Analysis of trace actinide elements in soil organic matter: Optimization of sample processing to improve chemical separation of U and Pu

Chemical separation yield of actinide elements from soil samples containing high amounts of organic matters was often low as compared to that for samples containing low organic matters. We compared chemical yield of uranium and plutonium from organic-rich Japanese soil and humic acid samples which were subjected to three different pretreatment procedures ((1) pulverization only. (2) dry-ashing at 510 degreesC after pulverization, and (3) 680 kGy gamma-ray irradiation after pulverization) prior to acid digestion. Separation of U and Pu was performed by U-TEVA resin and AGI-X8 anion exchange resin, respectively, For organic samples, pretreatment procedures governed the yield of actinide elements significantly. Chemical separation yield of U was low (6 +/- 1%) for Aldrich humic acid sample after dry-ashing at 510 degreesC. For such samples, gamma-ray irradiation improved the yield of U to 35 +/- 22%. Recovery of Pu was lower for some organic soil samples which were dry-ashed at 510 degreesC (27 +/- 2%) as compared to those which were not dry-ashed (62 +/- 10%).