Rejection of rare earth elements from a simulated acid mine drainage using forward osmosis: The role of membrane orientation, solution pH, and temperature variation

Abstract

The high demand for the rare earth elements (REEs) in the clean technological industries implies the increased demand to produce these elements from ores and REEs containing impaired water sources such as acid mine drainage (AMD). However, the presence of these elements in AMD has increased their toxic exposure to the water environment. Herein, we investigated the role of the orientation of the membrane (such as active layer facing feed solution (AL-FS) or active layer facing draw solution (AL-DS) mode), solution pH, and temperature variation on the flux performance and rejection of three REEs (e.g., lanthanum, cerium, and dysprosium) from a simulated AMD solution using the forward osmosis (FO) process. It was found that there was a greater water flux at high pH, AL-DS mode of the FO system and high feed and draw solution temperature. FO could effectively reject all three REEs in both AL-FS and AL-DS membrane orientations mode due to steric hindrance. The rejection of these REEs in the AL-DS mode was slightly lower (82–88%) than that in the AL-FS mode (86–96%). The rejection of all REEs was noticeably influenced by solution pH in both mode. This was due to the changes in membrane surface with pH variation. The rejection of REEs increased when the temperature of the feed and draw solution was 20 and 40 °C, respectively. However, the rejection of all REEs decreased markedly when the temperature of the feed and draw solution was 40 and 20 °C, respectively. The lower rejection of these REEs was due to the enhancement of their diffusivity at a higher temperature in the feed side.