The ferromanganese furnaces of the sponsor produce fines that are collected in scrubbers and are then impounded as a waste product (furnace sludge). The Council for Mineral Technology (Mintek) tested various leaching procedures to solubilize the manganese constituent (about 25 per cent) and to convert the manganese sulphate liquor to battery-grade electrolytic manganese dioxide (EMD) by electrolysis. Continuous runs were conducted on miniplant scale (with a 4-litre electrolytic cell) and on pilot-plant scale (with a 1500-litre electrolytic cell). Several types and shapes of electrode were tested, including carbon, graphite, and titanium rods, and titanium sheets. A number of Japanese and other international standard samples were analysed for comparison with the material produced at Mintek. A comparison was also made between the material produced from prereduced manganese ore and that produced from furnace fines. The recovery of manganese from the furnace fines was about 75 per cent. However, the leach liquors had to be purified for the removal of soluble organic matter. The operation of the electrolytic cell was optimized, and internationally acceptable grades of EMD were produced: Electrolyte 35 to 40 g of H2SO4 and 60 g of Mn per litre. Cell temperature 90 to 93 C. Current density 80 A/m2. Current efficiencies 85 to 90 per cent. Corrugated titanium sheets coated with ruthenium oxide to prevent passivation gave the best quality of EMD (with an available oxygen content, expressed as MnO2, of 92 per cent, which is better than the international specification of 90 per cent MnO2 as minimum). Batches of the material produced at Mintek were submitted to battery manufacturers in the UK, Japan, Germany, and the USA for evaluation.