抄録
The dissolution behavior of magnetite powder (as received) and pellet (prepared by sintering) in solutions containing EDTA or citrate was studied at different pHs (0.3-9) and temperatures (30-95°C). The concentration of dissolved Fe increased with time, and is highest at pH 2.4 with EDTA and at pH 3.7 with citrate. A rate equation of dissolution was derived from a consideration that the dissolution reactions consist of the following two coupled processes: (1) the transfer of Fe ions from solid to aqueous phase by reaction with chelating agents and (2) the transfer of lattice O2- ions by reaction with H+ ions to form H2O. The resulting rate equation in solutions with EDTA (H4Y) is
d[FeY]/dt=k′k″[H+]8/3α4([Y]T-[FeY])/(k′[FeY]+k″[H+]8/3)
where k′ and k″ are the rate constants for the processes (1) and (2), α4 is the ionization fraction of Y4-, and [Y]T is the total concentration of EDTA. The amount of dissolved Fe vs. pH peaks at a specific pH, which can be explained by the rate equation noted above.
