Metal finishing Q&As since 1989

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How to deal with galvanizers waste acids

Q. Increasingly, across many countries, I'm finding the issue of disposal of waste acid is a problem for hot dip galvanizers. Mainly in HCl, the most common acid used (exception USA where a few still use H2SO4), the "waste" acid is usually about 2-4% HCl, some Zinc chloride, and iron chlorides all in aqueous solution.
The volumes can be huge, thousands of tonnes a year per plant.
Traditionally contractors have removed the waste by road tanker, where they mostly neutralise, filter off solids and liquid remaining goes to sewer drain, and solids to landfill. Environmental limits on these two outlets have closed up, such that neither landfill nor sewer are attractive, at least not at reasonable cost. This seems to me a great opportunity for someone to resolve this issue for the industry. The application of such a solution is international. The presence of zinc chloride has caused problems in some suggested schemes, but I think that problem is likely to persist. Most galvanizers need to strip something, even if only jigging, and keeping Zn contaminated acid separate is difficult. So who will solve this industry wide problem and become a billionaire in the process?

Geoff Crowley
Crithwood Ltd.

Bathgate, Scotland, UK

December 12, 2023