Removal of heavy metal ions and humic acid from aqueous solutions by co-adsorption onto thermosensitive polymers

Abstract

An enhanced metal separation technique using thermosensitive polymers is proposed for the co-adsorption of undesirable heavy metals and humic substances in water and soil environments. In a model system consisting of metal ions (Cu(II) or Cr(III)), humic acid (HA), and thermosensitive N-isopropylacrylamide (NIPA) polymer, metal adsorption was successfully implemented; the bulk aggregates (floc) of the hydrophobic polymer were formed spontaneously above the lower critical solution temperature, and then metal–HA complexes were adsorbed onto the polymer. The proposed technique does not use centrifugation and filtration. Flocculation occurs more readily in solutions containing both HA and metal ions than in those containing only HA; this is because the negative charge of the HA is neutralized by the metal ions. Thermosensitive cation copolymers (derivatives of the NIPA polymer) show improved HA adsorption. A thermosensitive cation copolymer grafted onto a nonwoven polypropylene film adsorbed Cu(II)–HA complexes successfully. The reusable grafted polymer can permit temperature-swing adsorption and provide an environmentally friendly metal separation process.