Interim Report: Uranium Stabilization Through Polyphosphate Injection - 300 Area Uranium Plume Treatability Demonstration Project

Abstract

SummaryFor fiscal year 2006, the United States Congress authorized $10 million dollars to Hanford for "…analyzing contaminant migration to the Columbia River, and for the introduction of new technology approaches to solving contamination migration issues." These funds are administered through the U.S. Department of Energy Office of Environmental Management (specifically, . After a peer review and selection process, nine projects were selected to meet the objectives of the appropriation. As part of this effort, Pacific Northwest National Laboratory (PNNL) is performing bench-and field-scale treatability testing designed to evaluate the efficacy of using polyphosphate injections to reduce uranium concentrations in the groundwater to meet drinking water standards (30 μg/L) in situ. This technology works by forming phosphate minerals (autunite and apatite) in the aquifer, which directly sequesters the existing aqueous uranium in autunite minerals and precipitates apatite minerals for sorption and long-term treatment of uranium migrating into the treatment zone, thus reducing current and future aqueous uranium concentrations. Polyphosphate injection was selected for testing based on technology screening as part of the 300-FF-5 Phase III Feasibility Study for treatment of uranium in the 300 Area.The overall objectives of the treatability test include the following:• Optimize the use of multi-length polyphosphate amendment formulations, quantify the hydrolysis rates of polyphosphate, quantify the kinetics of autunite and apatite formation, and determine the long-term immobilization of uranium by apatite and longevity for polyphosphate injections to remediate uranium such that costs for full-scale application can be estimated effectively.• Inject polyphosphate to evaluate reduction of aqueous uranium concentrations and to determine the longevity of treatment of the process at full scale.• Demonstrate field-scale application of polyphosphate injections to evaluate whether a full-scale process can be implemented.This report presents results from bench-scale treatability studies conducted under site-specific conditions to optimize the polyphosphate amendment for implementation of a field-scale technology demonstration to treat aqueous uranium within the 300 Area aquifer of the Hanford Site. The general treatability testing approach consisted of conducting studies with site sediment and under site conditions, to develop an effective chemical formulation for the polyphosphate amendments and evaluate the transport properties of these amendments under site conditions. Phosphorus-31 nuclear magnetic resonance was used to determine the effects of Hanford groundwater and sediment on the degradation of inorganic phosphates. Static batch tests were conducted to optimize the composition of the polyphosphate formulation for the precipitation of apatite and autunite, and to quantify the kinetics, loading, and stability of apatite as a long-term sorbent for uranium. Dynamic column tests were used to further optimize the polyphosphate f...

DNA Profile Analysis and Interpretation

“…This suggests that chemical reaction nonequilibrium may influence the migration of polyphosphate compounds. Similar results were previously observed under saturated conditions (Wellman et al 2007c). Possible mechanisms that may have resulted in increased rate-limited sorption are 1) sorption of degradation products onto sedimentbound polymerized phosphate molecules, 2) degradation of polymerized phosphate compounds and subsequent sorption to the sediment matrix, or 3) rapid precipitation of heavy, fast-settling solid phases.…”

Use of Polyphosphate to Decrease Uranium Leaching in Hanford 300 Area Smear Zone Sediments

“…In addition to those noted in previous publications (Wellman et al 2007(Wellman et al , 2008a(Wellman et al , 2011Bovaird et al 2010;Vermeul et al 2009), some limitations of polyphosphate treatment technologies were identified, which impact field scale applicability in different treatment zones. The trend of increased sedimentphosphate contact time resulting in higher phosphate precipitate (and a greater decrease in uranium leaching) implies that polyphosphate injection into groundwater may not deposit sufficient phosphate precipitate due to high groundwater flow (i.e., insufficient contact time).…”

“…Although most contaminated sediment from the highly contaminated ponds was removed in the early 1990s, uranium continues to leach from variably saturated (i.e., smear zone) sediments beneath the original ponds seasonally and is the largest source of uranium in groundwater that eventually advects into the Columbia River (Catalano et al 2008;Bond et al 2008;Liu et al, 2008). The use of phosphate treatment of sediments has been shown to effectively decrease uranium leaching short-term column experiments (Shi et al 2009) and in numerous batch and one-dimensional (1-D) column studies (Wellman et al 2006a(Wellman et al , 2006b(Wellman et al , 2007(Wellman et al , 2008a(Wellman et al , 2008b(Wellman et al , 2011Bovaird et al 2010). However, a field-scale groundwater injection of a phosphate solution in the Hanford 300 Area showed limited effectiveness at decreasing uranium concentration in fast flowing groundwater (Wellman et al 2011;Vermeul et al 2009).…”

Challenges Associated with Apatite Remediation of Uranium in the 300 Area Aquifer

“…These values were adjusted for field conditions assuming that retardation was due to the <2-mm fraction and that the <2-mm fraction composed ~10% of the total sediment matrix. The field K d and retardation values were calculated using a porosity value of 0.2 and bulk density value of 2.19 g/cm 3 , which were quantified within the limited field investigation (LFI) ( Table 2.3) (Wellman et al 2007). Sorption of phosphate and calcium to the sedimentary matrix is relatively slow, requiring several hours.…”

“…The limited retardation observed under field conditions limited the mixing of the three remedy phases. Furthermore, Wellman et al (2007) previously noted that the ratio of calcium to phosphate needed to precipitate apatite is highly sensitive. The highly variable hydrodynamic conditions present in the 300 Area subsurface challenge the ability to control this variable.…”