Kinetics of Silica Leaching with Ammonium Hydrofluoride from Iron Ore Refinement Tailings

The waste from iron ore processing with high (over 50%) silica contents is stored in huge quantities in dumps, producing a negative impact on the environment and production economics. We have proposed hydrochemical desiliconization of tailings from wet magnetic separation of titanomagnetites, which ensures the production of pure amorphous silica during waste processing with regeneration of the ammonium hydrofluoride NH₄HF₂ reagent. Leaching with a 10% NH₄HF₂ solution under the chosen conditions led to 45% extraction of SiO₂. An analysis of the experimental data using a number of common kinetic equations showed mixed conditions of silica leaching in the temperature range of 313–363 K, for which the limitation of the chemical reaction of SiO₂ dissolution is simultaneously restrained by diffusion processes at the interphase boundary. The renewal of the particle surface of the raw material in the shrinking core model by mixing to remove the products of the ongoing fluorination reactions has a positive effect on the process efficiency.