Aqueous stability of rare earth and thorium elements during hydrochloric acid leaching of roasted bastnaesite
来源期刊：Journal of Rare Earths2017年第12期
论文作者：Genghong Shuai Longsheng Zhao Liangshi Wang Zhiqi Long Dali Cui
文章页码：1255 - 1260
摘 要：In order to study the aqueous stability of rare earth and thorium elements and the reaction mechanism of hydrochloric acid leaching of roasted bastnaesite,Eh-pH diagrams for La-,Nd-,Ce-,Th-（Cl）-（F）-H2 O systems at 20 ℃ were depicted using HSC Chemistry 6.0 software. Eh-pH diagrams of La-, Ce-,Nd-and Th-Cl-H2 O systems show that trivalent rare earth would be leached into solution by adjusting the acidity of the leaching solution, while tetravalent cerium and thorium would be remained in the leaching residue. And in the case that the pH value of the leaching solution is lower than 2, tetravalent cerium would be partially reduced by chlorine ions（Cl-）, which is well agreed with the industrial production. It can be inferred from Eh-pH diagrams for the systems La-, Nd-,Ce-, Th-F-H2 O that the leached trivalent rare earth ions(RE3+) and tetravalent thorium ions(Th4+) are preferentially combined with fluorine ions（F） to form sediment during non-reductive acid leaching of roasted bastnaesite. However,when controlling the pH value of the leaching solution below 0, fluorine and tetravalent cerium in the roasted bastnaesite would be leached out in the form of soluble [CeF3]+ complex. That means the precipitation of REF3 and ThF4·2.5 H2 O can be avoided in the leaching step. According to Eh-pH diagrams for the system Ce-F-Cl-H2 O, [CeF3]+ in the leaching solution would be reduced to CeF3 precipitate in the presence of Cl-, that is to say, tetravalent cerium and fluorine would be firstly leached out to form[CeF3]+,which would then be reduced to CeF3 precipitate by Cl-in the hydrochloric acid leaching process of roasted bastnaesite.
Genghong Shuai1,2，Longsheng Zhao1,2，Liangshi Wang1,2，Zhiqi Long1,2，Dali Cui1,2
1. National Engineering Research Center for Rare Earth Materials, General Research Institute for Non-Ferrous Metals2. Grirem Advanced Materials Co., Ltd.
摘 要：In order to study the aqueous stability of rare earth and thorium elements and the reaction mechanism of hydrochloric acid leaching of roasted bastnaesite,Eh-pH diagrams for La-,Nd-,Ce-,Th-（Cl）-（F）-H2 O systems at 20 ℃ were depicted using HSC Chemistry 6.0 software. Eh-pH diagrams of La-, Ce-,Nd-and Th-Cl-H2 O systems show that trivalent rare earth would be leached into solution by adjusting the acidity of the leaching solution, while tetravalent cerium and thorium would be remained in the leaching residue. And in the case that the pH value of the leaching solution is lower than 2, tetravalent cerium would be partially reduced by chlorine ions（Cl-）, which is well agreed with the industrial production. It can be inferred from Eh-pH diagrams for the systems La-, Nd-,Ce-, Th-F-H2 O that the leached trivalent rare earth ions(RE3+) and tetravalent thorium ions(Th4+) are preferentially combined with fluorine ions（F） to form sediment during non-reductive acid leaching of roasted bastnaesite. However,when controlling the pH value of the leaching solution below 0, fluorine and tetravalent cerium in the roasted bastnaesite would be leached out in the form of soluble [CeF3]+ complex. That means the precipitation of REF3 and ThF4·2.5 H2 O can be avoided in the leaching step. According to Eh-pH diagrams for the system Ce-F-Cl-H2 O, [CeF3]+ in the leaching solution would be reduced to CeF3 precipitate in the presence of Cl-, that is to say, tetravalent cerium and fluorine would be firstly leached out to form[CeF3]+,which would then be reduced to CeF3 precipitate by Cl-in the hydrochloric acid leaching process of roasted bastnaesite.
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