van Elteren Johannes T, Slejkovec Zdenka, Arčon Iztok, Beeston Michael P, Pohar Andrej
National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia.
J Environ Monit. 2011 Jun;13(6):1625-33. doi: 10.1039/c1em10104h. Epub 2011 May 6.
A soil with a relatively high Fe content (2.82% [w/w]) was loaded for up to one year with As(v) by equilibrating it with a solution containing 1000 mg l(-1) As(v) at a soil mass-to-solution ratio of 0.1 kg l(-1). The incorporation of As(v) into the soil and its distribution over the soil phases were monitored by sampling at strategic time intervals using an operationally defined five-step sequential extraction procedure (Wenzel et al., Anal. Chim. Acta, 2001, 436, 309) and subsequent As measurement. A multiple kinetic Langmuir model was developed to retrieve the dynamic parameters (adsorption and desorption rate constants, capacities and Langmuir equilibrium constants) for each of the soil phases by numerical fitting of the experimental adsorption data to the model. Under the equilibration conditions used the adsorption rate constants for all five operationally defined soil phases were very similar but the desorption rate constants decreased by a factor of ca. 150 from soil phase 1 (non-specifically sorbed As) to 5 (residual phases). This implies that As(v) incorporation "deeper" into the soil leads to stronger binding which is associated with the Langmuir equilibrium constants (adsorption rate constants/desorption rate constants). Equilibration of the soil with As(v) was complete in ca. 10 days with As(v) predominantly bound to soil phase 2 (specifically sorbed As) and soil phase 3 (amorphous and poorly crystalline hydrous oxides). X-Ray absorption spectroscopy techniques revealed that these binding characteristics may be related to adsorption of As(v) on Si- and/or Al-containing structures and natural hydrous iron oxide (HFO) surface sites, respectively. Since the model is independent of the initial As(v) concentration in the solution and the soil mass-to-solution ratio, the behaviour of the thus characterized soil-As(v) system can be predicted for a range of conditions. Simulations showed that in an accidental As(v) spill the soil studied would actively scavenge As(v) by instantaneous adsorption onto all soil phases followed by redistribution of As(v) from weaker binding sites to stronger ones over time.
将一种铁含量相对较高（2.82%[w/w]）的土壤与含1000 mg l⁻¹ 五价砷（As(v)）的溶液以0.1 kg l⁻¹ 的土液质量比进行平衡，使其吸附As(v)长达一年。通过采用一种操作定义的五步连续萃取程序（Wenzel等人，《分析化学学报》，2001年，436卷，309页）并在关键时间间隔进行采样，随后测定砷含量，来监测As(v)在土壤中的掺入情况及其在土壤各相中的分布。通过将实验吸附数据数值拟合到模型，建立了一个多重动力学朗缪尔模型，以获取各土壤相的动力学参数（吸附和解吸速率常数、容量和朗缪尔平衡常数）。在所使用的平衡条件下，所有五个操作定义的土壤相的吸附速率常数非常相似，但解吸速率常数从土壤相1（非特异性吸附的As）到土壤相5（残留相）降低了约150倍。这意味着As(v)向土壤“更深层”的掺入导致更强的结合，这与朗缪尔平衡常数（吸附速率常数/解吸速率常数）相关。土壤与As(v)的平衡在约10天内完成，As(v)主要结合在土壤相2（特异性吸附的As）和土壤相3（无定形和结晶性差的水合氧化物）上。X射线吸收光谱技术表明，这些结合特征可能分别与As(v)在含硅和/或铝结构以及天然水合氧化铁（HFO）表面位点上的吸附有关。由于该模型与溶液中初始As(v)浓度和土液质量比无关，因此可以预测在一系列条件下如此表征的土壤 - As(v)系统的行为。模拟表明，在As(v)意外泄漏的情况下，所研究的土壤会通过立即吸附到所有土壤相上而积极清除As(v)，随后随着时间推移，As(v)会从较弱结合位点重新分布到较强结合位点。
