Membrane contactors for the recovery of metallic compounds: Modelling of copper recovery from WPO processes

This work reports the comparative analysis of two types of separation processes aimed at the recovery of metallic compounds from residual waters by using hollow fiber modules as membrane contactors, i.e., emulsion pertraction, EPP, and non-dispersive solvent extraction, NDSX. As a representative example the recovery of the copper used as homogeneous catalyst in wet peroxide oxidation (WPO) processes is experimentally and theoretically analysed. The separation of the metal was enhanced by using LIX622N as selective extractant and its concentration took place in a concentrated sulphuric acid phase. Working with hollow fibers as membrane contactors, the mathematical modelling of the emulsion pertraction process is reported. Characteristic parameters have been determined as the membrane mass transfer coefficient, km = 2.2 × 10−6 m s−1, the equilibrium constant of the extraction/back-extraction reaction KEX = 22, the forward reaction kinetic constant k1 = 2.78 × 10−7 m s−1 and the specific area of the globules of the stripping phase Av = 2.54 × 104 m−1. Finally, the results of copper separation and concentration have been compared to previous results obtained working with two hollow fiber modules, one for the extraction and the second for the back-extraction process and, as expected, a good agreement was observed. Two main advantages of the EPP could be underlined: (i) reduction of the needed membrane area of the contactor and (ii) higher concentrations in the stripping phase can be obtained with the operation conditions used (at laboratory scale).