Technetium (Tc) remains a priority remediation concern due to persistent challenges, including mobilization due to rapid reoxidation of immobilized Tc, and competing comingled contaminants, e.g., Cr(VI), that inhibit Tc(VII) reduction and incorporation into stable mineral phases. Here Fe(OH)(s) is investigated as a comprehensive solution for overcoming these challenges, by serving as both the reductant, (Fe(II)), and the immobilization agent to form Tc-incorporated magnetite (FeO). Trace metal analysis suggests removal of Tc(VII) and Cr(VI) from solution occurs simultaneously; however, complete removal and reduction of Cr(VI) is achieved earlier than the removal/reduction of comingled Tc(VII). Bulk oxidation state analysis of the final magnetite solid phase by XANES shows that the majority of Tc is Tc(IV), which is corroborated by XPS measurements. Furthermore, EXAFS results show successful, albeit partial, Tc(IV) incorporation into magnetite octahedral sites. Cr XPS analysis indicates reduction to Cr(III) and the formation of a Cr-incorporated spinel, CrO, and Cr(OH) phases. Spinel (modeled as FeO), goethite (α-FeOOH), and feroxyhyte (δ-FeOOH) are detected in all reacted final solid phase samples analyzed by XRD. Incorporation of Tc(IV) has little effect on the spinel lattice structure. Reaction of Fe(OH)(s) in the presence of Cr(III) results in the formation of a spinel phase that is a solid solution between magnetite (FeO) and chromite (FeCrO).

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Contaminants disposed of at the land surface must migrate through the vadose zone before entering groundwater. Processes that occur in the vadose zone can attenuate contaminant concentrations during transport through the vadose zone. Thus, quantifying contaminant attenuation and contaminant transport processes in the vadose zone, in support of the conceptual site model (CSM) and fate and transport assessments, is important for assessing the need for, and type of, remediation in the vadose zone and groundwater. The framework to characterize attenuation and transport processes provided in U.S. Environmental Protection Agency (EPA) guidance documents was used to guide the laboratory effort reported herein.PNNL-26208 RPT-DVZ-AFRI-037 v all samples. In terms of desorption versus adsorption K d values, there was no clear trend across all of the samples.

The solubility and spectroscopy of sodium nitrite in sodium hydroxide solutions are detailed to provide insight into processes underlying solubility.