Nuclide migration and the environmental radiochemistry of Florida phosphogypsum

Phosphogypsum, a waste by-product derived from the wet process production of phosphoric acid, represents one of the most serious problems facing the phosphate industry in Florida today. This by-product gypsum precipitates during the reaction of sulfuric acid with phosphate rock and is stored at a ra...

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Bibliographic Details
Published in:Journal of environmental radioactivity 2001, Vol.54 (1), p.27-51
Main Authors: Burnett, William C, Elzerman, Alan W
Format: Article
Language:English
Subjects:
Calcium - analysis
Calcium Sulfate - chemistry
Florida
Lead - analysis
Migration
Natural radionuclides
Phosphate industry
Phosphogypsum
Phosphorus - chemistry
Radioactive Pollutants - analysis
Radiochemistry
Radium
Uranium - analysis
USA, Florida
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Summary:Phosphogypsum, a waste by-product derived from the wet process production of phosphoric acid, represents one of the most serious problems facing the phosphate industry in Florida today. This by-product gypsum precipitates during the reaction of sulfuric acid with phosphate rock and is stored at a rate of about 40 million tons per year on several stacks in central and northern Florida. The main problem associated with this material concerns the relatively high levels of natural uranium-series radionuclides and other impurities which could have an impact on the environment and prevent its commercial use. We have studied the potential release of radionuclides from phosphogypsum by: (i) analysis of stack fluids, groundwaters, and soils associated with gypsum stacks; and (ii) geochemical modeling. Stack fluids were observed to be very high in dissolved uranium and 210Pb with only moderate concentrations of 226Ra. Underlying soils tend to be enriched in U and 210Pb indicating precipitation when acidic stack fluids enter a buffered environment. Modeling results showed significant increases in radionuclide complexes with sulfate and phosphate, resulting in relatively mobile uncharged or negatively charged solution species within the stacks with likely precipitation of multicomponent solids with increasing pH below the stack. Our evidence thus suggests that, while phosphogypsum stacks do contain significant quantities of dissolved radionuclides, removal mechanisms appear to prevent large-scale migration of radionuclides to the underlying aquifer.
ISSN:0265-931X
1879-1700
DOI:10.1016/S0265-931X(00)00164-8