ADSORPTION AND COPRECIPITATION OF HEAVY-METALS FROM AMMONIACAL SOLUTIONS USING HYDROUS METAL-OXIDES

The importance of metal ion hydrolysis to the processes of adsorption and coprecipitation is investigated. The metal ions studied were Cr(II I), Zn(II) and Ni(II) and the substrates used were amorphous hydrous i ron(III) oxide (HFO) and amorphous hydrous chromium(III) oxide (HCO). Adsorption and coprecipitation experiments were performed using an amm oniacal background electrolyte, where the ammonia present could form a mmine complexes with the metal ions, and hence significantly suppress hydrolysis. It is suggested that this suppression of hydrolysis inhibi ts adsorption, both through competitive equilibria and also through di minished capability for hydrogen bonding in the presence of ammoniacal ligands. The removal profiles obtained for Zn(II) adsorption and copr ecipitation on HFO and HCO were modelled using a modified version of t he James-Healy model for metal ion adsorption. (C) 1997 Elsevier Scien ce B.V.