Sciencemadness Discussion Board

Mercury/HNO3 incident

Vanry - 31-10-2019 at 11:54

Hello there,

I was making nitric acid as i usually do, around 1,5L, but this time my mercury thermometer fell into the RBF and broke. I was "lucky" and my balloon is intact (i am really glad that i avoided the hot oil bath + nitric acid + mercury mix...) but i'm left with some mercury mess.

Theorically in my ballon there is HNaSO4, mercury(II)nitrate, water, nitric acid and maybe some sulfuric acid (but i highlty doubt it). Before any comment, I am aware of the danger of mercury and its salts.

So now, i need to clean this while making the less amount of waste possible (dissolving HNaSO4 in hot water would create ~5L of waste minimum)

My current idea is: basifying this with sodium bicarbonate till no CO2 is forming, then add elemental sulfur (or another form of sulfur ?) before heating at ~100°C for an hour to dissolve all salts to expose then to the sulfur, then cooling and rincing it 5 times with a little amount of very hot water, and storing everything in my mercuric waste.

From my point of view that sound correct, but i'm far from being an expert in mercury, and i'm not sure everything will stuck to the sulfur.

If someone could confirm this process, or give some more advice i'll be happy to have them ;)

12thealchemist - 31-10-2019 at 12:02

Rather than using elemental sulphur, a sulphide like sodium or potassium sulphide ought to be used to sequester mercury salts. Obviously, you'd need to neutralise the acids to use this, but you're doing this already.

DavidJR - 31-10-2019 at 12:30

I would distill off most of the nitric acid before treating the residue - no need to waste it all.

unionised - 31-10-2019 at 13:04

Quote: Originally posted by DavidJR  
I would distill off most of the nitric acid before treating the residue - no need to waste it all.

Good idea, but don't forget to add fresh anti bumping agent.

Once you have removed (at lest most of) the nitrate you can remove the mercury by reduction to the metal with zinc, aluminium, iron, or whatever is cheap.

To do that you need to get at least some of it into solution.
Fortunately, as the mixture cooled and crystallised most of the mercury (and other contaminants) in the NaHSO4 will have been left behind in the melt/ solution.
So they, as the last material to crystallise, will be the first to dissolve.
You probably don't need to dissolve all the NaHSO4- just wash it thoroughly.

That will get most of the Hg into solution and you can reduce it with a more reactive metal I would suggest steel wool as a first attempt.


On a related note, do you realise that you don't need to dissolve the whole of a sample in one batch to recrystallise it?

Take your flask with contaminated NaHSO4 and add a litre of water, heat it on a water bath and stir it so that litre of water gets saturated.
Pour the hot solution into a beaker and let it cool.
Pour the liquid (cool saturated contaminated solution) back into the flask and heat it again.
It will dissolve more of the salt. Once it's saturated, pour the liquid into the beaker again and let it cool.
You will get more crystals of reasonably pure material and you can repeat this process so you get a beaker contain recrystallised salt and a smaller volume (about 1 litre) of a solution containing nearly all the mercury.

Vanry - 31-10-2019 at 13:04

Quote: Originally posted by DavidJR  
I would distill off most of the nitric acid before treating the residue - no need to waste it all.

Yup, don't worry that's what's going on. but distilling so much HNO3 without vacuum takes a lot of time and it's not finished yet (30Hrs and i'm around 80% done) And I wan't to neutralize what's left anyway just to be sure that no further oxydations happens.
Quote: Originally posted by 12thealchemist  
Rather than using elemental sulphur, a sulphide like sodium or potassium sulphide ought to be used to sequester mercury salts. Obviously, you'd need to neutralise the acids to use this, but you're doing this already.


OK, good to know. But based on sciencemadness-wiki, i need a lot of reagent that I don't have to make it (aka, metallic sodium and THF)
Is there a clear advantage of using a sulphide ? My guess is that you get a good leaving group, yielding some stable sodium nitrate and thus facilitating the reaction, but the thing seems to be a PITA to get... Well, anyway, thanks for the advice.

