Study on Structure and Properties of La₂O₃-Doped Basaltic Glasses for Immobilizing Simulated Lanthanides

The La₂O₃-doped basaltic glass simulated high-level waste form (HLW) was prepared by the solid-state melt method. The simulated waste La₂O₃ maximum loading and the doping effect on structure, thermal stability, leaching behavior, density, and hardness of basaltic glasses were studied. XRD and SEM results show that the simulated waste loading of La₂O₃ in basaltic glass can be up to ~46 wt.%, and apatite (CaLa₄(SiO₄)₃O) precipitates when the content of La₂O₃ reaches 56 wt.%. Raman results indicate that the addition of La₂O₃ breaks the Si-O-Si bond of large-membered and four-membered, but the number of A1³⁺ involved in the formation of the network increase. Low content of La₂O₃ can help to repair the glass network, but it destroys the network as above 26 wt.%. DSC results show the thermal stability of simulated waste forms first increases and then decreases with the increase of La₂O₃ content. With the increase of La₂O₃ content, the density of the simulated waste form increases, and the hardness decreases. The leaching chemical stability of samples was evaluated by the ASTM Product Consistency Test (PCT) Method, which show that all the samples have good chemical stability. The leaching rates of La and Fe are three orders of magnitude lower than those of the other elements. Among them, L36 has the best comprehensive leaching performance.