Effects Of Dopped Metal Ions On The Leaching Behaviours Of Borosilicate Glass

Radiation damage from radionuclides and groundwater erosion are the main challenges to the stability of vitrification during geological disposal.Borosilicate glass is widely used as vitrification substrate due to its good waste inclusion capacity and proven preparation process.The composition of borosilicate glasses significantly affects their resistance to leaching and the leaching mechanism,and there is still a need for research on the leaching behaviour of specific compositions of borosilicate glasses.In this paper,the effect of metal ion doping on their anti-leaching properties and leaching mechanisms was investigated based on three borosilicate glasses.Among them,the simple glass NBS5 is a ternary borosilicate glass;the complex glass L0NBS was doped with aluminum and a variety of alkali and alkaline earth metals compared to the simple glass;and the simulated waste glass L4NBS was doped with metal ions such as La and V compared to the complex glass.Lanthanum doping can also simulate trivalent actinide vitrification.The leaching experiments were carried out using the MCC-1 static leaching method with deionized water as the leaching solvent at a constant temperature of 90℃.The morphological evolution,leaching behaviours and microstructural changes of the glasses were analyzed by scanning electron microscopy and inductively coupled plasma emission spectroscopy.The following conclusions were drawn from the above work:1.A complete leaching process,including interdiffusion,hydrolysis,rate drop,residual rate,and recovery stage,was reflected in the leaching of simple glass NBS5.An initial leaching rate of 4.98±0.44 g/（m²·d）was obtained based on boron element.After long-term leaching,there was no crystallization and the glass surface tended to a quartz structure.2.Complex glass L0NBS only developed to the residual rate stage during the 90-day period,and the initial leaching rate based on boron element was 0.7 times that of NBS5.Al³⁺ions enhanced the resistance to leaching by forming Si-O-Al bonds,and alkaline earth metal ions probably influenced the glass structure through ionic field strength.The leaching behaviors of Mg and Al was significantly different from that of other metal ions.After leaching,Al³⁺was enriched on the surface as the form of[AlO₄]^-.Mg²⁺ions were on the one hand deposited into the alteration layer,playing a charge-compensating role,and on the other hand participated in the formation of Hectorite minerals.The production of Hectorite minerals and the enrichment of Mg and Al strengthened the hindering effect of the altered structure on leaching.3.La³⁺and VO₄^3-were highly coupled with CO₃^2-in the leaching environment,resulting in the precipitation of LaVO₄ and LaCO₃OH crystals.The formation of a dense crystal layer further slowed the initial leaching rate of the glass,which was only 0.6 times that of NBS5 based on boron element.However,this made La,which was more evenly dispersed in the glass network,accumulate on the surface,thus increasing the risk of leakage.After long-term leaching,some Si,B and Na were likely to remain in the lanthanum-containing altered layer.At the same time,the accumulation of Mg and Al in L0NBS was also observed.The results showed that coupling between the vitrification composition,and between vitrification composition and environmental factors is another non-negligible mechanism in addition to ion exchange and network hydrolysis at the initial leaching stage.Additionally,the carbon environment of the disposal site should be taken into account.