Investigating Bisulfide Sorption onto Bentonite through Laboratory Experiments and Numerical Modelling

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.

Author dc:creator

• Papry, Sifat Azad

Advisor dc:contributor.advisor

• Krol, Magdalena

• Civil engineering
• Environmental engineering
• Geochemistry

Statement dc:rights

• Author owns copyright, except where explicitly noted. Please contact the author directly with licensing requests.

Language dc:language

en

Handle dc:identifier.uri

https://hdl.handle.net/10315/42414

OAI identifier oai:identifier

oai:yorkspace.library.yorku.ca:10315/42414