Letter 13006

Atmospheric evaporators/zinc chloride 

We are anticipating installing atmospheric evaporators on a zinc chloride plating solution and would like to know what the proper permitting requirements might be. Also, if you know of any problems we may encounter, that would be helpful!

Thanks!

G Zyskowski
Sun Metal Finishing - Paterson, NJ, USA

As the water evaporates, the salt content increases and evaporation rate goes down. When it becomes supersaturated, it settles out on the packing and is a bitch to remove it. Take care of it, and it works, If not--great grief.

James Watts
- FL

Two things that you need to watch out for are iron oxidation and precipitation (filter the solution from the evaporator before returning it to the plating tank), and a build-up of zinc in your plating tank.

Lyle Kirman
Kinetico Incorporated - Newbury, OH

Among the previously listed caveats for evaporating chloride zinc solutions I would like to add that unless you heat the solution your evaporation rate will be quite slow and you will rapidly get the mentioned salt formation in the evaporator. If you have not already purchased the evaporator, you should explore these concerns with the various manufacturers.

If it is your intention to return the solution to the process tanks, the other writers are correct in stating that the metal content will increase. The anode efficiency in acid chloride zinc plating is greater than the cathode efficiency - this is why most zinc platers never need to add zinc chloride to the bath. Also, you are concentrating your impurities by concentrating the solution. If you heat the solution you can break down some of the organic additives. I would suggest transfering back to the process tank by way of a carbon filtration unit. Also, these same additives are known to cause high foaming in atmospheric evaporators (packing type). Defoamers are generally not compatible with the brightener chemistries when returning the concentrate to the plating tank.

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Gene Packman
- Syosset, NY

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