Emulsion liquid membrane extraction of heavy metals using hollow-fiber contactors

Extraction and recovery of heavy metals from wastewater is more attractive than currently-employed techniques such as precipitation which result in secondary waste. Emulsion liquid membranes are capable of extracting metals from dilute waste streams to levels much below those possible by equilibrium-limited solvent extraction. Utilizing an emulsion liquid membrane within a hollow-fiber contactor retains the advantages of emulsion liquid membrane extraction, namely simultaneous extraction and stripping, while eliminating problems encountered in dispersive contacting methods, such as swelling and leakage of the liquid membrane.; The complexation reaction kinetics and equilibrium of copper-LIX84 system was studied in a stirred cell and with partitioning experiments respectively. Both apparent equilibrium constant based on concentrations of the species and real equilibrium constant which accounts for non-ideality and ionic equilibria in aqueous phase were determined. A model was developed and is capable of predicting equilibrium of the system over a wide range of pH and ionic strength.; Mass transfer properties of hollow-fiber contactors were studied using physical extraction systems having wide range of partition coefficients between aqueous phase and organic phase. The results were converted into dimensionless form and combined with equilibrium and kinetics information to develop overall models for extraction in hollow-fiber contactors. The models satisfactorily predict the outcome of both simple solvent extraction and emulsion liquid extraction of copper by LIX84 in a hollow-fiber contactor over a wide range of conditions. Emulsion liquid membrane extraction performs exceptionally well when the extraction is close to equilibrium limit. It is also capable of extracting a solute from very dilute solutions. Stability of the liquid membrane is not crucial when hollow-fiber contactors are used; the surfactant in liquid membrane may be reduced or even eliminated without severely damaging the performance.