Effects Of Microorganisms On The Surface Properties Of Pyrite And Optimization Of Pyrite Bioleaching Process

With the methods such as adsorption, contact angle and Zeta potential, the effects of microognisms on pyrite surface were studied; on the basis of pyrite bioleaching by pure culture, by means of such examination as the impact of mixed culture and nutrient for microbe on pyrite bioleaching, the main factor for jarosite formation, and the attempt of applying Ferroplasma thermophilum L1to pyrite bioleaching, we tried our best to find the optimum proposal for pyrite bioleaching.The results of adsorption experiment indicated that the equilibrium of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans on pyrite surfaces was reached in20min and the adsorption content of A. ferrooxidans grown on pyrite was higher than that grown on Fe2+. In the early pyrite bioleaching stage, its contact angles decreased rapidly because of bacteria adsorption, and later went to steady. The microbe grown on solid substrate showed higher isoelectric point (IEP) than that grown on solution substrate, because surfaces of the former contained more protein. IEP of pyrite decreased after interaction with microbe, and its electronegativity increased. Electronegativity of pyrite interacted with microbe increased, and IEP of it decreased, inclining to IEP of bacteria.The investigation of optimizing pyrite bioleaching indicated that other things being equal, the mixed culture of A. ferrooxidans and A. thiooxidans, L1and Acidthiobacillus caldus showed superior to the pure culture of A. ferrooxidans and L1, which was because the presence of sulfur oxidizing bacteria A. thiooxidans and A. caldus facilitated the oxidization of sulfur compound produced in the process. Adding yeast extract facilitated pyrite bioleaching by A. ferrooxidans effectively, particularly adding the amount of0.005%, in which amout pyrite leaching rate was up to81.4%. Pulp density, pH, redox potential and jarosite were the vital parameters for pyrite bioleaching. With the increase of pulp density, leaching rate declined. This phenomonen stood out in pyrite bioleaching by L1without cell wall in that the shear force between particles and bacteria in high pulp density induced bacteria death. In the course of pyrite bioleaching by A. ferrooxidans, modifying pH was adverse to pyrite solubilization. Modifying pH encouraged jarosite formation on pyrite surface, instead, there was no jarosite formed on pyrite suface, proved by XRD and SEM. Also, the test results indicated that reasonable combination of pulp pH and Fe concentration gave jarosite production an advantage. Both the case of low pH value (pH=1-1.3), high Fe3+concentration (2.2g/L-7.5g/L), and the other of high pH value (pH=1.89), low Fe3+concentration (1.86g/L) prevented jarosite formation with effect, and then promoted pyrite bioleaching.Pyrite bioleaching by L1was limited to low pulp density as a result of the properties of L1itself. Electrode reaction in the electrochemical system of L1and pyrite was controlled by electrochemical steps, proved by electrochemical impedance. From the measurements of electrochemical impedance and Tafel, we drew the conclusion that adding L1quikened electron transfer, and further accelerated pyrite oxidization.