(8)Extraction of Cu(II) ions through a process coupling an ionic liquid and supercritical CO_2

摘要

Conventional treatments for removal of metals ions from aqueoussolutions require large amounts of organic solvents, which involve severalproblems due to its high level of toxicity for human life and theenvironment. As a result, research efforts have been focused on findingnew eco-friendly alternatives.Ionic liquids (ILs) are organic salts that are liquid at room temperature,with melting points lower than 373K, the main advantage in the use ofthese compounds is their unique physicochemical properties that allowthem to be considered green solvents. ILs show a practically negligiblevapour pressure, which minimizes solvent losses related to its volatility.Thus, ILs could be coupled to other eco-friendly operations.This research is focused on the optimization of working conditions inthe removal process of Cu(II) from aqueous solutions, which are complexedwith 1,1,1-trifluoro-2,4-pentanedione (TFA), initially contained in the IL1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Metalcomplexes formed in the ionic liquid phase were re-extracted by usingsupercritical CO2.In a first step, the process was studied to assess the feasibility of theliquid/liquid extraction, an extraction efficiency of 77.6% was obtained whenthe initial concentration of Cu(II) in the aqueous solution was 250 mg/L,initial concentration of TFA in IL was 310 mol/m3, the volumetric IL/aqueousphase ratio was 1:1, initial pH of aqueous solution was equal to 5.3.To optimize the liquid/liquid extraction, a buffer solution was used tomaintain the pH at 5.3, and the best extractions conditions were identifiedat: Five min of stirring time, volumetric IL/aqueous phase ratio 1:7 and aninitial TFA concentration in IL of 60 mol/m3, obtaining a removal efficiencyof 83.54%. Preliminary assays, shows that the best condition for threstripping of metal complexes formed in the IL phase with supercriticalcarbon dioxide at 18 MPa and 40°C was 1 h of IL/CO2 contact time.