Phosphogypsum Radium

Coupled with the energy consumption is the environmental effect from production of these binders. For every ton of phosphoric acid, 5 ton of phosphogypsum (calcium sulfate) is produced [15]. This waste can be recycled into value-added products such as gypsum board, but often there is a radioactivity issue. Some phosphogypsum contains radium and emanates radon gas. At the present time, such waste can only be disposed in a landfill. 

KEY WORDS gypsum, phosphoric acid, radium, bypnxiuct gypsum, phosphogypsum, hazardous waste, phosphate fertilizer production... 

TABLE 7—Uranium (U), thorium (Th. and radium (Ra) analyses of sized samples of phosphogypsum, pCilg. 

TABLE 9—Radium analyses of 3-m interval sanities of phosphogypsum, pCilg. 

Table 8 shows the isotopic analyses of radium, uranium, and thorium in three samples. These results indicated that uranium-238, uranium-234, and thorium-230 were about in equilibrium. Radium was not in equilibrium and was more concentrated in the phosphogypsum than the radiological equilibrium with tho-rium-230 would allow. 

Sample G was low in radium compared to the other phosphogypsum stacks. This low content occurred because the phosphate rock that produced the phosphogypsum in Stack G contained about one-third uranium and radium that the phosphate rock that produced the phosphogypsum in the other stacks contained. Sample F is higher in radium than the other samples. We do not know, at this time, why this occurs. 

TABLE 14—Average radium concentrations of phosphogypsum samples. pCHg. 

The radium concentration in phosphogypsum in Florida averaged 21 pCi/g, and its concentration was greatest in the fine sizes. 

Evaluation of Radium and Toxic Element Leaching Characteristics of Florida Phosphogypsum Stockpiles... 

REFERENCE May A. and Sweeney. J. W.. Evaluation of Radium and Toxk Element Leaching Characteristics of Florida Phosphogypsum Stockpiles/ The Chemistry and Technology of Gypsum, ASTM STP 86 , R. A. Kuntze. Ed.. American Society for Testing and Materials. 1984. pp. 140-159. 

The first phase of the Bureau s research [1 ] showed that phosphogypsum was not corrosive by Environmental Protection Agency (EPA) criteria. The study also presented evidence that phosphogypsum would not be toxic by EPA criteria and that trace elements and radium would not be leached from the stockpiles. These conclusions were obtained from statistical analyses of extensive quantities of spectrographic and radiological data. More direct confirmation of these conclusions was needed to decisively answer the question of leaching of toxic elements and radium from phosphogypsum stockpiles. 

Statistical analysis of the radium data is shown in the analysis of variance (ANOVA, Table 8). At the 99% confidence level, these results show a significant difference between the radium concentrations in phosphogypsum and in the subsurface material. They show no significant differences among the cores or between the Oak Ridge and EPA results. The standard error of measurement was 4.68 pCi/g for 20 analyses. This is near the standard error of 4.S2 pCi/g... 

The background concentrations of radium in the subsurface material, before creation of the phosphogypsum piles, can be accurately estimated since longterm data are available 14.6], Interest in radioactivity in Florida dates back to 1942 through 1948, when there was an urgent need to find domestic sources of uranium. In addition, there has been environmental concern about radium in Florida for the last 20 years, and considerable data have been published, some of which are shown in Table 9. 

To help explain the results of this study and to aid in predicting the future stability of phosphogypsum stockpiles, the hydrology associated with the piles and the solubility and absorption of trace elements and radium were considered. How well the objectives of this investigation were met is also briefly considered. 

Radium sulfate has an axial ratio relative to gypsum of 1.93. From Eq 3. the absorption of radium by phosphogypsum would be 89% of the amount of radium originally present. This indicates that very little radium would be leached. 

The three objectives of this investigation were to determine (1) if the phosphogypsum piles were hazardous toxic wastes, (2) if toxic elements were leached from phosphogypsum, and (3) if radium was leached. 

Absorption of trace elements and radium by phosphogypsum is the major reason for their not being leached. 

Thirty-nine elements were detected in the phosphogypsum samples, but concentrations of the elements did not vary with depth within the stockpiles. Radium content averaged 21 pCi/g and varied inversely with particle size. 

Phosphogypsum contains small residual amounts of phosphoric acid and sulfuric acid, and also some trace concentrations of uranium and radium, which result in low levels of radiation... 

Fluorogypsum is not being used in any commercial applications however, it has been evaluated for use as a road base material, and in the production of impure plasterboard Phosphogypsum is a calcium sulfate hydrate that is pumped into ponds, eventually dewatered, and ultimately disposed of in large stockpiles called stacks. It has been recovered and reused with some success in stabilized road bases, unbound road bases, and roller-compacted concrete. It can be used for agricultural purposes, if the radium-226 concentration of the source material is less than 10 pCi/g... 

Phosphogypsum is chemically similar to natural gypsum but because of its radium content is unused and stockpiled. The production during the last 50 years is 700 Mt in Florida alone (USGS Fact Sheet FS 155-99 September 1999). 

A common problem is, however, the content of the radioactive element radium, which is a common impurity in many phosphorite deposits and which is carried forward to the products. This problem makes phosphogypsum particularly unacceptable for making constmction materials. The latter specifies less than 25 picocurie (a curie is a unit of radioactivity equal to the amount of a radioactive isotope that decays at the rate of 37 billion disintegrations per second) of radioactivity in the phosphogypsum. 

Installers of phosphogypsum plaster board can also be exposed to radium 226 and other radionuclides from the uranium 238 decay series in radioactive dusts from the plaster board. O Brien et al. (254) estimated potential doses to... 

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