Removal of heavy metal ions from acidic wastewater by constructing positively charged hollow fiber nanofiltration separating-layer based on Fe (III)/co deposition-quaternization

A surface positively charged nanofiltration (NF) membrane was successfully constructed to effectively remove heavy metal ions by co-deposition and quaternization strategy. The combination between Fe3+ and H2O2 accelerated the co-deposition of tannic acid (TA) and polyvinyl amine (PVAM) on the membrane surface. The mechanism by which metal ions accelerated co-deposition process to regulate membrane surface structure was elucidated. The convenient quaternary ammonium modification was carried out by reacting glycidyl trimethyl ammonium chloride (GTMAC), which significantly increased the potential and density of the membrane surface. The membrane had a high retention rate for heavy metal ions (1000 ppm (mg· L−1), Cr3+ (94.6 %), Fe3+ (93.7 %), Cu2+ (92.1 %), Ni2+ (90.2 %)), while maintaining an excellent water permeance (27.8 L m−2 h−1 bar−1). The membrane also presented outstanding separation performance for rare earth metal ion. In particular, the retention rate for 500 ppm (mg·L−1) Ce3+ was 95.3 %. The relationship between membrane surface potential, pore size and rejection of heavy metal revealed the removal mechanism. Furthermore, the membrane exhibited excellent acid-base resistance and long-term operation stability. This study supplies an effective surface modification method for preparing hollow fiber NF membranes used for removing heavy metal and recovering rare earth metal from wastewater.