Introduction Along 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.
Flue gas desulphurization It is a set of technologies used to remove sulfur dioxide (SO 2 ) 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 SO 2.
Microbial desulphurization During coal combustion heat is released to produce steam in boilers. After combustion process sulphur in the form of pyrite FeS 2 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.
Biological Cleaning Bioleaching – Two different mechanisms for biologically catalyzed oxidation of pyrite (sulfur combined with iron) Direct Indirect
Direct Bioleaching 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 FeS O H 2 O 2 FeSO H 2 SO 4
Indirect Bioleaching The indirect method is more prominent due to the limiting size of the coal pores compared to the size of the microorganism. Reactions FeS Fe H 2 O 15 Fe H SO 4 2 Fe H + + O 2 2 Fe 3+ + H 2 O
microbial 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.
Process 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.
Process Iron 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.
Biomining Presented by: Amra M Qadir Roll number:
Biomining: 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 : Chemistry Microbiology
Bioleaching: 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.
Common 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.
Mechanism: 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.
The 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.
Types 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.
Stirred 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.
Bioleaching 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.
Heap 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.
Advantages: Simple equipment. Low investment and operation costs. Acceptable yields for the treatment of lower grade ores.
Disadvantages: Plied material is very heterogenous. No close process control can be exerted. Rates of oxygen and carbon dioxide transfer can be obtained are low.
Gold: AU is finely divided in pyrite ores. These recalcitrant ores in which Au cant 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.
Biox 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
Advantages 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
Disadvantages: 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.
Gold 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.
Advantages 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.
Conventional mining produces acidic dump water and air pollution as enviromental problem. It tends to generate limited hazardous wastes.
BIOINSECTICIDES Raana Khokhar Vishal Sharoon
Insect Killers Insect pests Threat to agriculture system Animal & human diseases Chemical control Annual cost $350 million
Conventional Chemical Pesticides can be problematic? Lack of specificity Persistence in the environment Accumulation to damaging levels in high animals (birds)