Ionic liquids as extracting agents for heavy metals
Abstract
Ionic liquids are a family of organic salts with melting points lower than 100°C. Many of these salts are molten at room temperature and even below. They show unique features like extremely low vapor pressure, and a large liquidus range, and their properties are tunable by chemical modifications of their cations and/or anions. Several working groups have studied the metal extraction behavior of hydrophobic ionic liquids. However, considering the state of the art of ionic liquids as metal extracting agents, their application in real water systems is still limited due to the lack of basic knowledge regarding their stability and metal-uptake mechanism. The hydrophobicity of the commonly used metal-extracting ionic liquids is given by fluorine containing anions. A disadvantage of these systems lies in their instability towards hydrolysis since the formation of hydrofluoric acid may pose severe environmental risks. Other approaches try to enhance the metal ion selectivity by adding a complexing agent to the ionic liquid phase. The addition of organic coordinating compounds like crown-ethers directly to the ionic liquid -phase significantly increases the distribution ratios of metal ions between the ionic liquid- and the aqueous phase, however, the extraction mechanism involves the exchange of a cationic metal complex with the cation of the ionic liquid, which would result in the destruction of the ionic liquid during the extraction process. In order to overcome these disadvantages, we envisage to apply an iterative synthetic approach by producing novel task-specific ionic liquids, which are not prone to hydrolysis, with suitable extracting entities grafted onto their cation and/or their anion. Our studies have recently shown that task specific ionic liquids bearing thiol, urea, or thiourea moieties allow the uptake of metal ions, such as Hg(II), Pt(II) and Cd(II), or metal oxide ions such as uranyl (UO22+) from water, however, the dominant mechanism - which very likely depends on the ionic strength and pH in the water phase - is still unknown. We expect to uncover the mechanism of metal transfer processes for different ionic liquids and different real matrices (communal-, industrial-, hospital waste water as well as superficial and drinking water) based on liquid-liquid extraction experiments combined with extensive experimental investigations of the physico-chemical properties of the synthesized ionic liquids and their influence on the extraction process. The goal is to enhance fundamental understanding concerning ionic liquids potentially suitable for the extraction of toxic heavy-metal ions from wastewater and drinking water.
ionic liquids heavy metals ICP-MS
Publikationen
Project staff
Stephan Hann
Univ.Prof. Dr. Stephan Hann
stephan.hann@boku.ac.at
Tel: +43 1 47654-77001, 77191
Project Leader
01.01.2012 - 31.12.2015
BOKU partners
External partners
University of Wienna, Institute of Anorganic Chemistry
none
partner