Selective temperature-swing adsorption of Pd(II) ions onto a poly(N-isopropylacrylamide-co-allyl mercaptan) gel

A new type of thermosensitive adsorbent gel, poly(N-isopropylacrylamide-co-allyl mercaptan) gel (NIPA-co-AM gel), was developed to improve metal separation. The thiol group of the gel selectively adsorbs precious metal ions, especially Pd(II) ions, in aqueous HCl solution in accordance with the hard and soft acids and bases (HSAB) theory. The gel adsorbed and desorbed Pd(II) ions with a change in temperature, that is, temperature-swing adsorption (TSA) was accomplished. The effects of temperature, gel composition, and HCl concentration, and the adsorption isotherms and kinetics for Pd(II) ion adsorption were investigated. The adsorption capacity of the gel with NIPA:AM = 950:50 mol/m3 was 0.191 mol-Pd/kg-dry gel in 1 kmol/m3 HCl aqueous solution at 20 °C.