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Disposal of galvanizing flux

April 18, 2008

Its common for galvanizers to find their flux contaminated with Fe, HCl or other contaminants and decide to change it out for a fresh batch.
But these days disposing of the old flux is becoming increasingly difficult.
Has anyone found a simple, in-house method of dealing with flux to make it suitable for easier disposal.
Flux is a mixture of ammonium chloride and zinc chloride dissolved in water. Contaminants often include hydrochloric acid, iron hydroxide.
Any ideas?

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

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April 21, 2008

Geoff,

In the USA one flux company accepts contaminated liquid flux and reprocesses and resells it. A few galvanizers evaporate to dryness and dispose of the "dry" "spent" flux, but I do not know where it goes. This method reduces transport but requires energy to evaporate the water.

Galvanizers using sulfuric acid for pickling and two counter-current acid rinses never contaminate their flux. The sulphate stabilizes at about 0.8% and the iron at about 0.2%(Fe+2), which do not adversely affect the galvanizing.

Galvanizers using hydrochloric acid for pickling use contaminated flux without difficulty if they also use IQM.

If the dissolved iron (Fe+2) is under about 2%; and if the sodium chloride (dry W/W basis) is under 1%; and if the potassium chloride (dry W/W basis) is under about 2% then the flux could be purified (Fe+2 removal). This assumes no other major impurities. Hydrochloric acid in flux can easily be reacted with ammonium hydroxide to the proper pH. (HCL is NOT a contaminate.) A flocculating agent and a filter press are required if a rapid purification is needed.

In theory contaminated flux could be used as a micronutrient additive for fertilizer. There are USA companies that specialize in finding ways to recycle industrial wastes.

In the USA I estimate that the disposal of "spent" flux is only a few percent of what it was 30 years ago.

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA