# Easy way to scavenge Nox for weak Nitric Acid



## NobleMetalWorks (Aug 28, 2012)

I have found that many of the reactions do not require heat to readily dissolve what is reacting.

Before I built my enclosed system, I was conducting my reactions outside, then later under a fume hood. I was using 5L round bottom flasks to do this, and I wanted to scavenge as much NOx as possible to reduce the amount of NOx I was exhausting and to use the weak nitric acid for other processes.

This is what I did, I took a 5 gallon bucket and put several inches of DI water in the bottom, I then put a 5L round bottom flask in the bucket that had a long neck. The long neck will prevent the flask from tipping past a certain point so you are insured that what's in the flask, will never end up in the bucket, but instead stay in the flask. Set your reaction and place the lid on top. I never pushed the lid down until it sealed because I was concerned about the pressure that builds up. Always be careful removing the lid after the reaction is finished, there will probably be NOx gas inside, in concentrated amounts. Open the lid slightly, if you see gas leaking out then close the lid again and wait awhile for the gas to be absorbed by the water.

After the reaction, spray down the outside of the reaction flask, it will have weak nitric acid on it, and use nitric acid resistant gloves while doing this. What you are left with in the bucket is weak nitric acid. You can keep doing this over and over, and as you do, the weak nitric acid will become stronger over time. I have used this scavenged nitric acid for other processes, to good affect. 

Scott


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## goldenchild (Aug 28, 2012)

Neat little trick. One thing I always wanted to try was performing reactions in an actual distillation rig catching nearly all of the spent nitric. I guess I will try this once I get room for a dedicated distillation setup.


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## MysticColby (Aug 28, 2012)

double post :lol: 

I'm betting that pressure would indeed build inside the bucket, and that would push NOx out. It seems this is just a big watch glass on top of a beaker. And with a watch glass, a lot of NOx is kept inside and absorbed into the water but the pressure does push a steady amount out.
This is not bad for a secondary cover (how about a watch glass on top of a beaker inside a bucket of water with a cover?). Should have to wait a while for the gas to be absorbed, otherwise opening it is lethal.
I'd say bubbling all of the gasses through the water would be the best solution, though.


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## NobleMetalWorks (Aug 28, 2012)

I set this system up, but only used it a few times before I put my fume scrubber together.

1st 5 gallon bucket. 

Take a length of aquarium air hose.

Drill a hole into the lid, slightly smaller than the air hose.

Feed the air hose through the lid until it's just barely inside.

Only put a few inches of water in the bottom, NOx sinks because it's heavier than air. And the waters ability to absorb only has to do with the surface area. The more distance from the top to the water the more NOx will stay inside the first bucket.

Run the air line into a second 5 gallon bucket and secure it to the bottom.

Fill the second bucket 3/4 full with Bio Balls, or some other non reactive substrate to increase the length of time the NOx stays in the water.

Fill the bucket with water until it's about an inch above the substrate.

Place small plastic floating balls in the surface of the water until it totally covers the surface, there is no need to have it several layers thick, one layer will do, this also helps keep the NOx in water.

Create a third bucket the same as the second bucket, drilling a second hole in the lid of the second bucket, pulling the tube barely inside the bucket

Feed the line from the second bucket into the third bucket, then drill a hole as a vent in the third bucket as a relief.

This is a larger version of the same type of system that has been posted using beakers. It works great, as the pressure builds up in the first bucket some NOx goes into the water, the rest is pushed through the air line, into the bottom of the second bucket where the bubbles slowly make their way through the material, the longer the NOx is retained in water, the more is absorbed. Again pressure builds up in the bucket and is forced through the air line into the identical third bucket that operates the same, whatever pressure is left is force out of the vent hole.

Depending upon the amount of material being dissolved, you may have to use larger hoses. I used plastic clamps to keep the lids on, and experienced no problems, however pressure does build up and you do need to be very careful. I drilled another hole in each of the buckets, and forced a hard rubber plug through the hole so that if too much pressure built up, it would pop out before the bucket was pressurized too much. A relief system like this might be a good idea.

