The effects of Calcigel bentonite naturally occurring microorganisms on corrosion of cast iron

In light of Germany's exploration of clay formations as potential hosts for deep geological repositories (DGR), and the most likely use of bentonite as a buffer material, copper or carbon steel/cast iron would be the most appropriate container material [1]. The surface of the metal containers is a subject to anaerobic corrosion and microbially influenced corrosion in a DGR. The interactions at the metal/bentonite interface can determine the performance of such a multi barrier system [2].
This study investigates the microbial processes that can occur at the interface between metal container and bentonite, and evaluates the effects of the microbial communities naturally occurring in bentonite may have on the corrosion of the nuclear waste
container.
Microcosm experiments as described in [3] were performed with Calcigel bentonite. The microcosms, containing GGG40 cast iron coupons, artificial Opalinus Clay porewater and bentonite, were incubated in N2-atmosphere at 37 °C. Some of the microcosms were supplemented with sodium lactate to stimulate microbial activity. After the incubation period the content of the microcosms was investigated by various geochemical analysis, DNA isolation and amplification for microbial community analysis, SEM-EDX and RAMAN spectroscopy to characterize the surface structure of the cast iron coupons. Geochemical investigation of the samples showed a slight
lactate consumption. Surface analysis of the coupons with SEM confirmed a corrosion ofr the coupons incubated with Calcigel bentonite, as well as crystalline structures covering the coupons to some extent. The cast iron coupons incubated with bentonite including naturally occurring microorganisms showed a faster corrosion than control samples with sterilized bentonite. To get a better overview about the ongoing microbial processes, microbial diversity analysis and incubations for a longer time-frame are currently still under investigation.

References
1. Nieder-Westerman, G.H., et al. 2013, Radioactive Waste Management and Contaminated Site Clean-Up, 462-488.
2. Kaufhold, S., et al. 2020, ACS Earth Space Chem. 4, 5, 711–721.
3. Matschiavelli, N. et al., 2019, Environ. Sci. Technol., 53, 17, 10514–10524