Ultrasonic-enhanced purification of silica powder from iron ore tailings and preparation of high-grade silica with high value added: reaction optimization, kinetic analysis, and mechanism insights

• Ultrasound-enhanced silica powder leaching from IOTs for high-grade silica. • Thermodynamics show spontaneous acid-leaching of impurity minerals. • Ultrasonic can reduce reaction energy barrier and accelerate impurity leaching. • The SiO 2 purity of high-grade silica reached 99.59% after the UFCL process. The recovery and preparation of high-grade silica from iron ore tailings (IOTs) is of great significance for the high-value utilization of IOTs resources and the reduction of ecological and environmental hazards. Herein, an ultrasonic-enhanced fluoride-free acid leaching (UFCL) technology was proposed to remove impurities in silica powder obtained from IOTs through the S-HGMS preconcentration process and prepare high-grade silica. Thermodynamic analysis results show that the impurity elements (K, Ca, Na, Mg, Al, and Fe) in silica powder mainly existed as water-soluble ions under acidic conditions. Additionally, the decomposition Δ G of each impurity mineral in silica powder was less than 0, indicating that those impurity minerals can react spontaneously with the acid-leaching reagent. Various characterization techniques such as the X-ray diffraction (XRD), scanning electron microscope with energy dispersion spectrum (SEM-EDS), particle sizer, polarized optical microscopy (POM), thermogravimetric analysis (TG), inductively coupled plasma-optical emission spectrometer (ICP-OES) results show that HCl and H 2 C 2 O 4 could hydrolyze a large amount of H + , HC 2 O 4 - and C 2 O 4 2- ions, among the H + ions directly reacted with impurity minerals, while HC 2 O 4 - and C 2 O 4 2- ions would be complexed with impurity ions during the acid leaching process. Kinetic analysis revealed that the activation energy of impurity ions in the UFCL process was lower than that of the conventional acid leaching (CAL) process, indicating that the UFCL process could effectively reduce the reaction energy barrier and accelerate the reaction process. Moreover, it found that ultrasound can open the internal channel of H + into the quartz particles, thus increasing the mass transfer rate of impurity ions and promoting the removal of gas–liquid inclusions and impurity ions. Under the optimal conditions, the SiO 2 purity in high-grade silica increased from 97.42% to 99.59%. This study provides enlightenment for the purification of silica powder to prepare high-grade silica with high market value and high quality from IOTs waste.