Iron cyanide

Alkali or alkaline-earth salts of both complexes are soluble in water (except for Ba2[Fe(CN)g]) but are insoluble in alcohol. The salts of hexakiscyanoferrate(4—) are yellow and those of hexakiscyanoferrate(3—) are mby red. A large variety of complexes arise when one or more cations of the alkah or alkaline-earth salts is replaced by a complex cation, a representative metal, or a transition metal. Many salts have commercial appHcations, although the majority of industrial production of iron cyanide complexes is of iron blues such as Pmssian Blue, used as pigments (see Pigments, inorganic). Many transition-metal salts of [Fe(CN)g] have characteristic colors. Addition of [Fe(CN)g] to an unknown metal salt solution has been used as a quaUtative test for those transition metals. 

Environmental. The toxicity of cyanide in the aquatic environment or natural waters is a result of free cyanide, ie, as HCN and CN . These forms, rather than complexed forms such as iron cyanides, determine the lethal toxicity to fish. Complexed cyanides may revert to free cyanide under uv radiation, but the rate is too slow to be a significant toxicity factor. Much work has been done to estabhsh stream and effluent limits for cyanide to avoid harmful effects on aquatic life. Fish are extremely sensitive to cyanide, and the many tests indicate that a free cyanide stream concentration of 0.05 mg/L is acceptable (46), but some species are sensitive to even lower concentrations. 

Cyaneisen, n. iron cyanide, -kalium, n. potassium ferrocyanide, -verbindungt /. iron cyanogen compound, specif, a ferrocyanide. 

There is a discrepancy between the cyanide criteria for both aquatic and drinking water standards and the current analytical technology. The criteria are stated for free cyanide (which Includes hydrocyanic acid and the cyanide ion), but the EPA approved analytical methodology for total cyanide measures the free and combined forms (11). This test probably overestimates the potential toxicity. An alternative method (cyanides amenable to chlorination) measures those cyanide complexes which are readily dissociated, but does not measure the iron cyanide complexes which dissociate in sunlight. This method probably tends to underestimate the potential toxicity. Other methods have been proposed, but similar problems exist (12). The Department of Ecology used the EPA-approved APHA procedure which includes a distillation step for the quantification of total cyanide (13,14). A modification of the procedure which omits the distillation step was used for estimation of free cyanide. Later in the study, the Company used a microdiffusion method for free cyanide (15). 

J.E Duncan and P.W.R. Wrigley, The electronic structure of the iron atoms in complex iron cyanides. J. 

Hipps KW, Mazur U (1980) An inelastic electron tunneling spectroscopy study of some iron cyanide complexes. J Phys Chem 84 3162-3172... 

Cherryholmes KL, Comils WJ, McDonald DB, et al. 1985. Biological degradation of complex iron cyanides in natural aquatic systems. In Cardwell RD, Purdy R, Bahner RC, eds. Aquatic Toxicology and... 

Meeussen JCL, Temminghoff EJM, Keizer MG, et al. 1989. Spectrophotometric determination of total cyanide, iron - cyanide complexes, free cyanide and thiocyanate in water by a continuous-flow system. Analyst (London) 114 959-963. 

Janetski et al. (1977) also studied the behavior of a pyrite electrode in a solution of cyanide concentration in the absence and presence of xanthate using voltammetric technique. They reported that on increasing the concentration of cyanide at constant pH and xanthate concentration, the oxidation wave of xanthate is shifted to more anodic potential indicating that the presence of cyanide, which may react with the mineral surface to form an insoluble iron cyanide complex will result in the inhibition of the electrochemical oxidation of xanthate and the depression of pyrite. 

Solubility data (pA sp) for two dozen hexacyanoferrate(II) and hexacyanoferrate(III) salts, and Pourbaix (pe/pH) diagrams for iron-cyanide-water, iron-sulfide-cyanide-(hydr)oxide, iron-arsenate-cyanide-(hydr)oxide, and iron-copper-cyanide-sulfide-(hydr)oxide, are given in a review ostensibly dedicated to hydrometallurgical extraction of gold and silver. " The electrochemistry of Prussian Blue and related complexes, in the form of thin films on electrodes, has been reviewed. ... 

Rennert, T. Mansfeldt,V (2001) Sorption of iron-cyanide complexes on goethite. Eur. J. 

