Differential leaching mechanisms and ecological impact of organic acids on ion-adsorption type rare earth ores

The extraction of rare earth elements (REEs) via chemical leaching from ion-adsorption type rare earth ores has led to serious ecological and environmental risks. Organic acid leaching agents possessed advantages in environmental friendliness and differential leaching capabilities. This study investigated the leaching behaviors of REEs from ion-adsorption type rare earth ores using organic acids and focused on the differential leaching properties of light rare earth elements and heavy rare earth elements. The leaching conditions using acetic acid, malic acid, and citric acid were optimized, and the influences of organic acid on mineral properties and soil ecological functions were elaborated. The experimental results indicated that acetic acid, malic acid, and citric acid had unique REEs differential leaching properties, without significantly altering the mineral structure. The leaching efficiency of full-phase, and colloidal sediment phase REEs reached 49.75%, and 28.03% for acetic acid, 52.07%, and 26.65% for malic acid, 51.79%, and 33.07% for citric acid, respectively. Furthermore, the patterns of the soil enzyme activity also confirmed the perspective that the soil ecology had not been affected obviously by the organic acids leaching process and rapidly recovered after leaching. Subsequently, Visual Minteq simulation and Density Functional Theory calculations indicated the differential leaching mechanism of light and heavy rare earths depended on the differences in complexation effects of organic acid, and the leaching of colloidal sediment phase REEs was the result of combined effects of acid leaching and complexation competition. The work provided molecular-level insights into the colloidal sediment phase REEs leaching and differential leaching mechanisms of light and heavy rare earths by organic acids, contributing to the understanding of REEs extraction processes.