Activation Mechanism of Ammonium Fluoride in Facile Synthesis of Hydrated Silica Derived from Ferronickel Slag-Leaching Residue

Abstract

A novel process for the synthesis of hydrated silica derived from ferronickel slag (FNS)-leaching residue was proposed in this study. The products of the purification of hydrated silica with 99.68% grade and 95.11% recovery can be obtained through ammonium fluoride (NH4F) roasting, followed by the process of water leaching, ammonia precipitating, and acid cleaning under the optimized conditions. The effects of NH4F mass ratio, roasting temperature, and roasting time on the water-leaching efficiency were investigated in detail. The thermodynamic and X-ray diffraction analyses indicated that the amorphous silica in FNS-leaching residue was converted to water-soluble fluoride salts ((NH4)2SiF6) during the roasting process, which are also supported by the scanning electron microscopy and thermogravimetry analyses. The Si–O bonds in amorphous silica could be effectively broken through the ammonium fluoride activation during a low-temperature roasting process. This work provides a meaningful reference for further studies on the facile synthesis of hydrated silica with similar mineral compositions.