Radium in Phosphogypsum Leachates
- P. M. Rutherford,
- M. J. Dudas * and
- J. M. Arocena
Phosphogypsum (PG) is an acidic by-product of the phosphate fertilizer industry, and is produced in large quantities by the wet phosphoric acid process. Most PG is sluiced out to repositories, forming large stockpiles. Phosphogypsum is composed mainly of gypsum (Ca-SO4·2H2O), but contains impurities of environmental concern such as F−, acids, trace elements, and naturally occurring radionuclides, which originate from the phosphate rock used in processing. Possible movement of these impurities into groundwater is an issue. 226Radium is the major source of radioactivity in PG produced from sedimentary phosphate rock. Few studies have addressed the leachability of 226Ra because solid solutions of Ra, Ba, and Sr are very insoluble. The objective of this study was to investigate the concentrations of 226Ra, Ba, and Sr in leachate generated from PG produced from Togo phosphate rock. Phosphogypsum was extracted 30 times with deionized distilled (d.d.) H2O over 30 d. Extractable 226Ra was maximal (0.55 Bq L−1) for Day 1 but remained relatively constant between Day 2 and Day 30. Minimum extractable 226Ra (0.23 Bq L−1) occurred on the Day 30 extraction but still exceeded the current U.S. drinking water standard. Solid phase 226Ra increased between Day 0 (850 Bq kg−1) and Day 30 (1120 Bq kg−1). The 226Ra/Ba ratios in the solid phase and in the extractable liquid phase were nearly equal over the last half of the extraction period. If this relationship holds for other PGs, then solution 226Ra activities can be estimated if solid-phase 226Ra/Ba ratios are known and Ba solution concentrations are known or estimated.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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