Characteristics And Mechanisms Of Vanadium Leaching Using Single And Mixed Acidithiobacillus Ferrooxidans

Bioleaching process involving Acidithiobacillus ferrooxidans is a well-known method for the treatment of wide range of minerals such as copper, gold, uranium and so forth. Unfortunately, few of these researches were attempted for vanadium extraction from stone coal. The present investigation was carried out using unmixed and mixed culture of Acidithiobacillus ferrooxidans in order to leach the vanadium,and evaluate the growth characteristics of the microorganism. The characteristics and mechanisms of such biological leaching process are presented below.(1) Microorganisms growth characteristics. The experiment conducted with unmixed and mixed culture of Acidithiobacillus ferrooxidans showed that growth and respiratory activity of the microorganisms are both affected by temperature, pH,dissolved oxygen, metal ion concentration and other environmental factors. When unmixed culture of Acidithiobacillus ferrooxidans is used for a test running for 60 h,the microorganisms ATPase increase and reach the maximum of 2.8 U/mL under the conditions of temperature 30 ℃, pH 2.0, and shaking speed of 150 r/min. the optimum conditions established for the test carried out with mixed cultures of Acidithiobacillus ferrooxidans and Thiobacillus thiooxidans were: temperature 30 ℃,pH 1.8, shaking speed of 150 r/min, Mg2+concentration inferior to 0.02 mol/L,culture time 70 h for an increase of microorganisms ATPase which reaches the maximum of 3.1 U/mL.(2) Bioleaching characteristics study. The bioleaching efficiency of the unmixed and mixed Acidithiobacillus ferrooxidans were also affected by the slurry density,temperature, pH value, dissolved oxygen and the concentration of metal ions. Under the optimum condition of slurry density 3%, temperature 30 ℃, initial pH 2.0,agitation speed 150 r/min, the bioleaching efficiency of Acidithiobacillus ferrooxidans unmixed culture on stone coal give an extraction rate of 62% for vanadium. When the test is carried out with mixed culture of Acidithiobacillus ferrooxidans and Thiobacillus thiooxidans, the optimum conditions established for stone coal leaching were: slurry density 4%, temperature 30 ℃, initial pH 1.8, agitation speed 150 r/min,concentration of Mg2+ inferior to 0.02 mol/L, and 68% of vanadium was leached.(3) Bioleaching mechanism study. According to the particle size characterization analysis and the biological leaching test result, the activity of the microorganisms and the extent of time required during the mineral bioleaching operation can be understood. Moreover, the result leads to ascertain that the particle size of the mineral becomes smaller during the process. From the infrared test carried out in order to investigate the effect of the microorganisms on the mineral adsorption, it is found that the cell surface is composed of-OH,-NH,-C = O,-COH and adsorption active group.The investigation showed that not only the adsorption of sulfide minerals occurs onto the cell surface, through the inter-molecular, but also onto the hydrogen bond.Measurement of the microorganisms activity by scanning electron microscopy(SEM)reveals different level of stage at which adsorption is done. In the SEM image, it can be observed that the initial stage of bioleaching occurs onto the surface of the mineral.Further, the process produces an important quantity of jarosite due to the microbial metabolism. The jarosite produces will be adsorbed on the mineral surface in order to prevent the mineral decomposition. To improve the mineral bioleaching efficiency, it appears important to reduce the production of jarosite during the process.(4) Microbial interactions study. Comparison made between unmixed and mixed culture of bacteria on stone coal bioleaching efficiency revealed that it happens a synergistic activity when Acidithiobacillus ferrooxidans and Thiobacillus thiooxidans are both involved in the process. Actually, the presence of Thiobacillus thiooxidans in the system betters Acidithiobacillus ferrooxidans activity during the bioleaching process. It can be concluded that mixed culture of bacteria give better performance on vanadium bioleaching.