By employing boron isotope fingerprinting techniques, the team was able to track the release of boron from two distinct glass compositions, focusing on the role of diffusion through the altered surface layer. Their findings reveal how glass composition influences the formation of a protective altered layer and how this layer controls the long-term release of contaminants.
Glass is widely used to immobilize hazardous constituents—from radionuclides in vitrified nuclear waste to metals in industrial residues—yet it is metastable. In groundwater, it hydrolyzes, reorganizes, and precipitates more stable phases. Competing mechanistic pictures exist: “classical” interdiffusion (water moves in, mobile species move out, and a denuded hydrated layer forms) and interface-coupled dissolution–precipitation (congruent hydrolysis followed by silica-rich layer growth and transport slowdown). Boron is an especially sensitive tracer because its two stable isotopes (^10B and ^11B) fractionate during sorption, coprecipitation, and diffusion, providing a window into which mechanism dominates at a given time.
A study (DOI: 10.48130/ebp-0025-0004) published in Environmental and Biogeochemical Processes on 30 September 2025 by Thomas L. Goût’s team, Peking University, provides valuable insights into the dissolution behavior of waste glasses and enhances the ability to predict contaminant release over geological timescales.
The study employed boron isotope tracing techniques to investigate the dissolution mechanisms of two waste glass compositions, 6Li-Mg-EM (magnesium-bearing) and 10B-ISG (magnesium-free), over time. The glass samples were leached in deionized water at 90 °C for periods ranging from 0.25 to 112 days, and solution renewal experiments were conducted after 28 days. The initial stages (up to 7 days) showed rapid congruent release of boron from both glass types, with 6Li-Mg-EM exhibiting higher boron release rates compared to 10B-ISG. The altered layers formed on the glass surfaces, calculated to be around 0.29 µm for 10B-ISG and 0.41 µm for 6Li-Mg-EM after 7 days, did not significantly affect dissolution rates at early times. However, after 28 days, the release of boron from 6Li-Mg-EM continued at a higher rate than from 10B-ISG, linked to magnesium-driven secondary mineral precipitation, which enhanced hydrolysis and sustained a higher dissolution rate. Boron isotope analysis revealed that the dissolution of boron remained congruent at short times, but at longer times (28–98 days), the release of boron became more complex. For 6Li-Mg-EM, the δ^11B values increased, suggesting additional processes such as sorption or coprecipitation with secondary minerals. In contrast, 10B-ISG did not show significant protective effects from the altered layer beyond 28 days, with solution δ^11B values indicating continued congruent release. Numerical diffusion models revealed that boron release in 10B-ISG could be described using a time-dependent diffusion model for the first 28 days, but later times required additional processes like sorption or a spatially dependent diffusion coefficient to explain the observed changes. This study highlights the role of secondary mineral precipitation in controlling long-term contaminant release and demonstrates the utility of boron isotopes in studying glass dissolution mechanisms.
For performance assessment of geological disposal facilities, the results provide a practical tracer toolkit and a mechanistic update. Boron isotopes in leachates can diagnose when release transitions from congruent hydrolysis to diffusion through a passivating altered layer—the regime that governs century-to-millennium behavior. Composition matters: Mg promotes secondary-phase formation, layer densification, and ultimately diffusion-limited release, lowering the risk of sudden contaminant pulses after early alteration. Conversely, Mg-free systems may lack robust passivation, requiring more conservative release models and engineered barriers.
###
References
DOI
10.48130/ebp-0025-0004
Original Source URL
https://doi.org/10.48130/ebp-0025-0004
Funding Information
Thomas L. Goût was supported by the National Natural Science Foundation of China (NSFC) Research Fund for International Young Scientists programme (RFIS-I, Grant No. W2433099). The authors acknowledge financial support from UKRI EPSRC under an Industrial CASE award with Nuclear Waste Services (Grant No. EP/M507350/1).
About Environmental and Biogeochemical Processes
Environmental and Biogeochemical Processes is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.