title: Removal Capabilities of Zeolite and Zero Valent Iron With High-Level Waste Tank Radionuclides and Metals: Cesium, Strontium and Chromium
Creators: name: Towles, Colette
Publisher: name: University of Nevada, Las Vegas
publisherIdentifier: https://ror.org/0406gha72
publisherIdentifierScheme: ROR
Year: 2024

description: High level nuclear waste (HLW) has been disposed for temporary storage in underground steel tanks at the Department of Energy Nuclear sites. For example, at the Hanford Site, WA, and Savannah River Site (SRS), SC, HLW account for eighty-eight million gallons (Mgal) and 450 million Curies (MCi) of radioactivity. In the early nuclear activity at Hanford, the waste was discharged to single-shell steel tanks, and the lack of secondary containment allowed leaks, contaminating soil and groundwater. Despite tremendous efforts to stabilize the liquid waste at nuclear sites, treatment is complex, costly, and time-consuming; therefore, HLW may have to be stored in tanks for decades waiting for treatment. Until stabilization is achieved, there is a need to prevent, identify, and/or resolve leaks that occur in the waste tanks. To address this issue, the project’s purpose is to assess the removal capabilities of BRZTM and ZVI for the removal of Cs, Sr, and Cr (VI). In order to assess the removal capabilities of the BRZTM and ZVI, fixed-bed column tests were conducted. For safety reasons, non-radioactive isotopes were used in the original testing to prevent unnecessary radiation exposure. First, the adsorption performance of Cs and Sr was evaluated when they were used individually with 100% v/v of BRZTM. Column A had an influent concentration of 25 mg/L of Sr, column B had an influent concentration of 25 mg/L of Cs, column C had an influent concentration of 25 mg/L of Cs and 25 mg/L of Sr, and column D had an influent concentration of 25 mg/L of Cs and 2.5 mg/L of Sr. The results showed nearly 100% removal for all columns, which showed that BRZTM was a sufficient adsorbate for the subsequent experiments. The second set of columns was implemented to analyze the removal performance of ZVI for 10 mg/L of Cr when ZVI was used individually. Columns A and B had 10% v/v of ZVI, and columns C and D had 20% v/v of ZVI. The columns containing 20% v/v of ZVI showcased reduced effluent concentrations. The 20% v/v of the ZVI column exhibited approximately 50% removal at 125 bed volume, while 10% v/v of the ZVI column showed roughly half that performance. Next, the behaviors of the Cs, Sr and Cr were examined when mixed together in the influent while BRZTM and ZVI were mixed within the fixed-bed column. All of columns A, B, C, and D contained 20% v/v of ZVI and 80%v/v of BRZTM with an influent concentration of 1 mg/L of Sr and 50 mg/L of Cs while only Cr concentration was varied: 1 mg/L of Cr in columns A and B, and 5 mg/L of Cr in columns C and D. Based on the findings, BRZTM and ZVI are effective materials even when used for a combination of radionuclides and metals. ICP-MS, SEM and EDS analyses were conducted on the used and unused media in order to show the increase in the presence of Cs, Sr and Cr on the surface of the BRZTM and ZVI after usages. 
The characterization results and the fixed-bed column experimentation findings will play a crucial role in shaping future research aimed at optimizing the design and implementation of various adsorbents. For example, studies on materials such as activated carbon, zeolites, and metal-organic frameworks (MOFs) could help identify the most effective materials for capturing specific contaminants, such as heavy metals or radioactive isotopes, from waste streams. These insights will not only enhance the efficiency of adsorption processes but also contribute to the development of sustainable solutions that can extend the operational lifespan of waste storage tanks. Moreover, the findings from these studies will support the design of waste management systems that are both resilient and adaptable. For instance, advancements in the development of multi-stage filtration or hybrid adsorption technologies could be incorporated into current waste management infrastructure to improve their capacity to handle variable contamination loads. Such innovations will not only help safeguard the environment but also improve compliance with stringent regulatory standards, ensuring long-term environmental protection while awaiting the establishment of permanent waste storage solutions.