We exploit the unique properties of certain microorganisms for the stabilization of archaeological iron. To this end, two different approaches are taken, either with the formation of stable compounds with low molar volume or with the study of the chlorides translocation of halophilic fungi in natural environments (salt lakes).

Based on biomineralization processes involved, bacteria and fungi are exploited to precipitates magnetite (Fe₃O₄), vivianite (Fe₃(PO₄)₂∙8H₂O) or others stables iron compounds of low molar volume. In order to improve the removal of chlorides, we also study translocation processes.  

Tests on powders, analogues and real objects are considered in the study to validate the treatment.

Molecular Raman imaging on iron coupons treated with Desulfitobacterium hafniense TCE1: (a) secondary electrons image with a square box indicating the analyzed area by Raman, chemical maps (b) of vivianite (Vi, blue) and (c) of barbosalite (Ba, pink), and (d) Raman spectra of vivianite and barbosalite with the corresponding spectral regions selected for the elaboration of the chemical maps of vivianite (indicated with blue dash lines) and barbosalite (indicated with magenta dashed lines). From Comensoli (2020). https://doi.org/10.3390/ma13051176.

In order to enhance the removal of chloride ions from the iron object, the possible translocation of those by fungi will be studied. In chlorine-rich environments, some species of fungi develop strategies for detoxify their surrounding from the toxic chlorine. These halophiles will be isolated and cultured from natural places such as salt lakes. In addition, white-rot fungi are also studied in bioremediation for allowing chlorine migration.

Based on the results achieved, we could contribute to the development of a synergetic microbial consortium specially designed for the removal of chloride ions and the simultaneously formation of stable iron compounds. Particular attention will be devoted to the efficiency and the impact on metallographic structure of the proposed treatment to overcome the problems associated with the treatments in use nowadays. Real samples will be also included in this study in order to validate the new methodology. This research issue presents innovative aspects in biogeochemistry of micro-organisms and conservation science.

Others institutes involved in the project :

• Laboratory of microbiology (LAMUN)
• Haute Ecole Arc Conservation Restauration, HES-SO
• Laboratory of environmental biotechnology, EPFL
• Swiss National Museum