Surface Complexation of Ferrous Iron and Carbonate on Ferrihydrite and the Mobilization of Arsenic
详细信息 查看全文
- 作者：C. A. J. Appelo ; M. J. J. Van Der Weiden ; C. Tournassat ; and L. Charlet
- 刊名：Environmental Science & Technology
- 出版年：2002
- 出版时间：July 15, 2002
- 年：2002
- 卷：36
- 期：14
- 页码：3096 - 3103
- 全文大小：96K
- 年卷期：v.36,no.14(July 15, 2002)
- ISSN：1520-5851
文摘
Surface complexation models are commonly used topredict the mobility of trace metals in aquifers. For arsenicin groundwater, surface complexation models cannot beused because the database is incomplete. Both carbonateand ferrous iron are often present at a high concentrationin groundwater and will influence the sorption of arsenic,but the surface complexation constants are absent in thedatabase of Dzombak and Morel. This paper presentsthe surface complexation constants for carbonate andferrous iron on ferrihydrite as derived for the double-layermodel. For ferrous iron the constants were obtainedfrom published data supplemented by new experiments todetermine the sorption on the strong sites of ferrihydrite.For carbonate the constants were derived from experimentsby Zachara et al., who employed relatively low concentrationsof carbonate. The double-layer model, optimized forlow concentrations, was tested against sorption experimentsof carbonate on goethite at higher concentration byVillalobos and Leckie, and reasonable agreement wasfound. Sorption was also estimated using linear free energyrelations (LFER), and results compared well with ourderived constants. Model calculations confirm that sorptionof particularly carbonate at common soil and groundwaterconcentrations reduces the sorption capacity of arsenicon ferrihydrite significantly. The displacing effect of carbonateon sorbed arsenate and arsenite has been overlooked inmany studies. It may be an important cause for the highconcentrations of arsenic in groundwater in Bangladesh.Sediments containing high amounts of sorbed arsenic aredeposited in surface water with low carbonate concentrations. Subsequently the sediments become exposed togroundwater with a high dissolved carbonate content, andarsenic is mobilized by displacement from the sedimentsurface.