Abstract
In this study, phosphoric acid with different concentrations and activation times is used to active montmorillonite (mmt) powder to prepare a promising backfill and buffer material for radioactive waste repository. At the same time their performance are evaluated by cesium sorption experiments. The experimental results show that the amount of suspension solids in these sorption experiments is not significant, which stands for the stability of these phosphoric acid activated montmorillonite (PAmmt). According to the fitting results by Langmuir model, PAmmts behave a much higher sorption capacity toward Cs ions than the original mmt. The high sorption capacity is strongly related to the increased specific surface area, which is confirmed by the N2-BET method. Further XRD and FTIR analyses demonstrate that the mmt structure is deconstructed during the activation, at which the degree of deconstruction depends on the concentration of phosphoric acid and reaction time. Also these PAmmts show a high selectivity even in high saline potassium or ammonium solutions. This is attributed to the higher surface charge density produced by surface protonation, which is supported by experiments of potentiometric titration and cation exchange capacity. Based upon experimental results, three hours of phosphoric acid activation is suggested to prepare a high selectivity along with a good sorption capacity for use in the radioactive waste repository.