Mineralogical and microscopic evaluation of coarse taconite tailings from Minnesota taconite operations

Our plain-English summary of Mineralogical and microscopic evaluation of coarse taconite tailings from Minnesota taconite operations, by L.M. Zanko, H.B. Niles, J.A. Oreskovich (Regulatory Toxicology and Pharmacology, 2008).

The study

• Authors: L.M. Zanko, H.B. Niles, J.A. Oreskovich
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2008;52(1 Suppl):S51-65
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Eighteen coarse taconite tailings samples were collected in 2000-2001 from five western Mesabi Range taconite (iron ore) operations located in northern Minnesota, i.e., EVTAC, Hibbing Taconite (Hibtac), USX Minntac, Ispat Inland (Minorca), and National Steel Pellet Company (NSPC), to test their physical, geological, chemical, and mineralogical properties [Zanko, L.M., Niles, H.B., Oreskovich, J.A., 2003. Properties and aggregate potential of coarse taconite tailings from five Minnesota taconite operations, Minnesota Department of Transportation, Local Road Research Board, St. Paul, MN, Report No. 2004-06 (also as Natural Resources Research Institute technical report, NRRI/TR-2003/44)]. The goal was to assemble a body of technical data that could be used to better assess the potential of using a crushed taconite mining byproduct like coarse tailings for more widespread construction aggregate purposes, primarily in roads and highways. An important part of the mineralogical assessment included X-ray diffraction (XRD) analyses and microscopic (polarized light microscopy, scanning electron microscopy, and transmission electron microscopy, i.e., PLM, SEM, and TEM, respectively) evaluation of the size and shape (morphological) characteristics of potentially respirable microscopic mineral particles and fragments. Quantitative mineralogy, based on XRD analyses, showed that the dominant mineral in all samples was quartz (55-60%), followed by much smaller amounts of iron oxides, carbonates, and silicates. Specialized microscopic analyses and testing performed by the RJ Lee Group, Monroeville, PA, on both pulverized (-200 mesh, or 0.075mm) and as-is sample composites showed that no regulated asbestos minerals or amphibole minerals were detected in the western Mesabi Range samples. A small number (26) of non-asbestos and non-amphibole mineral cleavage fragments/mineral fibers were detected by SEM out of 1000 fields analyzed, but most were identified as minnesotaite and talc, silicate minerals common to the Biwabik Iron Formation. Amphibole minerals, absent in coarse tailings samples from the five western Mesabi Range taconite operations, were present in a single eastern Biwabik Iron Formation sample collected in 2003 for Lake County from the Cliffs Northshore operation in Silver Bay, MN. Importantly, the Superfund Method for the Determination of Releasable Asbestos in Soils and Bulk Materials [United States Environmental Protection Agency (USEPA), 1997. Superfund method for the determination of releasable asbestos in soils and bulk materials, EPA 540-R-97-028, U.S. Environmental Protection Agency, Washington], as modified by Berman and Kolk [Berman, D.W., Kolk, A.J., 2000. Modified elutriator method for the determination of asbestos in soils and bulk materials, Revision 1: Submitted to the U.S. Environmental Protection Agency, Region 8, May 23, 2000] failed to generate any protocol fibers, i.e., fibers longer than 5mum and thinner than 0.5mum, from either the western coarse tailings samples or the single eastern Biwabik Iron Formation sample. The combined findings suggest coarse tailings and other taconite mining byproducts should be treated with the same common sense safety and industrial hygiene approach practiced for all mineral-based materials that have the potential to generate respirable dust.

