Characterization of ferruginous cements related with weathering of slag in a temperate anthropogenic beachrock

Nikole Arrieta; Ane Iturregui; Irantzu Martínez-Arkarazo; Xabier Murelaga; Juan Ignacio Baceta; Alberto de Diego; María Ángeles Olazabal; Juan Manuel Madariaga

doi:10.1016/j.scitotenv.2016.12.132

Characterization of ferruginous cements related with weathering of slag in a temperate anthropogenic beachrock

Sci Total Environ. 2017 Mar 1:581-582:49-65. doi: 10.1016/j.scitotenv.2016.12.132. Epub 2017 Jan 11.

Authors

Nikole Arrieta¹, Ane Iturregui², Irantzu Martínez-Arkarazo², Xabier Murelaga³, Juan Ignacio Baceta³, Alberto de Diego², María Ángeles Olazabal², Juan Manuel Madariaga²

Affiliations

¹ Department of Analytical Chemistry, Faculty of Science and Technology, University of the Basque Country UPV/EHU, P.O. Box 644, 48080 Bilbao, Basque Country, Spain. Electronic address: nikole.arrieta@ehu.eus.
² Department of Analytical Chemistry, Faculty of Science and Technology, University of the Basque Country UPV/EHU, P.O. Box 644, 48080 Bilbao, Basque Country, Spain.
³ Department of Stratigraphy and Palaeontology, Faculty of Science and Technology, University of the Basque Country UPV/EHU, P.O. Box 644, E-48080 Bilbao, Spain.

PMID: 28086132
DOI: 10.1016/j.scitotenv.2016.12.132

Abstract

This work outlines a temperate latitude beachrock occurrence, which represents the legacy of heavy anthropogenic environmental disturbance. The units contain high amounts of slag and iron-rich wastes derived from metallurgical activities that attest the impact of the past industrial development on such coastal systems. The exposition of the anthropogenic wastes to weathering processes, such as the influence of marine aerosols and the chemical attack of acid gases like the SOx coming from the nearby urban-industrial atmosphere, gave rise to the formation of early diagenetic ferruginous cements. A new analytical methodology based on the combination of micro-Raman spectroscopy (MRS), Raman chemical imaging, SEM-EDS and the Structural and Chemical Analyzer (SCA, an emerging system that hyphenates micro-Raman and SEM-EDS), was applied for the first time to characterize the ferruginous cements. The MRS analyses revealed Fe²⁺/Fe³⁺ oxides and oxyhydroxides, CaCO₃ polymorphs and less frequently silicates. The Fe mineral species detected were hydrated goethite, hematite, magnetite, magnesioferrite, lepidocrocite and goethite. Complementary Raman imaging, SEM-EDS and SCA analyses unraveled the preferential distribution of hydrated goethite. The identified iron mineral phases are weathering sub-products of hematite commonly derived from atmospheric/aqueous leaching processes triggered by the chemical attack of the acid gases. EDS showed the existence of other elements such as Si, Mg, Cl, Na, Al, K and sporadically S that indicated the importance of permeability, atmospheric deposition and the acid attack. Additionally, calcite and gypsum minerals also evidenced the action of meteoric waters, dry deposition processes or the attack of SOx acid gases. The presence of such compounds is modifying the cement stratigraphy and suggests that the dissolution of carbonates is currently taking place. Those facts influence the erosive susceptibility and the release of the anthropogenic materials trapped originally in the beachrocks, which could act as potential secondary sources of contaminants to the coastal environment.

Keywords: Anthropocene; Beachrock; Raman SCA; Raman spectroscopy; Raman-imaging; Slag weathering.