부산대학교 도서관

The pH-dependence and reversibility of radium (Ra) and strontium (Sr) binding onto a modified bauxite refinery residue (MBRR), and the effects of sample aging, were studied in laboratory uptake / leaching experiments. Natural 226Ra and stable strontium (Srnat) were contacted with MBRR in an 8-day loading period (equilibrium pH c. 8.5). Following the addition of exchange isotopes 228Ra and 85Sr, the samples were then leached in pH-dependent experiments, where the pH was decreased incrementally from 9 to 3 over seven hours. A further suite of samples was aged at 4°, 23°, and 65°C for 6-months after the initial addition of 226Ra and Srnat and then studied in a similar set of pH-dependent exchange experiments. Relative concentrations of the Ra and Sr isotope pairs (226Ra/228Ra and Srnat/85Sr) provided insights into the adsorption strength, incorporation, reversibility and aging effects. The Srnat data showed that the release of bound Sr from aged MBRR samples as the pH decreases is substantially less than the unaged sample, showing that during the aging period, Sr has been incorporated in less accessible phases. It appears that the uptake of 228Ra by the higher temperature aged samples is somewhat stronger than the unaged samples, however Ra isotope exchange plots for aged and unaged samples are similar. Consequently, the stronger binding of 228Ra by the higher temperature aged samples is probably driven by translocation to kinetically less favourable surface sites rather than a significant incorporation of radium within the mineral solids during aging.