SORPTION OF INORGANIC C-14 ON TO CALCITE, MONTMORILLONITE AND SOIL

Although C-14 occurs naturally, it is also a waste product of the nucl ear industry, and can be important because of its long half-life, high mobility as an anion, and ready incorporation into biota. Some aqueou s inorganic species are anionic with migration minimally retarded by m ost geological and soil materials. Substantial retardation is expected when calcite is present, but there are few data to quantify this effe ct. The present study measured partition coefficient values, R-d (conc entration on solids divided by concentration in liquids), of 8-851 kg( -1) for a series of calcite materials and for a carbonated soil. In co ntrast, R-d was zero for montmorillonite. The series of calcite materi als varied in particle size. In order to investigate the effects of pa rticle size, dissolution and degassing of C-14 and C-12 were monitored as pH was slowly decreased. The change in pH with addition of acid wa s strongly affected by particle size, as expected, but there was no sy stematic effect of particle size on the relative dissolution rates of C-14 VS C-12, or on R-d. Apparently, surface area was not a limiting f actor in the interaction of C-14 with these materials. The C-14 in soi l behaved most like the very fine calcite, indicating that the specifi c surface of the soil carbonate was similar to that of the very fine c alcite. Crown copyright (C) 1998 Published by Elsevier Science Ltd. Al l rights reserved.