Non-ammonia enrichment of rare earth elements from rare earth leaching liquor in a magnesium salt system I: Precipitation by calcium oxide

Lai, Anbang; Fuguo, Lai; Li, Huang; Qiu, Jiang; Zhou, Xiaofang; Xiao, Yanfei

doi:10.1016/j.hydromet.2020.105318

Cited by 12 publications

(9 citation statements)

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“…In the early stage, extensive research on the magnesium salt leaching process and calcium oxide precipitation process had been performed by our research group, and good results had been achieved. ,− Therefore, to verify the feasibility of the new process, exploratory experiments were developed for the stirring washing process. In the exploratory experiment of the new process, a certain amount of aluminum sulfate was added to the simulated rare earth leaching liquor in a magnesium salt system to adjust the concentration of aluminum ions in the liquor to 200 mg/L.…”

Section: Results and Discussionmentioning

confidence: 99%

“…The calcined product was obtained after the precipitation enrichment was calcined in a muffle furnace at 950 °C for 2 h. The weight of the calcined product was approximately 1.45 g. Moreover, both rare earth hydroxide and alkaline rare earth sulfate are formed in the calcium oxide precipitation process. Therefore, the rare earth purity of the calcined product was approximately 82.6%; the SO 4 2– content in the calcined product was approximately 15.84%; and the contents of Al 2 O 3 , MgO, and CaO were all less than 2.0% …”

Section: Methodsmentioning

confidence: 97%

“…Among these, a green Mg–Ca salt extraction process of the ion-adsorption-type rare earth ore has been performed, , as shown in Figure . In this process, the use of a magnesium salt compound leaching agent can realize a rare earth leaching efficiency of more than 94%, and it can modify the content and ratio of ion-exchangeable calcium and ion-exchangeable magnesium in red soil. , The use of a calcium oxide precipitant can reduce the production costs and obtain rare earth hydroxide with a low calcination temperature, thus reducing energy consumption. , More importantly, the green Mg–Ca salt extraction process can realize the effective recycling of calcium and magnesium, and finally solve the ammonia–nitrogen problem in the whole extraction process of the ion-adsorption-type rare earth ore.…”

Section: Introductionmentioning

confidence: 99%

“…However, a high calcination temperature greatly increases energy consumption. Considering that the use of sodium hydroxide can transform the rare earth sulfate and its complex salt into rare earth hydroxides, , a new method to reduce SO 4 2– in mixed rare earth oxides by stirring washing the precipitation enrichment with sulfate-removal reagents was presented by our team. ,, An anion that had a strong coordination ability with rare earth was introduced into the sulfate-removal agent to compete with the sulfate ions in the stirring washing process; thus, the sulfate ions could be exchanged and enter the solution, and the SO 4 2– content in the mixed rare earth oxides would be decreased. In addition, the coordination ability between the anion and the rare earth elements should be lower than that between hydroxyl ions and rare earth elements, which would prevent the formation of soluble rare earth complexes and the loss of rare earth elements in the stirring washing process.…”

Section: Introductionmentioning

confidence: 99%

“…5,13 The use of a calcium oxide precipitant can reduce the production costs and obtain rare earth hydroxide with a low calcination temperature, thus reducing energy consumption. 14,15 More importantly, the green Mg−Ca salt extraction process can realize the effective recycling of calcium and magnesium, and finally solve the ammonia−nitrogen problem in the whole extraction process of the ion-adsorption-type rare earth ore.…”

Section: Introductionmentioning

confidence: 99%

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Removal of Sulfate Ions from Calcium Oxide Precipitation Enrichment of a Rare Earth Leaching Liquor by Stirring Washing with Sodium Hydroxide

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The use of calcium oxide as a precipitant can achieve a nonammonia enrichment of a rare earth leaching liquor. However, an alkaline rare earth sulfate forms during the precipitation process, thus resulting in excessive SO 4 2− content in the mixed rare earth oxides. Therefore, a stirring washing process for precipitation enrichment, which was obtained from calcium oxide precipitation, was investigated using a sodium hydroxide solution. It was determined that the Gibbs free energy of the stirring washing reaction, which was calculated by a group contribution method, was between −60 and −300 kJ/mol, depending on the different rare earth elements. The above results indicated that the reaction was thermodynamically feasible. The optimum conditions of the washing process were obtained, namely, a feed ratio of 2.85, a liquid−solid ratio of 6.5 mL/g, a stirring washing temperature of 35 °C, and a stirring washing time of 20 min. Under the optimal conditions, the purity and the SO 4 2− content of the mixed rare earth oxides were 94.38% and 3.48%, respectively, and the stirring washing process with the sodium hydroxide solution had good recyclability. Moreover, the washing product was tested using thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and scanning electron microscopy-energy-dispersive spectrometry (SEM-EDS), which verified that the stirring washing process with NaOH could effectively remove SO 4 2− from the precipitation enrichment into solution. On this basis, a new extraction process of the ion-adsorption-type rare earth ore by magnesium salt leaching−calcium oxide precipitation−sodium hydroxide stirring washing is proposed. This new process can eliminate the traditional aluminum-removal process and effectively reduces the rare earth loss in the process. It can also solve the problem of the excessive SO 4 2− content in the mixed rare earth oxides caused by the calcium oxide precipitation process. The research in this paper can have great significance for green, efficient extraction of the ion-adsorptiontype rare earth ore and the improvement of resource utilization.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 97%