School of the Environmental Studies, China University of Geosciences, Wuhan, 430074, China.
State Environmental Protection Key Laboratory of Integrated Surface Water-Groundwater Pollution Control, School of the Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen, 518055, China; Guangdong Provincial Key Laboratory of Soil and Groundwater Pollution Control, School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen, 518055, China.
J Hazard Mater. 2020 Feb 15;384:121287. doi: 10.1016/j.jhazmat.2019.121287. Epub 2019 Sep 23.
This study investigated the coupled dynamics of the redox transformation of arsenic-containing ferrihydrite, and arsenate desorption and re-adsorption in presence of sulfide. Batch experiments, various microscopic and spectroscopic analyses collectively revealed that electrons from sulfide competitively transferred to ferrihydrite and no arsenate was reduced. The reductive dissolution of ferrihydrite by sulfide led to the quick formation of FeS that competitively decreased the availability of sulfide for its subsequent reduction of ferrihydrite. The quick formation of FeS was followed by a relatively slow transformation of ferrihydrite to magnetite and other Fe(II)-Fe(III) minerals that were primarily bound to the residual ferrihydrite surfaces. As a result of the preservation of As-containing ferrihydrite and surface covering by the secondary minerals, the majority (> 90%)of sorbed arsenate resided in the solid phase, and <10% of arsenate participated in the desorption process during the ferrihydrite dissolution and transformation. The desorption of arsenate was fast, and followed by the kinetic re-adsorption. The rate and extent of the re-adsorption was consistent with the dynamic transformation of the secondary minerals and their sorption affinity toward As. The results have a strong implication to understanding of As concentration changes during the redox transformation of As-containing minerals in groundwater systems.
本研究考察了含砷水铁矿的氧化还原转化、砷酸盐的解吸和再吸附在硫化物存在下的偶联动力学。批量实验、各种微观和光谱分析共同揭示，硫化物中的电子竞争性地转移到水铁矿，而没有砷酸盐被还原。硫化物对水铁矿的还原溶解导致 FeS 的快速形成，这降低了硫化物对其随后还原水铁矿的可用性。FeS 的快速形成之后，水铁矿相对缓慢地转化为磁铁矿和其他主要结合在残余水铁矿表面的 Fe(II)-Fe(III)矿物。由于含砷水铁矿的保存和次生矿物的表面覆盖，大部分 (>90%)吸附的砷酸盐仍留在固相中，在水铁矿溶解和转化过程中，只有<10%的砷酸盐参与了解吸过程。砷酸盐的解吸速度很快，随后是动力学再吸附。再吸附的速率和程度与次生矿物的动态转化及其对 As 的吸附亲和力一致。研究结果对理解含砷矿物在地下水系统中的氧化还原转化过程中砷浓度变化具有重要意义。
