Chemical conditions in the AO Parcel of the long-term test of buffer material in Äspö (LOT)

The Long-Term Test of Buffer Material (LOT) is underway in the Äspö Hard Rock Laboratory in Sweden. The test parcels contain prefabricated bentonite blocks placed around a copper tube. The parcels are placed in vertical boreholes in a granitic rock structure. A heater is placed in the lower part of the copper tube. This report concerns the chemical studies performed on the parcel, which was excavated after about one and a half years of the experiment. porewaters were squeezed out from the bentonite samples and their pH, Eh and S(-II), Fe2+, Na+, K+, Ca2+, Mg2+, Cl-, SO42- and HCO3- concentrations were determined. The exchangeable cations and the water contents of the bentonite were also determined.The water contents were somewhat higher at the upper, cool part of the parcel and close to the rock surface. The additives, (cement, K-feldspar, CaSO4, CaCO3) did not have any clear effect on the water content.In the upper part of the parcel close to the rock surface, the TDS in the porewater was slightly below the TDS of the groundwater, but increased over that closer to the copper tube. In the lower, dryer parts, the TDS in the porewater was higher than the TDS of the groundwater at all distances from the copper tube. The general behaviour of the individual components mostly followed that of the TDS. The additives caused an increase in the TDS in some samples.The pH values varied from 6.8 to 9.2. In the blocks without additives they varied from 7.6 to 8.5, with the high values being found close to the copper tube. The effects of the additives could be clearly seen in some samples. The added cement changed the pH of the porewater, but the effects were different in the cool and hot areas. In the cool area, the pH was higher without additives, while in the hot area the pH was lower. The added CaSO4 clearly decreased the pH. The effects of the added K-feldspar were small. A low concentration of potassium could be found in the porewater, however. No special effects caused by the CaCO3 additive were seen.The concentration of the exchangeable calcium had increased in all the bentonite samples compared to the initial MX-80. This was in line with the low calcium concentrations in the porewater. The effects of the additives on the exchangeable cations were mostly within normal scattering