Preliminary design and optimisation of a PEUF process for Cr(VI) removal

The main purpose of this work is the study of the viability of a polyelectrolyte enhanced ultrafiltration (PEUF) process for the chromate recovery using poly(diallyldimethylammonium chloride) (PDADMAC) as water-soluble polymer. First of all, the interaction between PDADMAC and chromate ions was studied by potentiometric titrations of different poly(acrylic acid) (PAA) solutions in which its acidity constant (pKa) was determined using the Henderson-Hasselbach equation. This interaction is linked to the influence of the presence of PDADMAC and chromate in the PAA pKa value. Next, the operation conditions (pH, temperature and transmembrane pressure) that optimize the membrane hydrodynamic behaviour were studied with ultrafiltration runs in mode operation of total recirculation. Furthermore, working at the operation conditions determined in the previous stage and with solutions of PDADMAC and chromate, the influence of ionic strength on design parameters was studied. Finally, the viability of a chemical method to regenerate the polyelectrolyte, based on the addition of NaCl and subsequent ultrafiltration, was checked. We conclude that this method is not suitable, mainly because of the great amount of water spent in the diafiltration stage necessary to reduce the polyelectrolyte solution chloride concentration.