A comparative study of adsorption properties of zirconium (IV) phosphonates for removal of 90Sr

With as goal of improving on traditional α-ZrP, four zirconium phosphonate materials were prepared as potential adsorbents for the removal of 90Sr from nuclear wastewater. A typical sol–gel method was used, for phosphonates: hydroxy ethylidene diphosphonic acid (HEDP), amino tri-(methylenephosphonic acid) (ATMP), ethylene diamine tetra-(methylene phosphonic acid) (EDTMP), and diethylenetriamine penta-(methylenephosphonic acid) (DETPMP) to give ZrP-HEDP, ZrP-ATMP, ZrP-EDTMP and ZrP-DETPMP, respectively. These materials exhibit a similar crystalline phase to α-ZrP, but have a completely different morphology. After loading of these organophosphonate groups, the original sheet-morphology disappears, and the materials were consistent with smaller particles. However, the loading of organophosphonate groups expands the inter-layer distances. Remarkably, these materials have a stronger ability to remove Sr2+, with higher adsorption capacity than α-ZrP, especially ZrP-ATMP due to its wider layer distance. The maximum adsorption capacities for Sr2+ are 158 mg g−1, 175 mg g−1, 115 mg g−1 and 76 mg g−1for ZrP-HEDP, ZrP-ATMP, ZrP-EDTMP and ZrP-DETPMP, respectively, while that ofα-ZrP is 55 mg g−1. The higher adsorption capacities of these zirconium phosphonate materials is attributed to their wider interlayer spacing, allowing more room for Sr2+ to move.