Ionic Liquids / Alfa Chemistry

Ionic Liquids For Heavy Metal Extraction

Application

Online Inquiry

Ionic Liquids For Heavy Metal Extraction

Inquiry

The rapid development of the industrial use of heavy metals such as in metal plating facilities, batteries, and mining, unavoidably led to the increased metal emissions into aquatic environment and soils. Unlike many degradable organic pollutants, heavy metals (chromium, nickel, cadmium, copper, etc.) are non-biodegradable and tend to accumulate in different environmental compartments. Moreover, many heavy metal ions are toxic or cancerogenic. Therefore, it is very important to find an effective wastewater treatment technology to remove heavy metals from municipal and industrial wastewater streams. Scholars have proposed a variety of methods to separate heavy metal ions, such as solvent extraction, ion exchange, chemical precipitation, membrane technology, and electrolysis. However, despite a widespread use of the mentioned techniques, their application in many practical situations is limited because of high costs, environmental pollution, maintenance problems and other interferences [1]. Ionic liquid, as a new type of green solvent, is one of the research hotspots at present. Due to their superior properties (nonflammability, low vapor pressure, high thermal stability, environmentally friendly, good solubility, etc.), the application of ionic liquids in the extraction of heavy metals from wastewater has been extensively studied.

Schematic diagram of the ionic liquid for removal and highly sensitive detection of heavy metal ions [2].Figure 1. Schematic diagram of the ionic liquid for removal and highly sensitive detection of heavy metal ions [2].

Extraction Mechanism

The extraction of heavy metal ions by ionic liquids mainly follows the ion exchange mechanism. This mechanism refers to the fact that due to the different partition coefficients of different metal ion compounds in the insoluble two phases, the target metal ions enter the organic phase from the aqueous phase and are separated from other metal ions to achieve extraction when metal ions are extracted by ionic liquids. For example, Papaiconomou and co-workers [3] studied the extraction of Au3+ from aqueous solutions with several ionic liquids bearing halide or bis(trifluoromethanesulfonyl)imide NTf2 anions and cations 1-octyl-3-methylimidazolium, 1-octylpyridinium or 1-methyl-1-octylpyrrolidinium. Investigation on the extraction mechanism revealed an anion exchange between one anionic gold complex and one NTf2 anion (Figure 2). It was verified that the extraction of Au3+ by ionic liquids followed the ion exchange mechanism.

The equation for ion exchange between ionic liquid and AuX4− [4].Figure 2. The equation for ion exchange between ionic liquid and AuX4− [4].

Applications

The common ionic liquid extractants include imidazole ionic liquids, phosphonium ionic liquids, pyridine ionic liquids and quaternary ammonium ionic liquids. A few examples of their specific applications are shown below.

  • Imidazole ionic liquids for heavy metal extraction

Lertlapwasin and co-workers [5] synthesized 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) via the reaction of anion metathesis between 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) and hexafluorophosphoric acid. They used the synthetic imidazole ionic liquid to extract Pb2+ and Ni2+ in water by liquid–liquid extraction method. The results revealed that the extraction efficiency of Ni2+ is close to 100% when the pH value is greater than 4.0. As for Pb2+, its extraction efficiency gradually increased from 0% to 80% when the pH increased from 3.0 to 6.0.

  • Phosphonium ionic liquids for heavy metal extraction

Mahandra and co-workers [6] reported a novel and sustainable technology to recover gold from thiosulfate medium using ionic liquids, i.e., Cy IL 101 (tetradecyl-(trihexyl) phosphonium chloride) and Cy IL 102 (tetradecyl-(trihexyl) phosphonium bromide) diluted in toluene. Gold was extracted into the ionic liquid phase as [{P66614+}3{Au(S2O3)23−}] and stripped using NaCl solution, as depicted in Figure 3. It is found that efficient extraction and quantitative recovery (>98%) of gold is achieved from thiosulfate solutions with minimum production of waste. Cy IL 101 exhibited better extraction ability compared with the Cy IL 102 due to the difference in hydrophobicity of their anions.

Schematic diagram of extraction process for gold recovery from thiosulfate solution using phosphonium ionic liquids [6]Figure 3. Schematic diagram of extraction process for gold recovery from thiosulfate solution using phosphonium ionic liquids [6].

What Can We Do?

Alfa Chemistry has a profound research foundation in terms of heavy metal extraction, and at our company you can find the appropriate ionic liquid for heavy metal extraction. Alfa Chemistry will serve you with the most abundant experience and affordable prices. If you have any problems, we will provide technical support for you. Please don't hesitate to contact us.

References

  • Stojanovic, A.; Keppler, B. K. Ionic liquids as extracting agents for heavy metals. Separation Science and Technology. 2012, 47(2): 189-203.
  • Jin, Z.; et al. Bifunctional fluoroionphore-ionic liquid hybrid for toxic heavy metal ions: improving its performance via the synergistic extraction strategy. Analytical Chemistry. 2012, 84(10): 4253-4257.
  • Papaiconomou, N.; et al. Efficient removal of gold complexes from water by precipitation or liquid-liquid extraction using ionic liquids. Green Chemistry. 2012, 14(7): 2050-2056.
  • Chen, R.; et al. Advances in heavy metal ion extraction with ionic liquids. Chemical Industry and Engineering Progress. 2013, 32(11): 2757-2763.
  • Lertlapwasin, R.; et al. Ionic liquid extraction of heavy metal ions by 2-aminothiophenol in 1-butyl-3-methylimidazolium hexafluorophosphate and their association constants. Separation and Purification Technology. 2010, 72(1): 70-76.
  • Mahandra, H.; et al. Novel extraction process for gold recovery from thiosulfate solution using phosphonium ionic liquids. ACS Sustainable Chemistry & Engineering. 2021, 9(24): 8179-8185.

Please kindly note that our products and services are for research use only.