Characteristics of Electrical Resistance Alteration during In Situ Leaching of Ion-Adsorption-Type Rare Earth Ore

The chemical reaction of ion-adsorption-type rare earth ore during the in situ leaching process is accompanied by ion migration and charge movement, making the leaching process electrochemical in nature. The chemical reaction rate plays an important role in the leaching rate of rare earth elements. In this work, electrochemical impedance spectroscopy (EIS) was used to reveal the characteristics of electrical resistance alterations and leaching rate of rare earth elements during in situ leaching. The equivalent circuit model of the leaching process was established, and two critical parameters of solution resistance Rs and charge transfer resistance Rt were analyzed to reflect the electrochemical characteristics. According to the characteristics of electrical resistance alteration, the leaching process was divided into four stages: wetting, reaction, equilibrium, and top water stage. The resistance parameters Rs and Rt decreased first and then increased during the leaching process. The maximum value of Rs was 1330 Ω∙cm2 at the end of the top water stage, and the minimum value was 125 Ω∙cm2 at the beginning of the equilibrium stage. The maximum value of Rt was 8310 Ω∙cm2 at the beginning of the leaching stage, and the minimum value was 21 Ω∙cm2 at the end of the reaction stage. Rs and Rt were negatively correlated with the pore size and chemical reaction rate during leaching. With an increasing pore size and reaction rate, the resistance parameters decrease. This study provides a new idea for the intelligent monitoring of rare earth ore.