Recovery of red iron oxide pigment from zinc plant hematite precipitates

Hematite precipitates during zinc hydrometallurgy contain a certain amount of Zn and S impurities, which limit its applications. To remove these impurities and prepare high-value red iron oxide, a two-part study was carried out by atmospheric water washing and high-temperature hydrothermal treatment. The results showed that Zn2+ and SO42- existed two forms: adsorbed on the surfaces of hematite precipitates and via physical inclusions; as insoluble sulfates, jarosite, and basic ferric sulfate. During the high-temperature hydrothermal reactions (240 degrees C, 6h, 10g/L H2SO4, 6 mL/g liquid-to-solid ratio), the non-iron phases in hematite precipitates transformed into iron oxides. The iron content in the product increased from 58.7% to 68.8%, the sulfur content decreased from 2.96% to 0.63%, and the zinc content decreased from 1.03% to 0.07%. The specific surface area increased from 0.39m(2)/g to 1.44 m(2)/g. These products met the application requirements of ISO 1248-C-II-2-a for red iron oxide.