Investigating Bisulfide Sorption onto Bentonite through Laboratory Experiments and Numerical Modelling
Bibliographic record
Abstract
The long-term performance evaluation of the Canadian deep geologic repository (DGR) relies significantly on bentonite clay, a crucial material in the engineered barrier system. One safety concern is microbiologically influenced corrosion of the used fuel containers (UFCs) which may occur if bisulfide (HS-) transports through the bentonite buffer to the UFC surface. HS- sorption onto bentonite can reduce the corrosion risk, but its dynamics are not yet well-understood, especially in DGR environments. Hence, this study offers a comprehensive insight into HS- sorption process onto bentonite through extensive laboratory experiments and numerical modelling. First, a robust methodology was developed to build confidence in the experimental procedure. Subsequently, six sets of batch experiments (including desorption tests) were performed as a function of temperature (10-40°C), contact time (1-120 hours), liquid to solid mass ratios (L:S) (100-1000), initial HS- concentration (1-6 mg L-1), pH (9-11), and ionic strength (0.01 M-1 M NaCl). The experimental results indicated that HS- sorption onto bentonite occurred faster, and the equilibrium sorption capacity increased (by 3%) with increasing temperature. However, sorption decreased with increasing pH and ionic strength. Several established kinetic and isotherm models were applied to the experimental data to provide insight into HS- sorption dynamics onto bentonite. In addition, desorption test results indicated that HS- was irreversibly sorbed on bentonite. Surface analyses conducted using scanning electron microscopy along with energy dispersive spectroscopy, suggested that sorption might have occurred due to chemical reactions of HS- with the iron (Fe) present in bentonite. Lastly, a thermodynamic-based sorption model was developed in PHREEQC assuming that sorption was driven by three key processes: (i) redox reaction with the structural Fe3+ sites, (ii) surface precipitation as iron sulfide, FeS (likely mackinawite), and (iii) surface complexation reactions with surface hydroxyl group (OH) at the edge sites of montmorillonite. The model successfully described the experimental trends and provided valuable insights into the relative contribution of each process to the total sorption mechanism. Altogether, this study provides novel insights from experimental and numerical modelling that enhance the understanding of HS- sorption onto bentonite, which supports the Canadian DGR design and other nuclear repositories worldwide.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".