Scott


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## MysticColby (Aug 29, 2012)

does it still bubble trough the 3rd bucket? high pressure usually isn't a good way to go as it will always find any small hole between lids and escape there instead of pushing against the pressure of all that water.
If it is truly air-tight, then I like it! It's just hard to get things 100% air-tight.

low pressure is how I believe most people design these types of rigs. apply a vacuum at the end that supplies just enough force to push against the water. If there is a hole, air is pulled in and a bit more vacuum is needed (instead of NOx leaking out)

It also takes a LOT of pressure (relatively) to push against ~3 feet of water.
I looked it up: 1.3125 psi to push air through 3 feet of water.
That much pressure over the surface area of 5 gallon buckets can be a lot of force


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## samuel-a (Aug 29, 2012)

MysticColby said:


> low pressure is how I believe most people design these types of rigs. apply a vacuum at the end that supplies just enough force to push against the water. If there is a hole, air is pulled in and a bit more vacuum is needed (instead of NOx leaking out)



I agree with this 100% !


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## NobleMetalWorks (Aug 29, 2012)

MysticColby said:


> does it still bubble trough the 3rd bucket? high pressure usually isn't a good way to go as it will always find any small hole between lids and escape there instead of pushing against the pressure of all that water. It also takes a LOT of pressure to push against ~4 feet of water.
> If it is truly air-tight, then I like it! It's just hard to get things 100% air-tight.
> 
> low pressure is how I believe most people design these types of rigs. apply a vacuum at the end that supplies just enough force to push against the water. If there is a hole, air is pulled in and a bit more vacuum is needed (instead of NOx leaking out)



The idea is not to pull or push the NOx to the last bucket, the idea is to retain the gas in each bucket long enough to be absorbed by the water, if the pressure builds up, it's relieved into the next bucket. Pressure follows the path of least resistance so you don't have a situation where the lid leaks for example. The plastic clamps are just to provide a harder seal. You can use stopcock grease which doesn't react with AR or NOx, around the seal of the bucket, it works just fine. The tubes that go from one bucket to the next allow for any pressure that might build up, to be relived into the next bucket. Keeping the buckets all sealed for 24 hours is usually enough time. So you set your reaction and come back to look after 24 hours. Obviously this should be done outside, and not indoors. The little amount that might leak out of the buckets is far less than if you were reacting without this system, so in any case it's safer. If you open the last bucket first, then the second bucket, and last the first, you will be able to gauge if there is any NOx left in the system.

This is not intended to replace a fume scrubber, although if you used Urea in the water, or some substrate that acts as a base, you could neutralize the weak Nitric that builds up. I used this method to collect the nitric, so that I could use it for other processes. Now I just use the solution in my fume scrubber and replace with water, test with ORP/PH meter, etc. 

It works, I used it for awhile, I had no issues with leaks or other problems. But I didn't use it for an extended time because I build my fume scrubber soon after.

Scott


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## MysticColby (Aug 29, 2012)

oh, you're just going from the air on top of the water of one bucket to the next? it sounded like you had the tube running to the bottom of the water in each bucket after the first.


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## NobleMetalWorks (Aug 29, 2012)

MysticColby said:


> oh, you're just going from the air on top of the water of one bucket to the next? it sounded like you had the tube running to the bottom of the water in each bucket after the first.



That is exactly what I was doing, you take the tube from the TOP of bucket #1, and affix it to the BOTTOM of bucket #2, you take a second tube from the TOP of bucket #2 to the bottom of bucket #3. The pressure of the water against the tube, retains enough pressure in bucket #1 so that the NOx will only feed into bucket #2 if the pressure builds up enough to bubble out of the tube in bucket #2, and so on. This retains the NOx in each bucket for an extended length of time. Think of bucket #2 and #3 as a way to release the pressure of bucket #1 and still giving the NOx time to be absorbed into the water.

Scott


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## etack (Aug 29, 2012)

If yo were to only use it for nox then put it under vacuum and get a SS gas diffusion stone. http://morebeer.com/view_product/18254

This should work to trap your nox. Just like beer I would be best if cold first this will allow more gas to be absorbed in to the H2O. you might need to use a SS tube as well.

Eric


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## NobleMetalWorks (Aug 29, 2012)

etack said:


> If yo were to only use it for nox then put it under vacuum and get a SS gas diffusion stone. http://morebeer.com/view_product/18254
> 
> This should work to trap your nox. Just like beer I would be best if cold first this will allow more gas to be absorbed in to the H2O. you might need to use a SS tube as well.
> 
> Eric



Thanks for posting this, excellent suggestion.

I love this forum. :mrgreen: 

Scott


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