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 0.075 mm) 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 5 μm and thinner than 0.5 μm, 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.
Bibliographical noteFunding Information:
The Minnesota Local Road Research Board (LRRB), University of Minnesota Center for Transportation Studies (CTS), the Minnesota Department of Transportation (Mn/DOT), and the Natural Resources Research Institute (NRRI) are gratefully acknowledged for providing project funding, support, and guidance. Lake County, Minnesota, is also acknowledged for supporting the analysis of an eastern Mesabi Range taconite byproduct sample. Lastly, Messrs. Keith Rickabaugh and Drew R. Van Orden of the RJ Lee Group, Monroeville, PA, are thanked for their explanations and descriptions of the analytical procedures and testing methods used for evaluating the coarse tailings samples, as reported in this paper.
Production of the paper was funded by the Natural Resource Research Institute (NRRI). University of Minnesota Duluth, for whom the authors are and were employed. The paper’s content was based on research performed by NRRI and funded by the Minnesota Local Road Research Board (LRRB) and the University of Minnesota’s Center for Transportation Studies (CTS) via the Minnesota Department of Transoportation (Mn/DOT), as well as NRRI. The paper and its content are of the author’s own design. None of the original research funding sources (LRRB, CTS, Mn/DOT) has any involvement in the study design, collection, analysis and interpretation of data, and writing of the manuscript, and the decision to submit the manuscript for publication.
- Biwabik Iron Formation
- Mesabi iron range