Release of metals from iron oxyhydroxides under reductive conditions: Effect of metal/solid interactions

Solubilization of heavy metals from Fe oxyhydroxides in the presence of sodium ascorbate as a reducing agent were investigated as a function of pH. Amorphous iron hydroxide (HFO) and goethite were synthesized in the presence of Pb, Cd, and Zn, using two different processes, i.e., favoring either metal adsorption (ADS) or metal substitution (coprecipitation, COP). Characterization of solids showed that there were no structural differences among the three kinds of HFO. However in the case of goethite, it seemed that metal cations were located within the structure of COP goethite, but partially adsorbed in ADS goethite. Results evidenced that, under reductive conditions, the solubilization risk is greater for PB, than for Cd (Cd substituted in the structure) from the coprecipitation process. In the adsorption process, Cd was removed more than Pb (greater complexation constant of Pb). Moreover, irrespective of the crystalline state, solids may be partly dissolved, and release of metals could occur. (C) 2000 Academic Press.