Browsing by Subject "Taconite tailings"

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    Energy Efficiency Comparison Study of Concrete Block Structures
    (University of Minnesota Duluth, 1991-07) Zanko, Lawrence M; Johnson, T. B
    The Natural Resources Research Institute (NRRI), with a grant from the Minnesota Department of Administration, has evaluated the energy saving potential of an insulated concrete block product manufactured by Sparfil International, Inc. The blocks used in the study contained taconite tailings (Sparfil-Tac) in place of sand. A comparative evaluation of two 400 ft2 test buildings, identical in all respects except for wall construction (conventional 12-inch concrete block versus 12-inch Sparfil-Tac insulated block), shows the Sparfil-Tac product to have superior thennal insulating properties. Both buildings were heated electrically. The Sparfil-Tac test building consumed 44.6% less electricity than its conventional concrete block counterpart over a six-month test period (December 26, 1989, through June 27, 1990). This energy consumption differential, while significant, was less than expected. A 65 .4 % reduction in energy consumption should have been realized, based on heat loss calculations for all test building components. A guarded hot box test (ASTM C-236) perfonned by Twin City Testing Corporation showed the Sparfil-Tac product to have a thennal resistance (R-value) of 10.02 rather than the expected 24.5. This lower R-value is supported by the heat loss calculations which show the Sparfil-Tac test building to have an R-value of 8.45. To determine if the lower R-value was due to faulty block fabrication or some other factor, an additional guarded hot box test was performed on Sparfil's regular (non-taconite tailings) block. The second test showed these blocks to have an R-value of 10.80 rather than the R-value of 24.5 claimed in Sparfil product brochures. The R-value discrepancy is most likely due to the improper application of heat flow concepts by Sparfil International when calculating thermal resistances for their block products. This is particularly true for blocks whose hollow cores are filled with expanded polystyrene (EPS) inserts. The two guarded hot box tests show that the EPS inserts do not increase the insulating value of the blocks to the extent claimed. The economics of each building type were compared by using the difference in energy consumption between the two buildings. Based on quoted power and construction costs, a payback period ranging from 3.6 to 10.1 years was calculated for the 400 ft2 Sparfil-Tac product; had the block performed as expected, the payback period would have, instead, ranged from 2.5 to 7 years. The variable payback period reflects the range of construction costs used in the economic analysis. Economies of scale show the Sparfil-Tac product is more costcompetitive in larger building applications. Additional guarded hot box thermal testing of regular Sparfil blocks is recommended given the difference between the actual (test-based) and claimed (calculation-based) R-values. Calculated (in effect, idealized) values should only be relied on when they are supported by experimental results. Based on this additional testing, further economic analyses could then be performed. Based on the results of the study described in this report, Sparfil-Tac blocks are superior to regular concrete blocks in terms of R-value achieved per square foot of construction cost ($/ft2 + R-value). When construction does not require concrete blocks, other construction techniques will yield a considerably smaller ratio ($/ft2 + R-value), thus more insulating for the construction dollars spent.
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    Mineland Reclamation using Office Waste Paper De-Inking Residue
    (University of Minnesota Duluth, 1994-03) McCarthy, Barbara J; Monson Geerts, Stephen D; Johnson, Kurt W; Malterer, Thomas J; Maly, Craig C
    Pulp facilities which recycle office waste paper generate a large amount of waste by-products in the process of producing high-grade pulp. The paper-like residue, called de-inking residue, was evaluated for use in the restoration of vegetation on coarse taconite tailings in NE Minnesota. The mineland reclamation rules specify that a 90 percent vegetative cover shall be established on tailings after three growing seasons, however this level of cover on coarse tailings has not been consistently achieved in Minnesota using standard restoration practices. Research plots were established in 1992 at Eveleth Mines arranged in a randomized block design with three replications using five levels of de-inking residue, five levels of fertilization and two plant mixes. A total of twenty-five treatment combinations were assigned to 2.5m- by- 4.0m plots and lysimeters were installed to monitor changes in sub-surface water quality. Coarse tailings were evaluated to determine the effects of de-inking residue on their chemical properties. Vegetative cover was measured in July and September in 1992 and 1993 and nutrient levels were determined in plant samples. Fertilization and de-inking residue amendments had significant effects on the vegetative cover of both introduced and native plant species. De-inking residue had a minimal impact on the chemical properties of coarse tailings at rates up to 80 dry ton/acre and on sub-surface water quality at a depth of four feet. Vegetative cover for introduced species increased from no cover, to 49 percent the first growing season, to 90 percent at the end of the second growing season on tailings fertilized at the highest level and amended with residue at 10 ton/acre. At the same fertilizer and de-inking residue rate, vegetative cover for native plants increased from no cover to 7 percent the first growing season, to 69 percent at the end of the second growing season. Alfalfa had lower levels of boron, magnesium, and manganese on residue amended plots in 1992 and 1993. Bluestem had higher levels of calcium and zinc, but lower levels of magnesium and manganese on residue amended. plots. Cadmium, chromium, copper, nickel, lead, and zinc in alfalfa and bluestem did not accumulate to toxic levels. Deinking residue appears to have benefited vegetative growth after two growing seasons using deinking residue applied at 10 dry ton/acre with fertilizer applied at 160 lb/acre of nitrogen and 359 lb/acre of phosphorus.
