## 5 Conclusions  
Bentonite was slightly altered after 1 and 6 months, but the main alterations were observed after 22 months of reaction and well-defined mineralogical changes could be identified. The formation of secondary minerals coating the smectite were argued to explain the bentonite-specific surface area decreases at the steel interface. The enrichment in Fe in the bentonite was detected over the first 3 mm from the steel interface. However, the corrosion rate decreased to <5 \(\mu\)m/year with the reaction time up to 22 months. Minor changes were noticed along the bentonite column beyond the first 3 mm from the steel interface, maintaining its original properties. The iron-bentonite interactions allowed the formation of corrosion products, several iron oxides like magnetite, maghemite or hematite, and iron carbonates like siderite, ankerite and green rust (containing chloride) to be identified. The geochemical evolution of bentonite promoted the formation of a chlorite phase of ferri-sudotite-like composition through the montmorillonite modification. The use of X-ray diffraction, the photochemical method with 1,10-phenanthroline and scanning electron microscopy analyses allowed the identification of these minerals.  
The main mineralogical changes were found at the steel-bentonite interface, where the bentonite properties studied were modified by the precipitation of corrosion products, forming a low-porosity layer that could potentially clog bentonite pores and affect subsequent reactivity. Negligible smectite alteration was found in previous experiments of the Fe-bentonite interaction at low liquid/solid ratios, leading to uncertainties over the Fe-phyllosilicates that could form in such systems. However, the use of a bentonite containing Mg-smectite has favored the identification of bentonite mineral alteration, producing chlorite-type minerals that should be considered in future geochemical modeling of Fe-bentonite systems.  
**Supplementary Materials:** The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app14031259/s1](https://www.mdpi.com/article/10.3390/app14031259/s1)]([https://www.mdpi.com/article/10.3390/app14031259/s1](https://www.mdpi.com/article/10.3390/app14031259/s1)): Figure S1: XRD of sections from the steel interface: (a) 1 month; (b) 6 months; (c) 22 months.  
**Author Contributions:** Conceptualization, C.M.-H., R.F. and J.C.; methodology, C.M.-H., R.F. and J.C.; software, C.M.-H., R.F. and J.C.; validation, R.F. and J.C.; formal analysis, C.M.-H.; investigation, C.M.-H., R.F. and J.C.; resources, C.M.-H., R.F. and J.C.; data curation, C.M.-H., R.F. and J.C.; writing--original draft preparation, C.M.-H.; writing--review and editing, R.F., J.C. and C.M.-H.; visualization, C.M.-H., R.F. and J.C.; supervision, R.F. and J.C.; project administration, J.C.; funding acquisition, J.C. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research has been developed by the UAM AcMe research group to support the WP2 EURAD-ACED project results, which has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 847593.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.  
**Acknowledgments:** The authors acknowledge the contribution of two anonymous reviewers for their suggestions to improve the quality of the manuscript.  
**Conflicts of Interest:** The authors declare no conflicts of interest.