Uranium and radium-226 in Florida phosphate materials

Input materials, products and by-products from a number of Florida phosphate mines and chemical plants were analyzed for 226Ra and 238U by high resolution gamma spectrometry. Concentrations were distinctly lower in North Florida than in Central Florida. In the matrix, the two nuclides were essentially in radioactive equilibrium (North Florida, 8pCi/g; Central Florida, 38 pCi/g). Following beneficiation, concentrations in rock product, waste clays and sand tailings were approx. 100-300%, 100% and 10-25%, respectively, of those in the matrix. Radioactive equilibrium is markedly disrupted in phosphoric acid production; uranium follows the phosphoric acid while 226Ra appears in the by-product gypsum (North Florida, 14pCi/g; Central Florida, 26 pCi/g) and also in sediments and scales. Ammoniated phosphate fertilizers had relatively low levels of 226Ra but significant 238U (North Florida, 25 pCi/g; Central Florida, 70 pCi/g). On the other hand, triple superphosphate had significant concentrations of both 226Ra (North Florida, 12 pCi/g; Central Florida, 20 pCi/g) and 238U (North Florida, 26 pCi/g; Central Florida, 56 pCi/g). In the electric furnace process, radioactivity is transferred to the slag (Central Florida, 61 pCi/g of each nuclide). Within either region, nearly all sample types showed a considerable range of concentrations. (author)