*Article* **Investigation of Biogenic Passivating Layers on Corroded Iron**

#### **Lucrezia Comensoli 1,2,**†**, Monica Albini 1,2,**‡**,§, Wafa Kooli 1,2,§, Julien Maillard 3, Tiziana Lombardo 4, Pilar Junier 1 and Edith Joseph 2,5,\***


Received: 12 February 2020; Accepted: 3 March 2020; Published: 6 March 2020

**Abstract:** This study evaluates mechanisms of biogenic mineral formation induced by bacterial iron reduction for the stabilization of corroded iron. As an example, the *Desulfitobacterium hafniense* strain TCE1 was employed to treat corroded coupons presenting urban natural atmospheric corrosion, and spectroscopic investigations were performed on the samples' cross-sections to evaluate the corrosion stratigraphy. The treated samples presented a protective continuous layer of iron phosphates (vivianite Fe2<sup>+</sup>3(PO4)2·8H2O and barbosalite Fe2<sup>+</sup>Fe3<sup>+</sup>2(PO4)2(OH)2), which covered 92% of the surface and was associated with a decrease in the thickness of the original corrosion layer. The results allow us to better understand the conversion of reactive corrosion products into stable biogenic minerals, as well as to identify important criteria for the design of a green alternative treatment for the stabilization of corroded iron.

**Keywords:** iron corrosion; SEM; Raman spectroscopy; biogenic minerals; bacterial iron reduction; cultural heritage; conservation-restoration; corrosion stabilization
