Treated and untreated rock dusts: silica content and physical characterization

Details

• Personal Author:
  Chisholm W ; Farcas D ; Harper M ; Lee T ; Schwegler-Berry D ; Soo J
• Description:
  Objective: To assess the free silica content and physical characteristics of four selected rock dusts consisting of calcium and/or magnesium carbonate, in both treated and untreated form. Methods: Four selected rock dusts were investigated: AMC (untreated), AMC with X-10 (treated), Micro-White 100 (untreated) and Imerys Phase IV (treated blend of 87.5% Micro-White 100 and 12.5% Kotamite). For each rock dust, two different size fractions (bulk and respirable size fractions) were tested to determine quartz content (%). The selected rock dusts were aerosolized and introduced into an aerosol chamber. A total of 72 individual samples of respirable dust were collected using FSP10 cyclones. Particle size segregating samplings were conducted using a Micro-Orifice Uniform Deposit Impactor (MOUDI). Silica measurement was performed according to NIOSH Method 7603. Particle morphology was examined with a combination of scanning electron microscopy and energy-dispersive x-ray spectroscopy analysis (EDX). Results: The silica content of AMC in respirable dust (0.84%) was the largest but not significantly different from that of AMC X-10 (0.68%). The Micro-White 100 had significantly lower silica content than the other rock dusts but was not significantly different from Imerys Phase IV. The respirable fraction of AMC dust, treated and untreated, had a significantly higher silica content than did the bulk material. Silica is enriched in the respirable fraction but not above the Mine Safety and Health Administration (MSHA) limit for silica in bulk dust. All particle size distributions showed log-normal distributions, with the mass median aerodynamic diameters between 1.2 and 5.3 um and geometric standard deviations less than 2.8. The dust spectra from EDX analysis are predominantly from limestone, clay particles and gypsum particles. No free quartz particles were observed, but that is reasonable considering the low quantity of silica and the number of particles studied. Conclusions: All four dusts contained respirable silica. Treated rock dusts had slightly lower silica content than untreated ones. Silica can be elevated in the respirable fraction compared to the bulk, but this enrichment is not likely to lead to silica concentrations above the MSHA Permissible Exposure Limit (PEL), provided there is compliance with the PEL for respirable dust. [Description provided by NIOSH]
• Subjects:
  Aerosols Dust Occupational Health Particulate Matter Quartz Safety Silicon Dioxide Spectrum Analysis
• Keywords:
  Aerosol Particles Calcium Dusts Gypsum Limestone Magnesium Magnesium Compounds Microscopy Mine Safety And Health Administration MSHA Particulate Dust Particulates PELs Permissible Exposure Limits Quartz Dust Respirable Dust Sampling Sampling Methods Silica Silica Dusts Spectrographic Analysis

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• Publisher:
  American Industrial Hygiene Association
• Document Type:
  Text
• Genre:
  Abstract or Summary
• Place as Subject:
  Maryland ; OSHA Region 3 ; West Virginia
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  HELD - Health Effects Laboratory Division
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  97
• NIOSHTIC Number:
  nn:20048253
• Citation:
  AIHce 2016: American Industrial Hygiene Conference and Exposition Pathways to Progress, May 21-26, 2016, Baltimore, Maryland. Falls Church, VA: American Industrial Hygiene Association, 2016 May; :97
• Contact Point Address:
  J. Soo, CDC/NIOSH/HELD/EAB, Morgantown, WV
• CAS Registry Number:
  Calcium (CAS RN 7440-70-2) ; Gypsum (Ca(SO4).2H2O) (CAS RN 13397-24-5) ; Magnesium carbonate (CAS RN 546-93-0) ; Quartz (SiO2) (CAS RN 14808-60-7) ; Silica (CAS RN 7631-86-9)
• Federal Fiscal Year:
  2016
• NORA Priority Area:
  Mining
• Peer Reviewed:
  False
• Source Full Name:
  AIHce 2016: American Industrial Hygiene Conference and Exposition Pathways to Progress, May 21-26, 2016, Baltimore, Maryland
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:ca72711c6f2025f40e8c4232c7736d84d029a8ed49fdd18fab5e3081102b857a7a5f2fbb6c2c6659590b76f9c8e1c1fb13d9458cfe456e4278af640f448ddd38
• Download URL:
  https://stacks.cdc.gov/view/cdc/203058/cdc_203058_DS1.pdf
• File Type:
  [PDF - 1.49 MB ]