Sorption of Iron‐Cyanide Complexes in Soils

The Fe‐cyanide complexes ferricyanide, [Fe(CN) 6 ] 3− , and ferrocyanide, [Fe(CN) 6 ] 4− , are of an anthropogenic source in soils. As the complexes are largely charged, sorption on the soil matrix is a possible retention mechanism for these anions. To evaluate soil properties controlling Fe‐cyanide complex sorption, experiments were performed with 17 uncontaminated soil horizons by a batch technique. Soil organic matter (SOM) was destroyed in six horizons. The experiments were conducted at soil pH, reaction time of 24 h, and an ionic strength of 0.01 (NaNO 3 ). The affinity of the Fe‐cyanide complexes for the soil matrix differed, because 14 samples sorbed higher amounts of ferrocyanide than of ferricyanide. Calculated sorption maxima were quantitatively explained by physical and chemical soil properties using multiple regressions. The regression equations were checked by variance analysis. The regression equations for all samples showed that the sorption of both complexes depended on organic C (C org ), clay, and oxalate‐extractable Fe (Fe o ). The sorption of the complexes on soils containing <10 g C org kg −1 was governed by pH and clay contents. Clay and oxalate‐extractable Al (Al o ) were the most important properties influencing ferricyanide sorption on samples containing high amounts of C org On the same samples, ferrocyanide sorption was governed by Al o Organic matter promotes the sorption of both complexes, especially on Fluvisol samples. Destruction of SOM of these samples minimized the sorption by up to 99%. Therefore organic matter in these soils may have a special affinity for Fe‐cyanide complexes possibly because of the reaction between Fe‐cyanide N and reactive groups of SOM.