氧化亚铁硫杆菌与毒砂相互作用的阶段性及其机理研究

Mechanism of interaction between Acidithiobacillus ferrooxidans and arsenopyrite

设计了毒砂的生物氧化和化学氧化两组对比实验,并对反应35d的溶液化学、固相产物成分和矿物表面元素化合态变化进行了分析,以说明氧化亚铁硫杆菌(A.ferrooxidans)与毒砂的相互作用机理。研究发现,毒砂的生物氧化过程随A.ferrooxidans菌生长规律分为三个阶段:(1)反应前7d,生物氧化作用还很弱,以自然氧化反应为主;(2)反应8～21d,生物氧化反应开始发生,细菌进入迟缓生长期;(3)反应22～35d,细菌处于对数生长期,生物氧化作用强烈。由离子浓度变化规律反映,前两个阶段生物氧化速率低于化学氧化,第三阶段起生物氧化速率高于化学氧化。细菌生长受溶液累积的As抑制,A.ferrooxidans菌能促进As和Fe形成砷酸铁沉淀,以降低As的抑制作用。毒砂表面高价态元素的比例随细菌生长和溶液Fe离子浓度的升高而增大,生物氧化第三阶段毒砂表面高价态元素的比例高于化学氧化。氧化过程中毒砂表面覆盖中间氧化产物S0和As2S3沉积层,对比化学氧化,A.ferrooxidans菌能不断把Fe2+氧化成Fe3+,促进毒砂表面中间产物氧化,并间接氧化毒砂。

A strain of Acidithiobacillus ferrooxidans was used to study （FeAsS）. A series of experiments were designed to compare differences of arsenopyrite. Changes of solution chemistry, solid-phase products, the bio-oxidation mechanism of arsenopyrite between chemical oxidation and bio-oxidation surface structure and the chemical states of surface elements were examined over a period of 35 days. The results show that the bio-oxidation of arsenopyrite consisted of three stages with colonization and growth stages of A. ferrooxidans： （1） Arsenopyrite was oxidized in the acidified solution within 7 days and there was no interaction between mineral and bacteria; （2） A. ferrooxidans came into the lag phase and arsenopyrite began to interact with bacteria from the eighth to the twenty-first day of oxidation; （3） Ferric ion was regenerated quickly by bacteria and consequently chemically oxidized arsenopyrite as A. ferrooxidans reached the exponential phase after 21 da showed that the rate of chemical oxidation of arsenopyrite ys. Changes in ion concentrations during the experiments was higher than that of bio-oxidation in the first and the second stages, while the rate of bio-oxidation was higher than that of chemical oxidation after 21 days. Ferric ions and arsenates were deposited as insoluble iron arsenates by bacteria to reduce the toxic effects of arsenic ions on the growth of A. ferrooxidans. Oxidized species proportions of the three essential constituents of arsenopyrite were enhanced with bacterial population growing and Fe^3 ＋ concentration increasing. When the bacteria reached the exponential phase in the third stage, more oxidized species were formed on the mineral surface exposed to A.ferrooxidans than on the surface exposed to Fe^3 ＋. Overlayers were formed on mineral surfaces by the accumulation of intermediate products, elemental sulphur （S^0） and orpiment （As2S3）, in both bacterial and chemical oxidation process. In contrary to the surface reacted abiotically with Fe^3 ＋, the intermediate products were oxidized in biooxidation and arsenopyrite was indirectly oxidized by A. ferrooxidans by biologic consumption of Fe^2＋ and regeneration of Fe^3 ＋.