Taconite Iron Ore Research Articles

A comparison of asbestos fiber potency and elongate mineral particle (EMP) potency for mesothelioma in humans

We analyzed the mesothelioma mortality in cohorts of workers exposed to crocidolite, amosite, and chrysotile to estimate asbestos fiber potency for mesothelioma, using the method of Hodgson and Darnton (2000). We relied on the original 17 cohort studies in their analysis, along with 3 updates of those studies and 3 new asbestos cohort studies published since 2000. We extended the analyses to examine the mesothelioma potency of tremolite in vermiculite from Libby, Montana, and for non-asbestiform elongate mineral particles (EMPs) in taconite iron ore, talc, and South Dakota gold mining. Mesothelioma potency (RMeso) was calculated as the percent of all expected deaths that were due to mesothelioma per fiber/cc-year of exposure.The RMeso was 0.0012 for chrysotile, 0.099 for amosite, and 0.451 for crocidolite: thus, the relative potency of chrysotile:amosite:crocidolite was 1:83:376, which was not appreciably different from the estimates by Hodgson and Darnton in 2000. The RMeso for taconite mining fibers was 0.069 which was slightly smaller than that for amosite. The RMeso for Libby fibers was 0.028 which was greater than that for chrysotile and less than that for amosite. Talc and gold mining EMPs were non-potent for mesothelioma. Although there are a number of methods for estimating fiber potency of asbestos and non-asbestiform EMPs, the method of Hodgson and Darnton provides a uniform method by which fiber potency can be compared across many fiber types. Our estimates of RMeso provide a useful addition to our knowledge of mesothelioma potency for different asbestos and non-asbestiform EMP fibers.

A case–control study of mesothelioma in Minnesota iron ore (taconite) miners

ObjectivesAn excess of mesothelioma has been observed in iron ore miners in Northeastern Minnesota. Mining and processing of taconite iron ore generate exposures that include elongate mineral particles (EMPs) of...

A Comparison of the CATHIA-T Sampler, the GK2.69 Cyclone and the Standard Cowled Sampler for Thoracic Fiber Concentrations at a Taconite (Iron Ore)-Processing Mill

Several recommendations have been made to the effect that the most appropriate health-based size-selective criterion for fibers is the thoracic convention of the International Organization for Standardization (ISO). The performance of two thoracic samplers, the CATHIA-T (37-mm filter) and the GK2.69 cyclone (37-mm filter), was investigated against the standard 25-mm cowled sampler (current NIOSH 7400 standard method) to determine the effect of thoracic sampling on field results. A total of 270 samples: 80 field and 10 field blank samples for each sampler type, were taken from seven stations in the processing mill of an iron ore mine whose ore contains amphibole minerals. Slides were prepared using the dimethyl formamide/Euparal technique and relocatable cover slips. Two counters examined the slides according to NIOSH 7400 counting A rules with phase contrast microscopes. Prior to counting the sample slides, four reference slides were randomly selected and counted three times on different days to compare the coefficient of variation (CV) between and within counters. Also, seven reference slides were chosen to explore variability between the two microscopes. The average CV between counters (0.148) showed slightly higher than the average CVs within counters (0.072 for Counter 1 and 0.119 for Counter 2). The average CV between the two microscopes was 0.147. Compared to the standard cowled sampler, the overall fiber concentration was lower for the CATHIA-T sampler (CATHIA-T/Cowled = 0.63) and higher for the GK2.69 cyclone (GK2.69/Cowled = 1.66). The result for the CATHIA-T sampler is as expected from laboratory trials, but the result for the GK2.69 cyclone is not as expected. In conclusion, the CATHIA-T sampler has a potential advantage as a high-flow static sampler for screening coarse particles. However, these findings resulted from one field sampling site that contains amphibole minerals, not all of which are asbestiform. Thus, additional field samples from other environments might be helpful to confirm the performance of these samplers.

The search for asbestos within the Peter Mitchell Taconite iron ore mine, near Babbitt, Minnesota

