The increasing demand for battery-grade manganese products has created growing interest in recovering manganese from secondary resources. This study investigates the production of high purity manganese sulfate monohydrate (HPMSM) from two ferromanganese smelter waste streams; slag and manganese mud derived from furnace dust. The mud, mainly composed of manganese carbonate, contains approximately 40 per cent Mn, while the slag contains around 20 per cent Mn. Separate leaching approaches were developed for each material due to their differing characteristics. Mud was treated via direct sulfuric acid leaching, achieving high manganese dissolution. Under optimum conditions, Mn recovery was above 90 per cent. In contrast, conventional acid leaching of slag led to silica-related gel formation, which made filtration difficult and time-consuming. To address this, a water-starved leaching method, also known as the ‘quick leach’ method, was developed. This approach involves an acid curing step followed by controlled leaching with limited water addition, resulting in significantly improved solid–liquid separation. Using this method, Mn recovery of approximately 85 per cent was achieved. Following leaching, the pregnant leach solutions (PLS) from both streams were purified through a combination of neutralisation-precipitation and solvent extraction (SX) processes. Neutralisation using hydrated lime effectively removed impurities such as Al, Fe, Si, and some Zn. Solvent extraction under proper conditions enabled selective extraction of manganese, while Ca and Mg remained largely in the raffinate. The purified manganese solution obtained after stripping was suitable for crystallisation. Preliminary crystallisation tests produced manganese sulfate crystals approaching Class II industry specifications for HPMSM. The proposed flow sheet demonstrates a practical and promising hydrometallurgical route for converting ferromanganese smelter wastes into a high-value product, supporting more circular and sustainable manganese processing.