| Summary: | The mineral surface structure and ions’ interaction were of significant interest to understanding mineral dissolution and reaction. In this study, X-ray photoemission spectroscopy combined with ICP emission spectrometer was used to investigate the influence of the leaching reaction conditions of 8 M dilute sulfuric acid and 12 M concentrated sulfuric acid on the surface chemical composition, chemical (valence) state and ion distribution of Columbite-(Fe) (FeNb<sub>2</sub>O<sub>6</sub>). The binding energy of the cations (Fe, Nb) bonding with different anions (O<sup>2−</sup>, SO<sub>4</sub><sup>2−</sup>) and the ratio of Fe<sup>3+</sup>/Fe<sup>2+</sup> oxidation–reduction provided direct understanding of Fe and Nb releasing from the mineral surface during leaching. The results showed that the binding energy of the Nb<sup>5+</sup>-O bond was much smaller than that of Nb<sup>5+</sup>-SO<sub>4</sub>, and the binding energy decreased in sequence as Nb<sup>5+</sup>-O < Fe<sup>2+</sup>-O < Fe<sup>3+</sup>-O and increased in sequence as Fe<sup>3+</sup>-SO<sub>4</sub> < Fe<sup>2+</sup>-SO<sub>4</sub> < Nb<sup>5+</sup>-SO<sub>4</sub>. The mineral surface reaction during the leaching could be expressed with the formula: Fe-O + H<sub>2</sub>SO<sub>4</sub> → Fe-SO<sub>4</sub> + H<sub>2</sub>O, Nb-O + H<sub>2</sub>SO<sub>4</sub> → Nb-SO<sub>4</sub> + H<sub>2</sub>O. The results also revealed that Nb dissolution from Columbite-(Fe) occurred more easily compared to Fe. Nb dissolution from the mineral was owed to the content of H<sup>+</sup> in solution, and increasing the H<sup>+</sup> concentration could promote the dissolution. For Fe dissolution from the mineral, the oxidation potential could play an effective role in enhancement dissolution.
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