Zhang Dongliang, Li Mei, Gao Kai, Li Jianfei, Yan Yujun, Liu Xingyu
School of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China; Inner Mongolia Key Laboratory of Rare Earth Hydrometallurgy and Light Rare Earth Application, Inner Mongolia University of Science and Technology, Baotou 014010, China.
School of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China; Inner Mongolia Key Laboratory of Rare Earth Hydrometallurgy and Light Rare Earth Application, Inner Mongolia University of Science and Technology, Baotou 014010, China; School of Material and Metallurgy, Inner Mongolia University of Science and Technology, Baotou 014010, China.
Ultrason Sonochem. 2017 Nov;39:774-781. doi: 10.1016/j.ultsonch.2017.05.020. Epub 2017 May 19.
In this study, we investigated an alternative to the conventional hydrochloric acid leaching of roasted bastnaesite. The studies suggested that the rare earth oxyfluorides in non-oxidatively roasted bastnaesite can be selectively leached only at elevated temperatures Further, the Ce(IV) in oxidatively roasted bastnaesite does not leach readily at low temperatures, and it is difficult to induce it to form a complex with F ions in order to increase the leaching efficiency. Moreover, it is inevitably reduced to Ce(III) at elevated temperatures. Thus, the ultrasonically-assisted hydrochloric acid leaching of non-oxidatively roasted bastnaesite was studied in detail, including, the effects of several process factors and the, physical and chemical mechanisms underlying the leaching process. The results show that the leaching rate for the ultrasonically assisted process at 55°C (65% rare earth oxides) is almost the same as that for the conventional leaching process at 85°C. Based on the obtained results, it is concluded that ultrasonic cavitation plays a key role in the proposed process, resulting not only in a high shear stress, which damages the solid surface, but also in the formation of hydroxyl radicals (OH) and hydrogen peroxide (HO). Standard electrode potential analysis and experimental results indicate that Ce(III) isoxidized by the hydroxyl radicals to Ce(IV), which can be leached with F ions in the form of a complex, and that the Ce(IV) can subsequently be reduced to Ce(III) by the HO This prevents the Cl ions in the solution from being oxidized to form chlorine. These results imply that the ultrasonically-assisted process can be used for the leaching of non-oxidatively roasted bastnaesite at low temperatures in the absence of a reductant.
在本研究中，我们探究了一种替代传统盐酸浸出焙烧氟碳铈矿的方法。研究表明，非氧化焙烧氟碳铈矿中的稀土氟氧化物仅在高温下才能被选择性浸出。此外，氧化焙烧氟碳铈矿中的Ce(IV)在低温下不易浸出，并且难以诱导其与F离子形成络合物以提高浸出效率。而且，在高温下它不可避免地会还原为Ce(III)。因此，我们详细研究了非氧化焙烧氟碳铈矿的超声辅助盐酸浸出，包括几个工艺因素的影响以及浸出过程背后的物理和化学机制。结果表明，在55°C（稀土氧化物含量为65%）下超声辅助浸出的浸出率与在85°C下传统浸出过程的浸出率几乎相同。基于所获得的结果，可以得出结论，超声空化在所提出的过程中起关键作用，这不仅会产生高剪切应力，破坏固体表面，还会形成羟基自由基(OH)和过氧化氢(HO)。标准电极电位分析和实验结果表明，Ce(III)被羟基自由基氧化为Ce(IV)，Ce(IV)可以与F离子以络合物的形式浸出，随后Ce(IV)会被HO还原为Ce(III)。这可防止溶液中的Cl离子被氧化形成氯气。这些结果表明，在没有还原剂的情况下，超声辅助工艺可用于低温下非氧化焙烧氟碳铈矿的浸出。
