Metal ion recovery by polymer-enhanced ultrafiltration using poly(vinyl sulfonic acid): Fouling description and membrane–metal ion interaction

This work studied the effects produced on the ultrafiltration membrane during metal ion recovery by polymer-enhanced ultrafiltration (PEUF) using poly(vinyl sulfonic acid) (PVSA), as water-soluble polymer by means of enrichment method and at different pHs. The fouling was described (by permeability measurements, application of series resistance model, ATR-FTIR spectrum and AFM images) and membrane–metal ion interaction was studied (by calculating of interaction coefficient from metal ion concentration in the permeated as function of permeated volume). The resistance was observed to increase with decreases in pH (from 2.0 × 1012 at pH 6.0 to 10.7 × 1012 m−1 at pH 3.0; from 11.5 × 1012 at pH 6.0 to 19 × 1012 m−1 at pH 3.0 for clean and fouled membrane, respectively). The fouling layer thickness was found to be greater at more acid pHs, where it was similar at pH 3.0 (0.19 μm) and 4.5 (0.23 μm) in comparison with the thickness at pH 6.0 (0.08 μm). The increase in membrane–metal ion interaction was used to define a sequence of affinity between metal ion and the fouling layer formed (Ni2+ < Cu2+ < Co2+ < Zn2+ < Cd2+), although Pb2+ presented atypical behavior for all the pHs studied. Membrane–metal interaction coefficient (R0) was found to be associated to a good degree with a decrease of the respective hydrated ionic radius, indicating that the electrostatic nature is not the main interaction in the adsorption of metal ions on the clean and fouled membrane during PEUF when using PVSA.