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Kinetic study of the dehydroxylation of chrysotile asbestos with temperature by in situ XRPD 总被引：6，自引：0，他引：6
The kinetics of the dehydroxylation of chrysotile was followed in situ at high temperature using real-time conventional and
synchrotron powder diffraction (XRPD). This is the first time kinetics parameters have been calculated for the dehydroxylation
of chrysotile. The value of the order of the reaction mechanism calculated using the Avrami model indicates that the rate-limiting
step of the reaction is a one-dimensional diffusion with an instantaneous nucleation or a deceleratory rate of nucleation
of the reaction product. Hence, the rate-limiting step is the one-dimensional diffusion of the water molecules formed in the
interlayer region by direct condensation of two hydrogen atoms and an oxygen atom. The calculated apparent activation energy
of the reaction in the temperature range 620–750 °C is 184 kJ mol−1. The diffusion path is along the axis of the fibrils forming the fibers. The amorphous or short-range ordered dehydroxylate
of chrysotile is extremely unstable because forsterite readily nucleates in the Mg-rich regions. Moreover, it is less stable
than the dehydroxylate of kaolinite, the so-called metakaolinite, which forms mullite at about 950 °C. This difference is
interpreted in terms of the different nature of the two ions Mg2+ and Al3+ and their function as glass modifier and glass-forming ion, respectively.
Received: 10 April 2002 / Accepted: 7 January 2003
Acknowledgements This work is part of a COFIN project (04 Scienze della Terra, NR 17, 2000) supported by MURST. Dr Dapiaggi is kindly acknowledged
for help during the data collection at the Dipartimento di Scienze della Terra, University of Milan. 相似文献
2.
M. Ross 《Environmental Geology》1995,26(3):182-188
It is estimated that nearly $100 billion has been spent on removal of asbestos-bearing materials from schoolrooms, public and commercial buildings, and homes. This removal continues to this day despite the publication of an advisory document in 1990 by the US Environmental Protection Agency that states most removal is unnecessary and is even counterproductive both in terms health protection and costs. Concern over low exposure to substances that are designated as carcinogens is based on the false concept that even the smallest exposure to such substances can increase cancer risk. The expression one molecule of a chemical or one asbestos fiber can possibly produce a tumor is repeated over and over until it is accepted as a truth. Over 1400 air samples taken in 219 North American school buildings show the average fiber level to be 0.00022 fibers per milliliter of air. Using the most pessimistic models and attendance in the school for 6 h a day, five days a week, for 14 years, the calculated risk is one excess cancer death per million lifetimes. In contrast, the risk of dying from a lightning strike is 35 deaths per million lifetimes. Ambient air asbestos concentrations measured in the chrysotile asbestos mining towns of Quebec are 220 to 2200 times greater than that measured in the average schoolroom, yet the women living their entire lives in these towns show no increased cancer risk. The asbestos abatement program in the United States is a public policy debacle. 相似文献
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Jasmine Rita Petriglieri Christine Laporte-Magoni Peggy Gunkel-Grillon Mario Tribaudino Danilo Bersani Orietta Sala Monika Le Mestre Ruggero Vigliaturo Nicola Bursi Gandolfi Emma Salvioli-Mariani 《地学前缘(英文版)》2020,11(1):189-202
Covered by ultrabasic units for more than a third of its surface,the New Caledonia(South West Pacific)is one of the largest world producers of Ni-ore from lateritic deposits.Almost all outcrops of geological units and open mines contain serpentine and amphibole,also as asbestos varieties.In this geological context,in which weathering processes had a great contribution in the production and dispersion of mineral fibres into the environment,the development of a routinely analytical strategy,able to discriminate an asbestiform fibre from a non-harmful particle,is a pivotal requisite.However,the acquisition of all these parameters is necessary for determining the risk associated to fibres exposition.A multidisciplinary routinely approach,based on the use of complementary simply-to-use but reliable analytical methods is the only possible strategy.In addition,the instrumental apparatus must be easily transportable on the field,directly on the mining site.The employment of specialized tools such as Polarized Light Microscopy associated to Dispersion Staining method(PLM/DS)and portable Raman spectroscopy for identification of environmental asbestos,are proved extremely effective in the improvement of the performance and rapidity of data acquisition and interpretation.Both PLM/DS and handheld Raman devices confirmed to be discriminant in the detection and characterization of asbestos fibres for both serpentine and amphibole.Furthermore,these techniques proved extremely effective even in the presence of strongly fibrous and altered samples. 相似文献
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William C. Thayer Daniel A. Griffith Gary L. Diamond 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):461-471
Despite the dust cleanup and indoor air testing program led by the U.S. Environmental Protection Agency (EPA) and offered
to all residents of Lower Manhattan (south of Canal Street), concern remains about local chemical residues from the collapse
of the World Trade Center (WTC) buildings. Data on post-cleanup indoor airborne asbestos concentration, available from EPA
Region 2, were analyzed to assess the possibility that the WTC site is the source of geographically concentrated rare post-cleanup
exceedances of the health-based standard for asbestos. Recognizing that these rare exceedances may be attributable to sources
other than the WTC disaster, and that these sources are very likely to exhibit geographic patterns, the data were analyzed
using a spatial filter specification of the auto-Poisson probability model. Our analysis shows that ignoring geographic patterns
latent in these exceedances affects the empirical probability of exceeding the health-based standards for airborne asbestos.
We did not find any statistically-significant geographic pattern in the exceedance events that would indicate the WTC site
as the source of the post-cleanup exceedances. Apparent geographic patterns may be due to the geographic variability in sampling
intensity. Our analysis indicates the Residential Dust Cleanup Program lead by EPA Region 2 has been effective at reducing
the concentration of air-borne asbestos in indoor air to below the health-based benchmark. 相似文献
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L. van Rensburg S. Claassens J. J. Bezuidenhout P. J. Jansen van Rensburg 《Environmental Geology》2009,57(2):267-273
The much publicised problem with major asbestos pollution and related health issues in South Africa, has called for action
to be taken to negate the situation. The aim of this project was to establish a prioritisation index that would provide a
scientifically based sequence in which polluted asbestos mines in Southern Africa ought to be rehabilitated. It was reasoned
that a computerised database capable of calculating such a Rehabilitation Prioritisation Index (RPI) would be a fruitful departure
from the previously used subjective selection prone to human bias. The database was developed in Microsoft Access and both
quantitative and qualitative data were used for the calculation of the RPI value. The logical database structure consists
of a number of mines, each consisting of a number of dumps, for which a number of samples have been analysed to determine
asbestos fibre contents. For this system to be accurate as well as relevant, the data in the database should be revalidated
and updated on a regular basis. 相似文献
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Mark C. Roberts 《Natural Resources Research》1994,3(4):315-324
The future markets for industrial minerals depend on the business cycles of the industries that use these minerals. In this study, I develop a method to establish the relationships between the cycles in major sectors of the economy and the markets for minerals. This method is demonstrated for the use of cement, gypsum, salt, and asbestos in the United States since World War II. Assuming that past relationships will continue, we can forecast consumption for these minerals based on predictions of future trends in the economy. 相似文献
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