(609f) Solventless Extraction of Metals and Organics Using Trioctylphosphine Oxide Impregnated Hollow Fiber Membranes

Praveen, P., National University of Singapore
Loh, K. C., National University of Singapore

Liquid-liquid extraction using organic solvents is a very effective technique for removal of organic and inorganic contaminants from wastewater. However, phase dispersion and consequent downstream separation problems are major limitations. Membrane facilitated extraction, as in supported liquid membranes (SLM), can alleviate these challenges and provide a low-cost, low-energy alternative to conventional extraction. However, the instability of SLM during prolonged operation makes this technique unsustainable.

To alleviate the challenges in solvent extraction, we have immobilized a solid extractant, trioctylphosphine oxide (TOPO), into polypropylene hollow fiber membranes (HFM). The strategy was to dissolve TOPO in a volatile carrier solvent and soak the HFM in this solution. The carrier solvent was then evaporated from the HFMs using dry air, causing a phase change resulting in impregnation of TOPO within the HFM walls. The resulting extractant impregnated hollow fiber membranes (EIHFM) can facilitate solventless extraction of various organic and inorganic compounds and has the advantages of high solute retention capacity of extraction, non-dispersive mass transfer of adsorption and the large specific interfacial area of the HFM.

The EIHFMs were characterized and used as the organic phase in the extraction of organic compounds such as phenols and carboxylic acids, and inorganic metals such as chromium. The EIHFMs exhibited high sorption capacity and rates, and equilibrium was achieved within 30 min in most of the experiments. The effects of EIHFM concentration, contact time, feed solute concentration and pH on extraction was evaluated, and a kinetics model was developed to elucidate the mass transfer of solutes from the aqueous phase to the EIHFMs. Finally, the stability of the EIHFMs was demonstrated during repeated extraction/stripping cycles. These results indicate that the use of EIHFMs can be quite promising in the extraction of organic and inorganic chemicals from aqueous solutions.