Plutonium determination in mineral soils and sediments by a procedure involving microwave digestion and extraction chromatography

Abstract

A reliable and fast procedure with minimum waste generation for plutonium determination in soils and sediments is proposed. The procedure combines microwave-assisted digestion for sample dissolution, extraction chromatography for chemical separation, and coprecipitation and alpha-spectrometry for activity measurement. The work is focused on optimisation of the attack and separation steps. The microwave-assisted pre-treatment with mixtures of HF–HNO3 and HF–HClO4 achieved total mineralisation of samples in 2h and 30min. For the separation step, the influence on actinide chemical recovery of several ions usually present in soil and sediment matrices, particularly trivalent iron, were studied. The potential reusability of the chromatographic resins was also evaluated and, in spite of the preservation of plutonium recovery and selectivity, some memory effects in consecutive analysis were noticed. The column obstructions during the separation process were solved by using a peristaltic pump. Good accuracy, long-term repeatability (CV 6–7%) and minimum detectable activity (0.11–0.35Bqkg−1) for the proposed procedure were obtained by analysing 238Pu and 239+240Pu in the sediment CRM IAEA-135.