Abstract:

In the present work, a typical room temperature ionic liquids (RTILs), 1-octyl-3-methyl-imidazolium hexafluorophosphate ([C₈mim][PF₆]), was used as an alternative solvent to study liquid/liquid extraction of lithium from salt lake brine. In this system, the ionic liquids and tributyl phosphate (TBP) were used as extraction medium and extractant respectively. The effects of solution pH value, phase ratio and other factors on lithium extraction efficiency had been investigated. The preliminary experimental results had demonstrated that, compared with using conventional extraction system, the extraction efficiency had been increased greatly in this ionic liquid system. Optimal extraction conditions of this system include the ratio of TBP/ILs at 9/1(vol), O/A at 2:1 and unadjusted pH. Under the optimal conditions, the single extraction efficiency of lithium ion and magnesium ion were 80.64% and 5.30%, respectively. And total extraction efficiency of 99.42% was obtained by triple-stage countercurrent extraction. The single stripping rate of lithium ion and magnesium ion were 98.78% and 99.15%, respectively, at 80℃ when the A/O phase ratio was 2. The Mg/Li ratio was 3.03 in the aqueous phase after stripping, which have dropped 93.41% when compared with the initial value. To evaluate the potential use of RTILs to replace traditional volatile organic compounds (VOCs) in liquid/liquid extraction of lithium, the extractions of lithium ion with VOCs and ionic liquid were compared. Compared with using conventional extraction system, the extraction efficiency had been increased greatly in this ionic liquid system. In addition, the equipment corrosion and the environmental pollution had been avoided in this new extraction system. The extraction mechanism was deduced based on the ultraviolet-visible(UV) absorption. Cation exchange was proposed to be the mechanism of extraction followed in ionic liquid. So the ionic liquid was not only regarded as the solvent but also the co-extraction reagent to some extent. Preliminary results indicated that the ionic liquids had the potential to replace traditional volatile organic solvents in liquid/liquid extraction of metal ions.

Key words: ionic liquids, separation, extraction, lithium, tributyl phosphate

摘要：

将一种典型的室温离子液体(ionic liquids, ILs)1-辛基-3-甲基咪唑六氟磷酸盐作为替代溶剂用于盐湖卤水萃取锂。在该萃取体系中, 离子液体和磷酸三丁酯(TBP)分别用作萃取介质和萃取剂。详细考察了水相酸度、相比等因素对锂分离效率的影响。初步结果表明:与传统萃取体系相比, 该离子液体萃取体系能极大提高萃取效率。该体系最优条件包括: TBP/ILs=9/1(体积比), 相比O/A=2:1, 水相的pH萃取前不需要调节。在此条件下, 锂和镁的单级萃取效率分别为80.64%和5.30%。经过三级逆流萃取, 锂的萃取率高达99.42%。在温度为80℃, 反萃相比A/O为2的条件下, 锂和镁的单级反萃效率分别为98.78%和99.15%。反萃水相中的镁锂比(Mg/Li)降至3.03, 与初始值相比降低了93.41%。

关键词: 离子液体, 分离, 萃取, 锂, 磷酸三丁酯