【作者】 高扬；

【导师】 陈天虎；

【作者基本信息】 合肥工业大学 ， 地质学， 2019， 硕士

【摘要】 纳米磁铁矿和纳米磁赤铁矿是铁氧化物的重要组成部分,决定着岩石、土壤和沉积物的磁性。为研究两种磁性矿物在硫化环境中的潜在稳定性,研究开展了硫酸盐还原菌（SRB）作用下煅烧成因多孔纳米磁铁矿和磁赤铁矿的分解和转化实验,重点考察短期（31 d）和长期（165 d）及有/无硫酸盐条件下矿物分解、转化的过程和机制。初步获得如下结果:在有SRB的短期实验中,磁铁矿和磁赤铁矿体系的磁化率均持续上升,在31d实验结束时磁铁矿体系中磁化率达到最大,磁赤铁矿体系中磁化率已出现小幅下降。在含SO₄^2-的磁铁矿和磁赤铁矿实验中,SRB的还原作用分别导致22.4%和5.1%的硫酸盐转化为酸可挥发性硫（AVS）。X射线光电子能谱（XPS）分析发现,部分磁赤铁矿中的Fe（III）被AVS和SRB还原为Fe（II）,造成矿物溶解、粒径减小,同时有多种形态的硫化物沉淀生成。X射线衍射（XRD）和M?ssbauer谱分析表明,纳米磁赤铁矿有通过SRB的电子传递作用固相转化为磁铁矿的趋势,在此过程中有超顺磁相生成。在有SRB的长期实验中,前25 d磁铁矿体系中磁化率迅速上升,随后保持稳定;前20 d磁赤铁矿体系中磁化率迅速上升,随后缓慢下降,在140 d时达到稳定。在含SO₄^2-的磁铁矿和磁赤铁矿实验中,SRB的还原作用分别导致28.1%和7.1%的硫酸盐转化为AVS。透射电镜（TEM）和XPS分析表明,在磁铁矿实验中,单硫化物马基诺矿（FeS）、胶黄铁矿（Fe₃S₄）,以及多硫化物是主要的次生硫化物,而在磁赤铁矿实验中,除上述次生物相外还含有较高比例的黄铁矿（FeS₂）。XPS分析表明,AVS和SRB都能使磁铁矿及磁赤铁矿表面的Fe（III）还原为Fe（II）。XRD和M?ssbauer谱分析表明,在SRB的介导下,通过固相Fe（III）的还原,纳米磁赤铁矿可以完全转化为纳米磁铁矿,这种转化同时体现为磁赤铁矿磁化率变化及磁滞回线特征与磁铁矿不同。研究结果表明,磁赤铁矿与磁铁矿在结构上的相似性是SRB作用下磁赤铁矿固相转化为磁铁矿的前提;同时,磁性铁氧化物可作为SRB生长的电子受体,对硫化环境中的微生物生态起到一定的制约效应。更多还原

【Abstract】 Nanomagnetite and nanomaghemite are important components of iron oxides that determine the magnetic properties of rocks,soils and sediments.In order to study the potential stability of these two magnetic minerals in sulfate diagenetic environment,the decomposition and transformation experiments of calcine-forming porous nanomagnetite and nanomaghemite under the action of sulfate reducing bacteria（SRB）were carried out,focusing on the decomposition and transformation processes and mechanisms of minerals in the short-term（31 d）and long-term（165 d）and with/without sulfate.Preliminary results are as follows:In the short-term experiments with SRB,the magnetic susceptibility of magnetite and maghemite systems continued to rise.At the end of the 31-day experiment,the magnetic susceptibility of magnetite system reached the maximum,and the magnetic susceptibility of maghemite system had decreased slightly.In the experiments of magnetite and maghemite containing SO₄^2-,the reduction of SRB resulted in the conversion of 22.4%and 5.1%sulfates to acid volatile sulfide（AVS）,respectively.X-ray photoelectron spectroscopy（XPS）analysis showed that Fe（III）in part of maghemite was reduced to Fe（II）by AVS and SRB,resulting in mineral dissolution,particle size reduction,and the formation of sulfide precipitation of various forms.X-ray diffraction（XRD）and M?ssbauer spectrum analysis showed that nanomaghemite has the tendency of solid phase transformation into nanomagnetite through electron transfer of SRB,and superparamagnetic phase is formed in the process.In the long-term experiments with SRB,the magnetic susceptibility of magnetite system increased rapidly in the first 25 days,and then remained stable;the magnetic susceptibility of maghemite system increased rapidly in the first 20 days,then decreased slowly,and reached stability in 140 days.In the experiments of magnetite and maghemite containing SO₄^2-,the reduction of SRB resulted in the conversion of 28.1%and 7.1%sulfates to AVS,respectively.Transmission electron microscopy（TEM）and XPS analysis showed that in the magnetite experiment,the main secondary sulfides were monosulfide mackinawite（FeS）、greigite（Fe₃S₄）and polysulfide.In the maghemite experiment,besides the secondary phase mentioned above,there was a high proportion of pyrite（FeS₂）.XPS analysis showed that both AVS and SRB could reduce Fe（III）on the surface of magnetite and maghemite to Fe（II）.XRD and M?ssbauer spectrum showed that nanomaghemite could be completely transformed into nanomagnetite by the reduction of solid phase Fe（III）under the medium of SRB.This transformation was also reflected in the changes of magnetic susceptibility and hysteresis loop characteristics of maghemite,which were different from those of magnetite.The results show that the structural similarity between magnetite and maghemite is the precondition for solid phase transformation of maghemite into magnetite under the medium of SRB.At the same time,magnetic iron oxides can be used as electron acceptors of SRB growth,which has a certain restriction effect on microbial ecology in sulfide environment.更多还原