Effective recovery of rare earth from (bio)leaching solution through precipitation of rare earth-citrate complex

What are the different biomolecules involved in the selective recovery of REEs from mining wastewater using FeNPs synthesized from two plant extracts?

Extracting rare earth elements (REEs) from wastewater is crucial for saving the environment, sustainable use of natural resources and economic growth. Reported here is a simple, low cost and one-step synthesis of Fe nanoparticles (FeNPs) based on two plant extracts having the ability to recover REEs. The synthesis of FeNPs using Excoecaria cochinchinensis leaves extract (Ec-FeNPs) exhibited high selectivity for heavy rare earth due to unique biomolecules, achieving separation coefficients (Kd) of 3.16 × 103-4.04 × 106 mL/g and recovery efficiencies ranging from 71.7 to 100 %. Conversely, the synthesis of FeNPs using Pinus massoniana lamb extract (PML-FeNPs) revealed poorer REE recovery efficiencies of 7.2-86.7 %. To understand the differences between Ec-FeNPs and PML-FeNPs in terms of selectivity and efficiency, LC-QTOF-MS served to analyze the biomolecules differences of two plant extracts. In addition, various types of characterization were carried out to identify the different functional groups encapsulated on the surface of FeNPs. These results reveal the source of the difference in the selectivity of Ec-FeNPs and PML-FeNPs for REEs. Furthermore, during DFT calculations, it was found that biomolecules with varying affinities for the surface of FeNPs interact with each other, leading to the formation of structures that exhibit high reactivity towards REEs. Finally, incorporating Spearman correlation analysis demonstrates that the selective removal efficiency of REEs was closely linked to surface complexation, ion exchange, and electrostatic adsorption. Consequently, this work strongly highlights the potential for the practical application of novel adsorbents in this field.

Activated carbon from Camellia oleifera shells for adsorption of Y(iii): experimental and DFT studies

Yttrium is an important rare earth element and is widely used in fields such as special glass preparation, metallurgy, and materials science. However, it is difficult to recover yttrium ion waste from dilute solutions with traditional processes, resulting in a significant waste of rare earth resources. The simple, effective, and easy-to-operate adsorption method is the most promising method for recovering yttrium, which is of great significance for sustainable development of the rare earth industry. In this study, activated carbon was prepared from Camellia oleifera fruit shells (COS) using phosphoric acid activation, and efficient recovery of Y(iii) from the Camellia oleifera fruit shell activated carbon was studied. Adsorption equilibrium data showed that this activated carbon had a Y(iii) adsorption capacity of 35.41 mg g-1, indicating significant potential for recovery of yttrium ions. The adsorption of Y(iii) by the activated carbon prepared from COS was consistent with the Langmuir model, and the adsorption data were consistent with the pseudo second-order kinetic model, indicating that the adsorption process was primarily chemical adsorption. After adsorption, the surface of the activated carbon contained large amounts of N, O, and Y, indicating that Y(iii) was stably adsorbed. The mechanisms for adsorption of Y(iii) on three types of activated carbon were studied through DFT calculations. The results showed that Y(iii) interacted with the carbon atoms on the surfaces to form new chemical bonds. The yttrium ion adsorption capacities for the three different activated carbons decreased in the order C I > C II > C.

Heap leaching of ion adsorption rare earth ores and REEs recovery from leachate with lixiviant regeneration

In this work, semi-industrial scale heap leaching of 200 t ion adsorption rare earth ores (IRE-ore) and rare earth elements (REEs) recovery from lixivium was first conducted. Biosynthetic citrate/(Na)3Cit, a typical microbial metabolite, was chosen as the lixiviant to conduct heap leaching. Subsequently, an organic precipitation method was proposed, which used oxalic acid to effectively recover REEs and reduce the production cost by lixiviant regeneration. The results showed that the heap leaching efficiency of REEs reached 98 % with a lixiviant concentration of 50 mmol/L and a solid-liquid ratio of 1:2. The lixiviant can be regenerated during the precipitation process, with REE yields and impurity aluminum yields of 94.5 % and 7.4 %, respectively. The residual solution can then be cyclically used as a new lixiviant after simple adjustment. High-quality rare earth concentrates with a rare earth oxide (REO) content of 96 % can be finally obtained after roasting. This work provides an eco-friendly alternative for IRE-ore extraction to solve the environmental issues caused by traditional technology. The results proved feasibility and provided a foundation for in situ (bio)leaching processes in further industrial tests and production.