Liu Juan, Duan Yixin, Chen Hao, Ye Bangjiao, Zhang Hongjun, Tan Wenfeng, Kappler Andreas, Hou Jingtao
State Environmental Protection Key Laboratory of Soil Health and Green Remediation, Hubei Key Laboratory of Soil Environment and Pollution Remediation, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China.
State Key Laboratory of Particle Detection and Electronics, University of Science and Technology of China, Hefei 230026, China.
Sci Total Environ. 2024 Dec 1;954:176376. doi: 10.1016/j.scitotenv.2024.176376. Epub 2024 Sep 18.
Iron (oxyhydr)oxides are ubiquitous in terrestrial environments and play a crucial role in controling the fate of arsenic in sediments and groundwater. Although there is evidence that different iron (oxyhydr)oxides have different affinities towards As(III) and As(V), it is still unclear why As(V) adsorption on some iron (oxyhydr)oxides is larger than As(III) adsorption, while it is opposite for other ones. In this study, six typical iron (oxyhydr)oxides are selected to evaluate their adsorption capacities for As(III) and As(V). The characteristics of these iron minerals such as morphology, arsenic adsorption species, and pore size distribution are carefully examined using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), positron annihilation lifetime (PAL) spectroscopy, and X-ray absorption spectroscopy (XAS). We confirm a seesaw effect occurred in different iron minerals for As(III) and As(V) immobilization, i.e., at pH 6.0, adsorption of As(V) on hematite (0.73 μmol m) and magnetite (0.33 μmol m) is higher than for As(III) (0.61 μmol m and 0.27 μmol m, respectively), for goethite and lepidocrocite it is almost equal, while As(III) sorption on ferrihydrite (5.77 μmol m) and schwertmannite (28.41 μmol m) showed higher sorption than As(V) (1.53 μmol m and 12.99 μmol m, respectively). PAL analysis demonstrates that ferrihydrite and schwertmannite have a large concentration of vacancy cluster-like micropores, significantly more than goethite and lepidocrocite, followed by hematite and magnetite. The difference of adsorption of As(III) and As(V) to different iron (oxyhydr)oxides is due to differences in the abundance of vacancy cluster-like micropore sites, which are conducive for smaller size As(III) immobilization but not for larger size of As(V). The findings of this study provide novel insights into a seesaw effect for As(III) and As(V) immobilization on naturally occurring iron mineral.
铁的（氢）氧化物在陆地环境中广泛存在，并且在控制沉积物和地下水中砷的归宿方面起着关键作用。尽管有证据表明不同的铁（氢）氧化物对As(III)和As(V)具有不同的亲和力，但目前仍不清楚为什么在某些铁（氢）氧化物上As(V)的吸附量大于As(III)的吸附量，而在其他铁（氢）氧化物上情况却相反。在本研究中，选择了六种典型的铁（氢）氧化物来评估它们对As(III)和As(V)的吸附能力。使用透射电子显微镜（TEM）、能量色散X射线光谱（EDS）、正电子湮没寿命（PAL）光谱和X射线吸收光谱（XAS）仔细研究了这些铁矿物的形态、砷吸附物种和孔径分布等特征。我们证实了在不同的铁矿物中，As(III)和As(V)的固定存在一种跷跷板效应，即在pH 6.0时，As(V)在赤铁矿（0.73 μmol m）和磁铁矿（0.33 μmol m）上的吸附高于As(III)（分别为0.61 μmol m和0.27 μmol m），针铁矿和纤铁矿的情况几乎相同，而As(III)在水铁矿（5.77 μmol m）和施韦特曼石（28.41 μmol m）上的吸附高于As(V)（分别为1.53 μmol m和12.99 μmol m）。PAL分析表明，水铁矿和施韦特曼石具有大量类似空位簇的微孔，明显多于针铁矿和纤铁矿，其次是赤铁矿和磁铁矿。As(III)和As(V)对不同铁（氢）氧化物吸附的差异是由于类似空位簇的微孔位点丰度不同，这些位点有利于较小尺寸的As(III)固定，但不利于较大尺寸的As(V)。本研究结果为天然铁矿物上As(III)和As(V)固定的跷跷板效应提供了新的见解。
