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Potassium ferrocyanide (K4(Fe(CN)6) (anhydrous) or K4(Fe(CN)6).3H2O(hydrated)) is a pale yellow potassium iron cyanide salt that is relatively safe to handle and only have low toxicity. The ferrocyanide complex is so strongly bonded that it is only an irritant if you get it on your hands. It is still toxic to digest. Under strongly acidic conditions deadly hydrogen cyanide gas will be released.
Under strong acidic conditions, highly toxic hydrogen cyanide gas is created. For example reacting with hydrochloric acid:
6HCl + K4(Fe(CN)6) → 6HCN + FeCl2 + 4KCl
CAS number : 13943-58-3 (anhydrous) or 14459-95-1 (trihydrate)
Molecular weight :
Melting point : 70 °C (158 °F)
Boiling point : Decomposes
Density : 1.89 g/cm3
Usage as a gold leach
Potassium ferrocyanide might be usable as an alternative to cyanide leach and since it is much easier to get hold on it might be a working alternative for hobby refiners. Even if it is less toxic in its ferro form it still have all the dangers associated with cyanide and acids.
Under UV-light and deep blue light (<= 400 nm) the cyanide complex will break down and release free cyanide that can dissolve gold. The process is slow and depends on daylight but will dissolve gold after some time. The process is dependent on pH, too high and the process slows down, too low and HCN might be released from the leach. The recommended pH is 11.
Testing for iron
- GRF : Deano on potassium ferrocyanide leach
- GRF : Deano on ferri and ferro cyanide chemical equilibrium
- Wikipedia : Potassium ferrocyanide
- Using ferrocyanide for iron(III) test
- Fischer Scientific : MSDS of potassium ferrocyanide