Nitric acid treatment

[Emvir]

Hi,

I am trying to reduce my nitrate levels so that we are below our license limit. The main contributor to the nitrate level is a pickling solution which contains 35% nitric acid, 1.5% hydrogen peroxide and up to 1% nickel. Only 200 litres are dumped every 48 hours. We can reduce the nitrates to nitrites as our allowable limit for nitrites is much higher but biological treatment is not feasible for such a small volume. Please advise!

Thanks,
Chemicalenvironment

 

[25362]

What metal alloys are you cleaning ? Is it possible to recycle part of the spent pickling solution ?

 

[Emvir]

Hello 25362,

We are cleaning frames and mandrels from a nickel plating process. I am hoping to recycle some or all of the waste, but will need to convince production that it will not impact on their product. I am looking into nanofitration as an option to recover the acid - I have been informed that it is better than diffusion dialysis for my needs. Any suggestions?

Thanks,
Chemicalenvironment

 

[whylie]

Hi ChemicalEnvironment,

Check with (

http://www.eco-tec.com)

,they are a Canadian company specilaized in acid traetment and recovery

Regards,

 

[Graybeard]

You say that your waste generation rate is too small to use biodenitrification, but I think your rate is not that small. We have used biodenitrification in on a waste stream that varies from 2 to 4 times that volume with no adverse affects. You just have to keep the microbes comfortable. The nickel may be a problem, though.

 

[moltenmetal]

I'd be careful making nitrites from nitrate as a means of water treatment- if there are any amines around, even downstream of your effluent tailpipe, you could end up with a nitrosamine problem. Nitrosamines like nitrosodimethylamine (NDMA) are carcinogens and regulated to very low levels (parts per trillion in drinking water). They don't stick to activated carbon, they don't air strip, and they don't biodegrade rapidly, so they're not easy to treat. UV and UV/peroxide treatments do destroy NDMA, but it's far better not to make it in the first place. If you're going to de-nitrify, make sure the bugs take the nitrogen all the way to N2 gas. If this an "electroless" process and there are amines in the electroless plating solution, it would be best to stay away from denitrification. That being said, if you're interested in destroying nitrate prior to disposal, there are relatively few options available to you other than denitrification.

You'll also need to deal with the nickel- it's a toxic metal and is regulated in most jurisdictions. Plus it's a non-renewable resource which it would be great to recover and re-use rather than to lose forever. At 200 L/d and 1% nickel, you're only talking about ~ 2kg of nickel daily, which is only worth about US$10 or less, so there's no pure economic driving force to recover it- but that doesn't mean that you shouldn't do it.

Unfortunately, conc nitric acid with peroxide in it is a powerful solvent for nickel. It's doubtful that you could recover the nickel by IX or SX or EW efficiently from such a strong solvent to merely regenerate your acid, but others can comment on that much more knowledgeably than I can.

Neutralizing that much acid will take a lot of base, also costing $$$ and leaving you the nitrate to deal with, though it will permit you to precipitate most of the nickel as the hydroxide or rendering it more amenable to IX or EW. If you're going the neutralizaton/disposal route, perhaps you could switch to HCl instead of HNO3 (if this will work). At least then you'll only have to pay for the base and the metal sludge disposal- the chloride probably won't bother the regulators that much.

So you have a tough problem to solve! Perhaps others out there can comment on what people are doing with spent pickle liquour- enormous amounts of it are produced each year...

 

[fredE]

You could also look into distilling the spend pickle liquor and capturing the nickle as a solid. The clean liquor could then be recycled.

 

[tokyo]

Emvir,
Have you heard of PRO-pHx?
This additive is added to acid such as pcikling, stripping, passivation baths and it precipitaes metal iron as solid and collect through filter. Eventually you do not need to dispose acid. This means you can keep using the acid. Only thing you have to do is to spike acid.
You do not need a huge investment like Beta system, etc.
See

http://www.pro-phx.com.

 

[jmj5152]

The only reasonably economical way to recover HNO3 from such pickling solutions is by evaporation. You can look into vacuum distilation. NF is inappropriate due to the concs of HOOH and 35% HNO3. So is IX and EC, as the cation membranes let too many protons through.

 

[cub3bead]

HNO3 and styrene-divinyl benzene resins; not a good pairing. It can be done but you had better be careful.

 

[jmj5152]

cub3bead: Agreed. Not recommending use of IX.