Sorption of Fe(II) and As(III) on goethite in single- and dual-sorbate systems
Sorption of Fe(II) and As(III) on goethite in single- and dual-sorbate systems
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DOI：
10.1016/j.chemgeo.2005.11.015
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发表时间：
2006-04-16
期刊：
影响因子：
3.9
通讯作者：
Hering, JG
中科院分区：
文献类型：
--
作者：
Dixit, S;Hering, JG
在没有和存在As（III）的情况下，对铁（II）在针铁矿上的吸附进行了定量实验。在单山梨酸盐实验中获得的实验数据采用扩散双层表面络合模型进行建模，并用于预测和比较双山梨酸盐体系的吸附。用0.5 N HCl萃取后，吸附的Fe（II）完全回收，表明吸附过程可逆。铁（II）的吸附随着pH值的增加而增加，正如前面对各种氧化铁所观察到的。在pH 6.0 ~ 7.5之间的吸附等温线显示，随着溶解Fe（II）浓度的增加，吸附密度不断增加；在这些条件下，表面接近饱和，但没有达到饱和。在500 μ M总As（III）和1000 μ M总As（III）不存在和存在的情况下进行的实验中，Fe（II）的吸附密度没有显著差异。当砷总浓度为500 μ M时，As（III）的吸附密度不随Fe（II）浓度的增加而变化，而当As（III）总浓度为1000 μ M时，As（III）的吸附密度几乎随Fe（II）浓度的增加而线性增加。该模型在一系列实验条件下对单山梨酸体系中Fe（II）和As（III）的吸附提供了良好至充分的描述，但未能预测双山梨酸体系中的实验观察结果。预测的As（il）和Fe（II）的吸附密度均低于实际观测值。这些差异说明了当在单山梨酸体系中获得的模型参数用于预测多山梨酸体系中的吸附时可能出现的问题，其中假定所有山梨酸都竞争相同的位点。As（III）和Fe（II）在吸附位点上缺乏竞争表明，在氧化铁的还原溶解过程中，Fe（II）和As（III）的同时释放可能对As（III）随后被吸收到残留在沉积物中的残余氧化铁中产生相对较小的影响，这被推断为许多还原性地下水中砷动员的机制。(c) 2006 Elsevier B.V.版权所有
Experiments were conducted to quantify Fe(II) sorption onto goethite in the absence and presence of As(III). The experimental data obtained in single-sorbate experiments were modeled using a diffuse double layer surface complexation model and used to predict and compare sorption in dual-sorbate systems. The sorption process was shown to be reversible by the complete recovery of sorbed Fe(II) upon extraction with 0.5 N HCl. Sorption of Fe(II) increases with increasing pH, as observed previously for various iron oxides. Sorption isotherms obtained between pH 6.0 and 7.5 showed continuous increase in sorption density with increase in dissolved Fe(II) concentration; under these conditions, surface saturation was approached but not reached. Experiments conducted in the absence and presence of 500 and 1000 mu M total As(III) did not show any significant difference in the Fe(II) sorption density. As(III) sorption density did not change with increasing sorbed Fe(II) concentration when the total arsenic concentration was 500 mu M. However, when the total As(III) concentration was 1000 mu M, As(III) sorption densities increased almost linearly with increasing sorbed Fe(II) concentrations. The model provided a good-to-adequate description of Fe(II) and As(III) sorption in single-sorbate systems over a range of experimental conditions but failed to predict the experimental observations in dual-sorbate systems. The predicted sorption densities for both As(Ill) and Fe(II) were lower than those observed. These discrepancies illustrate problems that may arise when model parameters obtained in single-sorbate systems are used to predict sorption in multi-sorbate systems where all sorbates are presumed to compete for the same sites. The lack of competition observed between As(III) and Fe (II) for sorption sites indicate that the concurrent release of Fe(II) and As(III) during reductive dissolution of iron oxides, inferred as the mechanism of arsenic mobilization in many reducing ground waters, may have relatively minor effects on the subsequent resorption of As(III) to residual iron oxides remaining in the sediment. (c) 2006 Elsevier B.V. All rights reserved.