Exhalation of 222Rn from phosphogypsum piles located at the Southwest of Spain

Phosphogypsum (PG) is a waste product of the phosphoric acid production process and contains, generally, high activity concentrations of uranium series radionuclides. It is stored in piles formed over the last 40 years close to the town of Huelva (Southwest of Spain). The very broad expanse of the PG piles (about 1200 ha) produces a local, but unambiguous, radioactive impact to their surroundings. In 1992, the regional government of Andalusia restored an area of 400 ha by covering it with a 25-cm thick layer of natural soil and, currently, there is an additional zone of 400 ha in course of restoration (unrestored) and the same area of active PG stacks. Due to the high activity concentration of 226Ra in active PG stacks (average 647 Bq kg-1), a significant exhalation of 222Rn could be produced from the surface of the piles. Measurements have been made of 222Rn exhalation from active PG stacks and from restored and unrestored zones. The 222Rn exhalation from unrestored zones is half of that of the active PG stacks. Following restoration, the 222Rn exhalation is approximately eight times lower than the active PG stacks. The activity concentrations of natural radionuclides (226Ra, 40K, 232Th) in the mentioned zones have been determined. This study was also conducted to determine the effect of 226Ra activity concentration on the 222Rn exhalation, and a good correlation was obtained between the 222Rn exhalation and 226Ra activity, porosity and density of soil