铬取代针铁矿异化铁还原过程及铬的环境行为研究

Dissimilatory Reduction of Cr-substituted Goethite and Its Effect on Cr Behavior

铬(Cr)是环境中常见的重金属污染物,在土壤中常与铁氧化物结合在一起,其环境行为受到土壤铁循环过程的影响;尤其是在铁还原菌作用下,该类铁氧化物容易发生还原溶解,增强了Cr的移动性。以土壤中常见的Cr(Ⅲ)取代针铁矿(CrGoe)为研究对象,利用微生物生长Logistic方程拟合、相关分析等统计方法以及X射线衍射(XRD)表征手段,研究异化铁还原菌Shewanella oneidensis MR-1对不同铬取代量针铁矿的Fe(Ⅲ)还原、重金属释放固定以及矿物物相变化。不同反应体系中Fe(Ⅱ)的生成表明,Shewanella oneidensis MR-1具备还原Cr取代针铁矿的能力;与纯针铁矿相比较,铬的取代抑制了针铁矿的铁还原过程,且铁还原效果随Cr取代率的增加而降低,其大小顺序为针铁矿>1.5%Cr-Goe>3.4%Cr-Goe>9.03%CrGoe>10.3%Cr-Goe。铁还原速率k值与针铁矿中Cr(Ⅲ)的取代量呈指数关系(R2=0.999 5,P<0.001);当针铁矿中Cr(Ⅲ)的摩尔取代量大于9.03%时,Cr-Goe的铁还原速率呈最低值,约为0.26 d-1。在异化铁还原的同时,包裹于铁矿中的Cr被释放到环境中,且随矿物二次成矿,部分Cr(Ⅲ)再一次被包裹到矿物晶格中。XRD表征显示,矿物在异化铁还原过程中,矿物相仍为针铁矿。该研究结果可为土壤铁还原过程中重金属的环境行为提供理论依据。

Chromium(Cr) is an environmental contaminant, which is easily substituted into iron oxides and strongly influenced by interactions with iron redox process in soil. When being exposed to iron reducing bacteria, these minerals can undergo reductive dissolution by the effect of iron reducing bacteria, which further enhances the mobility of Cr. In this study, the reduction of Crsubstituted goethite(Cr-goethite) by Fe(Ⅲ)-reducing bacteria Shewanella oneidensis MR-1 was investigated, along with the release behavior of substituted Cr(Ⅲ) and mineral transformation, by the microbial growth logistic equation, correlation analysis, and X-Ray Diffraction analysis. Results from the aqueous Fe(Ⅱ) generation showed that the MR-1 was able to reduce Cr-goethite. Compared to the pure goethite, the Cr substitution inhibited the rates of Fe(Ⅲ) reduction, and the higher level of Cr-substituted content in Cr-goethite, the slower Fe(ⅡⅡ) reduction rate with MR-1. Iron reducing value calculated by logistic equation had a positive exponential relationship with the percentage of Cr(Ⅲ) substitution into goethite(R^2=0.999 5, P<0.001). Higher dosages of Cr(Ⅲ) substitution would not significantly decrease the rate of iron reduction. During dissimilatory Fe(Ⅲ) reduction, Cr(Ⅲ) released from Cr-goethite could be reincorporated into minerals during the secondary formation of iron oxides. The XRD results showed that the phase of minerals was still goethite during iron reduction. Our findings suggest an critical role for dissimilatory Fe(Ⅲ) reduction in changing soil metal characteristics, as well as their potential remediation process in Fe-rich soils.