Colloid Formation at Waste Plume Fronts
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- 作者：Jiamin Wan ; Tetsu K. Tokunaga ; Eduardo Saiz ; Joern T. Larsen ; Zuoping Zheng ; and Rex A. Couture
- 刊名：Environmental Science & Technology
- 出版年：2004
- 出版时间：November 15, 2004
- 年：2004
- 卷：38
- 期：22
- 页码：6066 - 6073
- 全文大小：563K
- 年卷期：v.38,no.22(November 15, 2004)
- ISSN：1520-5851
文摘
Highly saline and caustic tank waste solutions containingradionuclides and toxic metals have leaked into sedimentsat U.S. Department of Energy (DOE) facilities such as theHanford Site (Washington state). Colloid transport is frequentlyinvoked to explain migration of radionuclides and metalsin the subsurface. To understand colloid formation duringinteractions between highly reactive fluids and sedimentsand its impact on contaminant transport, we simulatedtank waste solution (TWS) leakage processes in laboratorycolumns at ambient and elevated (70 
C) temperatures.We found that maximum formation of mobile colloids occurredat the plume fronts (hundreds to thousands times higherthan within the plume bodies or during later leaching).Concentrations of suspended solids were as high as 3 mass%, and their particle sizes ranged from tens of nanometersto a few micrometers. Calcium carbonate is alwaysone of the dominant phases of the plume front colloids,while the other phases varied with solution pH andtemperature. During infiltration of the leaked high-Na+waste solution, rapid and completed Na+ replacement ofexchangeable Ca2+ and Mg2+ from the sediment causedaccumulation of these divalent cations at the movingplume front. Precipitation of supersaturated Ca2+/Mg2+-bearing minerals caused dramatic pH reduction at the plumefront. In turn, the reduced pH caused precipitation ofother minerals. This understanding can help predict thebehavior of contaminant trace elements carried by the tankwaste solutions and could not have been obtainedthrough conventional batch studies.
C) temperatures.We found that maximum formation of mobile colloids occurredat the plume fronts (hundreds to thousands times higherthan within the plume bodies or during later leaching).Concentrations of suspended solids were as high as 3 mass%, and their particle sizes ranged from tens of nanometersto a few micrometers. Calcium carbonate is alwaysone of the dominant phases of the plume front colloids,while the other phases varied with solution pH andtemperature. During infiltration of the leaked high-Na+waste solution, rapid and completed Na+ replacement ofexchangeable Ca2+ and Mg2+ from the sediment causedaccumulation of these divalent cations at the movingplume front. Precipitation of supersaturated Ca2+/Mg2+-bearing minerals caused dramatic pH reduction at the plumefront. In turn, the reduced pH caused precipitation ofother minerals. This understanding can help predict thebehavior of contaminant trace elements carried by the tankwaste solutions and could not have been obtainedthrough conventional batch studies.