Roasting Behaviors of Siliceous Black Shale and the Influence on Acid Leaching for Green Extraction of Vanadium and Nickel

Black shale, as a low-grade polymetallic mineral, is an important vanadium resource. The siliceous black shale is usually treated with a direct acid leaching process to extract valuable metals such as vanadium and nickel, which shows low efficiency and is non-environmentally friendly. Fluidized oxidation roasting pretreatment prior to sulfuric acid leaching was employed to improve the extraction process in the present work. The mechanism of fluidized oxidation roasting and the influence on sulfuric acid leaching was emphatically studied. After roasting at 800 ℃ for 30 minutes, carbon, sulfur, and hydrogen in the siliceous black shale were volatilized, vanadium-bearing minerals were destroyed as well as low valence vanadium was deeply oxidized, and nickel-bearing magnesite was decomposed. The pyrite in the siliceous black shale was transformed into hematite with poor acid solubility, and the spinel structure of chromite was basically maintained. Compared with direct acid leaching, the roasting-acid leaching effectively promoted the extraction of vanadium and nickel, the leached fractions of which reached 82.93% and 84.68%, respectively, and concurrently inhibited the leaching of the typical harmful impurities iron and chromium. The fluidized oxidation roasting pretreatment prior to sulfuric acid leaching of siliceous black shale can improve the efficiency and selectivity for the extraction of vanadium and nickel from iron and chromium. The discharge of acidic toxic wastewater containing heavy metals can be reduced at the source which will provide a cleaner and green production route for efficient utilization of siliceous polymetallic shale.