ADSORPTION AND COPRECIPITATION OF SINGLE HEAVY-METAL IONS ONTO THE HYDRATED OXIDES OF IRON AND CHROMIUM

The adsorption and coprecipitation characteristics of Cr(III), Ni(II), and Zn(II) with amorphous iron(III) oxide and Ni(II) and Zn(II) with amorphous chromium(III) oxide have been measured and modeled using the James-Healy model for metal ion adsorption.1 The results for the adso rption and the coprecipitation experiments have been compared. In all systems, coprecipitation is more efficient than adsorption although in the case of Zn(II) removal by amorphous iron(III) oxide the differenc e was minimal. The contributions of the chemical free energy of adsorp tion to the overall adsorption free energy changes have been determine d and found to be greater for coprecipitation than for adsorption, gre ater for Zn(II) than for Ni(II), and greater for hydrated amorphous ch romium(III) oxide than for hydrated amorphous iron(III) oxide.