Zhou Fengping, Xiao Ye, Guo Meina, Wang Shizhong, Qiu Rongliang, Morel Jean-Louis, Simonnot Marie-Odile, Zhang Wei-Xian, Zhang Weihua, Tang Ye-Tao
Guangdong Provincial Key Laboratory of Environmental Pollution and Remediation Technology, Guangdong Provincial Engineering Research Center for Heavy Metal Contaminated Soil Remediation, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, P. R. China.
Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou 510642, P. R. China.
Environ Sci Technol. 2023 Feb 28;57(8):3357-3368. doi: 10.1021/acs.est.2c08395. Epub 2023 Feb 15.
To cope with the urgent and unprecedented demands for rare earth elements (REEs) in sophisticated industries, increased attention has been paid to REE recovery from recycled streams. However, the similar geochemical behaviors of REEs and transition metals often result in poor separation performance due to nonselectivity. Here, a unique approach based on the selective transformation between ceria sulfation and iron/manganese mineralization was proposed, leading to the enhancement of the selective separation of REEs. The mechanism of the selective transformation of minerals could be ascribed to the distinct geochemical and metallurgical properties of ions, resulting in different combinations of cations and anions. According to hard-soft acid-base (HSAB) theory, the strong Lewis acid of Ce(III) was inclined to combine with the hard base of sulfates (SO), while the borderline acid of Fe(II)/Mn(II) prefers to interact with oxygen ions (O). Both characterization and density functional theory (DFT) calculation further revealed that such selective transformation might trigger by the generation of an oxygen vacancy on the surface of CeO, leading to the formation of Ce(SO) and Fe/Mn spinel. Although the electron density difference of the configurations (CeO-SO, FeO-SO, and MnO-SO) shared a similar direction of the electron transfer from the metals to the sulfate-based oxygen, the higher electron depletion of Ce ( = -1.91 e) than Fe ( = -1.66 e) and Mn ( = -1.64 e) indicated the higher stability in the Ce-O-S complex, resulting in the larger adsorption energy of CeO-SO (-6.88 eV) compared with FeO-SO (-3.10 eV) and MnO-SO (-2.49 eV). This research provided new insights into the selective transformation of REEs and transition metals in pyrometallurgy and thus offered a new approach for the selective recovery of REEs from secondary resources.
为了应对先进产业对稀土元素（REEs）紧迫且前所未有的需求，从回收流中回收稀土元素受到了更多关注。然而，稀土元素和过渡金属相似的地球化学行为常常因缺乏选择性而导致分离性能不佳。在此，提出了一种基于二氧化铈硫酸化与铁/锰矿化之间选择性转变的独特方法，从而增强稀土元素的选择性分离。矿物选择性转变的机制可归因于离子独特的地球化学和冶金性质，导致阳离子和阴离子的不同组合。根据软硬酸碱（HSAB）理论，Ce(III)的强路易斯酸倾向于与硫酸盐（SO）的硬碱结合，而Fe(II)/Mn(II)的交界酸更倾向于与氧离子（O）相互作用。表征和密度泛函理论（DFT）计算均进一步表明，这种选择性转变可能是由CeO表面氧空位的产生引发的，导致Ce(SO)和Fe/Mn尖晶石的形成。尽管构型（CeO-SO、FeO-SO和MnO-SO）的电子密度差在从金属到硫酸根氧的电子转移方向上相似，但Ce（ = -1.91 e）比Fe（ = -1.66 e）和Mn（ = -1.64 e）更高的电子耗尽表明Ce-O-S络合物具有更高的稳定性，导致CeO-SO（-6.88 eV）的吸附能比FeO-SO（-3.10 eV）和MnO-SO（-2.49 eV）更大。本研究为火法冶金中稀土元素和过渡金属的选择性转变提供了新见解，从而为从二次资源中选择性回收稀土元素提供了一种新方法。
