Equilibrium adsorption of thorium by metal oxides in marine electrolytes
- 標題
- Equilibrium adsorption of thorium by metal oxides in marine electrolytes
- 作者
- Keith A. Hunter, David J. Hawke, Lee Kwee Choo
- 文件屬性
- 國外期刊
- 知識分類
- 基礎研究
- 出版年
- 1988
- 刊名
- Geochimica et Cosmochimica Acta
- 點閱數
- 2618
摘要
The equilibrium adsorption of Th by the hydrous oxides goethite (α-FeOOH) and δ-MnO2 in marine electrolytes is not affected by the major cations Ca2+ and Mg2, relative to NaCl electrolyte, while SO2−4 decreased adsorption through competitive ion pairing with Th in solution. A triple layer model of surface speciation in NaCl electrolyte suggested that adsorption of Th mainly involves the hydrolysed forms Th(OH)2+2, Th(OH)+3 and Th(OH)4. Intrinsic surface binding constants for these species were determined by fitting the model calculations to experimental adsorption data. In sulphate-containing electrolytes, including seawater, the model correctly predicted the slope of the adsorption curves for both oxides, with the pH of the adsorption edge depending on values used for Th-sulphate ion-pairing equilibrium constants.
Competition experiments using synthetic organic ligands to buffer the Th concentrations with δ-MnO2 lowered the concentration free Th available for adsorption to within the range of oceanic dissolved Th concentrations. This gave rise to shifts in the adsorption edge to higher pH close to that of seawater, which were consistently predicted by the model. Application of the model to the deep ocean water column suggested that δ-MnO2 would not be a powerful scavenger for Th because of the development of a strong negative surface charge at pH 8, while adsorption on goethite should be significant.
Competition experiments using synthetic organic ligands to buffer the Th concentrations with δ-MnO2 lowered the concentration free Th available for adsorption to within the range of oceanic dissolved Th concentrations. This gave rise to shifts in the adsorption edge to higher pH close to that of seawater, which were consistently predicted by the model. Application of the model to the deep ocean water column suggested that δ-MnO2 would not be a powerful scavenger for Th because of the development of a strong negative surface charge at pH 8, while adsorption on goethite should be significant.