Adsorption of Ions on Zirconium Oxide Surfaces from Aqueous Solutions at High Temperatures

Surface titrations were carried out on suspensions of monoclinic ZrO 2 from 25 to 290 °C slightly above saturation vapor pressure at ionic strengths of 0.03, 0.1 and 1.0 mol⋅kg −1 (NaCl). A typical increase in surface charge was observed with increasing temperature. There was no correlation between the radius of the cations, Li + , Na + , K + and (CH 3 ) 4 N + , and the magnitude of their association with the surface. The combined results were treated with a 1-pK a MUSIC model, which yielded association constants for the cations (and chloride ion at low pH) at each temperature. The pH of zero-point-charge, pH zpc , decreased with increasing temperature as found for other metal oxides, reaching an apparent minimum value of 4.1 by 250 °C. Batch experiments were performed to monitor the concentration of LiOH in solutions containing suspended ZrO 2 particles from 200 to 360 °C. At 350 and 360 °C, Li + and OH − ions were almost totally adsorbed when the pressure was lowered to near saturation vapor pressure. This reversible trend has implications not only to pressure-water reactor, PWR, operations, but is also of general scientific and other applied interest. Additional experiments probed the feasibility that boric acid/borate ions adsorb reversibly onto ZrO 2 surfaces at near-neutral pH conditions as indicated in earlier publications.