Siphoning boiling nitric using a pump.

[Amol Gupta]

So in the image below we are parting the inquarted gold with nitric acid, we are able to achieve close to three nines fine gold which is good enough for us.
Parting with nitric requires multiple nitric boils and we wish to siphon the boiling nitric using a pump, we would like to collect any siphoned gold in an overflow tank and process it later.
We have attached a glass rod to the teflon pipe which will be submerged in the acid at all time and used for siphoning when needed.
We are in an ideation phase and looking for ideas to improve the design.

The key challanges we have at this point.
1. What should be the material used for siphoning(is the teflon pipe good enough and will last a long time(or what other materials can be used, is a peristaltic pump good for this use case(if so what consideration needs to be taken while choosing a pump), how to join the teflon tube and the glass pipe in the beaker).
2. Is there a way to isolate the inquarted gold during siphoning to minimise the gold in the overflow tank?

I have read through the forum and found people are using teflon pipes and teflon valves to connect the reaction vessel to a Condensor, I am guessing my piping and motor will be exposed to the same harsh conditions, my main concern is the longevity of the apparatus and a safe working environment.

Thanks.
Regards.
Amol

 

[Amol Gupta]

I would be glad to elaborate any parts of my design, it would be great to have input from people much more experienced than me.

 

[anachronism]

This may be a good starting point Amol. Sadly it doesn't incorporate temperature.

https://www.plasticsintl.com/chemical-resistance-chart

 

[4metals]

Boiling acids is a challenge to any pump and a boiling oxidizer like nitric is probably worse. One thing about inquarting and parting is the degree to which the parted gold "behaves" itself. Instead of pumping, why not mount the boiling tank on a trunnion so the full vessel is easy to tilt and pour off the acid gently (the trunnion supports the weight so it is easy to go slow) the heavy gold remains on the bottom so losses will be minimal. All you need is a boiling vessel with a pour spout and a cover. The exhaust NOx comes out of the spout and you can pick the fume up into a fume scrubber easily.

This setup has an additional benefit of good rinsing and decanting as well as easily removing all of the parted gold from the tank.

 

[Amol Gupta]

This may be a good starting point Amol. Sadly it doesn't incorporate temperature.

https://www.plasticsintl.com/chemical-resistance-chart

I will look into it. Thanks @anachronism

 

[Amol Gupta]

@4metals with respect to using a turnnion I am not sure how my hot plate will integrate in the design.
I am not sure what you mean by the inquarted gold "behaves" well.
Assuming the pump being difficult to find or a wildly expensive one if we do so, a solution I can think of is one you suggested year back for the fume hood, can I use a venturi to siphon off the acid...?

 

[4metals]

I am not sure how my hot plate will integrate in the design.

I have used a tilting stainless reactor with gas flame heat which was suspended below the reactor and pivoted with the reactor, always staying aligned with the bottom.

Another option is a glass vessel with an electric mantle on a tipper.

I am not sure what you mean by the inquarted gold "behaves" well.

By behaves well I mean it stays settled because it is so dense. It is easy to decant without losses.

can I use a venturi to siphon off the acid...?

a venturi for pumping liquids (also called an eductor) requires liquid pumped through it to generate the suction so you would either pump water and dilute your parting acids too much or have to pump hot nitric which defeats the purpose.

 

[Amol Gupta]

This is what i am trying to suggest as an eductor, the reactor will be placed at a higher altitude, if I am able to generate a low pressure in the siphoning pipe I will be able to pull the acid from the reactor.
If I am able to generate a low pressure at a height lower than the base of the reactor I should be able to pull the nitric acid without it being in direct contact with the pump.
The pump can take in air or water from the inlet to generate the low pressure.

Is this something that makes sense...?

 

[Yggdrasil]

What I fail to see is why you need the liquid to be boiling while siphoning it off.
Better just take it off and siphon or decant it while hot and not boiling.
Are you processing so much at the time that a few seconds between each lot will cause trouble?

 

[Yggdrasil]

You can of course use a vacuum setup with an e-ductor sucking it from one vessel to the other.

 

[4metals]

After years of working in refining, and all types of equipment, I like to always employ simplicity and things I can always count on. And it seems to me that whenever a vessel full of liquid is tipped over sufficiently the gravity kicks in and the liquid pours out. And it happens when the liquid is hot or cold.

The handling to set up a siphon and further complications to prime a venturi to assist this siphoning will be a task undertaken every time you want to siphon off hot nitric, or hot distilled rinse water, or any distilled rinse water.

Tip and pour is simple that's why I mention it. I would never suggest tip and pour when decanting something like ammonium chloroplatinate as the fluffy nature of the material will lead to losses. But in your case, what you are looking to move liquids off of, and add liquids to, the density of the remaining solids lends itself nicely to the simple process of decanting.

 

[Amol Gupta]

What I fail to see is why you need the liquid to be boiling while siphoning it off.
Better just take it off and siphon or decant it while hot and not boiling.
Are you processing so much at the time that a few seconds between each lot will cause trouble?

The issue is we process our batches in small lots and there are times when we need to process multiple batches at one given time, a setup like this will help me siphon the solution more easily without moving the beaker(reactor), which to me seams safer.

 

[4metals]

If the beakers are small enough make one of these

 

[Amol Gupta]

@4metals looks very good and maybe exactly what we are looking for, seems foolish of me not to think of something like before.
A couple of questions with this setup,
1. I'm guessing I do not need a specialised pump in this case.
2. How do I connect the glass tube to the teflon pipe to create a lasting joint it will be placed in a harsh environment...?

 

[Yggdrasil]

Read up on e-ductor, it only needs running water to create vacuum.
I think there are fittings for connecting tubes, pipes and hoses.
Check with your preferred supplier.

 

[4metals]

You can pull the needed vacuum with a venturi that screws on to a water faucet. They look like this

I always used CPVC pipe because I never used it on boiling chemicals but the only fit I ever used was a snug slip fit. Try to get at least 5 cm of the pipe into the tubing. It should work on glass as well as long as you get a tight fit when the tubing is slid on and it is hot.

The short piece of open pipe is important because it is a vent. When the vacuum is pulling and your finger is not over the hole you will not draw any liquids but once you place a finger over the pipe end suction will develop and you will draw liquid from your beaker. But as soon as you release the finger, suction is vented and the flow stops quickly. So it is a safety feature to control the flow.

 

[4metals]

Also, the stopper on top of the vacuum flask will last much longer if it is silicone and not black rubber. Nitric is tough on the rubber.

 

[4metals]

I assumed (my bad) you were processing larger lots in the 20 - 30 liters range, which is why I suggested the trunnion for pouring. If you had stated the size of your reaction vessels earlier we would have gotten to this point sooner.

 

[Amol Gupta]

@4metals and other members thank you for all the guidance and wisdom, it's a privledge to get in touch with people with such vast experience.
Also it is very interesting that such simple yet so effective solutions exist in plain sight if only we choose to see them.

Thanks a lot.
Regards
Amol

 

[snoman701]

Nitric can be pumped utilizing teflon, but it will reduce the lifespan of the diaphragm considerably. Make it hot and it's game over. Vacuum decanting is the best method. I have a four liter flask set aside just for it. Make sure you can control your vacuum exhaust, or you are scrubbing it....because it's likely going to have a lot of NOx.