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Titanium Pickling Line Help Requested!

2007

Hello,
I was recently placed in to a working supervisor position of a titanium pickle line. This line is currently used to remove alpha-case and machining soils from titanium aerospace parts. As the previous supervisor of the line who was also responsible for it inception left the company quite quickly, I am with out further technical support.I am not chemistry inclined so to speak as I am a trained metallurgist. What I am attempting to determine is the waste products associated with the neutralization of the spent acid. Our line currently functions with the following makeup:
30%by volume Regent Grade Nitric + Ammonium Bifluoride (amount to approx. 3% Hf solution)
we currently neutralize the acid to a Ph of 7-9 with Sodium Hydroxide.

As far as the neutralization is concerned I am only certain of the reaction between the Nitric and the Sodium Hydroxide

NaOH + HNO3 -> NaNO3 + H2O

What I am uncertain of is the reaction of the NH4HF2 and the Dissolved Titanium Solids


Could you please help me with the problem? My biggest concern is the waste products following neutralization, and the best method of disposal.

Callie J. Benson
Metallurgist - Eastford, Connecticut, USA

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First of two simultaneous responses --

Fluorides are best treated with Ca(OH)2 Potassium hydroxide. Sodium hydroxide will nor remove Fluorides.

Erik van der Staaij
- Netherlands
2007

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Second of two simultaneous responses --

Most Aerospace Ti is 6-4 Ti, so you will also have aluminum and vanadium in your waste.
I do not know the reaction or the exact products, but I would expect the Ti and the Al to have a complexed metal-fluoride molecule that is also hydrated to some extent..No clue on the vanadium.

James Watts
- Navarre, Florida
2007

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2007

Thanks.
I'm actually finally working with a chemist at the company which supplies our company with the Nitric and Ammonium Bi-Fluoride. That should help a lot but please continue to offer your help as every bit helps.

In respond to the above replies:

Erik van der Staaij, I was under the assumption, that most of the free fluoride would be consumed by the process. And Would in fact be the cause of the spent acid, as Fluoride salts are being created. But I will take your input into consideration.

James Watts, Thank You. We deal primarily with Ti 6-2-4-2, Ti 6-4 and a few high vanadium alloys. So your comment does make sense. However, the process is used primarily for removal of the alpha case layer which should be Ti Oxides and possible Aluminium Oxides. I'm not sure how much of the base material is attacked, so the Vanadium may be insignificant.


Thanks Everyone for there Help and I would appreciate any more that you can offer.

Callie J. Benson
- Eastford, Connecticut, USA

In the dark ages, we had to run monthly test panels to determining the amount of attack on the parent metal. As the TiF(x) molecule builds up, the process slows down, even when you add more acids, so you end up with more tank dumps than you would like. While I do not remember the amounts, I do not think that the Ti or any other metal ever reached the Haz waste level, so only had to be checked at dump time.

James Watts
- Navarre, Florida
2007