NdF3含量对NdF3-LiF熔盐局域结构和输运性质的影响

doi:10.11949/0438-1157.20250020

摘要/Abstract

摘要：

NdF₃-LiF熔盐的输运性质（如电导率、黏度）对稀土金属钕的电解制备过程及电解生产的电能消耗等技术经济指标影响很大。本研究采用分子动力学模拟，在温度为1323 K的条件下研究了NdF₃含量对NdF₃-LiF熔盐局域结构和输运性质的影响。结果表明，NdF₃含量增加时，[NdF₉]^6-和[NdF₈]^5-向[NdF₇]^4-和[NdF₆]^3-转变；氟离子连接类型中桥氟和端氟的占比均增加，其中桥氟占比上升幅度更大；[NdF₈]^5-多面体间的连接方式中，共顶角占比下降，共棱和共面的占比增加；离子的扩散能力排序为：Li⁺ > F^- > Nd³⁺。随着NdF₃摩尔含量从20%增加到55%，熔盐黏度从3.31 mPa·s增加到7.43 mPa·s，电导率由4.84 S·cm^-1降低到1.78 S·cm^-1。本研究明确了NdF₃-LiF熔盐的输运性质，并揭示了其变化的本质原因，为稀土金属钕的低碳、绿色、高效制备提供了科学指导。

关键词: 黏度, 电解质, 分子模拟, 局域结构, 输运性质, 电导率, 熔盐电解, 稀土金属

Abstract:

The transport properties of NdF₃-LiF molten salt, such as electrical conductivity and viscosity, significantly impact the electrolytic preparation process of rare earth metal neodymium and the technical economic indicators such as energy consumption in electrolytic production. In this study, molecular dynamics simulations (at 1323 K) were employed to investigate the effect of NdF₃ content on the local structure and transport properties of NdF₃-LiF molten salt. The results indicated that as the content of NdF₃ increased, [NdF₉]^6- and [NdF₈]^5- transformed into [NdF₇]^4- and [NdF₆]^3-. The proportions of bridge fluorine and end fluorine in the fluorine ion connection type increases, among which the proportion of bridge fluorine increases more. In the connection modes of [NdF₈]^5- polyhedrons, the proportion of common vertices decreases, and the proportion of common edges and common faces increases. The order of ion diffusion ability was: Li⁺> F^-> Nd³⁺. As the molar content of NdF₃ increased from 20% to 55%, the viscosity of the molten salt increased from 3.31 mPa·s to 7.43 mPa·s, and the electrical conductivity decreased from 4.84 S·cm^-1 to 1.78 S·cm^-1. This study clarified the transport properties of NdF₃-LiF molten salt and revealed the fundamental reasons for their changes, providing scientific guidance for the low-carbon, green, and efficient preparation of rare earth metal neodymium.

Key words: viscosity, electrolyte, molecular simulation, local structure, transport properties, conductivity, molten salt electrolysis, rare earth metals

中图分类号:

TF 845

林嘉豪, 付芳忠, 叶昊辉, 胡金, 姚明灿, 范鹤林, 王旭, 王瑞祥, 徐志峰. NdF₃含量对NdF₃-LiF熔盐局域结构和输运性质的影响[J]. 化工学报, 2025, 76(8): 3834-3841.

Jiahao LIN, Fangzhong FU, Haohui YE, Jin HU, Mingcan YAO, Helin FAN, Xu WANG, Ruixiang WANG, Zhifeng XU. Effect of NdF₃ content on local structure and transport properties of NdF₃-LiF molten salt[J]. CIESC Journal, 2025, 76(8): 3834-3841.

图/表 11

表1 成分、密度和盒子尺寸参数［5，13］

Table 1 Parameters of composition， density and box size［5，13］

组别	摩尔分数/%		质量分数/%		密度 ρ/(g·cm^-3)	原子数量				体系边长/Å
组别	NdF₃	LiF	NdF₃	LiF	密度 ρ/(g·cm^-3)	Nd	Li	F	总数	体系边长/Å
R1	20	80	65.98	34.02	3.15	500	2000	3500	6000	43.16
R2	25	75	72.11	27.89	3.28	600	1800	3600	6000	43.93
R3	30	70	76.87	23.13	3.41	692	1616	3692	6000	44.52
R4	35	65	80.68	19.32	3.54	778	1444	3778	6000	44.98
R5	40	60	83.80	16.20	3.67	857	1286	3857	6000	45.32
R6	45	55	86.39	13.61	3.80	931	1138	3931	6000	45.59
R7	50	50	88.58	11.42	3.93	1000	1000	4000	6000	45.78
R8	55	45	90.46	9.54	4.06	1065	870	4065	6000	45.93

表2 势参数［28-29］

Table 2 Potential parameters［28-29］

原子i	原子j	A_ij /eV	ρ(=1/B_ij )/Å
Nd	Nd	13630100	0.11700
Nd	Li	88906	0.11000
Nd	F	5813	0.26157
Li	Li	12659	0.10622
Li	F	1170	0.22824
F	F	1062	0.27645

图1 50% （摩尔分数）NdF3时各原子对的RDF和CN

Fig.1 RDF and CN of each atom pair at 50%(mol) NdF3

图2 RDF曲线随NdF3含量的变化

Fig.2 The variation of RDF with NdF3 content

图3 CNNd-F分布及平均CNNd-F

Fig.3 CNNd-F distribution and average CNNd-F

图4 F—Nd—F键角分布

Fig.4 The bond angle distribution of F—Nd—F

图5 [NdF x ](3-x)几何构型示意图

Fig.5 The geometric configuration of [NdF x ](3-x)

图6 氟类型占比情况

Fig.6 The proportion of F type

图7 [NdF8]5-各连接方式的占比

Fig.7 The proportion of [NdF8]5- connection mode

图8 50% NdF3下各离子的均方位移和不同NdF3含量下各离子的自扩散系数

Fig.8 MSD of each ion at 50 % NdF3 and the self-diffusion coefficient of each ion at different NdF3 content

图9 黏度和电导率随NdF3含量的变化

Fig.9 The change of viscosity and conductivity with NdF3 content

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NdF₃含量对NdF₃-LiF熔盐局域结构和输运性质的影响

Effect of NdF₃ content on local structure and transport properties of NdF₃-LiF molten salt

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