The ion exchange phase in corrosion of nuclear waste glasses

Alteration Development of the Simulated HLW Glass at High Temperature in Beishan Underground Water

“…When the glass is contacted with water, water molecules will diffuse through glass-water interface into the glass matrix [9], followed by ion exchange [10] as shown by reaction (1). The hydrogen ion will replace the alkaline metal ions such as sodium and lithium immobilized in glass and alkaline ions will be leached out of the glass.…”

Glassy Wasteforms for Nuclear Waste Immobilization

“…In dilute near-neutral solutions, ion exchange controls the initial cation release, and at low temperature and pH, it can dominate over hydrolysis for many hundreds of years. [58] Ion exchange involves the interdiffusion and exchange of the cation in the glass with a proton (probably as H 3 O + ) from the water. The ion exchange reaction of glass with water can be written as…”

“…The activation energy for interdiffusion is the sum of the enthalpy of motion of protons or H 3 O + cations, H mH , and the enthalpy of formation of NBO, H NBO : E dA = H mH + H NBO . The average normalized leaching rate caused by the ion exchange processes of cation A, NRx A (g/cm 2 day), is measured experimentally or it can be found theoretically by calculating the total normalized cation release via ion exchange and dividing it by the leach test duration t (days) resulting in [58] …”

“…Table VII gives D A for several silicate glasses tested in near-neutral waters. [58] The second mechanism of silicate glass corrosion-hydrolysis-is represented schematically by the reaction SiÀOÀSi þH 2 O $ 2ð SiOHÞ ½13…”

“…This occurs because the activation energy for hydrolysis E a is significantly higher than the activation energies of diffusive processes E dA . It has been shown that the diffusion-controlled ion exchange stage is dominant up to a time, s(T), given by [58,61] …”