Leaching tests with HIPed ashes

SCK CEN is investigating the chemical durability of HIPed ashes by performing leaching tests. The ashes, which are surrogates of solid organic wastes and ionic exchange resins, were provided by CEA. Their elemental composition was determined by ICP. The University of Sheffield prepared HIPed samples by first mixing 95 wt.% ashes with 5 wt. % Na2B4O7 in stainless steel cans. Then, the welded cans were heated to 300 °C for 12 hours under vacuum, and sealed. Afterwards, they were HIPed at 250 °C and 100 MPa for 2 hours. Two cans were sent to SCK CEN to carry out short- and long-term semi-dynamic leaching tests, following the reference protocol described in the Milestone 39. Before starting the tests, the unaltered HIPed samples were characterised by SEM-EDX and XRD, confirming that after HIPing a glass-ceramic material was produced. The HIPed samples are altered at 22 °C under anaerobic conditions with an alkaline solution at pH 12.7, which contains 2800 mg/L of K, 18 mg/L of Ca, and 1080 mg/L of SO42-. pH and elemental concentrations were measured in the leachates collected over 2 months. Preliminary results showed that pH was constant at the reference pH value of 12.7 and K, Ca and SO42- concentrations were similar to those measured in the initial leaching solution. Cl- concentrations were below the detection limit. Similar silicon concentrations were determined by ICP/MS and UV/Visible spectrophotometry, suggesting that there were no polymeric silicon species in the leachates. Many elements initially present in the ashes were not detected or were not measurable by ICP/MS. The treatment of the data available for a few elements is ongoing.