Highly effective emulsion liquid membrane based on Triethylamine for extraction of heavy metals: Investigation of extraction, de-extraction, swelling, and osmotic pressure gradient

The aim of this work is to produce a stable W/O primary emulsion which is able to extract a wide variety of heavy metals, namely Cu2+, Zn2+, Pb2+, Ni2+, Co2+ and Hg2+. The appropriate conditions through which a better extraction was obtained are: concentration of Span 80 (4 wt%); concentration of TEA (10 wt%); internal phase (HCl 0.5 M); emulsification time (4 min); V-memb/V-int (2.08); V-emul/V-ext (0.1); pH of the external solution (4.7) and stirring speed (150 rpm). A second recycling of the emulsion resulted in a drop in extraction about 40 %. The morphological study confirmed a good dispersion of internal globules and a good stability of emulsion for up to 60 days. The extraction of metal cations showed very high extraction (> 90 %) with very fast kinetics. However, it has been shown that the type of anion to which the metal cation is bound, only affects the extraction efficiency above 100 mg/L. Results extraction of heavy metals are in good analogy with evolution of the osmotic pressure difference between the internal and external phases, leading to a significant swelling of emulsion, while de-extraction also appears to be in accord with extraction with a slightly slower rate.