Asbestos crystallizes within rock formations undergoing intense deformation characterized by folding, faulting, shearing, and dilation. Some of these conditions have prevailed during formation of the taconite iron ore deposits in the eastern Mesabi Iron Range of Minnesota. This range includes the Peter Mitchell Taconite Mine at Babbitt, Minnesota. The mine pit is over 8 miles long, up to 1 mile wide. Fifty three samples were collected from 30 sites within areas of the pit where faulting, shearing and folding occur and where fibrous minerals might occur. Eight samples from seven collecting sites contain significant amounts of ferroactinolite amphibole that is partially to completely altered to fibrous ferroactinolite. Two samples from two other sites contain ferroactinolite degraded to ropy masses of fibers consisting mostly of ferrian sepiolite as defined by X-ray diffraction and TEM and SEM X-ray spectral analysis. Samples from five other sites contain unaltered amphiboles, however some of these samples also contain a very small number of fiber bundles composed of mixtures of grunerite, ferroactinolite, and ferrian sepiolite. It is proposed that the alteration of the amphiboles was caused by reaction with water-rich acidic fluids that moved through the mine faults and shear zones. The fibrous amphiboles and ferrian sepiolite collected at the Peter Mitchell Mine composes a tiny fraction of one percent of the total rock mass of this taconite deposit; an even a smaller amount of these mineral fragments enter the ambient air during mining and milling. These fibrous minerals thus do not present a significant health hazard to the miners nor to those non-occupationally exposed. No asbestos of any type was found in the mine pit.

Native Plant Productivity and Litter Decomposition in Reclamation of Taconite Iron Ore Tailing

Aboveground production and shoot and root litter decomposition rates were measured in amended coarse taconite tailing plots over the second and third growing seasons of a 3-yr study. Plots were seeded with a mixture of native prairie species that included Andropogon gerardii Vitm., Schizachyrium scoparium (Michx.) Nash, Elymus canadensis L., Bromus kalmii Gray, and Lespedeza capitata Michx. Reclamation treatments included inoculation with indigenous mycorrhizal fungi, three rates of fertilizer, and three rates of composted yard waste. Aboveground plant biomass in plots amended with 44.8 Mg ha -1 compost increased from 150 g m -2 in the second season to 330 g m -2 in the third season. The litterbag technique was used to assess the influence of reclamation treatments on the decomposition of plant litter. Shoot litter placed on the surface lost 60 to 70% of its original mass after 15 mo and was unaffected by treatment during the first season but was slower in plots amended with 44.8 Mg ha -1 composted yard waste in the second season. Buried root tissue lost 40% of its original mass after 15 mo and was unaffected by treatment. By significantly increasing plant biomass and reducing litter decomposition rate in tailing, additions of 44.8 Mg ha -1 compost should result in the continued accrual of soil organic matter and begin to meet reclamation goals to establish self-sustaining native plant communities on tailing deposits.

Revegetation of coarse taconite iron ore tailing using municipal solid waste compost: M. R. Norland & D. L. Veith, Journal of Hazardous Materials, 41(2–3), 1995, pp 123–134

Revegetation of coarse taconite iron ore tailing using municipal solid waste compost: M. R. Norland & D. L. Veith, Journal of Hazardous Materials, 41(2–3), 1995, pp 123–134

Field responses to added organic matter, arbuscular mycorrhizal fungi, and fertilizer in reclamation of taconite iron ore tailing

A three season study was conducted to determine the effect of added composted yard waste, arbuscular mycorrhizal (AM) fungi, and fertilizer on plant cover, standing crop biomass, species composition, AM fungal infectivity and spore density in coarse taconite iron ore tailing plots seeded with a mixture of native prairie grasses. Plant cover and biomass, percent seeded species, mycorrhizal infectivity and spore density were greatly increased by additions of composted yard waste. After three seasons, total plant cover was also greater in plots with added fertilizer. Third season plant cover was also greater in plots amended with the higher rate (44.8 Mg ha−1) of compost than the moderate rate (22.4 Mg ha-1). Field inoculation with AM fungi also increased plant cover during the second season and infectivity during the first two seasons. Seeded native species, consisting mostly of the cover species Elymus canadensis, dominated plot vegetation during the second and third seasons. Dispersal of AM fungal propagules into nonmycorrhizal plots occurred rapidly and increased infectivity in compost-amended plots during the third season. In plots with less than 10% plant cover, AM fungal infectivity of inoculated plots was greatly reduced after the second season. The high level of plant cover and the trend of increasing proportion of mycorrhizal-dependent warm-season grasses, along with increases in infectivity, forecast the establishment of a sustainable native grass community that will meet reclamation goals.

