Adsorption and desorption characteristics of rare earth ions on halloysite surfaces

Abstract

Rare earths (REs) are primarily adsorbed in ionic form on the surface of clay minerals such as halloysite in ionic rare earth ores. As a result, understanding the adsorption and desorption behaviors of RE ions on the surface of the halloysite may contribute to clarifying the mineralization process of ionic rare earth ores and provide a theoretical framework for the optimization of the extraction process. The adsorption and desorption characteristics of light (Nd<sup>3+</sup>), medium (Eu<sup>3+</sup>), and heavy (Lu<sup>3+</sup>) RE ions on the surface of halloysite-10 Å were comprehensively examined in this study. Because REs are more inclined to form an outer layer and inner layer adsorption when halloysite is protonated and deprotonated with the range of pH, respectively, pH has a significant impact on how halloysite adsorbs and desorbs. The experiment findings indicate that RE concentration, duration, and pH all increased the adsorption capacity of light, medium, and heavy REEs, and exhibited some selectivity for heavy REEs. Nd<sup>3+</sup>, Eu<sup>3+</sup> and Lu<sup>3+</sup> ions adsorption processes on the surface of Halloysite-10 Å are consistent with the Langmuir isothermal adsorption model and pseudo-second-order kinetic equations. The desorption efficiency of Lu<sup>3+</sup> decreases dramatically with increasing pH due to hydrolysis and more inner layer adsorption than that of Nd<sup>3+</sup> and Eu<sup>3+</sup>.