Selective adsorption and recovery of precious metal ions using protein-rich biomass as efficient adsorbents

• We propose a recycle system of precious metal ions using protein-rich biomass.
• The protein-rich biomass exhibited selective adsorption for precious metal ions.
• The biomass tested had high loading potentials for Au, Pd and Pt ions.
• The present study proposes the mechanism of the metal-ion adsorption.
• Precious metal ions were selectively recovered from actual industrial wastes.

Various types of protein-rich biomass were examined as selective and environment-friendly adsorbents for precious metal ions. In the presence of base metal ions, Au3+, Pd2+ and Pt4+ ions were selectively adsorbed to samples of protein-rich biomass. Among the biomass samples tested, egg-shell membrane exhibited the highest adsorption ability and had high selectivity for Au, Pd and Pt ions. The maximum adsorption amount of Au, Pd and Pt ions to egg-shell membrane was approximately 250, 110 and 50 mg/g, respectively, in the presence of 0.1 M HCl. Microscopic observations and metal-ion desorption studies suggested that the precious metal ions were adsorbed and a portion of them was reduced to form metal nanoparticles on the egg-shell membrane, leading to high adsorption ratios. Investigations using glycoproteins indicated the importance of sugar chains in the adsorption of Au ions to the egg-shell membrane. Successful recovery of Au, Pd and Pt ions from industrial waste solutions was also demonstrated using egg-shell membrane. Biomass sheets (1 mm thick) made from egg-shell membrane also exhibited adsorption abilities for precious metal ions.