Native prairie grasses and microbial community responses to reclamation of taconite iron ore tailing

The effect of reclamation treatments on seeded native grass cover and species composition, soil microbial biomass carbon, and populations of actinomycetes, fungi, free-living N2-fixing bacteria, and aerobic heterotrophic bacteria was compared in field plots in coarse taconite tailing. Reclamation treatments consisted of all possible combinations of three rates of composed yard waste, three rates of fertilizer, and inoculation with arbuscular mycorrhizal fungi. Composted yard waste increased plant cover, soil microbial biomass, and populations of all groups of microorganisms compared with unamended, non-inoculated control plots. Microbial populations and biomass in tailing plots were low compared with natural soils and were correlated with plant cover and available P. Mycorrhizal inoculation resulted in a 6% increase in plant cover, although this was not significant, and significantly enhanced N2-fixer populations in June but did not affect other groups of microorganisms. There were no differences between moderate and high rates of composted yard waste. We conclude that incorporation of a moderate rate of organic matter can ameliorate the stressful conditions of coarse taconite tailing and can enhance the initiation of a functional soil ecosystem able to support the establishment of seeded native prairie grasses and may provide a long-term solution to reclamation of taconite tailing. Key words: arbuscular mycorrhizal fungi, mine reclamation, soil microorganisms, composted yard waste.

Revegetation of coarse taconite iron ore tailing using municipal solid waste compost

On Minnesota's Mesabi Iron Range, coarse taconite iron ore tailing is often used as the principal material in the construction of dams for large tailing impoundments. Mineland reclamation rules in Minnesota require that tailing dams be vegetated to control erosion for dam stability and safety. Coarse taconite iron ore tailing is characterized chemically by an alkaline pH, low organic matter content, lack of plant-essential nutrients, and low cation-exchange capacity; physically by its coarse texture, lack of structure, low water-holding capacity, and dark color; and biologically by a lack of microorganisms. To investigate the potential of composted municipal solid waste to ameliorate these conditions and make the material more amenable to plant establishment and growth, the US Bureau of Mines implemented a series of factorial experiments at two active taconite mine sites in northeastern Minnesota. At each experimental site, vegetative cover has improved depending on the type of municipal solid waste compost used and rate of application. At site I, overall plant cover across all treatments has improved from zero prior to experimental manipulation to 72% after four years, with seven treatment combinations exceeding 90% cover. At site II, overall plant cover has improved from zero prior to experimental manipulation to 83% after four years, with 23 treatment combinations exceeding 90% cover. At both sites, total cover has progressively increased over four years and has not reached steady-state conditions. These results suggest a possible new strategy for reclaiming difficult sites through the use of municipal solid waste compost.

Interactions between native prairie grasses and indigenous arbuscular mycorrhizal fungi: implications for reclamation of taconite iron ore tailing

summaryIn a glasshouse experiment using coarse taconite iron ore tailing as the substrate, we examined interactions between the warm‐season grasses Andropogon gerardii (big bluestem) and Schizachyrium scoparium (little bluestem), and the cool‐season grass Elymus canadensis (Canada wild rye), and indigenous arbuscular mycorrhizal (AM) fungi from an adjacent fine tailing basin. Shoot dry mass (DM), P uptake, shoot P concentration, root DM, root length, spore density, percentage root length colonized, and length of external AM fungal hyphae were measured over a gradient of phosphate availability. Andropogon gerardii was highly dependent and responsive to inoculation at low P, whereas inoculation had no significant effect on the growth of 5. scoparium. Root DM and root lengths of both warm‐season grasses were unaffected by mycorrhizal inoculation. Elymus canadensis was responsive only at the lowest P level and not dependent on mycorrhizas; in fact, shoot DM, P uptake, root DM and root lengths were all greater in control than inoculated plants at moderate P levels. Despite a growth suppression, colonized root lengths for E. canadensis were approximately five times longer than warm‐season grasses at low P levels, making it suitable as an early succession species for increasing mycorrhizal inoculum potential and thus enhancing the successful reclamation of coarse tailing deposits by more persistent, mycorrhizal‐dependent species.

Standing Crop Biomass and Cover on Amended Coarse Taconite Iron Ore Tailings

Standing Crop Biomass and Cover on Amended Coarse Taconite Iron Ore Tailings

The Effect of VA Mycorrhizae on Shoot Biomass and P Uptake of Grasses Used to Revegetate Coarse Taconite Iron Ore Tailing

The Effect of VA Mycorrhizae on Shoot Biomass and P Uptake of Grasses Used to Revegetate Coarse Taconite Iron Ore Tailing

THE SUPERIORITY OF LOW-GRADE IRON ORE∗

At the mine, pelletized low-grade taconite iron ore requires more energy and labor than rich hematite. In blast furnaces, however, taconite pellets are much more efficient than hematite. Overall, pellets save energy and labor. Attempts to pelletize hematite have not worked well. Therefore, many hematite mines have closed and miners have relocated to taconite plants. Also, some jobs, capital investments, and pollution have decreased at steel mills while increasing in the sparsely populated mining regions as a result of pelletizing.