Iron in both the +2 and +3 valence states forms several stable hexacoordi-nated octahedral complexes with cyanide (CN ) ion, known as ferrocyanide or hexakiscyanoferrate(4—), [Fe(CN)6] and ferricyanide or hexakiscyanofer-rate(3-), [Fe(CN)6]3-, respectively. The simple iron(II) cyanide, Fe(CN)2 is unstable and all iron cyanide compounds known are coordination complexes. 

Such cyanide complexes are also known for several other metals. All the fer-rocyanide complexes may be considered as the salts of ferrocyanic acid H4Fe(CN)e and ferricyanide complexes are that of ferricyanic acid, H3Fe(CN)e. The iron-cyanide complexes of alkali and alkaline-earth metals are water soluble. These metals form yellow and ruby-red salts with ferro-cyanide and ferricyanide complex anions, respectively. A few of the hexa-cyanoferrate salts have found major commercial applications. Probably, the most important among them is ferric ferrocyanide, FeFe(CN)e, also known as Prussian blue. The names, formulas and the CAS registry numbers of some hexacyanoferrate complexes are given below. Prussian blue and a few other important complexes of this broad class of substances are noted briefly in the following sections ... 

Nitroprusside is a complex of iron, cyanide groups, and a nitroso moiety. It is rapidly metabolized by uptake into red blood cells with liberation of cyanide. Cyanide in turn is metabolized by the mitochondrial enzyme rhodanase, in the presence of a sulfur donor, to the less toxic thiocyanate. Thiocyanate is distributed in extracellular fluid and slowly eliminated by the kidney. 

The energy levels in the solution are kept constant, and the applied voltage shifts the bands in the oxide and the silicon. The Gaussian curves in Figure 4b represent the ferrocyanide/ferricyanide redox couple with an excess of ferrocyanide. E° is the standard redox potential of iron cyanide. With this, one can construct (a) to represent conditions with an accumulation layers, (b) with flatbands, where for illustration, we assume no charge in interface states, and (c) with an inversion or deep depletion layer (high anodic... 

A variety of toxins have been shown to give rise to selective neuronal loss and a parkinsonian syndrome in either humans, other primates, or rodents. These agents include manganese, iron, cyanide, azide, P-carbolines, isoquinolines, and MPTP. 

Total cyanide content (which includes water soluble cyanides, iron cyanides, and other insoluble cyanides) in solid matrices may be determined as follows ... 

To 1 g sample, add 100 mL of 10% caustic soda solution and stir for 12 h. (This treatment is required only if iron cyanides are suspected to be present in the sample.) After this, adjust the pH to less than 8.0 with 1 1 H2S04. Add about 0.2 g sulfamic acid to avoid nitrate/nitrite interference. This is followed by addition of 25 mg lead carbonate (to prevent interference from sulfur compounds). The mixture is distilled and collected over NaOH solution. This distillate is analyzed for CN by colorimetric, titrimetric, or ion-selective electrode method. 

Leita, L., De Nobili, M., Catalano, L., Moira, A., Fonda, E., and Vlaic, G. (2001). Complexation of iron-cyanide by humic substances. In Understanding and Managing Organic Matter in Soils, Sediments and Waters, Swift, R. S., and Sparks, K. M., eds., International Humic Science Society, St. Paul, MN, pp. 477 82. 

Zinc prevents the formation of rust, which is required to form long-term stable iron cyanides. 

The reaction products of interest to us in this respect are the salts of hydrogen cyanide, called cyanides,314 in particular, the iron cyanide group, formed by a compound of iron and cyanide. Iron occurs universally in nature. It is iron which gives brick its red color, sand its ochre color, and clay its color ranging from yellowish to reddish-brown. More precisely, we are speaking of iron oxide, popularly known as rust . Basically, all walls consist of at least 1% rust, as a result of sand, gravel, clay, and cement, of which the wall is constructed. 

The iron cyanides have long been known for their extraordinary stability, one of them having achieved particular fame as one of the most commonly used blue pigments during the last three centuries ... 

Iron Blue is the ISO designation (ISO 2495) for iron cyanide blue pigments of various composition, which are also known as Berlin Blue, Turnbull s Blue, Prussian Blue, Vossen Blue , Milori Blue, Paris Blue, French Blue, China Blue, Bronze Blue, Steel Blue, Ink Blue, among others. 

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