American Manganese recently received the report “The Recovery of Manganese From Low Grade Resources: Bench Scale Test Program Completed ” prepared by Kemetco Research, which describes and summarises the extensive bench-scale metallurgical tests of the unit operations – operations which when linked together form the basis of a complete innovative conceptual flowsheet complete with heat, mass and energy balances – designed to process lower-grade manganese mineralisation into high purity manganese metal. In May 2009, Kemetco was commissioned to develop a robust energy efficient hydrometallurgical process that would yield high purity manganese metal and/or manganese dioxide while minimising potential environmental impacts. The work integrates and builds upon the extensive research carried out most notably by the US Bureau of Mines intermittently from the 1940s through the 1980s and proprietary third party research conducted by other mining companies.
The report confirms that American Manganese’s proprietary process can extract manganese at greater than 90% efficiency while minimising water use and potential environmental impacts. The conceptual process flowsheet is based on a unique application of commercially available process equipment so that the process is deemed to be robust and energy efficient. In addition to the production of electrolytic manganese metal, a saleable anhydrous sulphate by-product will also be produced.
Treatment of typical manganese samples containing between 4 and 7% Mn by weight (primarily in the form of pyrolusite, psilomelane and wad), is carried out in a hydrometallurgical process whereby four-valent Mn is reduced and leached by sulphur dioxide dissolved in water. The hydrometallurgical processing of friable lower-grade material avoids intensive crushing and grinding, as well as the undesirable high temperature reduction roasting that is conventionally used in processing hard high grade material. Roasting at temperatures typically between 800 and 1,000°C is energy intensive and would not be economical for lower-grade material.
Leaching studies performed on typical manganese samples of large particle size (greater than 9.5 mm) with dilute SO 2 in stirred tanks indicates that the material is readily leachable. The material is friable and large particles break down easily during stirred tank leaching. SO 2 leachant is produced on-site by burning elemental sulphur with 20% excess air. At a feed processing rate of 3,500 t/d, heat exchanging the exhaust gases from the sulphur burner will produce an estimated 20 t/h of steam at 400°C and 45 bar pressure. In a condensing turbine, this steam can produce 5 MW of continuous electrical power.
The pregnant leach solution (PLS) is purified in two stages prior to separating the manganese by precipitation. Dissolving the precipitate with recycled electrolyte produces a Mn-containing solution that is conducive to producing high-grade Mn metal by EW. Solid tailings with minimum water content are produced by filtration of the final counter current decantation underflow material, minimising water requirements for the overall process. The solid tailings produced from test work were shown to be benign by the Toxicity Characteristic Leaching Procedure, and can be returned to mined-out areas of an open pit facilitating immediate progressive reclamation of disturbed areas.
Based on the successful test work, conceptual flowsheets have been developed which include applications of novel, proprietary, innovative technology to minimise process operating costs through low water use, low overall energy use and economic destruction of unwanted by-products. American Manganese has requested Kemetco to file an application for patent protection.