Research On Optimum Cultivation Of Acidithiobacillus Ferrooxidans And Interface Effects In Coal Biodesulfurization Process

Coal is the main energy resource in China. This comes a time when coal energy has been consumed too fast and mechanized coal mining developed rapidly resulting in more proportion of high-sulfur, high-ash and fine particles coals. Research on coal biodesulfurization before combustion,which is of low cost, low energy consumption and environmental friendship, will contribute to the clean coal processing and efficient utilization and the ecological environment protection, and have very important economic and social significance.With the research of Acidithiobacillus ferrooxidans (A.f) optimum cultivation as a start, the bacterial oxidation of ferrous ions and the influences of electrochemistry and bioreactor scale-up culture to A.f growth were analyzed. On the basis of solution chemistry studies of medium with A.f and element sulfur or pyrite, the processing parameters in coal biodesulfurization were optimized. The surface characteristics of A.f and solid substrates were investigated with the employment of integrated approaches such as sulfur K-edge X-ray near structure spectrums. The research of interface effects in coal desulfurization system with A.f leaching was concluded and the interface bio-oxidation model was proposed to support the design of coal biodesulfurization process theoretically. The detailed research contents and results were summarized to four aspects as follow.(1) The optimum flasks cultivation of A.f with ferrous ions as energy source were tested by varying the conditions of initial pH, initial ferrous ions concentration and applied potential. In the scaled-up batch cultivation of A.f with ferrous ions as energy source, culture temperature and initial ferrous ions concentration were analyzed to be the more important influence factors by factor variance analysis. Adding energy source FeSO4 into the medium to maintain ferrous ion concentration of (4-5) g/L were experimented to be the optimum feeding strategy. The results above proved the promotion of applied negative potential to A.f growth and the high-density and fast cultivation of A.f in bioreactor with the maximum bacterial concentration of 2.30×109 cells per mL in 70 hours.(2) The additions of ferric ions and L-Cysteine into the medium were discussed for the influence of bacterial growth activities on element sulfur. The bioleaching behaviors of pyrite were experimented. After A.f oxidation, the surface characteristics of element sulfur and pyrite changed significantly through the methods of K-edge XANES, FTIR, SEM, XRD, Zeta potential and contact angle. The results above indicated that the extracellular proteins with sulfhydryl group played a big role in the activation of circular sulfur to linear sulfur, and the sulfhydryl group of L-Cysteine served as the bridge between A.f and solid substrates.(3) The coal slurry concentration, coal size and bacterial incubation were explored for the influence of coal biodesulfurization effects. The orthogonal experiments for gaining optimum desulfurization conditions with applied potential were carried out and in 7 days bioleaching, the desulfurization ratio of coal reached 59.47%. The fed-batch experiments using bioreactor for coal desulfurization achieved good results of depyritization ratio 80.45% and deash ratio 44.80%. Experimental results demonstrated that, the utilization of applied potential methods positively influenced A.f growth activity and coal surface modification, as well as the feasibility of coal bioleaching using bioreactor was proved. On these theoretical basis above, a set of apparatus including electrochemical catalyzed culture of A.f, scaled-up optimized culture of A.f and coal desulfurization by bioleaching was designed.(4) The adsorption behavior of A.f cells to coal surfaces was studied. Comparison of A.f cells grown in ferrous ion solutions and on solid substrates showed different surface characters. After the coal bioleaching for depyritization, SEM, XRD, FTIR and sulfur K-edge XANES methods were used to compare the coal surface characteristics. The research of interface effects in coal desulfurization system with A.f leaching was concluded and the interface bio-oxidation model was proposed: planktonic cells with more extra-secretion become sessile on coal surface through electrostatic attraction, hydrophobic interaction, hydrogen bonding and chemical bonding. Pyrite is dissolved to ferric ions and a series of sulfur compounds by A.f. The ferric ions act as a mediator to oxidize sulfur compounds and pyrite producing ferrous ions, which is utilized as energy source by A.f and form the precipitation of jarosite. The catalytic oxidation of sulfur in pyrite by A.f results in the formation of the intermediate products of element sulfur, linear sulfur, tetrathionate and persulfate.The thesis contains 92 figures, 27 tables and 156 references.