Methods and systems for regenerating and pretreating oxides of manganese and precipitation of oxides of manganese from manganese salt solutions. The oxides of manganese and manganese salt solutions are processed utilizing heated aqueous oxidizing solutions at or near boiling at atmospheric pressure. Solution temperature, Eh value and pH value are monitored and adjusted so as to move solution conditions into and to maintain them within the MnO.sub.2 stability area. This results in regenerated, pretreated and precipitated oxides of manganese having high or increased pollutant loading capacities and/or oxidation states. Oxides of manganese thus produced are, amongst other uses; suitable for use as a sorbent for capturing or removing target pollutants from industrial gas streams. Filtrate process streams containing useful and recoverable value present as spectator ions may be further processed to produce useful and marketable by-products.