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  Remediation of Radium From Contaminated Soil (64 pp, 1.45 MB) (EPA/600/R-01/099) December 2001

The objective of this study was to demonstrate the application of a physicochemical separation process for the removal of radium from a sample of contaminated soil at the Ottawa, Illinois, site near Chicago.

The size/activity distribution analyzed among particles coarser than 5 microns showed that the activity was uniformly distributed. Almost 50 percent of the Radium-226 (Ra-226) activity was associated with particles of size 5 microns and smaller. The size fractions are coarse (+300 microns), medium (300 x 10 microns), and fine (-10 microns).

A series of mild chloride washing and flotation experiments showed that the +300 micron and 300 x 10 micron fractions can be remediated below a criterion level of 6 picoCuries per gram (pCi/g). This criterion was based on the 5-pCi/g plus background standard in 40 Code of Federal Regulations 192.

The criterion is often a relevant and appropriate requirement for Superfund remediation. Also, chemical washing using the chloride-based lixiviants was found to be potentially useful for the remediation of -10 micron soil fraction. The radium from coarse fraction up to 50 mesh (+300 microns) could be easily removed by screening and chloride washing. However, it was difficult to achieve a low radium value in the medium-sized fractions using flotation. In order to accomplish this goal, the effect of several different reagents (specific to radium) on temperature and the effect of chloride washing were evaluated.

Experimental results demonstrated that a combination of reagent using R-801+8-HQ was uniquely specific for radium. Using the combined flotation reagent, a volume reduction of 80 percent with a radium level of 6 pCi/g was obtained. The tests showed that with chloride washing of coarse materials (+300 microns) and flotation of 300 microns x 10 microns, the overall volume reduction of 80 percent could be accomplished. The typical results are summarized below:

Contaminated Soil Fraction Weight % Average
Ra-226 Activity (pCi/g)
% of Original Soil as "Clean Soil" After Application of UNR Technologies
+300 microns 43 26.2 40–41
-300 + 10 microns 33 92.3 26–30
-10 microns 24 180 19–22
Total Volume Reduction = 85–93%

The gross count analysis conducted at the University of Nevada, Reno, was found to be consistent with the Ra-226 gamma scan data analyzed by Thermo NUtech on the selected samples.

A flowsheet of this project’s work was developed and can be used for on-site demonstration.


Mary Gonsoulin

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