Radioactivity of phosphogypsum in the south-west of Spain

Phosphogypsum is the by-product of producing phosphoric acid by reacting phosphate rock with sulphuric acid. In the south-west of Spain, and near the town of Huelva, there is a big industrial complex with some factories devoted to the production of phosphoric acid, which produce annually 3 x 10(6) metric tonnes of phosphogypsum. Of this amount 80% is stored in nearby sites named 'gyp-stacks'. The phosphate rock treated in these factories for the production of phosphoric acid has U-238 activities between 1000 and 1600 Bq.kg(-1), being their daughters in approximately secular equilibrium. A fraction of these radionuclides, and in different proportion, goes with the phosphogypsum. The radionuclide activity concentrations in various phosphogypsum samples collected at different places in the gyp-stacks are given, and an average dose rare in air due to gamma rays at a point 1 m above these areas is also determined.