Neutralizing nitric acid.

[grayseal]

I have a 20% nitric acid solution that was used for passivating a small quantity of stainless steel parts. I plan to neutralize the solution with soda ash. The soda ash is several years old. Will this affect its neutralizing properties?

grayseal

 

[unclesyd]

No, but be careful as the old soda ash will clump and there exist the possibility that a big clump will cause a local violent reaction.

You will need to mix the two materials very carefully.

Make sure any personnel involved have the proper Personal Protective Gear.

 

[grayseal]

unclesyd,

Thanks for the prompt reply. You are correct about the large clumps. They do create a rather vigorous reaction.

grayseal

 

[EdStainless]

How are you going to dispose after neutralizing?
Have you tested for metals? Esp Cr+6

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[kenvlach]

Nitic acid solutions used for passivating austenitic SS accumulate metals in roughly these proportions:

Fe⁺³ ~ 10x Ni⁺² >> Cr^+3,+6

If the solution contains enough Fe⁺³ to appear yellow to the naked eye, then it should be treated for the hazardous metals. First reduce Cr⁺⁶, then co-precipitate the metals as hydroxides at about pH 9.5.

 

[bimr]

No, but be careful with the nitric acid.

Nitric will evolve a noxious gas that combines with water vapor already in the air (humidity) to form a very corrosive gas. The gas is very highly corrosive and will attack all metallic objects including building structures, sprinkler heads, copper wiring, stainless steel, etc. Therefore, if HNO3 is used it must be properly vented or used outdoors where the gasses can easily dissipate.

http://www.finishing.com/128/91.shtml

 

[kenvlach]

Neutralize within the original passivation tank or in another plastic, fiberglass or stainless steel tank. The nitric acid is only 20 vol% (14 wt%), so neutralization can even be done in a polyethylene tank w/o overheating.

The nasty reddish fumes (nitrogen dioxide & tetroxide) only form by reaction of nitric acid with ordinary metals, e.g., Cu, Fe, Ni, Zn, etc. Some photos of nitric acid-copper reaction and fuming:

http://www.angelo.edu/faculty/kboudrea/demos/copper_HNO3/Cu_HNO3.htm

An often useful fact is that adding hydrogen peroxide to the nitric will prevent the fumes -- it catalyzes the decomposition of the gases back to nitric w/o leaving the solution. A former employer suffering from brain drain neglected this, told an employee to strip electroless nickel from a plated out tank using concentrated nitric --> massive red cloud, employees evacuated, Fire Dept. came, Police barricaded streets & HazMat people came. HazMat couldn't reach the company's emergency contacts, so they called me (former contact) & I had them go to drugstores & purchase hydrogen peroxide, which was then added by firemen in full chemical protective suits (described by witnesses as "spacemen").
A costly lesson for my evil ex-boss.
Scheudenfreude!

 

[CoryPad]

Ken,

Close, but it is Schadenfreude:

http://dict.leo.org/?lp=ende&lang=d...sectHdr=on&spellToler=on&search=Schadenfreude

Regards,

Cory

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