The pilot plant testing program performed by Kemetco Research has been successfully completed. The work has confirmed the technical viability of the American Manganese’s patent pending hydrometallurgical manganese extraction and EW circuit on a semi-continuous operation basis of the overall flowsheet. The process is designed to recover manganese from lower grade manganese resources in an energy efficient manner with low water use, thus providing significant environmental benefits compared to the conventional recovery process which is energy intensive based on high grade resources.The pilot plant treated material from the Artillery Peak resource situated at Mojave County, Arizona. Operation of the pilot plant produced high purity electrolytic manganese metal (EMM) of greater than 99% purity. Chilling the mixed sulphate/dithionate solution produced by the intermediate precipitation of manganese from the pregnant leach solution produced sodium sulphate/dithionate crystals that were further processed to produce anhydrous sodium sulphate. The mother solution from the chilling circuit was shown to have salt concentrations that were suitable for feed in a nanofiltration circuit. Operation of the nanofiltration unit using a commercially available membrane achieved 97% rejection of sodium sulphate and 95% rejection of sodium dithionate, thus producing clean water suitable for reuse in the process.Solid/liquid separation testing conducted by Pocock Industrial showed that practical dewatering of the tailings can be achieved with a paste type thickener and pressure filtration following the multistage Counter Current Decantation (CCD) stages. Final tailings dewatered to a stackable low water content (33.6%) was achieved. Environmental testing confirmed that the solid residues are not acid generating.Mass and energy balances on the anhydrous sodium sulphate and water recovery circuit were provided by Swenson Technologies. As a result of its study, a more energy efficient sodium sulphate crystallisation process option was identified which may provide further significant reductions in energy requirements for this circuit. Further work on this process option will be conducted in the feasibility stage.The new process developed by Kemetco Research on behalf of American Manganese is shown to be significantly more energy and water efficient than previous work conducted by the US Bureau of Mines (USBM) some 30 to 60 years ago on the same resource material. In addition, the use of modern commercial equipment in a unique configuration has removed a significant amount of technical risk for the new process.