Synthesis of Fe-doped chrysotile and characterization of the resulting chrysotile fibers

Cation Doping Approach for Nanotubular Hydrosilicates Curvature Control and Related Applications

The past two decades have been marked by an increased interest in the synthesis and the properties of geoinspired hydrosilicate nanoscrolls and nanotubes. The present review considers three main representatives of this group: halloysite, imogolite and chrysotile. These hydrosilicates have the ability of spontaneous curling (scrolling) due to a number of crystal structure features, including the size and chemical composition differences between the sheets, (or the void in the gibbsite sheet and SiO2 tetrahedron, in the case of imogolite). Mineral nanoscrolls and nanotubes consist of the most abundant elements, like magnesium, aluminium and silicon, accompanied by uncontrollable amounts of impurities (other elements and phases), which hinder their high technology applications. The development of a synthetic approach makes it possible to not only to overcome the purity issues, but also to enhance the chemical composition of the nanotubular particles by controllable cation doping. The first part of the review covers some principles of the cation doping approach and proposes joint criteria for the semiquantitative prediction of morphological changes that occur. The second part focuses on some doping-related properties and applications, such as morphological control, uptake and release, magnetic and mechanical properties, and catalysis.

X-ray synchrotron microtomography: a new technique for characterizing chrysotile asbestos

Over the last decades, many studies have been conducted on rocks containing Naturally Occurring Asbestos (NOA) to determine the potential health risks to exposed neighboring populations. It is difficult to accurately characterize the asbestos fibres contained within the rocks as conventional techniques are not effective and have drawbacks associated with the disturbance of the sample under study. X-ray synchrotron microtomography (SR-μCT) supplemented with polarized light microscope (PLM), scanning electron microscopy analysis combined with energy dispersive spectrometry (SEM/EDS), electron probe micro-analysis (EPMA) were used for identifying asbestos fibres in a mineral matrix. As a case study, we analyzed a representative set of veins and fibrous chrysotile that fills the veins, taken from massive serpentinite outcrops (Southern-Italy). We were able to identify respirable chrysotile fibres (regulated asbestos) within the serpentinite matrix. SR-μCT of NOA veins achieved the resolution and reconstructed 3D structures of infill chrysotile asbestos fibres and other phase structures that were not resolvable with PLM, SEM or EPMA. Moreover, due to differences in chemical composition between veins and matrix, the data obtained enabled us to evaluate the vein shapes present in the massive serpentinite matrix. In particular, iron and aluminum distribution variations between veins and matrix induce different radiation absorption patterns thus permitting a detailed image-based 3D geometric reconstruction. The advantages of the SR-μCT technique as well as limitation of conventional methods are also discussed. These analytical approaches will be used for conducting future research on NOA of other minerals, which exhibit asbestiform and non-asbestiform habits within veins, including asbestos amphiboles.

Mineralogical Asbestos Assessment in the Southern Apennines (Italy): A Review

This paper deals with petrography and mineralogy of serpentinitic rocks occurring in the Southern Apennines (Italy) with the aim to review the already available literature data and furnish new details on asbestos minerals present in the studied area. Two sites of Southern Italy were taken into account: the Pollino Massif, at the Calabrian-Lucanian border, and the surroundings of the Gimigliano and Mt. Reventino areas where serpentinites of Frido Unit are mainly exposed. Textural and mineralogical features of the studied rocks point to a similar composition for both sites including asbestos minerals such as chrysotile and tremolite-actinolite series mineral phases. Only in the Pollino Massif serpentinites edenite crystals have been detected as well; they are documented here for the first time. This amphibole forms as fibrous and/or prismatic crystals in aggregates associated with serpentine, pyroxene, and calcite. Metamorphism and/or metasomatic alteration of serpentinites are the most probable processes promoting the edenite formation in the Southern Apennine ophiolitic rocks.

Cation Redistribution along the Spiral of Ni-Doped Phyllosilicate Nanoscrolls: Energy Modelling and STEM/EDS Study

Here, we study the stress-induced self-organization of Mg²⁺ and Ni²⁺ cations in the crystal structure of multiwalled (Mg_1-x ,Ni_x )₃ Si₂ O₅ (OH)₄ phyllosilicate nanoscrolls. The phyllosilicate layer strives to compensate size and surface energy difference between the metal oxide and silica sheets by curling. But as soon as the layer grows, the scrolling mechanism becomes a spent force. An energy model proposes secondary compensation of strain: two cations distribute along the nanoscroll spiral in accordance with preferable radii of curvature. To reveal this, we study synthetic (Mg_1-x ,Ni_x )₃ Si₂ O₅ (OH)₄ nanoscrolls by the scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy (STEM/EDS) technique. For a number of scrolls, we have found indeed a change of Ni concentration with increase in distance from the nanoscroll central axis. The concentration gradient, according to our estimates, can reach 50 at.% over 25 nm of the wall thickness.

Multi-Analytical Approach for Identifying Asbestos Minerals In Situ

An innovative and, as yet, untested approach is to analyze serpentinite and metabasite rocks containing asbestos using a portable multi-analytical device, which combines portable digital microscopy (p-DM), portable X-ray Fluorescence (p-XRF) and portable micro-Raman Spectroscopy (p-µR). The analyses were carried out in two inactive quarries of serpentinitic and metabasitic rocks from the Gimigliano-Mount Reventino Unit (Southern Italy) already characterized in previous studies, with the aim of testing the efficiency of these portable tools. In this study, a portable X-ray fluorescence analyzer was used to obtain the in situ rapid chemical discrimination of serpentinite and metabasite rocks. The characterization of outcropping rocks using portable devices enabled us to detect the presence of chrysotile and asbestos tremolite. The results obtained were consistent with the findings from previous research studies and therefore combining p-DM, p-XRF and p-µR could be a useful approach for discriminating asbestos contained in outcropping rocks, especially when sampling is prohibited or for field-based sampling.

Trace elements in hazardous mineral fibres

Both occupational and environmental exposure to asbestos-mineral fibres can be associated with lung diseases. The pathogenic effects are related to the dimension, biopersistence and chemical composition of the fibres. In addition to the major mineral elements, mineral fibres contain trace elements and their content may play a role in fibre toxicity. To shed light on the role of trace elements in asbestos carcinogenesis, knowledge on their concentration in asbestos-mineral fibres is mandatory. It is possible that trace elements play a synergetic factor in the pathogenesis of diseases caused by the inhalation of mineral fibres. In this paper, the concentration levels of trace elements from three chrysotile samples, four amphibole asbestos samples (UICC amosite, UICC anthophyllite, UICC crocidolite and tremolite) and fibrous erionite from Jersey, Nevada (USA) were determined using inductively coupled plasma mass spectrometry (ICP-MS). For all samples, the following trace elements were measured: Li, Be, Sc, V, Cr, Mn, Co, Ni, Cu, Zn, As, Rb, Sr, Y, Sb, Cs, Ba, La, Pb, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, U. Their distribution in the various mineral species is thoroughly discussed. The obtained results indicate that the amount of trace metals such as Mn, Cr, Co, Ni, Cu and Zn is higher in anthophyllite and chrysotile samples, whereas the amount of rare earth elements (REE) is higher in erionite and tremolite samples. The results of this work can be useful to the pathologists and biochemists who use asbestos minerals and fibrous erionite in-vitro studies as positive cyto- and geno-toxic standard references.