Extraction of Radiostrontium Coprecipitated with Calcium Carbonate in Soil1
- B. P. Spalding2
The fraction of soil 90Sr coprecipitated with calcium carbonate (CaCO3) was determined by extraction into 0.1M hydrochloric acid (HCl)-0.5M potassium chloride (KCl) after an initial extraction with either 1M ammonium acetate (NH4OAc) or 1M KCl to remove soluble salts and exchangeable cations. This procedure was tested on soil samples supplemented with 85 g CaCO3/kg containing coprecipitated 85Sr. The 85Sr and calcium (Ca) in this Ca(85Sr)CO3 behaved identically in the extraction sequences. In the absence of soil, about 95% of the Ca(85Sr)CO3 dissolved into the 0.1M HCl-0.5M KCl following the KCl extraction. In the presence of soil, a significant amount of both 85Sr and Ca remained undissolved in this extractant but were subsequently removed by extraction with 8M HNO3. Ammonium acetate, however, extracted more Ca and 85Sr from Ca(85Sr)CO3, with or without soil, than did KCl. The extraction procedure was also applied to a group of 16 90Sr-contaminated soil and streambed sediment samples which contained from 0 to 7.9 g carbonate-carbon/kg (0 to 66 g CaCO3/kg). The amount of Ca + Mg extracted by 0.1M HCl-0.5M KCl, following KCl extraction, was well correlated with but slightly lower than the amounts expected for a complete dissolution of the CaCO3. Pre-extraction with NH4OAc, rather than KCl, dissolved significantly more CaCO3 resulting in a lower estimate of the soil CaCO3. Several soil samples, taken from a radioactive waste burial trench that had received sodium carbonate (Na2CO3) treatment injections, revealed that up to 98% of the total 90Sr was observed in a CaCO3 phase. Untreated soils typically exhibited 80 to 95% of their 90Sr in a cation exchangeable form, i.e., extractable by either NH4OAc or KCl.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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