{"title":"Recovery of indium by solvent extraction with crown ether in the presence of KCl and stripping with HCl: A mechanistic study","authors":"","doi":"10.1016/j.hydromet.2024.106378","DOIUrl":null,"url":null,"abstract":"<div><p>Hydration of In<sup>3+</sup> is the main factor limiting its extraction efficiency from an aqueous solution during a liquid-liquid extraction process. In this study, KCl was introduced into the aqueous solution to facilitate the formation of InCl<sub>4</sub><sup>−</sup> of low charge density, which is expected to possess much weaker hydration compared with In<sup>3+</sup>, promoting the solvent extraction of indium. The crown ethers (CEs) with varied cavity sizes, benzo-18-crown-6 (B18C6), benzo-15-crown-5 (B15C5), and benzo-12-crown-4 (B12C4), were synthesized. The extraction performance of the CEs toward indium in the presence of sufficient KCl in the aqueous solution was investigated. The liquid-liquid extraction process was analyzed theoretically based on density functional theory (DFT) from the aspects of thermodynamics, geometric structure optimization, electrostatic potential (ESP), and independent gradient model (IGM). The theoretical evaluations agreed well with the experimental results that the hydration of indium could be significantly weakened through the formation of InCl<sub>4</sub><sup>−</sup> and the complexation ability of the CEs toward indium is in the order of B18C6 > B15C5 > B12C4. The complexation mechanism between the CEs and indium during the extraction process was further explored with the assistance of <sup>1</sup>H NMR spectrum and SEM-EDS. The results indicate that crown ether coordinates with K<sup>+</sup> to form [CE-K]<sup>+</sup> at the two-phase interface, which further associates with InCl<sub>4</sub><sup>−</sup> to create the complex of CE-KInCl<sub>4</sub>, realizing the efficient indium extraction. Moreover, B18C6 showed excellent selectivity toward In<sup>3+</sup> over the competing ions such as Fe<sup>3+</sup>, Al<sup>3+</sup>, Zn<sup>2+</sup>, Sn<sup>2+</sup> and Ca<sup>2+</sup> in a complex system. Indium could be efficiently recovered from the loaded organic phase by using 1 M HCl as the stripping agent with a stripping efficiency of 98.1%.</p></div>","PeriodicalId":13193,"journal":{"name":"Hydrometallurgy","volume":null,"pages":null},"PeriodicalIF":4.8000,"publicationDate":"2024-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Hydrometallurgy","FirstCategoryId":"88","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0304386X2400118X","RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"METALLURGY & METALLURGICAL ENGINEERING","Score":null,"Total":0}
引用次数: 0
Abstract
Hydration of In3+ is the main factor limiting its extraction efficiency from an aqueous solution during a liquid-liquid extraction process. In this study, KCl was introduced into the aqueous solution to facilitate the formation of InCl4− of low charge density, which is expected to possess much weaker hydration compared with In3+, promoting the solvent extraction of indium. The crown ethers (CEs) with varied cavity sizes, benzo-18-crown-6 (B18C6), benzo-15-crown-5 (B15C5), and benzo-12-crown-4 (B12C4), were synthesized. The extraction performance of the CEs toward indium in the presence of sufficient KCl in the aqueous solution was investigated. The liquid-liquid extraction process was analyzed theoretically based on density functional theory (DFT) from the aspects of thermodynamics, geometric structure optimization, electrostatic potential (ESP), and independent gradient model (IGM). The theoretical evaluations agreed well with the experimental results that the hydration of indium could be significantly weakened through the formation of InCl4− and the complexation ability of the CEs toward indium is in the order of B18C6 > B15C5 > B12C4. The complexation mechanism between the CEs and indium during the extraction process was further explored with the assistance of 1H NMR spectrum and SEM-EDS. The results indicate that crown ether coordinates with K+ to form [CE-K]+ at the two-phase interface, which further associates with InCl4− to create the complex of CE-KInCl4, realizing the efficient indium extraction. Moreover, B18C6 showed excellent selectivity toward In3+ over the competing ions such as Fe3+, Al3+, Zn2+, Sn2+ and Ca2+ in a complex system. Indium could be efficiently recovered from the loaded organic phase by using 1 M HCl as the stripping agent with a stripping efficiency of 98.1%.
在液-液萃取过程中,铟的水合作用是限制其从水溶液中萃取效率的主要因素。在本研究中,向水溶液中引入 KCl 以促进低电荷密度 InCl 的形成,与 In 相比,InCl 的水合作用会更弱,从而促进铟的溶剂萃取。合成了不同空腔尺寸的冠醚(CEs):苯并-18-冠醚-6(B18C6)、苯并-15-冠醚-5(B15C5)和苯并-12-冠醚-4(B12C4)。研究了这些 CEs 在水溶液中有足够氯化钾的情况下对铟的萃取性能。基于密度泛函理论(DFT),从热力学、几何结构优化、静电位(ESP)和独立梯度模型(IGM)等方面对液液萃取过程进行了理论分析。理论评估结果与实验结果吻合,即铟的水合作用可通过 InCl 的形成而显著减弱,且 CEs 对铟的络合能力依次为 B18C6 > B15C5 > B12C4。利用 H NMR 光谱和 SEM-EDS 进一步探讨了萃取过程中 CEs 与铟的络合机制。结果表明,冠醚与 K 在两相界面上配位形成[CE-K],再与 InCl 结合形成 CE-KInCl 复合物,实现了铟的高效萃取。此外,在复杂的体系中,B18C6 对 In 的选择性优于 Fe、Al、Zn、Sn 和 Ca 等竞争离子。使用 1 M HCl 作为剥离剂,可以从负载的有机相中高效地回收铟,剥离效率高达 98.1%。
期刊介绍:
Hydrometallurgy aims to compile studies on novel processes, process design, chemistry, modelling, control, economics and interfaces between unit operations, and to provide a forum for discussions on case histories and operational difficulties.
Topics covered include: leaching of metal values by chemical reagents or bacterial action at ambient or elevated pressures and temperatures; separation of solids from leach liquors; removal of impurities and recovery of metal values by precipitation, ion exchange, solvent extraction, gaseous reduction, cementation, electro-winning and electro-refining; pre-treatment of ores by roasting or chemical treatments such as halogenation or reduction; recycling of reagents and treatment of effluents.