Dixit Suvasis, Hering Janet G
California Institute of Technology, 1200 East California Boulevard, Environmental Science and Engineering (138-78), Pasadena, California 91125, USA.
Environ Sci Technol. 2003 Sep 15;37(18):4182-9. doi: 10.1021/es030309t.
Arsenic derived from natural sources occurs in groundwater in many countries, affecting the health of millions of people. The combined effects of As(V) reduction and diagenesis of iron oxide minerals on arsenic mobility are investigated in this study by comparing As(V) and As(III) sorption onto amorphous iron oxide (HFO), goethite, and magnetite at varying solution compositions. Experimental data are modeled with a diffuse double layer surface complexation model, and the extracted model parameters are used to examine the consistency of our results with those previously reported. Sorption of As(V) onto HFO and goethite is more favorable than that of As(III) below pH 5-6, whereas, above pH 7-8, As(II) has a higher affinity for the solids. The pH at which As(V) and As(III) are equally sorbed depends on the solid-to-solution ratio and type and specific surface area of the minerals and is shifted to lower pH values in the presence of phosphate, which competes for sorption sites. The sorption data indicate that, under most of the chemical conditions investigated in this study, reduction of As(V) in the presence of HFO or goethite would have only minor effects on or even decrease its mobility in the environment at near-neutral pH conditions. As(V) and As(III) sorption isotherms indicate similar surface site densities on the three oxides. Intrinsic surface complexation constants for As(V) are higher for goethite than HFO, whereas As(III) binding is similar for both of these oxides and also for magnetite. However, decrease in specific surface area and hence sorption site density that accompanies transformation of amorphous iron oxides to more crystalline phases could increase arsenic mobility.
许多国家的地下水中存在源自天然来源的砷，影响着数百万人的健康。本研究通过比较在不同溶液组成下五价砷（As(V)）和三价砷（As(III)）在无定形氧化铁（HFO）、针铁矿和磁铁矿上的吸附情况，研究了As(V)还原和氧化铁矿物成岩作用对砷迁移率的综合影响。实验数据用扩散双层表面络合模型进行模拟，提取的模型参数用于检验我们的结果与先前报道结果的一致性。在pH值低于5 - 6时，As(V)在HFO和针铁矿上的吸附比As(III)更有利，而在pH值高于7 - 8时，As(II)对固体具有更高的亲和力。As(V)和As(III)吸附量相等时的pH值取决于固液比、矿物的类型和比表面积，并且在存在竞争吸附位点的磷酸盐时会向较低的pH值偏移。吸附数据表明，在本研究调查的大多数化学条件下，在HFO或针铁矿存在的情况下As(V)的还原对其在近中性pH条件下在环境中的迁移率只会产生轻微影响甚至降低其迁移率。As(V)和As(III)的吸附等温线表明三种氧化物上的表面位点密度相似。针铁矿对As(V)的固有表面络合常数高于HFO，而对于这两种氧化物以及磁铁矿，As(III)的结合情况相似。然而，随着无定形氧化铁向更结晶相的转变，比表面积减小从而吸附位点密度降低，可能会增加砷的迁移率。
