INFLUENCE OF ULTRASOUND ON NITRIC ACID LEACHING OF ALUMINA FROM KAOLIN CLAYS.

Аннотация

This article presents the results of a comprehensive study on the application of ultrasound to intensify the nitric acid leaching of alumina from calcined kaolin clays of the Angren deposit. The propagation of ultrasonic waves in liquid media induces cavitation phenomena that enhance mass transfer and reaction kinetics, especially at the solid–liquid interface. A specially designed ultrasonic bath equipped with a PMS-6M magnetostrictive transducer powered by a UZG-2.5A generator was used to investigate process intensification under controlled conditions. The experiments were conducted using a statistical design of experiments (DoE), specifically a fractional factorial design (2⁴⁻¹), to assess the influence of key parameters: temperature, leaching time, stoichiometric acid dosage, and nitric acid concentration. The optimization criterion was the yield of Al₂O₃ in solution. A regression model was developed, and the method of steepest ascent was applied to identify optimal process conditions. At the optimal point, alumina recovery reached 93% within a significantly reduced leaching time. Keywords: ultrasonic cavitation, alumina leaching, kaolin clay, nitric acid, Angren deposit, hydrometallurgy, process intensification, magnetostrictive transducer, factorial design, aluminum extraction. Introduction. The application of ultrasound to enhance various processes and address specific technological challenges in hydrometallurgy has garnered https://scientific-jl.com/luch/ 3 3 8 Часть-46_ Том-5_ июнь-2025 significant interest among researchers. This growing attention is largely attributed to the distinctive effects produced by the propagation of ultrasonic waves through liquid media. A central mechanism in this context is the formation of cavitation zones, along with a range of chemical and physicochemical transformations that occur within the liquid phase. These effects are particularly pronounced at the interfaces between different phases in heterogeneous, fluid-based technological systems, where ultrasound can significantly influence reaction kinetics and mass transfer. Cavitation phenomena — specifically the formation of gas-filled voids or discontinuities within a liquid — arise from the inherent asymmetry in a liquid's mechanical response: while liquids can resist high compressive forces, they are highly susceptible to rupture when subjected to tensile (negative) pressures, leading to the emergence of vapor-filled cavities. Building upon this physical property, B.A. Agranat [2] proposed and provided a theoretical foundation for the controllability of ultrasonic cavitation processes. In recent years, a wide range of innovative ultrasonic equipment has been developed both domestically and internationally. Among the most widely used configurations are systems incorporating vacuum tube-based generators coupled with magnetostrictive transducers, which remain prevalent due to their reliability and effectiveness in industrial applications. In modern metallurgical practices aimed at extracting metals and other valuable components from various types of ores, a broad spectrum of mechanical vibrations—spanning diverse frequencies and intensities—is actively employed. In particular, high-energy elastic oscillations with frequencies exceeding 18 kHz (i.e., in the ultrasonic range) are increasingly applied to enhance and accelerate a number of critical technological operations. Among the equipment capable of generating such oscillations, vacuum tube-based ultrasonic generators equipped with appropriate transducers are considered highly suitable, as they fulfill key https://scientific-jl.com/luch/ 3 3 9 Часть-46_ Том-5_ июнь-2025 performance criteria for industrial implementation in terms of power stability, frequency range, and operational reliability. In the processing of low-grade alumina-bearing raw materials, leaching represents the central stage in the recovery of the target component — alumina. However, when employing nitric acid leaching techniques, particularly agitation or autoclave methods, the treatment of iron-rich alumina-containing feedstocks often results in relatively low alumina recovery rates, accompanied by significantly increased consumption of acid reagents. This not only reduces process efficiency but also raises concerns regarding economic viability and environmental impact. Methods and Results. In order to optimize leaching efficiency, minimize nitric acid consumption, and reduce processing time, a series of experiments were carried out involving the ultrasonic-assisted leaching of alumina from kaolin clays using nitric acid. The application of ultrasound was intended to intensify the dissolution process, enhance phase contact at the solid-liquid interface, and thereby improve the overall recovery of aluminum from the raw material. Fig. 1. Ultrasonic leaching bath apparatus https://scientific-jl.com/luch/ 3 4 0 Часть-46_ Том-5_ июнь-2025 1 – Ultrasonic bath body (housing) 2 – Structural frame (support