Retention and Remobilization of Stabilized Silver Nanoparticles in an Undisturbed Loamy Sand Soil

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• 作者：Yan Liang ; Scott A. Bradford ; Jiri Simunek ; Marc Heggen ; Harry Vereecken ; Erwin Klumpp
• 刊名：Environmental Science & Technology
• 出版年：2013
• 出版时间：November 5, 2013
• 年：2013
• 卷：47
• 期：21
• 页码：12229-12237
• 全文大小：455K
• 年卷期：v.47,no.21(November 5, 2013)
• ISSN：1520-5851

文摘

Column experiments were conducted with undisturbed loamy sand soil under unsaturated conditions (around 90% saturation degree) to investigate the retention of surfactant stabilized silver nanoparticles (AgNPs) with various input concentration (C_o), flow velocity, and ionic strength (IS), and the remobilization of AgNPs by changing the cation type and IS. The mobility of AgNPs in soil was enhanced with decreasing solution IS, increasing flow rate and input concentration. Significant retardation of AgNP breakthrough and hyperexponential retention profiles (RPs) were observed in almost all the transport experiments. The retention of AgNPs was successfully analyzed using a numerical model that accounted for time- and depth-dependent retention. The simulated retention rate coefficient (k₁) and maximum retained concentration on the solid phase (S_max) increased with increasing IS and decreasing C_o. The high k₁ resulted in retarded breakthrough curves (BTCs) until S_max was filled and then high effluent concentrations were obtained. Hyperexponential RPs were likely caused by the hydrodynamics at the column inlet which produced a concentrated AgNP flux to the solid surface. Higher IS and lower C_o produced more hyperexponential RPs because of larger values of S_max. Retention of AgNPs was much more pronounced in the presence of Ca²⁺ than K⁺ at the same IS, and the amount of AgNP released with a reduction in IS was larger for K⁺ than Ca²⁺ systems. These stronger AgNP interactions in the presence of Ca²⁺ were attributed to cation bridging. Further release of AgNPs and clay from the soil was induced by cation exchange (K⁺ for Ca²⁺) that reduced the bridging interaction and IS reduction that expanded the electrical double layer. Transmission electron microscopy, energy-dispersive X-ray spectroscopy, and correlations between released soil colloids and AgNPs indicated that some of the released AgNPs were associated with the released clay fraction.