RADON EMANATION COEFFICIENTS FOR PHOSPHOGYPSUM

Phosphogypsum is a by-product of the phosphate fertilizer industry whi ch is stockpiled in large quantities world-wide. Phosphogypsum consist s mainly of dihydrate gypsum (CaSO(4)2H(2)O) but also contains elevate d concentrations of Ra-226 and other inorganic species which originate from the processing of phosphate rock. Rn-222 gas is the first decay product of Ra-226 and has been identified as one of the major environm ental concerns associated with phosphogypsum. This study was conducted to determine effects of particle size, weathering, and moisture conte nt on the Rn-222 emanation coefficient (epsilon) for phosphogypsum. Av erage epsilon for air-dry, unfractionated phosphogypsums derived from Togo, Florida, or Idaho rock was approximately 12%. Average epsilon fo r fine fraction phosphogypsum (< 20 mu m diameter) was greater than fo r unfractionated phosphogypsum by a factor of 4.6, 1.4, and 4.4 for sa mples derived from Idaho rock, Togo rock, and Florida rock, respective ly. Phosphogypsum samples subjected to an artificial weathering proced ure lost 40% mass, with no change in epsilon. Increasing water content was found to first slightly decrease, then to increase a compared to; air-dry samples; epsilon for 100% saturated phosphogypsum was 1.9-fol d greater than in air-dry phosphogypsum. Particle size sorting could a ccount for variability of Rn-222 exhalation at repositories. Very high moisture contents could slightly increase Rn-222 emanation, but exhal ation would likely be reduced due to slow diffusion through porosity o f saturated phosphogypsum.