Chromium ferrocyanide

Chromium Ferrocyanide, Cr2[Fe(CN)g], is obtained as a yellow precipitate -when chromous chloride is added to a solution of potassium ferrocyanide. ... 

In detecting a small amount of aluminum in the presence of much iron and chromium, a control test should be carried out on an aluminum-free iron-chromium solution. After addition of the alizarin, the paper should be placed in hot water for 1 minute and then dried. The potassium ferrocyanide is removed, and the paper becomes white. The lake coloris thus renderedmore visible. The control flecks show only a very slight color change, if any, because the chromium ferrocyanide is also washed away. The concentrations... 

To address this concern, several organic and inorganic reagents were evaluated as precipitants for heavy metals in a 10-34-0 (N-P2O5-K2O) fluid fertilizer and WPA. Trisodium trithiocyanuric acid (TMT-15), sodium polythiocarbonate (Thio-Red II), and sodium trithiocarbonate (5% Na2 CS3) precipitated arsenic, cadmium, copper, mercury, lead, and zinc from 10-34-0. Ammonium cyanurate was ineffective in removing cadmium from 10-34-0. Thio-Red II and 5% Na2CS3 precipitated mercury, lead, cadmium, copper, and chromium from WPA. A water-insoluble starch xanthate adsorbed mercury, copper, and lead from 10-34-0 and WPA. Sodium sulfide, sodium polysulfide, and potassium ferrocyanide were tested as inorganic precipitants. The polysulfide was twice as effective as the sulfide alone, and concentrations of less than 10 ppm of arsenic, cadmium, mercury, and lead were achieved in 10-34-0. Ferrocyanide reduced the concentrations of cadmium and nickel to less than 10 ppm in WPA. 

Iron, uranium, chromium and manganese form colored alizarin lakes and, therefore, interfere in the Al-alizarin test. In some cases, the interference can be eliminated by precipitation as ferrocyanides. Thus, when the precipitation is carried out on filter paper impregnated with potassium ferrocyanide, the aluminum salt diffuses through the capillaries to the water zone encircling the fleck of precipitate and can be detected there by the alizarin reaction. 

Alkali ferricyanides oxidize acid solutions of diethylaniline and other aromatic amines, as well as certain monoazo dyestuffs a change of color results and ferrocyanide is formed. This reversible redox reaction, proceeds very slowly and incompletely. However, if the ferrocyanide ions are removed as insoluble white zinc ferrocyanide, the oxidation proceeds rapidly. This acceleration is a result of raising the oxidation potential of ferricyanide ions through removal of ferrocyanide ions. The white zinc ferrocyanide is deeply tinted by adsorption of the colored quinoidal oxidation products of the amines, and thus affords a sensitive test for zinc. The test is especially useful in the presence of chromium and aluminum. It can also be used in other instances provided no other cations are present, which form colored precipitates with potassium ferrocyanide (Co+, Ni+, Fe+, Mn+ , Cu+ ). Traces of iron, which in practice are always to be reckoned with, do not interfere with the zinc test. Anions which oxidize the amines must be absent, e.g., permanganate, chromate, vanadate, persulfate, iodate. 

A drop of the test solution is placed on dry filter paper that has been impregnated with potassium ferrocyanide. Any iron or chromium is held back in the paper, while the aluminum diffuses through the capillaries and accumulates in a circular zone. A drop of a saturated alcoholic solution of alizarin is added and the paper is held over ammonia. The violet color of ammonium alizarinate then appears. In the presence of considerable amounts of aluminum, the strawberry red of the aluminum alizarinate can be seen at the same time. For smaller amounts the filter paper is warmed (held briefly near a flame or placed in an oven) and the violet ammonium alizarinate decomposes (volatilization of ammonia). The red aluminum lake then becomes clearly visible. 

Chatterjee found an analogous behaviour in the case of an uranium ferrocyanide sol with potassium fcrrocyanidc. The, investigation by Fisher and SoRUM on chromium hydroxide peptized with Cr CI3 is still more complete. For monovalent ions they found the same behaviour as for Fe(OH),. 8-16. Flocculation valuw of iron T a w 1 1 r i oxidc sols to which Fed- has been... 

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