Adsorption of heavy metal ions from aqueous solution by crosslinked carboxymethyl konjac glucomannan

Crosslinked carboxymethyl konjac glucomannan (CMKGM) with degrees of substitution (DS) 0.265 and 0.550 were prepared through reaction of monochloroacetic acid (MCA), konjac glucomannan (KGM) and epichlorohydrin and used to adsorb Cu²⁺, Pb²⁺ and Cd²⁺ ions from the aqueous solutions. Regardless of the metal ion species, the adsorption capacity rapidly reached equilibrium within 20 min and adsorption followed second-order kinetic equation. The effect of pH on adsorption was apparent, the appropriate range was 5-6. The adsorptions of three metal ions are well followed as the Langmuir adsorption isotherm. The maximum adsorption capacity (Q_m) and Langmuir constant (b) of CMKGM (DS = 0.550) for Pb²⁺ were 41.7 mg/g and 0.305 mg/L. These values were higher than those for Cu²⁺ and Cd²⁺. Among the tested ions, the order of adsorption capacity was Pb²⁺ > Cu²⁺ > Cd²⁺ in mass basis. The regeneration study indicates that CMKGM could be used repeatedly without significantly changing their adsorption capacities and desorption percentage.