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

Abstract

Executive 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, EM-22). 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 objective of the treatability test was to evaluate the efficacy of using polyphosphate injections to treat uranium-contaminated groundwater in situ. A test site consisting of an injection well and 15 monitoring wells was installed in the 300 Area near the process trenches that had previously received uranium-bearing effluents. This report summarizes the issues limiting the formation of apatite within the test. Two separate overarching issues impact the efficacy of apatite remediation for uranium sequestration within the 300 Area: 1) the efficacy of apatite for sequestering uranium under the present geochemical and hydrodynamic conditions, and 2) the formation and emplacement of apatite via polyphosphate technology. iv Acronyms and Abbreviations

Impact of phosphate on U(VI) immobilization in the presence of goethite

“…Biologically-mediated release of orthophosphate from a soluble organophosphate compound resulted in precipitation of uranium as chernikovite (Beazley et al, 2007(Beazley et al, , 2009. Uranium remediation by injecting soluble phosphates has been tested in field trials at the US Department of Energy's (DOE) Hanford site (US DOE, 2005;Vermuel et al, 2006;Wellman et al, 2006aWellman et al, , 2007aWellman et al, , 2008. Related bench-scale experiments revealed the likely precipitation of autunite minerals (X ðnÞ þ 3Àn ½ðUO 2 ÞðPO 4 Þ 2 Á xH 2 O) in sediments amended with phosphates.…”

300 Area Uranium Stabilization Through Polyphosphate Injection: Final Report

“…Dependence of Uranium Uptake Expressed as Aqueous Uranium Concentration as a Function of Time in Hydroxyapatite-Equilibrated Groundwater (fromWellman et al 2008).…”

Gamma Ray Spectrometry and Landsat Tm Satellite Images Applied to the Study of the Sedimentary Phosphates of Irecê Bahia (Brazil)

“…Measurements in the areas rich in stromatolites showed in general, for soils, higher isotopic values of 232 Th and small ones for 232 U (Wellman et al, 2008). However, as part of the apatite appears in the soil constitution, whether in the cuttings or in its clay matrix, it still holds a signature of the radioactive elements, allowing using these elements as tracers for phosphate mineralization.…”