(143d) Phosphorous-Doped Mesoporous Carbon As an Efficient Adsorbent for the Recovery of Neodymium (III) Metal Ion from an Aqueous Medium

Owing to their unique and excellent optical, catalytic, magnetic, chemical, and physical properties, rare earth elements (REEs) are essential resources in modern industries, such as batteries, metallurgy, medicine, turbines, electric cars engines, and communication devices. With the rapid development of high-technology industries, the demand for REEs has significantly increased throughout the world. However, the deposits of REE-containing minerals are very limited, and their supply is primarily controlled by China. Additionally, radioactive elements like Th (IV) co-exist with REE minerals causing major environmental pollution from the production of REEs from virgin ore. Hence, with the ever-increasing REE demand, lack of diversity in suppliers, and environmental challenges, efficient strategies for REE recovery (i.e., Neodymium) from REE containing End-of-life (EoL) scrap are becoming an attractive option.

Various methods have been explored to recover and separate REEs from industrial effluents and end products that contain REEs such as solvent extraction, chemical precipitation, ion exchange, and adsorption. Compared with other methods, recovery of REEs using adsorption is more viable due to its simplicity of design and operation, low environmental pollution, low cost, and high recovery efficiency. Carbon-based adsorbents are promising materials for the recovery of REEs from aqueous solutions, due to the advantage of good thermal, mechanical, and chemical stability, environmental friendliness, low cost, tunable pore size, and high surface area. On top of that, the preparation of these materials from abundant, cheap, and renewable raw materials makes them great candidates for efficient adsorption of REEs. Rare-earth phosphate precipitates are stable in an aqueous solution and most of the natural REEs ore is in the form of phosphate-bearing minerals, indicating that REEs have strong complexation abilities for phosphorus-based adsorbents.

Herein, phosphorus-doped mesoporous carbon (P-MC) was prepared by employing KIT-6 mesoporous silica as a hard template, saccharose, and phytic acid (PA) as a precursor of carbon and phosphorous source. The synthesized material was characterized using different techniques and explored for its potential application in the recovery of Neodymium ion (Nd³⁺) from an aqueous solution. The parameters that affect the adsorption process such as solution pH, contact time, initial metal ion concentrations, and presence of interfering ions were investigated by batch adsorption experiments. The P-doped mesoporous carbon adsorption capacity was much greater than that of the pristine or un-doped mesoporous carbon, which verifies the importance of phosphorous functionalization on mesoporous carbon. Apart from adsorption kinetic and isotherm models, FTIR, XPS, and EDX analyses were performed before and after the adsorption to predict the binding mechanism Nd (III) with P-MC. Various organic and mineral acids were tested to strip the adsorbed metal ion from the adsorbent P-MC for its reusability performance. Finally, durability for adsorption capacity was assessed using adsorption/desorption runs to observe its potential for practical application.

This work was supported by NRF funded by the Ministry of Science and ICT (2020R1A2C1003560, 2021R1A2C2093746, and 2021R1H1A2008284), Ministry of Education (2020R1A6A1A03038817).