An isotope dilution–precipitation process for removing radioactive cesium from wastewater

Highlights: ► Developed an isotope dilution–precipitation treatment process for Cs-137 contaminated water. ► Waste seeded with non-radioactive Cs-133 prior to precipitation with sodium tetraphenylborate. ► Final Cs-137 concentrations below DOE discharge limit of 3.0 × 10−6 μCi/mL can be achieved. ► Synthetic wastewater, and industrial low level radioactive proof of principle studies completed. - Abstract: A novel isotope dilution–precipitation method has been developed to remove cesium-137 from radioactive wastewater. The process involves adding stable cesium chloride to wastewater in order to raise the total cesium concentration, which then allows both the stable and radioactive cesium ions to be precipitated together using sodium tetraphenylborate. This process was investigated utilizing laboratory solutions to determine stable cesium dose rates, mixing times, effects of pH, and filtration requirements. Once optimized, the process was then tested on synthetic wastewater and aqueous low-level waste. Experiments showed the reaction to be very quick and stable in the pH range tested, 2.5–11.5. The wastewater may need to be filtered using a 0.45-μm filter, though ferric sulfate has been shown to promote coagulation and settling, thereby eliminating the necessity for filtration. This investigation showed that this isotope dilution–precipitation process can remove Cs-37 levels below the U.S. Department of Energy's (DOE) Derived Concentration Standard (DCS) of 3.0 × 10−6 μCi/mL using a single dosage, potentially allowing the wastewater to be discharged directly to sanitary sewers.