Preparation of polyelectrolyte-modified membranes for heavy metal ions removal

Polyethersulfone membranes were modified by polyelectrolyte (PE) multilayers, made of poly(allylamine hydrochloride) with poly(styrene sulfonate), to remove Cu²⁺, Zn²⁺ and Ni²⁺ heavy metal cations from aqueous solutions in a wide range of metal concentration (50-1200 ppm). After characterization of the modified membranes, the efficiency of the process was estimated for single heavy metal ions solution leading to high rejection rates (>90% for 50 ppm) and good adsorption capacities (7.0-8.5 mg cm^-2) whatever the metal ion tested. The stability in time of the modified membranes was proved by repeating successive filtrations with the same membrane. The filtration process was also used with mixed solutions composed of Cu²⁺, Zn²⁺ and Ni²⁺ ions. The rejection rates obtained for these ternary systems were very similar to the ones obtained for the single metal solutions, showing that the filtration process is still efficient for mixed solutions and can be applied for the decontamination of complex solutions. The long-term stability of the modified membranes was also demonstrated for mixed solutions. The high efficiency of the filtration process and the good adsorption capacities of the modified membranes are due to the ability of the PEs used to complex all the metallic dications tested in this study.