Effect Of PH On The Extracellular Polymeric Substances And Adhesion From Acidithiobacillus Ferrooxidans

The bioleaching of chalcopyrite which is the most abundant and the most refractory copper sulphide reserves in the world is still a major challenge. The extracellular polymeric substances of microorganism play an important role in biofilm formation and the oxidation and dissolution of chalcopyrite. Bioleaching of chalcopyrite is a process of the coupling of multi-factors, on which pH, temperature, pulp density and efficiency of oxygen have important influences. In this process, the extracellular polymeric substances of microorganism would be affected certainly. In this paper, the amount of EPS of A. ferrooxidans ATCC23270during bioleaching of chalcopyrite under different controlled pH values with explored. Comparison of iron and copper enclosed in EPS layer of the attached microorganisms in different pH value conditions during bioleaching of chalcopyrite was studied. Dynamic quantity changes of the free and attached microorganisms based on variation of A. ferrooxidans gyrB gene copies during bioleaching of chalcopyrite under different controlled pH was analyzed.In this paper, firstly the influence of pH on EPS of A. ferrooxidans ATCC23270was studied in9K medium. The result showed when pH was controlled at1.0、1.5、2.0and2.5extracellular polysaccharide and protein were significant differences. pH had a great influence on EPS of both free microorganisms and attached microorganisms in the bioleaching of chalcopyrite. The amount of extracellular polysaccharide of free microorganisms at four phase ws related to many factors such as the acidity of environment, the concentration of the ions of the solute in the solution, bioleaching microbial activity and metabolism conditions. At logarithmic phase, it was extracted most, with the bioleaching time goes away it showed less and less. The laws of the attached microorganisms are similar with the free microorganisms but the amount of extracellular polysaccharide of attached microorganisms is far more than that of free microorganisms in total.It was also showed that pH had a great influence on copper and iron adsorption performance. At pH2.0and2.5which is suitable for growth the amount of adsorption iron ion of bacteria has positive correlation with metabolic capacity. At low pH value, to iron ion adsorption it shows the quantity of adsorption iron of the unit EPS was more in the bad environment. It was found that copper ion adsorption was also under the influence of different controlled pH.Real-time quantity PCR was used to detect dynamic quantity changes of the free and attached microorganisms based on variation of A. ferrooxidans gyrB gene copies during bioleaching of chalcopyrite under different controlled pH. It was showed that the growth activities of A. ferrooxidans either free or attached microorganisms inhibited with low pH. The EPS containing complexed ions play an active role in the dissolution of sulphide minerals by creating a reaction space for the dissolution process to take place. At the end of the bioleaching, chalcopyrite concentrate was blocked by the formation of passivation layer, so microorganisms would decrease in a large scale at the final stage of bioleaching.