Wei Dongning, Liu Jing, Luo Zirui, Xie Xiande
College of Environment and Ecology, Hunan Agricultural University, Changsha 410128, China.
State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Taipa, Macau 999078, China.
Water Res. 2023 Apr 1;232:119681. doi: 10.1016/j.watres.2023.119681. Epub 2023 Jan 29.
Manganese oxides (MnO) are critical for determining the environmental behaviors and fate of antimonite (Sb(III)). However, little is known about the qualitative/quantitative connection between MnO structures and Sb(III) fate. Herein, the reactions of Sb(III) and six MnO with different structures were systematically investigated. The initial oxidation rates of Sb(III) (r) on six MnO decreased in the order of γ-MnO>δ-MnO>α-MnO>γ-MnOOH>MnO>β-MnO (pH=7.0), from 0.32 ± 0.04 to 11.17 ± 1.61 mmol/min/mol-Mn. The amounts of antimony retained (i.e., the sum of Sb(III) and antimonate (Sb(V))) on these MnO followed the same trend as that of oxidation. Oxidation of Sb(III) released Mn(II) and created more sites for adsorption. Outwardly, MnO with higher reduction potential (E) and specific surface area (SSA) favored faster Sb(III) oxidation. Inwardly, Mn(III) and oxygen vacancies (O) exhibited a synergistic effect on Sb(III) oxidation. Mn(III) can easier accept electron than Mn(IV) based on the change in Gibbs free energy calculation. O can adsorb free oxygen to form surface oxygen (O) which is much more reactive than lattice oxygen (O). Moreover, O is in close proximity to Mn(III) in high-valent MnO which facilitated the reactions between Sb(III) and Mn(III) through the enhancement of Sb(III) adsorption and electron transfer. O in low-valent MnO is adjacent to Mn(II), thus it showed weaker enhancement than that in high-valent MnO. Part of δ-MnO and almost all MnO were converted to γ-MnOOH during their reaction with Sb(III), while the other four MnO were barely changed. The results obtained provide mechanistic insight into the reactions occurring within Sb(III) and MnO, which are helpful for better understanding and prediction of the fate of Sb(III) in Mn-rich environments.
氧化锰（MnO）对于确定亚锑酸盐（Sb(III)）的环境行为和归宿至关重要。然而，关于MnO结构与Sb(III)归宿之间的定性/定量联系却知之甚少。在此，系统研究了Sb(III)与六种不同结构的MnO的反应。在六种MnO上，Sb(III)的初始氧化速率（r）在pH = 7.0时按γ-MnO>δ-MnO>α-MnO>γ-MnOOH>MnO>β-MnO的顺序降低，从0.32±0.04降至11.17±1.61 mmol/min/mol-Mn。这些MnO上保留的锑量（即Sb(III)和锑酸盐（Sb(V)）的总和）遵循与氧化相同的趋势。Sb(III)的氧化释放出Mn(II)并产生更多吸附位点。从表面上看，具有较高还原电位（E）和比表面积（SSA）的MnO有利于更快的Sb(III)氧化。从本质上讲，Mn(III)和氧空位（O）对Sb(III)氧化表现出协同作用。基于吉布斯自由能计算的变化，Mn(III)比Mn(IV)更容易接受电子。O可以吸附游离氧形成表面氧（O），其活性比晶格氧（O）高得多。此外，在高价MnO中，O与Mn(III)紧密相邻，通过增强Sb(III)吸附和电子转移促进了Sb(III)与Mn(III)之间的反应。低价MnO中的O与Mn(II)相邻，因此其增强作用比高价MnO中的弱。部分δ-MnO和几乎所有的MnO在与Sb(III)反应过程中转化为γ-MnOOH，而其他四种MnO几乎没有变化。所获得的结果为Sb(III)与MnO之间发生的反应提供了机理见解，这有助于更好地理解和预测富锰环境中Sb(III)的归宿。
