Abstract
The potentially toxic Fe-CN complexes ferricyanide,[FeIII(CN)6]3−, and ferrocyanide,[FeII(CN)6]4−, undergo a variety of redox processes in soil, which affect their mobility. We carried out microcosm experiments with suspensions of a humic topsoil (pH 5.3;Corg107 gkg-1) to which we added ferricyanide (20 mgl-1). We varied the redox potential (EH) from −280 to 580 mV by usingO2,N2and glucose. The decrease ofEHled to decreasing concentrations of Fe-CN complexes and partial reductive dissolution of (hydrous) Fe and Mn oxides. The dynamics of aqueous Fe-CN concentrations was characterized by decreasing concentrations when the pH rose and theEHdropped. We attribute these dependencies to adsorption on organic surfaces, for which such a pH/EHbehavior has been shown previously. Adsorption was reversible, because when the pH andEHchanged into the opposite direction, desorption occurred. This study demonstrates the possible impact of soil organic matter on the fate of Fe-CN complexes in soil.
Highlights
As a consequence of anthropogenic inputs, the Fe-CN complexes ferrocyanide, [FeII(CN)6]4−, and ferricyanide, [FeIII(CN)6]3−, may be present in soil
The initial pH measured in both experiments is higher than the soil pH determined in CaCl2. This is caused by the stronger release of Al3+ from soil in the presence of CaCl2 compared to the release from soil suspended in water as in the microcosm experiments
The establishment of reducing conditions was accompanied with the disappearance of NO3− (c < 0.1 mg l−1) in both experiments after the EH had dropped to
Summary
As a consequence of anthropogenic inputs, the Fe-CN complexes ferrocyanide, [FeII(CN)6]4−, and ferricyanide, [FeIII(CN)6]3−, may be present in soil. Their occurrence is mainly due to the deposition of wastes originating from industrial processes such as coal gasification, pig Fe production, or paper recycling [1]. In these wastes, FeCN complexes are mainly present as sparingly soluble compounds, for example, Fe4[FeII(CN)6]3, KFe[FeII(CN)6], or K2Zn3[FeII(CN)6]2 [2]. The solubility of Fe4[FeII(CN)6]3, KFe[FeII(CN)6], and K2Zn3[FeII(CN)6]2 increases under neutral and alkaline conditions resulting in a release of Fe-CN complexes into the soil solution [4]. The presence of dissolved Fe-CN complexes is an environmental concern because they tend to decompose to extremely toxicfree CN (HCNg,aq and CN−aq) when irradiated by daylight [5]
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