ABSTRACT
Ion-adsorbed rare earth minerals are rich in medium and heavy rare earth (RE), which are important strategic resources. In this article, a novel approach for the extraction of RE from ion adsorbed minerals was developed. Through a comprehensive assessment of their extraction and separation performance, the hydrophobic deep eutectic solvents (HDES) with a composition of trioctylphosphine oxide (TOPO): dodecanol (LA): 2-thiophenoyltrifluoroacetone (HTTA) = 1:1:1 was determined as the optimal configuration. Under optimized conditions, only RE were extracted by the HDES, while Al, Ca, Mg were not extracted at all. The HDES based extraction obviated the need for diluent such as kerosene, eliminating the generation of impurity removal residues. The RE in the stripping solution could be successfully enriched by saponified lauric acid, achieving an impressive precipitation rate of 99.7%. The RE precipitate underwent further enrichment, resulting in a RE concentration of 176 g/L (REO = 210 g/L). Unlike industrial precipitants such as oxalic acid and ammonium bicarbonate, lauric acid can be effectively recycled, thereby avoiding a large amount of wastewater and carbon dioxide emissions. The obtained RE solution product exhibits high yield and purity, this study provides an eco-friendly and high-yield approach for extracting RE.
ABSTRACT
A novel rare earth separation system composed of lauric acid (LA) and primary ammonium (RNH2) was studied. Compared with individual LA and RNH2, the mixed extraction system can significantly improve the extraction and separation ability of rare earth (RE). When LA and RNH2 are mixed in an equal molar ratio, the synergistic coefficient for extracting Nd(III) in the system reaches 136.85. Effective separation of Nd from Co and Ni can be achieved, with the separation coefficients of 1503 and 2762 for Nd/Co and Nd/Ni, respectively. The ion association mechanism of developed extraction system can avoid the generation of saponification wastewater. Thus, the negative impact of saponification wastewater on the economy and environment can be reduced. The extraction system is simple to be prepared and easy to be stripped, which helps to reduce acid and alkali consumption. Application of this extraction system can effectively realize the separation of RE elements La, Ce, Pr, Nd and transition metals Co, Ni, Mn in nickel-metal hydride (NiMH) battery. This paper provides a new strategy for the development of ionic liquid saponification technology without saponified wastewater.
Subject(s)
Lauric Acids , Metals, Rare Earth , Nickel , Amines , Wastewater , MetalsABSTRACT
In this work, the new hydrophobic deep eutectic solvents (HDESs) based on 2-hexyldecanoic acid (HDA) as a hydrogen bond donor (HBD) were used to selectively enrich trace Th from radioactive waste leach solution. These HDESs are characterized by low toxicity, bio-friendliness, low viscosity and sufficient hydrophobicity. Compared with Al, Mg, Ca and RE, HDESs exhibited exceptional selectivity for Th extraction, along with high loading capacity, easy stripping and stable reusability. The mechanism of Th extraction by the HDES is a cation exchange reaction. Based on the thymol (TL):HDA (1:3) HDES, a short flow closed-loop recovery process of Th in the leach solution of radioactive waste residue was developed. After a single-step extraction, the extraction percentage (E%) of Th exceeded 98.0%, while the E% of other elements was less than 0.14%. After stripping, the concentration of Th in the concentrated solution reached 2.16 × 103 mg/L with a purity of 74.2%, which could be directly used for subsequent purification. By adjusting the pH to 4.00, the raffinate was used as a feed solution for RE elements recovery. The HDES-based extraction strategy for Th is simple, safe, efficient and environmentally friendly, providing a new idea for the recovery of radioactive waste residues.
