Abstract & first few paragraphs of article --i added some boldfacing for emphases...
Minerals & Metallurgical Processing, 2012, Vol. 29, No. 1, pp. 61-74. An official publication of the Society for Mining, Metallurgy and Exploration, Inc. [SME]
New developments in the recovery of manganese from lower-grade resources
N. Chow, A. Nacu, D. Warkentin, H. Teh and I. Aksenov
Kemetco Research Inc., Richmond, BC, Canada
J.W. Fisher
American Manganese Inc., White Rock, BC, Canada
Abstract
The recovery of manganese from lower-grade resources has been studied for a number of years. Of key importance in prior work was the discovery that higher-valent manganese can be readily leached with sulfurous acid. This eliminates the need for high-temperature reduction roasting that is conventionally used in processing high-grade material. High-temperature roasting is energy intensive, emits a large amount of carbon dioxide and would not be economical for processing lower grade material. While the prior work provides important information for extracting manganese from lower-grade resources, the production of unwanted byproducts and high water and energy usage has limited its commercial use. This paper describes the results from laboratory work that demonstrate solutions to problems that to this point have precluded commercial development. Preliminary mass and energy balances show that a significant opportunity exists in producing manganese with this hydrometallurgical scheme in a low-cost, environmentally friendly manner. The emphasis of the work is on low water use, low overall energy use and economic destruction of unwanted byproducts.
Paper number MMP-10-055. Original manuscript submitted November 2010. Revised manuscript accepted for publication July 2011. Discussion of this peer-reviewed and approved paper is invited and must be submitted to SME Publications Dept. prior to August 31, 2012. Copyright 2012, Society for Mining, Metallurgy, and Exploration, Inc.
Introduction
The recovery of manganese from lower-grade resources has been studied for a number of years. Henn et al. (1968) provide a detailed review of the major processes using hydrometallurgical techniques. The report by Henn et al. makes reference to forty-eight research reports, with a significant number by the U.S. Bureau of Mines. Pahlman and Khalafalla (1988), in a more recent U.S. Bureau of Mines report, provide detailed reactions that take place when leaching four-valent manganese (Mn4+) minerals with sulfur dioxide (SO2) dissolved in water. The motivation for the prior work was to develop a process to provide North American steelmakers with a stable supply of manganese from lower-grade domestic resources in the event of imported supplies becoming unavailable. North American steelmakers are solely dependent on foreign sources of manganese to meet their requirements. There is no substitute for manganese in the steelmaking process.
Of key importance to the prior work in the development of manganese extractive metallurgy was the discovery that four-valent manganese is readily leachable with sulfurous acid, which is a reducing acid formed by dissolving SO2 in water. Leaching the Mn resource with sulfurous acid eliminates the need for roasting and, as such, vastly improves the potential for economic recovery of Mn.
The important reactions occurring when four-valent manganese resources are leached with aqueous SO2 are shown in the following two equations:
MnO2 + SO2 ¨ MnSO4 (1)
MnO2 + 2SO2 ¨ MnS2O6 (2)
Reaction 1 is most desirable, as Mn is leached into solution with minimal use of SO2, and because manganese sulfate (MnSO4) in solution can be directly used for electrowinning at the correct concentration. Reaction 2 is less desirable, because of the higher consumption of SO2. The manganese dithionate (MnS2O6) precludes proper control for electrowinning high-purity Mn metal and must be removed before electrolysis.
A report by Allen (1954) describes methodology to evaporate the pregnant leach solution to form MnSO4 and MnS2O6 crystals. Sintering the crystals at 1,100 to 1,200‹ C will produce a Mn3O4 product, as well as evolve SO2 gas, which can be recycled to the leach stage. The high temperature for sintering was used in this case in order to decompose MnSO4 into Mn3O4 […]
Key words: Manganese, Acid leaching