Weakening of mechanical parameters of ion-absorbed rare-earth ores subjected to leaching

Abstract

Ion-adsorbed rare-earth ores are mined using in-situ leaching, and their mechanical properties significantly affect the efficient and safe recovery of rare earth elements. However, the mechanism of the change in the mechanical properties of the ore body due to the physicochemical processes caused by leaching remains unclear. To explore the strength evolution characteristics of the ore body during the leaching process, unconsolidated undrained triaxial tests were conducted to confirm how the stress–strain curve and shear strength of rare-earth samples change during leaching. Magnetic resonance imaging and T2 spectral characterizations were obtained by using nuclear magnetic resonance technology to measure the interior pore structure of samples during leaching. A scanning electron microscope equipped with an energy dispersive spectrometer was used to investigate the morphology evolution and the composition changes of the internal micro-area of the samples, to demonstrate the correlation between the microstructural change and the macroscopic mechanical properties. The results show that when a 2% ammonium sulfate solution is employed for mineral leaching, the effective leaching duration is 0–3 h. During this time, ion exchange occurs along the direction of solution seepage, resulting in the dispersion and migration of fine particles from the top to the bottom of the sample, which further triggers a change in the sample's pore structure and pore size. In addition, the local loss of fine particles resulted in a reduced bond strength between minerals, forming an unstable soil structure with a loose upper part and a dense lower part, which is macroscopically expressed as a declining shear strength parameter of the rare-earth sample.Graphical abstract