Abstract
Naturally occurring asbestos and asbestiform miner als can be found in metamorphic rocks and in the soil of the alluvial plains. Problem statement: The definition of the free-asbestos and the limit to consider a rock or a soil safe is still a controversial issue. American and European laws did not present any method to define the hazard of the green stones, instead Italian law, in Ministeri al Decree1996, established a limit value obtaoined by the determination of the Release Index. In order to detect an asbestos concentration in the rocks, a re liable analytic methodology has been necessary. Approach: An abrasion trial, using the mechanism action of a rotary cylinder, and a Phase Contrast Optical Microscopy (PCOM) method to analyze the powder obtained from the mill, had been used. To simplify PCOM analysis, the sample, recovered from the mill, was selected in particle size classes: large, medium and small. Each class was separated b y means of sedimentation in fibrous and granular fractions. Results: The separation of asbestos in large and medium clas ses was quite good and the fibers had been weighed. For the small class the tr ansformation of visible data into numerical data wa s complex, but the results had been reliable. Conclusion/Recommendations: The suggested method, although semi-quantitative, could be useful to solv e the difficult problem of the analysis of the asbe stos content in the rocks or soils. The division into gr anular classes allowed a more representative sample to be analyzed and better quality slides to be prepare d. From the results obtained, the analysis of the s mall classes by means of PCOM was a critical point: The use of the SEM method can improve it.
Highlights
The term “asbestiform” is used to describe the specific crystal habit in polyfilamentous fibers organized in bundles, while the term “Asbestos” indicates a group of six minerals (Chrysotile, Tremolite, Actinolite, Antophyllite, Crocidolite and Amosite Table 1) which have the same fibrous crystalline habit and the similar properties like flexibility, high tensile strength, long shape, high mechanical thermal stability, low thermal and electrical conductivity, high absorbency and resistance to acid and bases
The main instruments used were a microscope with positive phase contrast, 5X, 10X, 40X objective, a diaphanizator and a mill characterized by dimensions defined according to Italian M.D. 14/05/96
The fibers can be recovered through filtering which is carried out using a vacuum pump equipped with a nitrate of cellulose membrane
Summary
The term “asbestiform” is used to describe the specific crystal habit in polyfilamentous fibers organized in bundles, while the term “Asbestos” indicates a group of six minerals (Chrysotile, Tremolite, Actinolite, Antophyllite, Crocidolite and Amosite Table 1) which have the same fibrous crystalline habit and the similar properties like flexibility, high tensile strength, long shape, high mechanical thermal stability, low thermal and electrical conductivity, high absorbency and resistance to acid and bases Due to these characteristics the asbestos minerals, already used since Romans for their resistance to fire, became from the 19th century very important as industrial minerals[1]. The asbestos of amphibole is less common than chrysotile, they can be present in the same rocks as serpentine asbestos and all these fibrous minerals may occur in slip-fiber and cross-fiber veins and as mass fiber deposits.
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