Alkali fusion followed by a two-step leaching of a Brazilian zircon concentrate

This work describes the processing of a Brazilian zircon (ZrSiO4) concentrate via fusion with sodium hydroxide. The goal was to produce a zirconyl sulphate solution (ZrOSO4). The effects of NaOH/ZrSiO4 mass ratio, temperature and reaction time were investigated. The fused mass was leached with pure water, followed by leaching of the insoluble matter with sulfuric acid. The effects of temperature and liquid/solid ratio on water leaching were investigated, as well as the influence of temperature and acid concentration on ZrOSO4 purity. The best fusion conditions were: NaOH/ZrSiO4 mass ratio = 1.5:1; temperature, 575 °C; reaction time, 30 min. Water leaching was best conducted with a water/fused mass ratio = 3.75 at 25 °C. Acid leaching required 100 mL 3 mol L− 1 H2SO4 g− 1 water-insoluble solid at 25 °C. 97 wt.% of ZrSiO4 was decomposed and around 91.5 wt.% of Zr was recovered in the final product.