How to convert cyanide galvanizing bath into alkaline cyanide-free galvanizing

- Oct 22, 2018 -

The original cyanide galvanizing bath can be gradually converted into alkaline cyanide-free galvanizing. The specific method is: the solution is no longer added with sodium cyanide, which is gradually consumed in the electroplating process. It can be gradually changed to the zincate galvanizing process by the following steps, which is to gradually transition the plating solution from high cyanide to medium cyanide to low cyanide to microcyanide to no cyanide.

The galvanizing solution of high cyanide and medium cyanide may be added with or without additives. However, low-cyanide, micro-cyanide and cyanide-free galvanizing solutions must be supplemented. If the high cyanide or medium cyanide plating solution you are using now is without additives, then the additive must be added in time as the free cyanide content in the bath is reduced.

As the content of sodium cyanide in the bath decreases, since the zinc ions do not form a complex with sodium cyanide, the electrode potential is corrected, that is, the zinc layer is easily deposited on the cathode, so that It will cause rough coating; in order to obtain crystallized and bright coating, we need to add brightener in time, and on the other hand, we should increase the content of sodium hydroxide properly; because with the increase of sodium hydroxide, zinc ion and hydrogen The complex formed by sodium oxide will also stabilize. Zn2+ and OH- can form four kinds of complex ions with different coordination numbers, among which tetrahydroxylated zinc [Zn(OH)4]2- is the most stable, and its K is unstable = 2.8×10-16, which is only better than sodium zinc cyanide. Complex ions are an order of magnitude smaller. Sodium zinc cyanide [Zn(CN)4]2-, K is unstable = 1.3 × 10-17. Therefore, in addition to adding additives and increasing the sodium hydroxide content, it is necessary to simultaneously reduce the concentration of zinc ions. It is possible to hang less zinc plates and replace them with an insoluble iron plate as an anode. This transformation will not affect production, nor will it cause waste, and will not bring pollution.

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