Identification of iron-cyanide complexes in contaminated soils and wastes by Fourier transform infrared spectroscopy

Persistent cyanide species in soil are mainly iron-cyanide (Fe-CN) complexes. They originate from anthropogenic inputs of compounds such as Fe(4)[Fe(II)(CN)(6)](3) in deposited gas-purifier wastes (GPW) or K(2)Zn(3)[Fe(II)(CN)(6)](2) in deposited blast-furnace sludge (BFSl). Fe-CN species in de-inking sludge (DIS) and sewage farm soils (SF) are still unknown. We investigated 35 soil and waste samples from 15 European sites and five synthesized Fe-CN-containing compounds by Fourier transform infrared spectroscopy. Furthermore, we determined the contents of total and adsorbed CN and pH. In all samples (pH 2.2-9.5), adsorbed Fe-CN complexes were negligible. In GPW and DIS samples, Fe(4)[Fe(II)(CN)(6)](3) and KFe[Fe(II)(CN)(6)] were the only Fe-CN compounds (total CN contents 0.4-449 g kg(-1)). Several BFSl samples were free of CN. The spectra of other BFSl samples partially indicated dissolution of the characteristic compound K(2)Zn(3)[Fe(II)(CN)(6)](2), resulting in a loss of CN (contents < 12.3 g kg(-1)). Distinctive changes in BFSl with respect to CN speciation occurred within relatively short periods, < 20 years. Dissolution of K(2)Zn(3)[Fe(II)(CN)(6)](2) was followed by dissociation of free CN from [Fe(CN)(6)](3-/4-) and adsorption of [Fe(II)(CN)(6)](4-) on organic surfaces. In DIS and SF samples, Fe(4)[Fe(II)(CN)(6)](3) and K(2)Zn(3)[Fe(II)(CN)(6)](2) (SF only) were identified.