Nanofiltration process for separating Cr(III) from acid solutions: Experimental and modelling analysis

This study aims to analyse the nanofiltration process at laboratorial scale, for separating Cr(III) from acid solutions. Thus, several experiments were tested and the results interpreted with a suitable mathematical model. The rejection of trivalent chromium salts under acidic conditions using the nanofiltration membrane Desal 5 DK was investigated. The experimental data were described by a Donnan steric partitioning pore and dielectric exclusion model which was based on the extended Nernst–Planck equation and incorporates also the concentration polarization effect in the membrane/feed solution interface. Such approach enabled to estimate the charge membrane density which varies from 1.5 × 10− 3 to 0.1 mol m− 3, and the pore dielectric constant nearly 50. The predictions obtained with the mathematical model are in good agreement with the experimental data. The parametric sensitivity analysis showed that Cr(III) concentration profile across the membrane is particularly sensitive to initial concentrations of chromium and chloride. The pore dielectric constant also has a significant effect on the observed rejections of counter-ions (Cr(III) and H+) and co-ion (Cl−). The model used may be helpful to optimize NF process applied to the treatment of metal salt solutions under acidic conditions.