Alanine containing porous beads for mercury removal from artificial solutions

N-methacryloyl-(L)-alanine (MALA) was synthesized by using methacryloyl chloride and alanine as a metal-complexing ligand or comonomer. Spherical beads with an average diameter of 150-200 μm were obtained by suspension polymerization of MALA and 2-hydroxyethyl methacrylate (HEMA) conducted in an aqueous dispersion medium. Poly(HEMA-MALA) beads were characterized by SEM, swelling studies, surface area measurement, and elemental analysis. Poly(HEMA-MALA) beads have a specific surface area of 68.5 m²/g. Poly(HEMA-MALA) beads with a swelling ratio of 63%, and containing 247 μmol MALA/g were used in the removal of Hg²⁺ from aqueous solutions. Adsorption equilibrium was achieved in about 60 min. The adsorption of Hg ²⁺ ions onto PHEMA beads was negligible (0.3 mg/g). The MALA incorporation into the polymer structure significantly increased the mercury adsorption capacity (168 mg/g). Adsorption capacity of MALA containing beads increased significantly with pH. The adsorption of Hg²⁺ ions increased with increasing pH and reached a plateau value at around pH 5.0. Competitive heavy metal adsorption from aqueous solutions containing Cd ²⁺, Cu²⁺, Pb²⁺, and Hg²⁺ was also investigated. The adsorption capacities are 44.5 mg/g for Hg²⁺, 6.4 mg/g for Cd²⁺, 2.9 mg/g for Pb²⁺, and 2.0 mg/g for Cu ²⁺ ions. These results may be considered as an indication of higher specificity of the poly(HEMA-MALA) beads for the Hg²⁺ comparing to other ions. Consecutive adsorption and elution operations showed the feasibility of repeated use for poly(HEMA-MALA) chelating beads.