion of the ore needs to be decomposed to allow high Au recovery.Capital costs are 50% for roasting/ pressure oxidation.Waste disposal is easy ( PH increased to 5 with lime causes to precipitate
28Disadvantages: Maximum solid concentration is about 20% solids. A higher concentration of solids damages fermenters for a given oxygen transfer rate and damages microorganisms by shear forces. This maximum limits bio-oxidation to high value minerals.
29Gold Bio-oxidation: It is extracted from ores using cyanide. First stirred tank bileach plant was commissioned in 1986 to pretreat a sulfidic gold concentrate to enhance gold recovery.Recalcitrant ores are those in which gold is encased in a matrix of pyrite.
30Advantages of biomining: Rich surface ores are naturally exhausted, and lower grade ores must be used.It can be carried out n in situ. That is, recovery can be conducted without bringing vast quantities of ore and waste rock to the surface.Conventional mining processes ( roasting, smelting) consume large quantities of energy,whereas biomining consumes minimal energy.
31Conventional mining produces acidic dump water and air pollution as enviromental problem. It tends to generate limited hazardous wastes.
36Why use Microbial Pathogens? SpecificCheap to produceNarrow activity spectrumNo residue problems0% resistanceBut,Not cultured at a large scale
37Successful Bioinsecticide genus BacillusSpore formingGram positiveRod-shaped soil bacterium
38Bacteria-effectiveness produce Protein Endotoxins during Sporulationnot contact poison but,Ingestionsingle Bacillus species/subspecies may attack entire order or a single species
39Production Fermentation process Product: Bacillus thuringiensis (δ-endotoxin)30° CpH25-30 hoursMedia: starch, corn-steep liqour, casein, and yeast extract3000 tones per year
40δ -endotoxin Insecticidal Crystal Proteins Produced alongside spores 30% of cell massGenes encoding ICPs are on PlasmidsVariations in amino acid residues causes dramatic effect in the activity
41Septicemia-Blood Poisoning Solubilization inInsect mid-gut (alkaline)Activation by Proteolysis by insect gut enzymesActive ICPs bind to receptor sites on EpitheliumComplex with 6 toxin unitsLoss of K⁺Osmoregulation is renderedDeath (2-3days)
42δ-endotoxin In human & animal guts, ICPs denature due to low pH Hydrolyzed by proteases
43Eco-FriendlyB. thuringiensis endotoxins breakdown to non-toxics due to UV light