Lithium extraction by n-octyl salicylate extraction system: influence of structural alterations in the synergist on extract performance

doi:10.11949/0438-1157.20250186

CIESC Journal ›› 2025, Vol. 76 ›› Issue (10): 5190-5202.DOI: 10.11949/0438-1157.20250186

• Separation engineering • Previous Articles Next Articles

Lithium extraction by n-octyl salicylate extraction system: influence of structural alterations in the synergist on extract performance

Jiguang DONG¹(), Shaolei XIE²^,³, Dong SHI²^,³, Lijuan LI³, Chenyu ZHAO¹, Yujie HUANG¹, Chenglong SHI¹(), Taoshan XU³(), Dawei CAO²^,³()

^1.School of Chemistry and Materials Science, Qinghai Minzu University, Xining 810007, Qinghai, China
^2.Key Laboratory of Green and High-end Utilization of Salt Lake Resources, Qinghai Institute of Salt Lake, Chinese Academy of Sciences, Xining 810008, Qinghai, China
^3.Qinghai Engineering and Technology Research Center of Comprehensive Utilization of Salt Lake Resources, Xining 810008, Qinghai, China

Received:2025-02-26 Revised:2025-05-28 Online:2025-11-25 Published:2025-10-25
Contact: Chenglong SHI, Taoshan XU, Dawei CAO

邻羟基苯甲酸正辛酯萃取体系提锂：协萃剂结构变化对萃取性能影响

董纪广¹(), 谢绍雷²^,³, 时东²^,³, 李丽娟³, 赵晨宇¹, 黄雨婕¹, 石成龙¹(), 许淘善³(), 曹大伟²^,³()

^1.青海民族大学化学与材料科学学院，青海西宁 810007
^2.中国科学院青海盐湖研究所盐湖资源绿色高值利用重点实验室，青海西宁 810008
^3.青海省盐湖资源综合利用工程技术中心，青海西宁 810008

通讯作者: 石成龙,许淘善,曹大伟
作者简介:董纪广（2000—），男，硕士研究生，dongjiguang354@163.com
基金资助:
青海省科技厅项目(2021-ZJ-971Q);青海省科技厅项目(2024-ZJ-921);国家自然科学基金项目(U21A20305);中国科学院引进人才B类项目(2025000005);青海省“昆仑英才”项目(2021000030);青海省“昆仑英才”项目(2024000061);引进高层次骨干人才启动经费项目(2023000011)

Abstract

Abstract:

The structure-activity relationship of extractants holds significant position in solvent extraction research. Notably, studies exploring the impact of the structure-activity relationship of synergists on extraction performance are even more scarce. In this study, two aromatic substituted phosphodiester co-extractants were synthesized, namely, phenyl di(2-ethylhexyloxy) phosphate (BPPO) and p-methylphenyl di(2-ethylhexyloxy) phosphate (BTPO). Utilizing octyl 2-hydroxybenzoate (OHB) as the main extractant, we constructed two mixed extraction systems. First, we investigated the effects of various factors on the extraction experiment. These factor included the composition of the organic phase, the alkalinity of the aqueous phase, the phase ratio, the lithium concentration in the aqueous phase, and the saturated loading of the organic phase. The results demonstrated that the extraction performance and phase separation effect of the methyl-substituted OHB/BTPO extraction system were remarkably superior to those of the unsubstituted OHB/BPPO system. Given the better extraction performance of the OHB/BTPO extraction system, we employed it for lithium extraction from the mother liquor after lithium precipitation. By implementing a three-stage countercurrent extraction process, the extraction rate of lithium (E_Li) could reach 94%. Subsequently we conducted an in-depth study of the extraction mechanism using ultraviolet, fluorescence, and infrared spectroscopy. The results indicated that a Keto-Enol transformation took placed in the configuration of OHB during the extraction process. When it is in the Keto configuration, it has a 308 nm ultraviolet absorption peak and no fluorescence emission; when it is in the Enol configuration, it has a 340 nm ultraviolet absorption peak and produces 410 nm blue fluorescence under 340 nm wavelength light excitation. Meanwhile, obvious changes occurred in the CO stretching vibration (ν_C_O) and the skeletal vibration of the benzene ring (ν_Ph) in the infrared spectrum.

