Abstract
Three samples of phosphogypsum of different ages were analyzed for natural radioelements using high-resolution gamma-ray spectrometry. The phosphogypsum samples were taken from the filter of a 10-year old pile, and a 50 year old pile. The distribution of 226Ra remains relatively constant as a function of storage time (up to 50 years) which confirms the immobility of 226Ra in the phosphogypsum matrix. However, the concentration of 238U and 232 Th have shown a decreasing tendency going from the most recent sample to the oldest. For radionuclides belonging to the 232 Th series, we noticed an enrichment factor of 1.5 for 228Ac in the most recent phosphogypsum, whereas the right proportions exist for the other two samples. This is due to the fact that most of the thorium fractionates to the phosphoric acid during the production process and the equilibrium between 232 Th and its descendants is not yet reached for fresh phosphogypsum.
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