Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

Chemical Fume Suppressant for Nitric HF Pickling bath

Hello, My name is Richard Carter, and I work as the Manufacturing Engineering supervisor for an industrial boiler and water heater manufacturer. We recently began pickle/passivation of stainless steel with a bath consisting of Nitric Acid/HF/Water. I am searching for information on an additive to the bath that will help suppress fumes. Any help is greatly appreciated.

It would be very nice if there were such a thing, but nitric acid rapidly destroys even the most resilient fume suppressants. You are going to have to add ventilation instead. On top of that, nitric fumes require a wet fume scrubber with significant packing depth. Sorry for the bad news.

Hydrofluoric acid burns

Never use HF anywhere unless trained!
If you do, you MUST have the antidote gel on hand for instant use!

Calcium Gluconate
for HF acid burns

on eBay or

Amazon

(affil links)

Hi Richard

With HF you cannot afford ANY exposure of the workforce. Check the manufacturer's safety data sheet (MSDS).
HF is very nasty and pickle plant is usually fully enclosed with fume extraction and scrubbing.
Your workers must have specialist training in handling HF and have readily available first aid measures. This is normally calcium gluconate which requires immediate application in case of skin exposure.
You also need provision for dealing with spills or tank leakage.
You should also urgently check any local legislation regarding storage and discharge of waste.
All this and more should be addressed before installing the process.
Personally, I would place an embargo on the process until these matters have been addressed.

Also, when developing a safety plan for your workers, be aware that there is no respirator (at least that I've ever found) that can handle the Nitric acid in the pickling solution. Going from memory, I believe it has a 2ppm PEL. Either ventilate or provide supplied air to any workers with potential exposure.

Hi Richard,
I also never found any good additives for an HF/HNO3 bath.
But
Lowering the bath temperature a few degrees significantly reduces the amount of NOx fumes.
Use a close sealing bath-lid as much as possible, also helps a lot.
NOx fumes are heavier than air, so place your bath between the workers and an effective wall ventilation.
Build the wall ventilation with like 3 lines of 20" PVC pipes, with plenty 2" holes. Place the lower ventilation pipe only 2 feet above the floor.
Let the pickle workers use a multifunctional gasfilter like standard EN 14387.
Clean the ventilation air according to local governance.
Keep aware of the toxic HF and then there is no problem in this traditional pickling method.
BR Hans

Sir:

I did some experiments in chem lab in a beaker [beakers on eBay or Amazon [affil links] in an exhaust hood with HF to clean iron castings and it worked very well.

I knew a guy in Washington state who worked in a plant using HF pickle. He noticed that the glass on the wall clock became etched by the HF fumes. He also noted that the glass on his wrist watch became cloudy from the HF fumes. He died a few years later from a lung problem.

Regards,