富里酸和胡敏酸对水铁矿转化过程中铁氧化物上铜释放动力学特性的影响

在受重金属污染的土壤中,天然有机质（NOM）和重金属通常会同时参与铁氧化物的转化.但关于这一重要的环境反应过程中重金属释放动力学的研究目前还比较少.为阐明NOM对铁氧化物转化过程中Cu释放行为的影响,本研究使用两种代表性NOM：富里酸（FA）和胡敏酸（HA）,开展了二者存在下的"铁氧化物-重金属-NOM"转化研究,并对转化不同时间点的铁氧化物进行了Cu释放动力学实验.动力学实验中采用了一个流动搅拌装置模拟pH=5.5环境条件下Cu的释放过程.结果表明,Cu的释放量随着铁氧化物的转化而降低,NOM的存在增加了Cu在流动搅拌实验中的释放量.球差校正扫描透射电子显微镜（Cs-STEM）结果显示,铜可以掺入铁氧化物纳米颗粒中,可以有效固定Cu,而FA和HA处理均产生了具有疏松结构的椭球形颗粒,为Cu的吸附提供了丰富的位点.这种疏松的结构导致了更多吸附态Cu的存在,阻碍了铜的掺入,与Cu释放结果一致.因此,Cu释放能力的差异性主要是铁氧化物老化的结果,与Cu和NOM的络合关系不大.这项研究的结果将有助于更好地理解在NOM存在下铁氧化物转化过程中Cu的环境行为,同时在纳米尺度上阐明Cu和C与赤铁矿相互作用的机理.

Copper release kinetics during the iron oxide transformation in the presence of fulvic acid and humic acid

Natural organic matter (NOM) and heavy metals (HMs) can both participate in the iron oxide transformation process in HM contaminated soils. However, there is still a lack of knowledge concerning the HM release kinetics during the iron oxide transformation especially under the influence of NOM. In this study, iron oxide transformation was conducted in the presence of Cu and two types of representative NOM, fulvic acid and humic acid (FA and HA). Release kinetic experiments were conducted for the iron oxides at various aging times to elucidate the influence of NOM on the Cu release during the iron oxide transformation process. A stirred-flow (SF) system and a pH of 5.5 were set to imitate the natural dynamic solid-liquid reaction process. Results showed that the leachability of Cu decreased during the iron oxide transformation, while NOM increased Cu leachability compared with the non-NOM treatment. The spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) showed that Cu could be incorporated into the iron oxide nano particles to sequester Cu in iron oxides, while both FA and HA resulted in the ellipsoidal particles with a loose structure, which provided abundant sites for Cu adsorption. Overall, the different leachability of Cu was mainly due to the aging of Fe oxides, not to the aging of Cu-NOM complexes. Results in this study would help to get a better understanding of the environmental behaviors of Cu during the iron oxide transformation process in the presence of NOM, and also, shed lights on the nano scale mechanism of Cu and C interaction with iron oxides.