Control of pertechnetate sorption on activated carbon by surface functional groups

The isotope 99Tc is highly soluble and poorly adsorbed by natural materials under oxidizing conditions, thus being of particular concern for radioactive waste disposal. Activated carbon can potentially be used as an adsorbent for removing Tc from aqueous solutions. We have tested six commercial activated carbon materials for their capabilities for sorption of pertechnetate (TcO−4). The tested materials can be grouped into two distinct types: Type I materials have high sorption capabilities with the distribution coefficients (KdKd) varying from 9.5×1059.5×105 to 3.2×103 ml/g3.2×103 ml/g as the pH changes from 4.5 to 9.5, whereas type II materials have relatively low sorption capabilities with KdKd remaining more or less constant (1.1 × 103–1.8 × 103 ml/g) over a similar pH range. The difference in sorption behavior between the two types of materials is attributed to the distribution of surface functional groups. The predominant surface groups are identified as carboxylic and phenolic groups. The carboxylic group can be further divided into three subgroups, A, B, and C, in the order of increasing acidity. The high sorption capabilities of type I materials are found to be caused by the presence of a large fraction of carboxylic subgroups A and B, while the low sorption capabilities of type II materials are due to the exclusive presence of phenolic and carboxylic subgroup C. Therefore, the performance of activated carbon for removing TcO−4 can be improved by enhancing the formation of carboxylic subgroups A and B during materials processing.

Six commercial activated carbon materials have been tested for their capabilities (KdKd) for sorption of pertechnetate (TcO−4). The results show that the materials can be grouped into two general types with very distinct sorption behaviors, which can be attributed to the different distributions of functional groups on material surfaces.Figure optionsDownload as PowerPoint slide