Sorption of iron-cyanide complexes on goethite in the presence of sulfate and desorption with phosphate and chloride.
Soils are contaminated with potentially toxic iron-cyanide complexes by some industrial activities. The influence of sulfate on the sorption of the iron-cyanide complexes ferricyanide, [Fe(CN)6]3-, and ferrocyanide, [Fe(CN)6]4-, on goethite was investigated in batch experiments. The experiments were conducted as influenced by pH and varying sulfate/iron-cyanide complex concentration ratios. Furthermore, the desorption of iron-cyanide complexes sorbed on goethite was studied using phosphate and chloride solutions as influenced by pH and anion concentration. Over the whole pH range (pH 3.5 to 8), ferricyanide and sulfate showed similar affinities for the goethite surface. The extent of ferricyanide sorption strongly depended on sulfate concentrations and vice versa. In contrast, ferrocyanide sorption was only decreased (approximately 12%) by sulfate additions at pH 3.5. Ferricyanide was completely desorbed by 1 M chloride, ferrocyanide not at all. Unbuffered phosphate solutions (pH 8.3) desorbed both iron-cyanide complexes completely. Even in 70-fold excess, pH-adjusted phosphate solutions could not desorb ferrocyanide completely at pH 3.5. For ferricyanide we propose a sorption mechanism that is similar to the sulfate sorption mechanism, including outer-sphere and weak inner-sphere surface complexes on goethite. Ferrocyanide appears to form inner-sphere surface complexes. Additionally, we assume that ferrocyanide precipitates probably as a Berlin Blue-like phase at pH 3.5. Hence, ferrocyanide should be less mobile in the soil environment than ferricyanide or sulfate.
Rennert
Thilo
T
Arbeitsgruppe Bodenkunde und Bodenökologie, Fakultät für Geowissenschaften, Ruhr-Universität Bochum, Germany.
Mansfeldt
Tim
T
D000327:Adsorption; D005292:Ferricyanides / Q000737:chemistry*; D005295:Ferrocyanides / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D058085:Iron Compounds / Q000737:chemistry*; D008903:Minerals; D010710:Phosphates / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis*; D012995:Solubility; D013431:Sulfates / Q000737:chemistry
D005292:Ferricyanides; D005295:Ferrocyanides; D058085:Iron Compounds; D008903:Minerals; D010710:Phosphates; D012989:Soil Pollutants; D013431:Sulfates; C094886:goethite; C007931:hexacyanoferrate III; C020354:hexacyanoferrate II