Effect of polymer nature and hydrodynamic conditions on a process of polymer enhanced ultrafiltration

Technical viability of two polymers, poly(ethyleneimine) and poly(acrylic acid), with different acid-basic behaviour, structure and molecular weight, in a reactive separation process for the recovery of nickel ions across zirconia ultrafiltration tubular membranes, has been studied in a laboratory-scale installation. Suitable experimental conditions (e.g., pH, feed flow rate, polymer and metal concentrations, transmembrane pressure) for the two steps of the process (metal recovery and polymer regeneration) have been optimised and justified with acid-base behaviour of each polymer and measures of polymer-nickel complex formation constants. For this reason, global stability constant of PAA-Ni and conditional complex formation constant of PEI-Ni were measured by potentiometric and spectrophotometric analyses, respectively. Furthermore, the effect of hydrodynamic conditions on two important factors limiting permeate flux (concentration polarization and fouling) have been analysed. The mass transfer coefficient in our system has been studied by means of stagnant layer model and dimensionless analysis.