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Extraction of Radiostrontium Coprecipitated with Calcium Carbonate in Soil¹

ABSTRACT

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.

¹ Research sponsored by the Office of Defense Waste & By-Product Management, U. S. Dep. of Energy, under contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc. Environmental Sciences Division Publication no. 2441.

² Research Staff Member, Environmental Sciences Division, Oak Ridge National Lab., Oak Ridge, TN 37831.

Received for publication April 16, 1984. Accepted for publication July 31, 1984.