Morphological Characteristics of Asbestos in Ground Bulk Mineral Powders

Julie W Pier^*

• Magrist Talc, Greenwood Village, CO, United States

Morphological characteristics of asbestos as a trace component in spiked ground mineral powders at 100 and 500 ppm concentrations were evaluated. Three types of asbestos, Lone Pine tremolite, HSL chrysotile, and short-fiber Calidria chrysotile were spiked into a coarsely crushed talc matrix. Spiked samples were aggressively co-ground to simulate a milled mineral powder final product. The coarsest particles in the mixture were isolated using a wet sieving technique and evaluated by SEM and PLM. The coarsest particles in the ground mixture are the ones suspected of retaining the most information about the asbestiform habit. This approach is opposite to conventional types of asbestos analyses (such as TEM) where that concentrate on the finest particles are analyzed (such as those performed by TEM), which and can sometimes be inconclusive. Asbestos was confirmed to be resistant to grinding, especially in comparison to the softer mineral talc, and was readily detected by both SEM and PLM in the coarsest size fraction at these low concentrations, despite aggressive grinding. Classic morphology features of asbestos, such as occurrence in bundles and presence of long, thin fibers showing curvature were observed for all types of asbestos by both SEM and PLM at both trace concentrations. There was no difference in the morphology between 500 and 100 ppm concentrations; although fewer particles were observed in the latter, as expected. This means that analyzing the coarsest size fraction is a valid approach and detection is limited only by the amount of material analyzed. A production-scale ultrafine milled talc sample containing trace amounts of amphibole obtained from a non-US source, provided proof of concept for this approach. In this sample, trace amounts of amphibole with an asbestos component were isolated and analyzed by the wet sieve approach and asbestos particles showed classic asbestiform morphology even though the sample had been ground to a 1.5 µm median particle size. Techniques described can be used to accurately determine if a mineral product contains asbestos or an asbestos component.