Recovery of pigment-quality magnetite from jarosite precipitates

Sodium and ammonium jarosite precipitated from the sulfuric acid leaching of deep-sea nodules were converted into pigment-quality magnetite by alkali decomposition of jarosite using sodium hydroxide or ammonia solutions at 60 °C and subsequent reaction with FeSO4 at 95 °C. It was found that the base-strength of alkali solutions affected the kinetics of conversion reactions and the morphology of solid phase. The main impurities in jarosite precipitates such as Mn, Cu and Ni were reported into the final products. The sulfur-free magnetite products with the same chroma difference (∆Cab⁎) and the hue difference (∆Hab⁎) as commercial pigments Bayferrox were obtained.