Carrero Sergio, Fernandez-Martinez Alejandro, Pérez-López Rafael, Cama Jordi, Dejoie Catherine, Nieto José Miguel
Institute of Environmental Assessment and Water Research (IDÆA-CSIC), 08034, Barcelona, Spain.
Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, IRD, IFSTTAR, ISTerre, 38000 Grenoble, France.
Environ Sci Process Impacts. 2022 Sep 21;24(9):1383-1391. doi: 10.1039/d2em00029f.
Schwertmannite is a common nanomineral in acid sulfate environments such as Acid Mine Drainage (AMD) and Acid Sulfate Soils (ASS). Its high surface area and positively charged surface result in a strong affinity towards toxic oxyanions such as arsenate in solution. However, natural precipitation of schwertmannite also involves the accumulation of other impurities, in particular aluminum, an element that is often incorporated into the structure of Fe-oxide minerals, such as goethite and ferrihydrite, affecting their structural and surface properties. However, little is known about the effect of Al incorporation in schwertmannite on the removal capacity of toxic oxyanions found in AMD and ASS ( arsenate). In this paper, schwertmannite samples with variable Al concentration were synthetized and employed in arsenate adsorption isotherm experiments at a constant pH of 3.5. Solid samples before and after arsenate adsorption were characterized using high energy X-ray diffraction and pair distribution function analyses in order to identify structural differences correlated with the Al content as well as variations in the coordination of arsenate adsorbed on the mineral surface. These analyses showed limited Al accumulation on schwertmannite (up to 5%) with a low effect on its structure. The maximum arsenate sorption capacity (258 mmol mol) was in the range of that with pure schwertmannite, but a higher proportion of inner-sphere coordination was observed. Finally, Al was found to desorb from schwertmannite, with adsorbed arsenate preventing this effect and increasing the stability of the mineral. These results are useful to interpret observations from the field, in particular from river water affected by AMD and ASS, where similar conditions are observed, and where aluminum incorporation is expected.
施韦特曼石是酸性硫酸盐环境（如酸性矿山排水（AMD）和酸性硫酸盐土壤（ASS））中常见的纳米矿物。其高比表面积和带正电的表面使其对溶液中的有毒含氧阴离子（如砷酸盐）具有很强的亲和力。然而，施韦特曼石的自然沉淀也会涉及其他杂质的积累，特别是铝，这种元素经常会掺入针铁矿和水铁矿等铁氧化物矿物的结构中，影响它们的结构和表面性质。然而，关于铝掺入施韦特曼石中对AMD和ASS中发现的有毒含氧阴离子（砷酸盐）去除能力的影响知之甚少。在本文中，合成了铝浓度可变的施韦特曼石样品，并在pH值为3.5的恒定条件下用于砷酸盐吸附等温线实验。使用高能X射线衍射和对分布函数分析对砷酸盐吸附前后的固体样品进行表征，以确定与铝含量相关的结构差异以及吸附在矿物表面的砷酸盐配位的变化。这些分析表明，铝在施韦特曼石上的积累有限（高达5%），对其结构影响较小。最大砷酸盐吸附容量（258 mmol/mol）与纯施韦特曼石的范围相当，但观察到更高比例的内球配位。最后，发现铝从施韦特曼石上解吸，而吸附的砷酸盐可防止这种影响并提高矿物的稳定性。这些结果有助于解释实地观测结果，特别是受AMD和ASS影响的河水的观测结果，在这些地方观察到类似的条件，并且预计会有铝掺入。
