Removing cadmium ions from water via nanoparticle-enhanced ultrafiltration

Here we evaluate removal of cadmium ions from water by nanoparticle-enhanced ultrafiltration using polymer and zeolite nanoparticles. This evaluation considered nanoparticle physical-chemical properties, metal-binding kinetics, capacity and reversibility, and ultrafiltration separation for a Linde type A zeolite nanocrystals, poly(acrylic acid), alginic acid, and carboxyl-functionalized PAMAM dendrimers in simple, laboratory prepared ionic solutions. The three synthetic materials exhibited fast binding kinetics and strong affinity for cadmium, with good regeneration capabilities. Only the zeolite nanoparticles were completely rejected by the ultrafiltration membranes tested. Overall, colloidal zeolites performed similar to conventional metal binding polymers, but were more easily recovered using relatively loose filtration membranes (i.e., lower energy consumption). Further, the superhydrophilic colloidal zeolites caused relatively little flux decline even in the presence of divalent cations which caused dense, highly impermeable polymer gels to form over the membranes. These results suggest zeolite nanoparticles may compete with polymeric materials in low-pressure hybrid filtration processes designed to remove toxic metals from water.