HETEROGENEOUS DISTRIBUTION OF RADIONUCLIDES, BARIUM AND STRONTIUM IN PHOSPHOGYPSUM BY-PRODUCT

Phosphogypsum (PG) is a high volume by-product of the phosphate fertil izer industry which is composed mainly of CaSO4 . 2H(2)O. Impurities i n PG include F, trace elements and naturally-occurring radionuclides. Radium-226 content is sufficiently high in some PGs that it has limite d PG usage in building materials and as an amendment to agricultural s oils. Radium likely exists in PG as a sulfate solid solution with Ba, and possibly Sr. This study determined the distribution of Ra-226, Ba, Sr, U, Th and Pb-210 among three size fractions (fine: <20 mu m; medi um: 20-53 mu m; coarse: >53 mu m) in PGs derived from three different phosphate rock sources. All chemical species, except for Sr in PG deri ved from Idaho rock, were enriched in the <20-mu m fraction relative t o the other size fractions and relative to unfractionated PG. On avera ge, fine fraction Ra-226 and Pb-210 contents were enriched approximate ly sixfold over unfractionated PG. Ra-226 was enriched in the fine fra ction to a greater degree than were Ba or Sr, indicating that Ra behav ior in PG is distinct from these other elements. The combination of (i ) particle sorting during PG deposition, and (ii) non-uniform distribu tion of radionuclides in PG, may contribute to radionuclide heterogene ity at PG repositories.