Recovery of ruthenium resources from red mud via phosphoric acid leaching: A comprehensive investigation of leaching effects and kinetics
Abstract
Typical industrial solid waste, red mud, contains significant amounts of ruthenium, an important secondary resource for valuable metals. This study aimed to investigate the efficient leaching of ruthenium from red mud by comparing the leaching efficiency of different inorganic acids. The results indicated phosphoric acid exhibited the highest leaching effect compared to sulfuric acid, nitric acid, and hydrochloric acid. The influences of leaching temperature, phosphoric acid concentration, leaching time, liquid-solid ratio, and stirring speed on the leaching of ruthenium were examined. Under the conditions of a leaching temperature of 90°C, a phosphoric acid concentration of 5 mol/L, a leaching time of 6 h, a liquid-solid ratio of 12:1, and a stirring speed of 500 rpm, ruthenium leaching efficiency of 93.53%. SEM-EDS characterization of red mud before and after leaching confirmed that most of the ruthenium is transferred into the liquid phase, while a small portion remains in the leach residue. X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectra analyses also revealed significant changes in the mineral structure of red mud during leaching, along with the presence of recoverable iron, aluminum, and calcium in the leach solution. Furthermore, the shrinkage kernel model described the kinetics of ruthenium leaching. The leaching process of ruthenium is primarily governed by chemical reactions at temperatures of 40-60°C, with an activation energy of 57.36 kJ/mol, as expressed by the kinetic equation . At temperatures of 70-90°C, the leaching process is controlled by chemical reactions and solid film diffusion, with an activation energy of 39.80 kJ/mol, as expressed by the kinetic equation . These findings provide innovative insights into the recovery of ruthenium resources and the comprehensive utilization of red mud.