Adsorption of Hg (II) by Ferric Hydroxide

Abstract

Abstract Iron (III) oxide precipitated from Fe2(SO4)3 by NaOH was found to adsorb Hg (II) over the pH range from 3 to 10. Adsorption was not found to be affected by pH in the range from 4 to 10, but dropped off sharply between pH 4 and pH 3. Chloride additions at the 0.6M level inhibited adsorption of Hg (II) at neutral pH, but not above pH 10; Hg(OH)2 was found to be the adsorbed species. In solutions with low ionic strength the adsorption by Fe(OH)3 follows the form of the Freundlich isotherm in the neutral range; Hg (II) is adsorbed less strongly on Fe(OH)3 than on MnO2. The corresponding exponential Freundlich constants for Fe(OH)3 are: 293 for the coefficient and 0.76 for the exponent of the equilibrium concentration of Hg (II) in solution. This is far less than 1.9 × 1010 for the coefficient and 1.73 for the exponent of the equilibrium concentration of mercury in solution in the case of MnO2 adsorbent.