High-Efficiency Removal of Silica and Alumina from Rough Concentrate of Refractory Oolitic Hematite Ore via High-Pressure Alkaline and Acid-Leaching Process

Abstract

Despite the abundant reserves of high-phosphorus oolitic iron ore, its complex mineral structure, ultrafine crystal grains, and elevated phosphorus content render conventional beneficiation techniques ineffective for the deep removal of silicon, aluminum, and phosphorus impurities. This study innovatively proposes a synergistic impurity removal process that combines high-pressure alkaline leaching with acid leaching. Compared with conventional alkaline leaching, the high-pressure leaching process has significant advantages: the leaching duration decreases from 60 min to 20 min, the NaOH consumption decreases from 300 kg/t to 200 kg/t, the iron concentration increases from 58.14% to 61.95%, and the SiO₂, Al₂O₃, and P contents decrease to 2.53%, 6.58%, and 0.052%, respectively. Mechanistic studies reveal that elevated temperature and pressure conditions significantly enhance the penetration of NaOH solution into particle interiors, where the alkaline medium selectively reacts with silicate gangue phases. This reaction disrupts the oolitic structure, exposing fresh reactive surfaces and accelerating gangue dissolution kinetics. The synergistic effects establish a three-dimensional leaching channel network on particle surfaces, providing critical thermodynamic and kinetic conditions for efficient impurity removal. These findings offer theoretical insights into the high-value utilization of similarly refractory iron ores and propose a transformative technical framework for deep impurity extraction in complex ore systems.