硫酸盐对磁赤铁矿—磁铁矿厌氧转化过程的影响

Effects of Sulfate on the Anaerobic Transformation of Maghemite-Magnetite

磁赤铁矿可以在厌氧微生物作用下固相转化为磁铁矿,这种转化过程具有重要的矿物学及环境磁学意义。文章通过开展硫酸盐还原菌(SRB)-磁赤铁矿交互作用实验,重点探讨了SRB活性对磁赤铁矿-磁铁矿固相转化速率的影响。在31 d培养期内,SO42-+SRB+磁赤铁矿体系中SRB的生长导致16.7%的SO42-转化为酸可挥发性硫(AVS),部分还原释放的Fe(Ⅱ)与AVS反应生成单硫化物、双硫化物和多硫化物,同时铁氧化物因溶解作用粒径减小;在无SO42-的SRB+磁赤铁矿体系中,SRB还原产生的Fe (Ⅱ)主要存在于铁氧化物中,没有次生沉淀产生。X射线衍射和穆斯堡尔谱分析结果表明在SRB作用下纳米磁赤铁矿逐渐向磁铁矿转化,加入SO42-时转化速率加快,与矿物接触的SRB菌体的数量及其向磁赤铁矿传递电子的能力均得到了增强。在天然或人工厌氧条件下,SO42-是制约磁赤铁矿向磁铁矿转化的重要因素。

Maghemite can transform to magnetite by anaerobic bacteria through solid route.This transformation has important significance both to mineralogy and environmental magnetism.This study investigates the interactions between sulfate-reducing bacteria(SRB)and maghemite,with special emphasis on the effect of bacterial activity on mineral transformation rate.Two types of experiments were designed:one with sulfate and the other without sulfate.After incubating for 31 days,in experiments with SO4^2-and SRB,about 16.7%sulfate was reduced to acid volatile sulfides.Some Fe(II)that was derived from the reduction of maghemite reacted with AVS to form monosulfides,bisulfides,and polysulfides.The decrease in particle sizes of maghemite was associated with the release of Fe(II).In experiments without sulfate,Fe(II)reduced by SRB remained in the mineral and no secondary precipitates was observed.X-ray diffraction and Mössbauer spectroscopy analyses showed that maghemite transformed gradually to magnetite,at a greater rate in experiments with sulfate,which suggests that sulfate promoted both the activity and the electron transfer ability of SRB.Under natural and artificial anaerobic conditions,sulfate could be an important factor that constrains the transformation of maghemite to magnetite.