Enhancing the pyrophyllite ore grade for filler applications by acid leaching

Abstract

Pyrophyllite possesses unique physical and chemical properties, but it rarely occurs naturally in high-grade form. This study investigates the upgrading of low-grade Saudi pyrophyllite ore through oxalic acid leaching to remove iron impurities. The ore was characterised using transmitted and reflected light microscopy, X-ray fluorescence, scanning electron microscopy, X-ray diffraction, and wet chemical analysis. Key parameters affecting iron dissolution—including particle size, acid concentration, temperature, leaching time, stirring speed, and solid concentration—were systematically evaluated. Optimal leaching conditions were determined as follows: 0.8 M oxalic acid, 60 min leaching time, 90°C temperature, 1000 rpm stirring speed, 5% solids concentration, and a particle size of −125 µm. Under these conditions, up to 90.5% of iron was removed, yielding a final concentrate with only 0.13% Fe₂O₃ and 0.24% TiO₂. The resulting product achieved a high whiteness index of 89%, making it suitable for filler applications.