Safe Sr confinement in feldspar structures

Samples of synthetic Na-A zeolite, pre-exchanged in Sr form, were heat treated at various temperatures up to 1150◦C, in order to entrap the toxic cation in a non-exchanging ceramic matrix. It has been demonstrated that the Sr-loaded zeolite undergoes the following sequence of transformations: zeolite →amorphous phase (at 900◦C) → hexagonal strontium aluminosilicate (at 1000◦C)→ monoclinic strontium aluminosilicate (above 1100◦C). Strontium retention performances of the above Sr-based compounds were compared to each other, estimating cation leaching either by a back-exchange with NaCl solution or by a prolonged contact with distilled water at different pHs (availability test). Thermal treatments from 900◦C onwards were able to safely immobilize Sr2+. The immobilization level depended on the relevant phase formed and resulted the highest (only 0.14% of theinitial Sr concentration), when monoclinic Sr-aluminosilicate structure (Sr-feldspar) was obtained