Serpentine

Methodologies for determining the sources, characteristics, distribution, and abundance of asbestiform and nonasbestiform amphibole and serpentine in ambient air and water.[Pubmed:25825806]

J Toxicol Environ Health B Crit Rev. 2015;18(1):1-42.

Anthropogenic and nonanthropogenic (erosion) processes contribute to the continuing presence of asbestos and nonasbestos elongated mineral particles (EMP) of amphibole and Serpentine in air and water of urban, rural, and remote environments. The anthropogenic processes include disturbance and deterioration of asbestos-containing materials, mining of amphibole- and Serpentine-bearing rock, and disturbance of soils containing amphibole and Serpentine. Atmospheric dispersal processes can transport EMP on a global scale. There are many methods of establishing the abundance of EMP in air and water. EMP include cleavage fragments, fibers, asbestos, and other asbestiform minerals, and the methods employed do not critically distinguish among them. The results of most of the protocols are expressed in the common unit of fibers per square centimeter; however, seven different definitions for the term "fiber" are employed and the results are not comparable. The phase-contrast optical method used for occupational monitoring cannot identify particles being measured, and none of the methods distinguish amphibole asbestos from other EMP of amphibole. Measured ambient concentrations of airborne EMP are low, and variance may be high, even for similar environments, yielding data of questionable value for risk assessment. Calculations based on the abundance of amphibole-bearing rock and estimates of asbestos in the conterminous United States suggest that amphibole may be found in 6-10% of the land area; nonanthropogenic erosional processes might produce on the order of 400,000 tons or more of amphibole per year, and approximately 50 g asbestos/km(2)/yr; and the order of magnitude of the likelihood of encountering rock bearing any type of asbestos is approximately 0.0001.

Analysis of serpentine polymorphs in investigations of natural occurrences of asbestos.[Pubmed:25942071]

Environ Sci Process Impacts. 2015 May;17(5):985-96.

This work investigates potential analytical variability in environmental investigations of natural occurrences of asbestos (NOA) due to intergrown Serpentine minerals. Franciscan complex and serpentinite rock samples were obtained from likely NOA sites in coastal Northern California with geographic information system (GIS) maps, then analyzed using polarized light microscopy (PLM), transmission electron microscopy with energy-dispersive X-ray analysis and selected area electron diffraction (TEM/SAED/EDS), and environmental scanning electron microscopy with EDS (ESEM/EDS). Non-asbestos Serpentine fibers were superficially similar to chrysotile but were differentiated quickly using TEM morphology criteria and reference SAED overlays. 94 NOA fibers were classified as asbestiform chrysotile (62%), polygonal Serpentine (34%), lizardite scrolls (2%), and lizardite laths (2%). Chrysotile fibril widths (mean = 42 nm) were significantly different from those of polygonal Serpentine and lizardite laths (167 and 505 nm, respectively), but not lizardite scrolls (37 nm). Due to differing preparations and microscope resolutions, TEM analyses investigated a distinct, smaller population of particles (0.01-10 mum) than did PLM analyses (10-100 mum). A higher proportion of asbestiform phases in the finer fraction could potentially bias TEM bulk percent asbestos determinations. ESEM/EDS of intermediate particle size ranges revealed 20-200 mum, elongated particles with intermixed asbestiform and non-asbestiform structures on their surfaces. These particles were too thick and complex to be resolved by PLM, and too massive to be detected by TEM. These large particles are likely to exist in samples prepared by mechanical crushing or grinding, but are not likely to be generated by "releasable asbestos" methods.

A facile route to preparation of high purity nanoporous silica from acid-leached residue of serpentine.[Pubmed:25924349]

J Nanosci Nanotechnol. 2014 Sep;14(9):6915-22.

As the current cost of mineral carbonation is too high for an economically viable industrial process, it is desirable to produce value-added products from CO2 mineralization process. In this work, a facile and cost-effective process was developed for the production of high purity SiO2 from acid-leached Serpentine residue. The Si extraction rate is fast even under ambient conditions due to the highly defective structure of the residue. The reaction kinetics were studied and it was found that the Si extraction rate was under a combination of chemical reaction control and film diffusion control. The SiO2 sample prepared has high purity with a nanoporous structure, which renders it a potential candidate for applications such as an adsorbent and a catalyst support.