Removal of heavy metal ions from aqueous solution by ultrafiltration assisted with copolymer of maleic acid and acrylic acid

• The carboxylic group content of copolymer was firstly measured.
• The degree of deprotonation of copolymer with pH was firstly measured.
• The order of copolymer binding ability to heavy metal ions was obtained.
• Selective separation of heavy metal ions was studied by PAUF with copolymer.
• Regeneration of the complexing agent was studied by acidification-diafiltration.

Copolymer of maleic acid and acrylic acid (PMA-100), combining with polyvinyl butyral (PVB) hollow fiber ultrafiltration membrane were applied into a complexation–ultrafiltration process for the removal of heavy metal ions from an aqueous solution. Potentiometric and conductimetric titrations of the copolymer revealed that carboxylic group content was 9.5 mmol.g− 1 and the degree of deprotonation as pH was plotted. When low concentration (10 mg/L) of solution containing heavy metal ion was processed, like Cu2 +, Zn2 +, Ni2 + and Mn2 +, two most important factors (mass ratio of copolymer to metal and pH) were investigated and optimized to maximize both the rejection rate and permeate flux. The results show that at pH 6.0 and copolymer/metal ratio 6–7 (w/w), the complexation is rapid and completed within 5 min, reaching a removal efficiency above 98.8%. The copolymer could be efficiently regenerated by acidification-diafiltration and the residual concentration of Cu2 + in the concentrated copolymer solution decreased from 100 mg/L to 2.6 mg/L. In addition, the difference in binding ability to copolymer was studied and the relative affinity was Cu2 + > Zn2 + > Ni2 + > Mn2 +. The sequence is of great importance for guiding the selective separation of these metal ions in the future work.