Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.
Environ Sci Technol. 2012 Oct 16;46(20):11128-34. doi: 10.1021/es302574j. Epub 2012 Oct 5.
Uranium (U(VI)) sorption in systems containing titanium dioxide (TiO(2)) and various Fe(III)-oxide phases was investigated in the acidic pH range (pH 2.5-6). Studies were conducted with physical mixtures of TiO(2) and ferrihydrite, TiO(2) with coprecipitated ferrihydrite, and with systems where Fe(III) was mostly present as crystalline Fe(III) oxides. The presence of ferrihydrite resulted in decreased U(VI) sorption relative to the pure TiO(2) systems, particularly below pH 4, an unexpected result given that the presence of another sorbent would be expected to increase U(VI) uptake. In mixtures of TiO(2) and crystalline Fe(III) oxide phases, U(VI) sorption was higher than for the analogous mixtures of TiO(2) with ferrihydrite, and was similar to U(VI) sorption on TiO(2) alone. X-ray absorption spectroscopy of the TiO(2) system with freshly precipitated Fe(III) oxides indicated the presence of an Fe(III) surface phase that inhibits U(VI) sorption-a reaction whereby Fe(III) precipitates as lepidocrocite and/or ferrihydrite effectively blocking surface sorption sites on the underlying TiO(2). Competition between dissolved Fe(III) and U(VI) for sorption sites may also contribute to the observed decrease in U(VI) sorption. The present study demonstrates the complexity of sorption in mixed systems, where the oxide phases do not necessarily behave in an additive manner, and has implications for U(VI) mobility in natural and impacted environments where Fe(III) (oxyhydr)oxides are usually assumed to increase the retention of U(VI).
在酸性 pH 值范围（pH 2.5-6）下，研究了含有二氧化钛 (TiO(2)) 和各种三价铁氧化物相的系统中铀 (U(VI)) 的吸附。研究采用 TiO(2) 和水铁矿的物理混合物、TiO(2) 与共沉淀水铁矿以及主要以结晶三价铁氧化物形式存在 Fe(III) 的系统进行。水铁矿的存在导致 U(VI) 的吸附相对于纯 TiO(2) 体系降低，特别是在 pH 4 以下，这是一个出乎意料的结果，因为预计另一种吸附剂的存在会增加 U(VI)的摄取。在 TiO(2) 和结晶三价铁氧化物相的混合物中，U(VI) 的吸附高于 TiO(2) 与水铁矿的类似混合物，并且与 TiO(2) 单独吸附 U(VI)相似。对新沉淀的三价铁氧化物的 TiO(2) 系统进行的 X 射线吸收光谱表明，存在一种抑制 U(VI) 吸附的 Fe(III) 表面相——一种反应，其中 Fe(III) 以纤铁矿和/或水铁矿的形式沉淀，有效地阻止了底层 TiO(2) 上的表面吸附位点。溶解的 Fe(III) 和 U(VI) 之间对吸附位点的竞争也可能导致观察到的 U(VI) 吸附减少。本研究表明，在混合系统中，氧化物相不一定以加和的方式表现出复杂性，并且对自然和受影响环境中 U(VI) 的迁移性具有影响，在这些环境中，通常认为三价铁 (氧) 氧化物会增加 U(VI) 的保留。
