Association of 226Ra in different fractions of Phosphogypsum

In the present work, studies were conducted in order to determine the distribution of 226Ra within the different phases of solid phosphogypsum by carrying out sequential extraction. Phosphogypsum is an impure gypsum (CaSO4.2H2O) formed as a byproduct during the manufacture of phosphoric acid from sedimentary phosphate ore. 226Ra present in the phosphate rock is considered to be the major source of radioactivity in these materials. The distribution of 226Ra was quantified in six different stages i.e. water soluble, ion exchangeable, specifically adsorbed and bound in carbonates, associated with Fe/Mn oxides, organically bound and associated with insoluble residue. The isolated 226Ra was analysed with high resolution gamma spectrometry. The three different gypsum samples having concentrations of 226Ra, 843.7Bq/kg, 1091Bq/kg and 750.6Bq/kg were taken for study. The experimental results showed that about 97% 226Ra is distributed in water soluble (56%), Fe/Mn oxide fraction (20%), carbonate fraction (10%) and in organic fraction (11 %). Negligible amount of 226Ra is present in exchangeable fraction and in the insoluble residual fraction. (author)