The crystal structure of mineral fibres. 2. Amosite and fibrous anthophyllite

This study reports for the first time crystal-structure data for amosite and fibrous anthophyllite. The chemical composition of the two fibre species was determined from EMPA. Crystal structures were refined using powder-diffraction data, using both laboratory sources and synchrotron radiation. Results were compared with the available literature data for the non-fibrous varieties grunerite and anthophyllite, respectively. The calculated site-occupancies for all samples are in agreement with the chemical compositions calculated from EMPA. The existing structure models of grunerite and orthorhombic anthophyllite also applies to the corresponding fibrous varieties amosite and fibrous anthophyllite, respectively. In amosite, both Fe2+ and Fe3+ atoms are found at the sites M(1), M(2) and M(3) and Fe2+ ions is the only atomic species found at site M(4). Mg is disordered over the C sites with a preference for site M(2). Minor Ca and Na have been assigned to the A site. In fibrous anthophyllite, Mg is the only atomic species found at the M1, M2 and M3 sites. Fe2+, Mg (and minor Mn) have been assigned to the M4 site, whereas minor Ca has been assigned to the A site. In both structures, the environment at the M(4) site in amosite and M4 site in fibrous anthophyllite is highly distorted. This work can be considered a basis for studies aimed at understanding the potential toxicity/ pathogenicity of these mineral fibres

THE CRYSTAL STRUCTURES OF MINERAL FIBRES

Since 2011, a research project on mineral fibres entitled “Sviluppo di un modello generale di interazioni tra fibre minerali e cellule biologiche”, has been conducted as part of the long term Italian Research Project of National Interest (PRIN) “Interazione fra minerali e biosfera: conseguenze per l'ambiente e la salute umana”. The research project is specifically focussed on mineral fibres and is aimed at understanding the biochemical reactions that make them cytoand geno-toxic and at the development of a general model capable to classify each mineral fibre based on its toxicity potential. The attempt to understand the complex biochemical mechanisms between the mineral fibres and the organic matter requires a basic systematic mineralogical-crystallographic study. Hence, eight mineral fibres samples have been selected for the study based on their socio-economic and industrial importance: three chrysotile of different origin (UICC, Canada; Balangero and Val Malenco, Italy), four amphibole asbestos species (amosite UICC, anthophyllite UICC, crocidolite UICC and tremolite from Val d'Ala) and the fibrous zeolite erionite (from Jersey, Nevada, USA). The surface reactivity and the chemical environment of iron within the crystal structure of these samples have been recently investigated (Pollastri et al. 2014; 2015). In order to complete the crystal structural characterization, X-ray powder and single crystal diffraction experiments have been conducted using both conventional and synchrotron radiation sources (Elettra, Trieste, Italy; SLS, Villigen, Switzerland), for the determination of impurities and the refinement of the crystalline structures. Concerning the chrysotile samples, because of the low to null effect of conventional grinding techniques on chrysotile fibre bundles, we have opted for a cryo-milling process in wet conditions; this procedure allowed to obtain perfectly powder samples. For chrysotile and erionite samples, diffraction patterns were collected with either resonant radiation at the absorption K-edge of Fe (≈7 keV, λ 1.7428 Å) and with wavelength off of the absorption edge (≈10 keV, λ 1.2408 Å) in order to investigate the crystal chemistry of iron within the fibres. The collected data were analysed both with the TOPAS and GSAS. The results of the structural refinements, in particular occupancy and position of the iron atoms within the crystal structures (a primary cause of toxicity as it generate active oxygen species, mobilization by chelators and iron-catalyzed reactions; Hardy and Aust, 1995), were compared to that obtained from the previously performed spectroscopic investigations. The obtained structures of chrysotile samples are similar to each other and quite similar to the only available structure of chrysotile present in literature (Falini et al., 2004). Also the structures of other samples were compared to the few data reported in literature to highlight differences between the fibrous and non fibrous forms of the mineral

Determination of the concentration of asbestos minerals in highly contaminated mine tailings: An example from abandoned mine waste of Crètaz and Èmarese (Valle d’Aosta, Italy)

For the first time, this work reports concentration maps of asbestos minerals in contaminated mine tailings drawn using the results of Rietveld quantitative phase analysis (QPA). The investigated sites are located in the Valle d’Aosta region (Italy): Crètaz, the most important Italian magnetite mine, active until 1979 and Emarèse, one the most important chrysotile asbestos mines in Italy, active until 1968. The results of the study permit to draw the spatial distribution of the asbestos (chrysotile and tremolite in this specific case) concentration, useful to plan reclamation of the sites, with priority given to the areas with the highest asbestos concentration. Because of the complexity of the mineral assemblage, which includes, among the others, antigorite, chlorite, talc, and tremolite, the concentration of chrysotile was cross-checked using different experimental techniques such as X-ray powder diffraction (XRPD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), polarized light optical microscopy (PCOM), and differential thermal analysis (DTA). The accuracy of the results was validated by analyzing standard samples with known concentrations of chrysotile and tremolite. The comparison allowed to point out the advantages and disadvantages of each experimental method. At Crètaz, chrysotile ranges from 4.4 to 22.8 wt% and tremolite from 1.0 to 10.3 wt%, whereas at Emarèse the concentration of chrysotile varies from 3.3 to 39.5 wt% and tremolite from 5.9 to 12.4 wt%. Antigorite and chlorite are the major accompanying phases with variable amounts of other accessory minerals including magnetite, carbonates, talc, olivine, pyroxene, talc, and brucite. The results of our study are of key importance for the local environmental policies as the knowledge of the spatial distribution of the asbestos concentration allows to plan a detailed reclamation agenda of the contaminated sites. The spots with the highest surface contamination of both chrysotile and tremolite were identified and classified as priority areas in the reclamation plan