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    Taconite Tailings and Water Quality - A Survey of Existing Data
    (University of Minnesota Duluth, 2010-09) Patelke, Marsha Meinders; Zanko, Lawrence M
    For over 40 years, taconite tailings, a by-product of taconite iron ore processing, has been used in northeastern Minnesota road construction projects as aggregate. The dominant uses have been as fill materials and in bituminous pavements. Over 125 million tons of tailings are produced annually by Minnesota’s iron mining industry (Oreskovich et al., 2007). The Natural Resources Research Institute (NRRI), University of Minnesota Duluth, has been involved in a multiplephase project to evaluate the quality and use of this material. When used as aggregate for bituminous pavements, the taconite tailings grains are encapsulated in the asphalt mix that separates the tailings from contact with water. As fill, taconite tailings can be in contact with water, intermittently, seasonally, or continuously. Do taconite tailings affect water quality? In an effort to evaluate this question, a compilation and review of existing groundwater and surface water chemistry associated with tailings in contact with water has been completed. We evaluate water quality by comparing existing water sample chemical analyses data to published State of Minnesota ground and surface water standards. Data utilized for this study include: Minnesota Department of Natural Resources (DNR) reports from 1989 and 1999, Minnesota Pollution Control Agency (MPCA), Keetac Pollutant Discharge Elimination System (NPDES) permit water sampling data from several mines, and previous investigations completed by the Natural Resources Research Institute (NRRI). Based on our review, the data from water quality and taconite tailings revealed the following findings: 1. Most Minnesota water quality standards are met. The exceptions include arsenic, cobalt, iron, and manganese. Iron and manganese exceed secondary drinking water standards that are based on attributes of the water like taste, odor, and appearance, and not because of health risk issues. Arsenic and cobalt exceed the MPCA’s 2A chronic standard for surface waters of 2 ppb and 2.8 ppb, respectively. These elements do not exceed the drinking water standards or Class 7 surface water standards; 2. Mercury is typically an environmental concern. Based on the NPDES data reviewed, the following information was noted. Chemical analyses completed on surface water collected at three of the mines had the following reported numbers: maximum value 7.24 ng/L, minimum value 0.45 ng/L and a median value of 1 μg/L. Minimum and median reported mercury values meet the most stringent surface water standard, the Great Lakes Initiative, of 1.3 ng/L. Thirty-four water samples were analyzed for total mercury. A total of 678 NPDES water sample data were reviewed. DNR reports do not contain mercury data for water samples. Atmospheric mercury could add to the amount detected by chemical analyses in surface water samples; 3. Iron formation contains arsenic, cobalt, manganese, and iron; 4. Taconite tailings do contain arsenic, cobalt, manganese, and iron. Arsenic occurs at a minimum value of 8.8 mg/kg, maximum value of 39.4 mg/kg, and a median value of 17 mg/kg. Cobalt occurs at a minimum value of 4.4 mg/kg, maximum value of 15.4 mg/kg, and a median value of 7.7 mg/kg. Manganese and iron were not reported as trace metals but were included in whole rock analyses; 5. NRRI completed Toxicity Characterization Leaching procedure (TCLP) and Synthetic Precipitation Leaching Procedure (SPLP) chemical analyses on three samples of taconite tailings. Results indicated that arsenic results ranged from < 2 μg/L to 4.3 μg/L, slightly above the surface water quality chronic standard of 2.0 μg/L for 2A waters; 6. Further evaluation is recommended. Testing on taconite tailings samples, as well as other typical aggregates, should include physical and chemical parameters. Testing on samples of aggregate and water should be done to evaluate all sites by the same methods and current detection limits. Analytes should include: RCRA metals as well as cobalt. Additional testing should include grain size analyses and hydraulic conductivity; and 7. Mechanisms for the potential release of metals into surface water by tailings are dependent on water characteristics such as pH, Eh, time, hydrology, and reduction (redox) potential. Therefore, it is site specific. Additional testing of leachate from taconite tailings is suggested using SPLP test methods and could include pH dependent leaching and liquid to solid (L/S) ratio dependent leaching as described by Jambeck and Greenwood (2007) and Kosson (2002). Data derived from these test methods may produce results more applicable to use of taconite tailings as fill material in contact with wet environments.