The Mechanism of Selective Dissolution Reaction of Columbite with H 2 SO 4

The chemical states and ions interaction were significant interest to understanding columbite mineral/acid solution interface dissolution and reaction. The present research work was focus to explore the specific cations (Nb 5+ , Fe 2+ , Fe 3+ ) distribution near the ferrocolumbite mineral/acid solution interface, and determine these cations leaching sequence in sulfuric acid solution. X-ray photoelectron spectroscopy had the potential to provide detailed dissolution information by resolving chemical state and ion distribution of ferrocolumbite during sulfuric acid leaching process. The binding energy decreased in sequence as Nb 5+ -O < Fe 2+ -O < Fe 3+ -O, and increased in sequence as Fe 3+ -SO 4 < Fe 2+ -SO 4 < Nb 5+ -SO 4 which revealed Nb in ferrocolumbite mineral more easily leached comparing to Fe. The ratio of Fe 2+ -O/Fe 3+ -O on leaching residue decreased, and Fe 2+ -SO 4 /Fe 3+ -SO 4 ratio increased as sulfuric acid contraction increasing suggested that the Fe 2+ oxidized to Fe 3+ and released Nb from mineral and dissolved into leaching solution. The ratio of Nb/Fe was lower 0.07 with sulfuric acid contraction increasing which meant Nb dissolution promoted by oxidation of iron. The dissolution mechanism of Fe element in ferrocolumbite mineral was Fe 2+ - O broken and generated Fe 2+ . Fe 2+ was oxidized to Fe 3+ in concentrated sulfuric acid leaching solution. The dissolution mechanism of Nb in ferrocolumbite was that Nb 5+ -O was directly digested by H + , and the released Nb 5+ complex with SO 4 2− ion formed cation − anion pairs. The coordination of formation Nb 5+ -SO 4 pairs and oxidation Fe 2+ in mineral could promote ferrocolumbite dissolution.