Low-temperature fusion using NH4HSO4 and NH4HF2 for rapid determination of Pu in soil and sediment samples

Highlights: • Novel low-temperature fusion methods were developed for rapid Pu analysis. • Fusion conditions are set as 250 °C fusion for 15 min with a sample:flux ratio = 1:5. • Portable hot plate is employed for fusions instead of cumbersome furnace. • NH₄HF₂ fusion can completely release Pu from sediment pre-calcined at 450^oC-1000 °C. • Both the whole analytical procedures of the two fusion methods take merely 8 h. -- Abstract: Two fusion methods were established for rapid determination of Pu in soil and sediment samples. The methods consisted of NH₄HSO₄ or NH₄HF₂ fusion procedures incorporated with procedures for CaF₂/LaF₃ co-precipitation, extraction chromatography and SF-ICP-MS measurement. The fusion procedures were done on a portable hot plate instead of in a cumbersome muffle furnace and took only 15 min heating-up time from room temperature to 250 °C and 15 min fusion time at 250 °C. Chemical recoveries of Pu after completing the NH₄HSO₄ and NH₄HF₂ fusion methods for 0.5–1 g sample were approximately 70% and more than 90%, respectively, and decreased with the increase of sample weight from 0.5 g to 5 g. Sediment samples were pre-ignited at different temperatures ranging from 450 °C to 1000 °C to form refractory fractions of Pu, with which the dissolution rates of Pu by the NH₄HSO₄ and NH₄HF₂ fusion were investigated. With the increase of pre-ignition temperature of the sediment samples, the dissolution rates of Pu from the samples prepared by NH₄HSO₄ fusion declined dramatically from near 100% for 450 °C to 8% for 1000 °C. In contrast, the NH₄HF₂ fusion was capable of completely releasing Pu from samples that were pre-ignited at temperatures over 450 °C to 1000 °C, which was comparable to releases obtained by the hazardous and time-consuming HNO₃-HF digestion, and was superior to the conventional HNO₃ digestion. Additionally, because HF is not used in any procedure of the NH₄HF₂ fusion, a safer and greener alternative to NH₄HSO₄ fusion and HNO₃-HF digestion is realized for rapid Pu determination in environmental samples for nuclear emergency response and application in environmental studies.