RADIOCHEMISTRY OF FLORIDA PHOSPHOGYPSUM

Phosphogypsum is the by-product of producing phosphoric acid by reacti ng phosphate rock with sulfuric acid. The phosphoric acid industry in Florida is the largest in the world and it is estimated that 1 x 10(9) tonnes of phosphogypsum will soon be stored in 18 subaerial sites, th e so-called Florida ''gyp-stacks''. Florida phosphate rock samples ana lyzed in this study have U-238 activities which range from approximate ly 250 to 2000 Bq kg(-1) with U-234, Th-230, Ra-226, Pb-210 and Po-210 in approximate radioactive equilibrium. During production of phosphor ic acid, about 990-100% of the Ra-226, Pb-210 and Po-210 in the phosph ate rock is fractionated to the phosphogypsum. In most cases the activ ities of Ra-226, Pb-210 and Po-210 in the phosphogypsum are directly a nd predictably proportional to the activities in the input phosphate r ock. Studies carried out on the disequilibrium relationships in 74 sam ples of Florida phosphogypsum show that Ra-226 is relatively immobile on the unsaturated, aerobic portions of these gyp-stacks. The Pb-210 s eems to be remobilized preferentially to Po-210 or Ra-226 and solution s percolating through Florida gyp-stacks have added Pb-210 to some pho sphogypsum samples. Copyright (C) 1996 Elsevier Science Limited