硫化亚铁矿物的生物合成及其对六溴环十二烷的还原脱溴研究

Study on biosynthesization of Fe S and reductive debromination of hexabromocyclododecane(HBCD)

选用两种不同的硫酸盐还原菌（一种是嗜酸性硫酸盐还原菌Desulfosporosinus sp．，另一种是嗜中性硫酸盐还原菌Desulfomicro biumbaculatum）合成了两种硫化亚铁（FeS）矿物，并采用BET、SEM、XRD、XPS对其进行表征。结果显示，嗜酸性硫酸盐还原菌合成的FeS矿物（S-FeS）比表面积为13．35m^2／g，铁硫原子比为0．91，表面活性组分FeS相对含量是63．6％；嗜中性硫酸盐还原菌合成的FeS矿物（Z-FeS）比表面积为7．64m^2／g，铁硫原子比为0．84，表面活性组分FeS相对含量为77．2％；两种FeS矿物的主要成分均为不定形FeS和结晶程度较差的四方硫铁矿。通过批处理实验，研究了这两种FeS矿物对六溴环十二烷（HBCD）的还原脱溴效果。结果显示，两种FeS体系下HBCD的还原脱溴反应均遵循假一级反应动力学；反应速率常数随着FeS浓度的增加而增加，当FeS的浓度从0；3g／L增加至1．2g／L时，S-FeS和Z-FeS转化HBCD的反应速率常数分别从0．0049h^-1增至0．3194h^-1和0．3868h^-1；反应体系pH值（4～8）的变化极大地影响FeS对HBCD的还原脱溴效率：两种FeS均能还原转化HBCD的三种主要同分异构体，转化率大小依次为β-HBCD〉γ-HBCD〉α-HBCD；在两种FeS反应体系中均检测出四溴环十二碳烯（c12H18Br4）、二溴环十二碳二烯（C12H18Br2）和环十二碳三烯（C12H18）等HBCD还原脱溴的中间产物（GC-MS方法鉴定），由此推测S-FeS和Z-FeS还原脱溴HBCD的途径均为逐步邻位双脱溴。以上研究结果表明，两种不同类型硫酸盐还原菌合成的FeS矿物均具有还原脱溴HBCD的能力，并且它们的还原脱溴的能力和机制差异不大。

In this study, two types of sulfate-reducing bacteria （SRB： Desulfosporosinus sp. and Desulfomicrobium baculatum, which are acidophilic and neutrophilic, respectively） were employed to biosynthesize two kinds of ferrous sulfide （FeS） minerals, which were then characterized by BET, SEM, XRD and XPS. The results showed that the specific surface area, iron/sulfur atomic ratio and relative content of FeS on the surface of the FeS mineral synthesized by acidophilic SRB （S-FeS） were 13.35 m^2/g, 0.91 and 63.6%, respectively and that the figures for the FeS mineral synthesized by neutrophilic SRB （Z-FeS） were 7.64 m^2/g, 0.84 and 77.2%, correspondingly. S-FeS and Z-FeS were found to consist largely of amorphous FeS and poorly crystalline mackinawite. Furthermore, batch experiments were conducted to explore the characteristics of reductive debromination of hexabromocyclododecane （HBCD） by S-FeS and Z-FeS. It was found that the debromination of HBCD by both FeS minerals was best de- scribed by pseudo-first-order reaction models and that the rate constants increased with increasing initial FeS concentration. Specifically, the rate constants increased from 0.0049 h^-1 to 0.3194 h^-1 and 0.3868 h^-l, respectively, as the initial FeS concentration increased from 0.3 g/L to 1.2 g/L. In addition, pH of the reaction system was demonstrated as an important factor affecting the rate of reductive debromination of HBCD. All the three major isomers of HBCD were transformed by the two FeS minerals, and their transformation percentages were ranked in a decreasing order of β-HBCD 〉 γ-HBCD 〉 α-HBCD. Three intermediate products of HBCD, i.e. tetrabromo- cyclododecane （C12H18Br4）, dibromocyclododecane （ClzH18Br2） and cyclododecatriene （C12H18）, were identified in both reaction systems by GC-MS analysis, indicating that S-FeS and Z-FeS were able to transform HBCD through sequential reductive debromination. Taken together, the results of this study provided evidence that the two bio- synthetic FeS minerals were composed largely of amorphous mackinawite and had the ability to transform HBCD via highly similar pathways.