Change of arsenite adsorption mechanism during aging of 2-line ferrihydrite in the absence of oxygen. (January 2018)

• Record Type: Journal Article
• Authors: Xiu, Wei; Guo, Huaming; Zhou, Xiaoqian; Wanty, Richard B.; Kersten, Michael
• Is Part Of: Applied geochemistry. Volume 88:Part B(2018)
• Page Start: 149
• Page End: 157
• Publication Date: 2018-01
• Subjects: As immobilization -- Ferrihydrite transformation -- Pseudo-second order model -- Iron isotope -- Surface complexes; Environmental geochemistry -- Periodicals; Water chemistry -- Periodicals; Geochemistry -- Social aspects -- Periodicals; Geochemistry -- Periodicals; 551.9
• DOI: 10.1016/j.apgeochem.2017.08.001
• Languages: English
• ISSNs: 0883-2927

Abstract

Abstract: Arsenite was effectively immobilized by 2-line ferrihydrite at different pH values (4.0, 5.5 and 7.4) and adsorbent dosages (0.4, 1, and 2 g/L) in the absence of oxygen, showing an initial surface diffusion-controlled period (Stage I, <2 h) and a second mixed intra-particle and surface diffusion-controlled period (Stage II, >2 h). Dissolved δ 56 Fe increased during Stage I and decreased during Stage II, resulting from aging of ferrihydrite and equilibrium isotopic exchange, respectively. The ferrihydrite aging was hampered by both high As concentrations and high pH values close to the pHzpc, due to inhibition of mineral dissolution as a prerequisite for mineral transformation. During Stage I, As was adsorbed by both bidentate binuclear corner-sharing ( 2 C ) and monodentate mononuclear corner-sharing complexes ( 1 V ), while 2 C dominated during Stage II. At stage I, As stability was mainly controlled by As-complexation, by both mineral transformation and As complexation at stage II. It is suggested that adsorbed-As stability can be optimized by regulating As complexation and mineral phases, which are of great significance for remediation of As-contaminated groundwater. Graphical abstract: Image 1 Highlights: Kinetics changed in the course of As(III) adsorption on ferrihydrite. As(III) was adsorbed first via both 2 C and 1 V complexes and then via 2 C complexes. High pH and high As adsorption restrained ferrihydrite transformation. Stability of adsorbed-As was related to mineral transformation and As surface complexes. The 2 C complexed-As was more stable, adsorbed at lower pH with lower As coverage.