Synthesis of Silicas with Amino Moieties and their Adsorption Properties of Precious Metal Ions in Hydrochloric Acid

Bis[(N-ethylaminomethyl)-2-pyridine]amino-silica (BEPS) and bis[(N-propylaminomethyl)-2-pyridine]aminosilica (BPPS) as adsorbents have been synthesizing by the sol-gel process. The adsorption experiments were carried out by a bath method. The adsorption ability of palladium(II) on BEPS was higher than that of BPPS whereas adsorption ability of gold(III) on BPPS was higher than that on BEPS. The thermodynamic parameters showed that entropy change of palladium(II) on BEPS was higher than that on BPPS and gold(III) on BPPS was higher than that of BEPS. These indicate that BEPS and BPPS formed high stable chelating complexes with palladium(II) and gold(III), respectively. While the thermodynamic parameters and adsorption rate constants of platinum(IV) on BPPS indicated that the platinum(IV) adsorption on BPPS is due to an electrostatic interaction.