Comparative performance of non-dispersive solvent extraction using a single module and the integrated membrane process with two hollow fiber contactors

Hollow fiber non-dispersive solvent extraction (HFNDSX) was carried out with one module (batch process) using (0.562 M) 18 % LIX79/n-heptane by passing Ag(CN)(2-) alkaline feed through the tube side and organic extractant through the shell side in counter-current mode. Similarly, stripping was done by passing NaOH through the tube side and loaded organic through the shell side using the same module after washing (in batch operation). On the other hand, in the integrated membrane process (IMP), non-dispersive solvent extraction of silver cyanide and stripping of silver cyanide from organic complex were performed simultaneously using two hollow microporous hydrophobic polypropylene fiber contactors each for extraction and stripping, respectively. The overall mass transfer coefficient obtained in the integrated process was observed to be greater than the values of the mass transfer coefficient (K-Ag(E)) obtained with the single module (no stripping). The various hydrodynamic and chemical parameters, such as linear flow velocity of the feed aqueous phase (3.07 cm/s greater than or equal to v(f) greater than or equal to 0.92 cm/s), linear flow velocity of the organic phase (1.18 cm/s greater than or equal to v(f) > 0.39 cm/s), NaCN concentration in the feed, pH variation in the aqueous feed and NaOH concentration in the stripping phase, were optimized in the single module. Some selective experiments were performed with two modules in order to compare the performance of IMP with that of HFNDSX. The mass transfer coefficients were calculated under different hydrodynamic and chemical conditions with a single module, and rate-controlling steps in extraction and stripping were identified. Similarly, the mass transfer coefficients were evaluated using IMP and attempts were made to solve operational problems with HFNDSX using a single module in counter-current mode. (C) 2004 Elsevier B.V. All rights reserved.