Abstract
A research project supported by the Minnesota Department of Natural Resources and the Iron Ore Cooperative Research Committee was undertaken to reduce the dissolution of fluoride into process water during taconite processing. Leach tests were conducted using rod mill feed samples and water containing varying concentrations of calcium and sodium. Laboratory liberation grinds were performed to evaluate fluoride rejection during grinding and magnetic separation. Tube furnace tests were conducted to evaluate fluoride volatilization during pellet induration. The results indicate that fluoride concentration of process water is a function of both calcium and sodium concentration in the process water. It appears that less than 1% of the fluoride present in rod mill feed will dissolve in process water during grinding. More than 90% of the fluoride present in rod mill feed is rejected with tailings during size reduction and magnetic separation. The furnace tests demonstrate that bentonite and fluxstone (calcite and dolomite) addition to taconite concentrate during pellet production increases the amount of fluoride that volatilizes during induration. Lime hydrate addition to pellets decreases the amount of fluoride that volatilizes during pellet induration. During acid pellet production, approximately three times more fluoride enters the wetter during induration-off-gas scrubbing than during grinding. When fluxed pellets are produced, three to eight times more fluoride enters the water during off-gas scrubbing than during taconite grinding.
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References
40 Code of Federal Regulations, 2000a, “National Primary Drinking Water Regulations,” Chapter 1 (7-1-00 Edition), Part 141, Appendix B Subreport 1, p. 555.
40 Code of Federal Regulations, 2000b, “National Secondary Drinking Water Regulations,” Chapter 1 (7-1-00 Edition), Part 143.3, p. 613.
Engesser, J., 1998, “The removal of Sulfate and Fluoride from Process Water — The Effect of Water Chemistry on Filtering and Flotation,” Iron Ore Cooperative Research Project, Minnesota Department of Natural Resources Division of Lands and Minerals, March 16.
Engesser, J., 2001, “The Reduction of Fluoride during Off-Gas Induration Scrubbing,” Iron Ore Cooperative Research Project, Minnesota Department of Natural Resources Division of Lands and Minerals, May 10.
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Engesser, J. Reduction of fluoride dissolution during induration off-gas scrubbing. Mining, Metallurgy & Exploration 22, 43–51 (2005). https://doi.org/10.1007/BF03403195
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DOI: https://doi.org/10.1007/BF03403195