Key words: lithium, solvent extraction, synthesis, extraction mechanism

摘要：

萃取剂构效关系是溶剂萃取研究的重要内容，但是协萃剂构效关系对萃取性能影响的研究却较少见。本研究合成了两种芳基取代磷酸二酯协萃剂，分别为苯基磷酸二（2-乙基己氧基）酯（BPPO）和对甲基苯基磷酸二（2-乙基己氧基）酯（BTPO）。以邻羟基苯甲酸正辛酯（OHB）作为主萃剂，构建了两个混合萃取体系。研究了有机相组成、水相碱度、相比、水相锂浓度以及有机相饱和负载等因素对萃取实验的影响。结果显示，甲基取代的OHB/BTPO萃取体系萃取性能和分相效果上明显优于无取代的OHB/BPPO体系。将萃取性能较好的OHB/BTPO萃取体系用于沉锂母液提锂。通过采用三级逆流萃取工艺，锂的萃取率E_Li可达94%。借助紫外、荧光、红外光谱对萃取机理展开了深入研究，结果表明，在萃取过程中OHB构型发生Keto-Enol转化，当其处于Keto构型时，具有308 nm紫外吸收峰，且无荧光发射；当其处于Enol构型时，具有340 nm紫外吸收峰，在340 nm波长的光激发下产生410 nm的蓝色荧光。同时，红外光谱上CO伸缩振动（ν_C_O）、苯环的骨架振动（ν_Ph）等均发生了明显变化。

关键词: 锂, 溶剂萃取, 合成, 萃取机理

CLC Number:

TQ 131.1

Jiguang DONG, Shaolei XIE, Dong SHI, Lijuan LI, Chenyu ZHAO, Yujie HUANG, Chenglong SHI, Taoshan XU, Dawei CAO. Lithium extraction by n-octyl salicylate extraction system: influence of structural alterations in the synergist on extract performance[J]. CIESC Journal, 2025, 76(10): 5190-5202.

董纪广, 谢绍雷, 时东, 李丽娟, 赵晨宇, 黄雨婕, 石成龙, 许淘善, 曹大伟. 邻羟基苯甲酸正辛酯萃取体系提锂：协萃剂结构变化对萃取性能影响[J]. 化工学报, 2025, 76(10): 5190-5202.

Figures/Tables 9

Fig.1 Structures of extractant and synergist

Fig.2 Synthetic route of aryl phosphate diester compounds

Fig.3 (a) The effect of concentration of extractant and synergist on extraction efficiency; Synergistic extraction diagrams of extraction systems (b) OHB/BPPO and (c) OHB/BTPO; Eeffects of (d) aqueous phase alkalinity, (e) extraction phase ratio, (f) lithium concentration in the aqueous phase on the lithium extraction in the OHB/BPPO and OHB/BTPO extraction systems

Fig.4 Saturation loading of the organic phase of (a) OHB/BPPO and (b) OHB/BTPO

Table 1 Main components of lithium precipitation mother liquor

类型	Li ⁺	Na ⁺	K ⁺	Ca²⁺	Mg²⁺	pH
浓度/(g•L^-1)	2.74	44.18	0.50	2.97×10^-3	0.75×10^-3	11.5
浓度/(mol•L^-1)	0.39	1.92	2.09×10^-3	0.74×10^-4	0.19×10^-4	11.5

Fig.5 (a) Effect of NaOH concentration on the lithium extraction by OHB/BTPO; (b) Effect of phase ratio on lithium extraction; (c) McCabe-Thiele diagram; (d)Three-stage counter-current extraction experiment

Fig.6 (a),(c),(e) UV spectra and (b),(d),(f) fluorescence spectra of the titration experiment of lithium hydroxide with OHB, OHB/BPPO and OHB/BTPO

Fig.7 (a) The Keto-Enol tautomerism of OHB structure; (b) Infrared spectrum of OHB, BPPO and BTPO; (c) Changes in the Infrared spectrum before and after the reaction of lithium hydroxide with OHB

Fig.8 Changes in the infrared spectrum before and after the reaction of lithium hydroxide with (a) OHB/BPPO and (b) OHB/BTPO

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Lithium extraction by n-octyl salicylate extraction system: influence of structural alterations in the synergist on extract performance

邻羟基苯甲酸正辛酯萃取体系提锂：协萃剂结构变化对萃取性能影响

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