Vanadium selective separation enhancement from iron in black shale using oxalic acid due to FeS2 (100) surface passivation: A theoretical and experimental study

Iron impurity tends to precipitate and reduces vanadium product purity during vanadium extraction from black shale. Oxalic acid is an eco-friendly leachant which can enhance vanadium selective separa-tion from iron impurity. In this paper, the separation mechanism was systematically investigated. The mineral phases transformations and thermodynamics analysis indicate that the FeS2 in black shale can react with H2C2O4, HC2O4-, C2O42-and O2, as a result, the pyrite surface was coated by ferrous oxalate pas-sivation layer, which can depress pyrite dissolution reaction. Meanwhile, the density functional theory (DFT) calculations show that the H2C2O4, HC2O4- and C2O42-can reconstruct FeS2 (100) surface by adsorp-tion, and the adsorption energy can be as low as-3.73 eV for C2O42-adsorption configuration. The elec-trons in Fe atoms were transferred to O atoms and the stable Fe-O bands together with closed seven/ eight-membered rings structures were formed as passivation layer, which can weaken and reduce Fe atoms reactive activation for the FeS2 during oxalic acid leaching. This study reveals vanadium separation from iron due to pyrite passivation in presence of oxalic acid at an atomic level.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the separation mechanism of vanadium from iron impurity during vanadium extraction from black shale using oxalic acid. It reveals that oxalic acid can react with iron impurity, forming a ferrous oxalate passivation layer on pyrite surface, which inhibits the dissolution of pyrite and enhances vanadium purity. Density functional theory calculations show that oxalic acid can reconstruct the surface of pyrite and form a stable passivation layer, reducing the reactivity of iron atoms.