Efficient Removal of Impurities from Refractory Oolitic Magnetite Concentrate via High-Pressure Alkaline Leaching and Ultrasonic Acid Leaching Process

Acid leaching is an effective method for dephosphorization; however, it is time-consuming and requires a high amount of acid consumption, resulting in increased production costs and environmental risks. This work aims to remove silicon, aluminum, and phosphorus from high-phosphorus oolitic magnetite concentrate through high-pressure alkaline leaching and ultrasonic acid leaching. Compared with traditional acid leaching processes, the sulfuric acid dosage can be significantly reduced from 200 kg/t to 100 kg/t, and the pickling time is shortened from 60 min to 10 min. Thermodynamic and kinetic studies have demonstrated that acid leaching facilitates apatite dissolution at low temperatures, whereas the dephosphorization reaction is controlled mainly by diffusion. The application of ultrasonic waves leads to finer particle sizes and greatly increased specific surface areas, thereby accelerating the diffusion rate of the leaching agent. Furthermore, microscopic analysis revealed that under the influence of ultrasonic waves, numerous micro-fragments and pores form on particle surfaces due to cavitation effects and mechanical forces generated by ultrasonic waves. These factors promote both the reaction rates and diffusion processes of the leaching agent while enhancing the overall leaching efficiency.