STUDY OF LEACHING BEHAVIOR OF RARE EARTH ELEMENTS FROM SISODING GRANITE WEATHERED SOIL, NORTH SUMATRA IN HYDROCHLORIC ACID

• Main Author: M. Al Wafi, T.
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/69419
• Institution: Institut Teknologi Bandung

Rare earth elements (REE) have many uses in advanced technology. One of the ores that are widely used to extract REE is the ion-adsorption clay type from weathered granite soil. Currently, the production and market of REE are still dominated by several countries such as China and the United States. In Indonesia, there are several areas with REE potential, one of which is in the Sisoding area, North Sumatra Province. In this study, the extraction process of REE from weathered granite soil originating from the Sisoding area was studied, which has ion-adsorption clay type. The extraction process is carried out by leaching in a solution of ammonium sulfate and a solution of hydrochloric acid. The preliminary experiment (1st stage) began with the leaching of weathered granite using ammonium sulfate and hydrochloric acid with various concentrations of leaching agents. Furthermore, the second stage of the experiment was carried out to determine the optimum conditions for extraction of REE using hydrochloric acid (HCl) solution and identify the significant effect of the experimental variables on the extraction percentage of REE, and determine the activation energy of the leaching. In determining the optimum conditions and the significance of the experimental variables on the extraction of REE, the leaching experimental design was carried out using the Taguchi method with L9 orthogonal matrix. The concentration of HCl was varied at 2 mol/L, 4 mol/L, and 6 mol/L. Leaching times were varied at 1 hour, 2 hours, and 3 hours. The solid/liquid ratio (S/L) was varied at 142.9 g/L, 166.7 g/L, and 200 g/L. The leaching temperature varied at 50 oC, 70 oC, and 90 oC. The percentage of REE extraction was calculated based on the total mass of dissolved REE and the total mass of REE in the residue obtained from the inductively coupled plasma mass spectrometry (ICP-MS) analysis. The data of extraction percentage obtained from the second stage of the experiment was processed using the Taguchi and ANOVA methods to determine the optimum conditions and the significance influence of the experimental variables on the extracted REE and metal impurities (Al and Fe). The kinetics analysis of REE leaching with the Shrinking Core Model was also carried out, and its activation energy was determined. The experimental results showed that leaching with ammonium sulfate was not effective in extracting REE. In the experiment with HCl, the optimum condition was obtained at an HCl concentration of 6 mol/L, leaching time of 2 hours, S/L ratio of 200 g/L, and temperature of 90 oC with the extrated REE, Al, and Fe was 82.1%, 26.7%, and 80.28%, respectively. The contribution of the effect of HCl concentration, leaching time, S/L ratio, and temperature to REE extraction was 14.60%, 1.26%, 1.38%, and 80.26%, respectively. Kinetic analysis showed that the leaching of REE from weathered granite with hydrochloric acid was controlled by the interfacial chemical reaction with an activation energy of 46,35 kJ/mol.