Reactivity of Primary Soil Minerals and Secondary Precipitates beneath Leaking Hanford Waste Tanks

Nagy, Kathryn L. ; Serne, R. Jeff ; Yabusaki

University of Colorado

关键词: Aluminium;    Saturation;    Surface Area;    Sediments;    Reaction Kinetics;   

DOI  :  10.2172/833513
RP-ID  :  EMSP-70070--2001
RP-ID  :  FG07-99ER15009
RP-ID  :  833513

美国|英语

来源: UNT Digital Library

【 摘 要 】

Since the late 1950s, leaks from 67 single-shell tanks at the Hanford Site have released about 1 million curies to the underlying sediments. At issue is the distribution of contaminants beneath the tanks, and the processes that led to their current disposition and will control their future mobility. The high ionic strength, high pH, and high aluminum concentrations in the tank liquids can significantly alter the vadose zone sediments through dissolution of primary minerals and precipitation of secondary minerals. Dissolution and precipitation directly influence (1) the flow paths that control contaminant transport and (2) the reactivity of the solid matrix that controls contaminant mobility. The impact of these processes, however, depends on mineral reaction kinetics and the dynamic interaction of the reactions with the flow field and contaminant sorption, neither of which are well-known for this extreme chemical system. Data obtained will be directly useful to other EMSP projects addressing contaminant mobility in the vadose zone. We are addressing three specific issues: (1) Recognized factors that control the kinetics of dissolution and precipitation must be quantified for the unnatural system of tank solutions mixing with soils, including effects of high pH, high ionic strength (especially NaNO3 solutions), temperature, and saturation state. (2) A clear understanding of the roles of nucleation mechanism, nucleation sites on soils minerals, and the role of reactive surface area in simultaneous dissolution and precipitation reactions are the key unknown components in comprehending this contaminated soil system. (3) Results obtained will help build a mechanistic understanding of how tank fluids migrate through the vadose zone. Local changes in porosity and permeability will dictate preferential flow paths which directly regulate the transport of later arriving chemical species. Changes in mineral surface area affect sorption site distribution. A comprehensive model is needed that integrates these feedback mechanisms with all the critically available data.