Cysteine-metal affinity chromatography: determination of heavy metal adsorption properties

摘要

Various adsorbent materials have been reported in the literature for heavy metal removal. We have developed a novel approach to obtain high metal sorption capacity utilising cysteine containing adsorbent. Metal complexing aminoacid-ligand cysteine was immobilised inot poly(hydroxyethylmethacrylate) (PHEMA) microbeads. PHEMA-cysteine affinity microbeads containing 0.138 mmol cysteine/g were used in the removal of heavy metal ions (i.e. copper, lead and cadmium) from aqueous media containing different amounts of these ions (50-400 mg/l for Pb(II) and Cd(II), 25-60 mg/l for Cu(II) and at different pH values (4.0-7.0). The maximum adsorption capacity of heavy metal ions onto the cysteine-containing microbeads under non-competitive conditions were 0.259 mmolg for Pb(II), 0.330 mmol/g for Cd(II) and 0.229 mmol/g for Cu(II). The affinity order was obsrved as follows: Cd(II)>Pb(II)>Cu(II). The competitive adsorption capacities of the heavy metals were 0.0260 mmol/g for Cd(II) and 0.120 mmol/g for Cu(II). Pb(II) adsorption onto cysteine-immobilised microbeads was zero under competitive conditions. the affinity order was as follows: Cd(II)>Cu(II)>Pb(II). The formation constants of cysteine-metal ion complexes have been investigated applying the method of Ruzic. The calculated value of stability constants were 1.75X10~4 l/mol for Pb(II)-cysteine complex and 4.35X10~4 l/mol for Cd(II)-cysteine compelx and 1.39X104 lmol for Cu(II)-cysteine complex. PHEMA microbeads carrying cysteine can be regenerated by washing with a solution of hydrochloric acid (0.05 M). The maximum desorption ratio was greater than 99%. These PHEMA microbeads are suitable for repeated use for more than three adsorption-desorption cycles without considerable loss in adsorption capacity.