In plain English

This laboratory study examined coarse taconite tailings, a crushed byproduct of iron-ore (taconite) mining, to assess their potential as road and construction aggregate. Eighteen samples were collected quarterly over one year, beginning in fall 2000, at five western Mesabi Range operations in northern Minnesota. A contract laboratory, the RJ Lee Group, tested as-is and pulverized composites. It used X-ray diffraction, three kinds of microscopy (polarized light, scanning electron and transmission electron) and an EPA Superfund method for releasable asbestos. Quartz was by far the dominant mineral. No regulated asbestos minerals or amphibole minerals were detected in the western samples. Scanning electron microscopy found 26 elongated particles in 1000 fields; most cleavage fragments were consistent with minnesotaite or talc. One eastern comparison sample, from the Northshore operation, contained tremolite/actinolite amphibole cleavage fragments, but no asbestos was detected in it. The Superfund method generated no fibers longer than 5 micrometers and thinner than 0.5 micrometers from any sample. The authors concluded these byproducts should be handled with the same safety and industrial hygiene approach used for any dust-generating mineral material. They noted that only one eastern sample was tested.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory mineralogical and microscopic analysis of mining byproduct samples (X-ray diffraction, polarized light microscopy, scanning and transmission electron microscopy, EPA Superfund releasable-asbestos method)
• Who was studied: 18 coarse taconite tailings samples from five western Mesabi Range taconite operations in northern Minnesota (EVTAC, Hibtac, Minntac, Ispat Inland (Minorca), NSPC), collected quarterly over one year beginning in fall 2000. There was also one eastern Biwabik Iron Formation comparison sample: dry cobber lean ore collected in January 2003 from the Cliffs Northshore operation in Silver Bay and submitted by Lake County.
• Exposure: No human exposure was studied. The material tested was coarse taconite tailings, as-is and pulverized to pass a 200 mesh (75 micrometer) screen. It was examined for regulated asbestos minerals, amphibole minerals, and elongated mineral cleavage fragments.
• Main results:
  • In the composite of all 18 samples, quartz was by far the dominant mineral, followed by smaller amounts of iron oxides, carbonates and silicates.
  • Western samples, X-ray diffraction: no amphibole minerals were observed.
  • Western samples, polarized light microscopy: four cleavage fragments in total across all samples, with length-to-width ratios greater than 3:1 and no fibril structure.
  • Western samples, polarized light microscopy: no regulated asbestos minerals were detected.
  • Western samples, scanning electron microscopy: no asbestos minerals or amphibole minerals were observed.
  • Western samples, scanning electron microscopy: 26 particles with length-to-width ratios over 3:1 and diameters greater than 0.25 micrometers were found out of 1000 fields analyzed.
  • Western samples: most of the cleavage fragments were consistent with minnesotaite or talc.
  • Western samples: of the 26 elongated particles, only one (talc) was longer than 10 micrometers and thinner than 0.4 micrometers.
  • Western samples, transmission electron microscopy: no asbestos minerals or amphibole cleavage fragments were observed.
  • Western samples, EPA Superfund method: no asbestos fibers or cleavage fragments longer than 5 micrometers and thinner than 0.5 micrometers were observed.
  • Eastern Northshore sample, polarized light microscopy: approximately 10–15% cleavage amphibole fragments, identified as tremolite/actinolite.
  • Eastern Northshore sample, scanning electron microscopy: 51 particles with length-to-width ratios over 5:1 and diameters between 0.25 and 2 micrometers, in 35 of the 50 fields analyzed.
  • Eastern Northshore sample, transmission electron microscopy: cleavage fragments measured at 0.02 weight percent, which the laboratory said indicates the fragments were mostly larger than about 20 micrometers.
  • Eastern Northshore sample, overall: the RJ Lee Group concluded that amphibole cleavage fragments, but not asbestos, were detected.
  • Eastern Northshore sample, EPA Superfund method: no protocol fibers were generated from the as-is sample.
• The authors' conclusion: The authors concluded that coarse tailings and other taconite mining byproducts should be treated with the same common-sense safety and industrial hygiene approach used for all mineral-based materials that can generate respirable dust.
• Limitations the authors state:
  • Only one eastern Biwabik Iron Formation sample was tested, and the authors said further testing of eastern byproducts would be desirable.
  • The authors said that characterizing the tailings from all five operations with these samples was a compromise in sampling practicality, given the very large tonnage produced.
  • X-ray diffraction cannot tell fibrous mineral forms apart from cleavage fragments.

Topics

Medical terms in this study, explained in our Lexicon: Taconite, Tailings, Mesabi Range, X-Ray Diffraction (XRD), Polarized Light Microscopy (PLM), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Mineralogy.

Related studies

• The search for asbestos within the Peter Mitchell Taconite iron ore mine, near Babbitt, Minnesota — M. Ross, R.P. Nolan, et al. (2008)
• A case-control study of mesothelioma in Minnesota iron ore (taconite) miners — C.S. Lambert, B.H. Alexander, et al. (2016)
• Mortality experience among Minnesota taconite mining industry workers — E.M. Allen, B.H. Alexander, et al. (2014)
• Cancer incidence among Minnesota taconite mining industry workers — E.M. Allen, B.H. Alexander, et al. (2015)
• Occupational exposures and lung cancer risk among Minnesota taconite mining workers — E.M. Allen, B.H. Alexander, et al. (2015)
• Amphibole fibers in a taconite mine and in the lungs of the miners — B. Gylseth, T. Norseth, et al. (1981)

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