Emulsion liquid membranes (ELMs) can contribute to process intensification of zinc extraction, by significantly reducing the solvent and carrier
requirements in comparison with conventional solvent extraction. Di(2-ethylhexyl)phosphoric acid (D2EHPA) was used as a highly selective
carrier for the transport of zinc ions through the emulsified liquid membrane. The hollow-fiber extractor appears to offer significant advantages
over conventional liquid–liquid contactors for this separation because emulsion leakage and swell are practically eliminated even when treating
high concentration feeds. Various hydrodynamic and chemical parameters, such as variation in feed pH; zinc concentration in feed; variation in
concentrations of D2EHPA; variation in feed/emulsion volume ratios and variation in feed and emulsion flow rates, were investigated. The content
of sulfuric acid as an internal did not show in the studied range any significant influence on zinc extraction through the ELM, although a minimum
hydrogen ion concentration is suggested in the internal aqueous solution to ensure acidity gradient between both aqueous phases to promote the
permeation of zinc ions toward the internal phase. The experimental mass-transfer coefficients have shown a stronger dependence on hydrodynamic
conditions in both the external feed phase and emulsion among the parameters studied. For emulsion flow rate, mass-transfer coefficient increased
from 16.3×10−6 m/s at 200 ml/min to 31.2×10−6 m/s at 640 ml/min. Significant increasing in mass-transfer coefficient observed with increasing
aqueous flow rate from 9.7×10−6 m/s at 170 ml/min to 37.2×10−6 m/s at 740 ml/min. The overall mass-transfer coefficient increases from
12×10−6 m/s at 2% D2EHPA to 28×10−6 m/s at 8% D2EHPA. This means that this process is chemically controlled and the interfacial resistance
has a more significant role in the extraction of zinc by emulsion liquid membrane through hollow-fiber contactor. From the results obtained, it
seems that the diffusion processes in aqueous feed phase and the membrane phase have the same importance as the chemical process. |
