Role Of Interfacial Phenomena In Bioprocessing Of Minerals Using Bacillus Polymyxa
In this research work the effect of ionic strength and pH in deteraiining the surface properties and hence adhesion of the bacterium Bacillus polymyxa to minerals such as hematite, quartz and coal has been studied in detail. The effect of the ionic strength and pH on the electrokinetics of the minerals and bacteria and its subsequent effect on adhesion and flocculation were investigated in detail. Contact angle measurements along with the zeta potential results were used to calculate the interaction energies between the mineral and the microorganism to establish a mechanism for the interaction.
The following major conclusions can be drawn from this study. Results indicate that increase in the ionic strength significantly changes the zeta potential of hematite and bacteria without varying the isoelectric point. Increase in the ionic strength caused very little change in the zeta potential of quartz and coal. The adhesion of bacterial cells on to the minerals was found to be dependent on pH, ionic strength and conditioning time. Adhesion of bacterial cells was found to be more on hematite and coal when compared to quartz. The adsorption isotherms of Bacillus polymyxa cells with respect to all the three minerals were found to obey Langmuir isotherm. Flocculation studies demonstrated that the settling rate of hematite and coal was enhanced in presence of bacterial cells and electrolyte. However quartz settled much slower under the same conditions indicating that the quartz particles are being dispersed. Thus, selective flocculation of hematite and coal is possible which can be used in separating them from quartz effectively.
The different components of total interaction energy arising from Lifshitz-van der Waal forces, acid/base forces and electrostatic forces were calculated using the van Oss approach. Calculation of the components of the acid base free energy showed that coal and hematite were hydrophobic compared to quartz and the bacterium. From total interaction energy calculation based on the extended DLVO theory, hematite and coal were found to have a net negative interaction energy in acidic pH values and hence attractive forces are predominant. Quartz was found to have a net repulsive energy at all the pH values at low ionic strengths but increase in ionic strength the interaction energy become attractive. The AGLW values of quartz was found to be attractive which is probably responsible for bacterial adhesion onto quartz.
Advisor:Raichur, Ashok M
School:Indian Institute of Science
Source Type:Master's Thesis
Keywords:metallurgy bacterial leaching bacillus polymyxa zeta potential bioflocculation flocculation mineral processing
Date of Publication:02/01/2001