INQUISUR, Departamento de Química, Universidad Nacional del Sur, Bahía Blanca, Argentina.
J Hazard Mater. 2011 Feb 28;186(2-3):1713-9. doi: 10.1016/j.jhazmat.2010.12.074. Epub 2010 Dec 25.
The adsorption-desorption kinetics of arsenate on a Fe(III)-modified montmorillonite (Fe-M) was studied at different arsenate concentrations, pH and stirring rates. The synthesized solid was a porous sample with Fe(III) present as a mix of monomeric and polymeric Fe(III) species in the interlayer and on the external surface. Adsorption took place in a two-step mechanism, with an initial fast binding of arsenate to Fe(III) species at the external surface (half-lives of 1 min or shorter) followed by a slower binding to less accessible Fe(III) species in pores and the interlayer (half-lives of around 1 h). Desorption kinetics also reflected the presence of externally and internally adsorbed arsenate. At pH 6 the maximum adsorbed arsenate was 52 μmol/g, a value that is low as compared to adsorption on ferrihydrite (700 μmol/g) and goethite (192-220 μmol/g). However, since the Fe(III) content of Fe-M is much lower than that of ferrihydrite and goethite, Fe(III) species in Fe-M are more efficient in binding arsenate than in ferrihydrite or goethite (one As atom is attached every 8.95 iron atoms). This high binding efficiency indicates that Fe(III) species are well spread on montmorillonite, forming small oligomeric species or surface clusters containing just a few iron atoms.
砷酸盐在 Fe(III)-改性蒙脱石 (Fe-M) 上的吸附-解吸动力学研究在不同的砷酸盐浓度、pH 和搅拌速率下进行。合成的固体是一种多孔样品，Fe(III) 以单体和聚合态 Fe(III) 物种的混合物存在于层间和外表面。吸附通过两步机制进行，最初是砷酸盐快速结合到外表面的 Fe(III) 物种上（半衰期为 1 分钟或更短），然后是较慢地结合到孔中和层间中较难接近的 Fe(III) 物种上（半衰期约为 1 小时）。解吸动力学也反映了外吸附和内吸附砷酸盐的存在。在 pH 6 时，最大吸附的砷酸盐为 52 μmol/g，与在水铁矿（700 μmol/g）和针铁矿（192-220 μmol/g）上的吸附相比，这个值较低。然而，由于 Fe-M 中的 Fe(III) 含量远低于水铁矿和针铁矿，因此 Fe-M 中的 Fe(III) 物种在结合砷酸盐方面比在水铁矿或针铁矿中更有效（每个 Fe 原子结合一个 As 原子）。这种高结合效率表明 Fe(III) 物种在蒙脱石上分布良好，形成了仅包含几个铁原子的小寡聚体或表面簇。
