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

Surface titrations were carried out on suspensions of monoclinic ZrO2 from 25 to 290 A degrees C slightly above saturation vapor pressure at ionic strengths of 0.03, 0.1 and 1.0 mola <...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 (CH3)(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 A degrees C. Batch experiments were performed to monitor the concentration of LiOH in solutions containing suspended ZrO2 particles from 200 to 360 A degrees C. At 350 and 360 A degrees 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 ZrO2 surfaces at near-neutral pH conditions as indicated in earlier publications.