Thiourea grafted PVDF affinity membrane with narrow pore size distribution for Au (III) adsorption: Preparation, characterization, performance investigation and modeling

Abstract

Thick and hydrophilic microporous poly(vinylidene fluoride) (PVDF) affinity membranes were prepared for low-concentration gold separation by grafting thiourea on alkali treated PVDF resin. The modified polymer was easily cast into membranes by non-solvent induced phase separation through two coagulation processes, and the addition of N-methyl-2pyrrolidone into the second coagulation bath improved the pore size distribution effectively. The grafted polymer and membrane were characterized by FTIR, Raman, 1H NMR, XPS, SEM and pore size distribution measurement. Static adsorption of Au (III) with the membranes followed pseudo-second order kinetics and Langmuir isotherm. Dynamic adsorption was investigated by using stacked membranes in the form of a membrane chromatography. The results showed that increasing the number of membrane layers improved the membrane bed utilization, which was attributed to the increased adsorption sites and a combined effect of reduced average membrane pore size and narrowed pore size distribution (PSD). The effect of PSD on performance of the membrane chromatography was further separated from that of the mean pore size, and it was shown that narrower PSD indeed was favorable. A new mathematical model based on dispersive mass transfer through the membrane pores and incorporating PSD was established. The model was found to be able to predict the membrane breakthrough behavior very well. Finally, the elution performance of gold laden membrane was studied, and an optimized formulation of the eluent consisting of thiourea and HCl was determined.