Institut de Radioprotection et Sûreté Nucléaire (IRSN), DEI/SECRE/Laboratoire de Radioécologie et d'Ecotoxicologie, Cadarache, Bât 186, BP3, 13115 Saint-Paul-lez-Durance Cedex, France.
J Environ Radioact. 2011 Sep;102(9):843-51. doi: 10.1016/j.jenvrad.2011.05.004. Epub 2011 Jun 16.
This study was conducted to identify the principle selenate carrier phases for two selected soils, by comparing their reactivity with selenate to that of pure phases of the solids. Silica, calcium carbonate, aluminium hydroxide, goethite, bentonite and humic acid were selected as the main soil carrier phases. Comparisons were made first on the parameter values obtained with the best fit of a kinetic sorption model which can discriminate instantaneous sorption from kinetically limited sorption. Then comparisons were made of the ability for each solid to stabilise selenate by measuring the ratio of the partition coefficient for sorption (Kd(sorption)) over that of the desorption (Kd(desorption)). Kinetics and stabilisation were used to help elucidate the nature of interactions with the test solid phases for a large range of selenate concentrations. The experiments were conducted over 165 h in batch reactors, the solid being isolated from the solution by dialysis tubing, at two pH (5.4 and 8) and three selenate concentrations (1 × 10(-3), 1 × 10(-6) and 1 × 10(-8) mol L(-1)). The results obtained showed that only aluminium hydroxide can sorb selenate throughout the studied pH range (pH 5.4 to 8.0). The sorption capacity on this mineral was high (Kd(sorption) > 100 to 1 × 10(4) L kg(-1)) and the selenate was mainly stabilized by the formation of inner sphere complexes. The sorption on goethite occurred at pH 5.4 (Kd(sorption) 52 L kg(-1)), mainly as outer sphere complexes, and was null at pH 8. On silica, a weak sorption was observed only at pH 5.4 and at 165 h (Kd(sorption) 4 L kg(-1)). On bentonite, calcium carbonate and humic acid no significant sorption was observed. Concerning the two soils studied, different behaviours were observed for selenate. For soil Ro (pH 5.4), Kd(sorption) was low (8 L kg(-1)) compared to soil Bu (pH 8) (70 L kg(-1)). The sorption behaviour of selenate on soil Ro was mainly due to outer sphere complexes, as for goethite, whereas for soil Bu the sorption was mainly attributed to inner sphere complexes followed by reduction mechanisms, probably initiated by microorganisms, in which no steady state was reached at the end of the 165 h experiments. The sorption of selenate decreased when concentrations reached 1 × 10(-3) mol L(-1), due to solid saturation, except for aluminium hydroxide. Reduction of selenate seemed also to occur on goethite and soil Ro, for the same concentration, but without preventing a decrease in sorption. Thus, this work shows that the comparison of selenate behaviour between soil and pure phases helps to elucidate the main carrier phases and sorption mechanisms in soil.
本研究旨在通过比较两种选定土壤中硒酸盐的反应活性与纯固相的反应活性，来确定硒酸盐的主要载体相。选择了二氧化硅、碳酸钙、氢氧化铝、针铁矿、膨润土和腐殖酸作为主要的土壤载体相。首先比较了最佳拟合动力学吸附模型得到的参数值，该模型可以区分瞬时吸附和动力学限制吸附。然后通过测量吸附分配系数（Kd(sorption)）与解吸分配系数（Kd(desorption)）的比值，比较了每种固体稳定硒酸盐的能力。动力学和稳定性用于帮助阐明与测试固相相互作用的性质，实验在间歇反应器中进行了 165 小时，在两个 pH 值（5.4 和 8）和三个硒酸盐浓度（1×10(-3)、1×10(-6)和 1×10(-8)mol L(-1))下，固体通过透析管与溶液隔离。结果表明，只有氢氧化铝可以在整个研究的 pH 范围内（5.4 至 8.0）吸附硒酸盐。这种矿物的吸附能力很强（Kd(sorption)>100 至 1×10(4)L kg(-1))，硒酸盐主要通过形成内圈络合物稳定下来。针铁矿在 pH 5.4 时发生吸附（Kd(sorption)52 L kg(-1))，主要为外圈络合物，而在 pH 8 时则不存在。在二氧化硅上，仅在 pH 5.4 时观察到较弱的吸附，并且在 165 小时时（Kd(sorption)4 L kg(-1))。在膨润土、碳酸钙和腐殖酸上没有观察到明显的吸附。关于研究的两种土壤，硒酸盐的行为不同。对于 Ro 土壤（pH 5.4），与 Bu 土壤（pH 8）相比，Kd(sorption)较低（8 L kg(-1))。Ro 土壤中硒酸盐的吸附行为主要归因于外层络合物，与针铁矿相同，而 Bu 土壤中吸附主要归因于内圈络合物，随后是还原机制，可能是由微生物引发的，在 165 小时的实验结束时没有达到稳定状态。当浓度达到 1×10(-3)mol L(-1)时，由于固体饱和，除了氢氧化铝外，硒酸盐的吸附减少。在相同浓度下，针铁矿和 Ro 土壤上似乎也发生了硒酸盐的还原，但没有阻止吸附的减少。因此，这项工作表明，比较土壤和纯相之间的硒酸盐行为有助于阐明土壤中的主要载体相和吸附机制。