Thank you both for the rapid answer :)

Vanry - 31-10-2019 at 13:12

Quote: Originally posted by unionised  
Quote: Originally posted by DavidJR  
I would distill off most of the nitric acid before treating the residue - no need to waste it all.

Good idea, but don't forget to add fresh anti bumping agent.

Once you have removed (at lest most of) the nitrate you can remove the mercury by reduction to the metal with zinc, aluminium, iron, or whatever is cheap.

To do that you need to get at least some of it into solution.
Fortunately, as the mixture cooled and crystallised most of the mercury (and other contaminants) in the NaHSO4 will have been left behind in the melt/ solution.
So they, as the last material to crystallise, will be the first to dissolve.
You probably don't need to dissolve all the NaHSO4- just wash it thoroughly.

That will get most of the Hg into solution and you can reduce it with a more reactive metal I would suggest steel wool as a first attempt.


On a related note, do you realise that you don't need to dissolve the whole of a sample in one batch to recrystallise it?

Take your flask with contaminated NaHSO4 and add a litre of water, heat it on a water bath and stir it so that litre of water gets saturated.
Pour the hot solution into a beaker and let it cool.
Pour the liquid (cool saturated contaminated solution) back into the flask and heat it again.
It will dissolve more of the salt. Once it's saturated, pour the liquid into the beaker again and let it cool.
You will get more crystals of reasonably pure material and you can repeat this process so you get a beaker contain recrystallised salt and a smaller volume (about 1 litre) of a solution containing nearly all the mercury.


When i read that kind of post i realize how bad i am in metallic chemistry :D
I've been doing metallic reduction of gold and silver for weeks and i didn't even thought of applying this to the mercury....

And the same apply for the use of the saturate solvent... Gosh, how stupid I've been all this time...
Wonderfull, this solution seems a lot more simple, and I may even get this mercury back :D

G-Coupled - 31-10-2019 at 13:22

Do it! Recover that Hg! :cool:

Good luck with it and be sure to report back how it goes.

Sulaiman - 31-10-2019 at 17:36

I have been careful to not let my mercury filled thermometers drop into the boiling flask because I was concerned with physical damage and leakage,
I had never considered or prepared for the mercury reacting with the pot contents,
thanks for sharing.

Vanry - 31-10-2019 at 18:16

Quote: Originally posted by Sulaiman  
I have been careful to not let my mercury filled thermometers drop into the boiling flask because I was concerned with physical damage and leakage,
I had never considered or prepared for the mercury reacting with the pot contents,
thanks for sharing.

To be honnest I never use mercury thermometer, I've always been aware and affraid of the mess they can cause, some bad accident that happened during my studies. But in the last weeks, my hight use of nitric acid, and hight production of it destroyed all the graduation of my alcoohol based thermometer :D
In france we say: "when we're lacking soor, we'll eat blackbirds"....

woelen - 1-11-2019 at 00:47

Don't you have a municipal waste processing facility, where you can bring small chemical waste?

I would distill off most HNO3 and then decant the last remains of liquid. Next, i would rinse the flask well with water to remove most adhering mercury salts. You can neutralize your waste with Na2CO3 or NaHCO3, but be sure to keep it somewhat acidic. The solution I would bring to a waste processing facility (say that it is photography dark room waste and put on the bottle a mark that it contains Hg).

Any metallic Hg you can recover easily and keep that under water. Dissplve all your solid NaHSO4 waste and flush through the drain.

12thealchemist - 1-11-2019 at 09:35

Quote: Originally posted by Vanry  
Quote: Originally posted by 12thealchemist  
Rather than using elemental sulphur, a sulphide like sodium or potassium sulphide ought to be used to sequester mercury salts. Obviously, you'd need to neutralise the acids to use this, but you're doing this already.


OK, good to know. But based on sciencemadness-wiki, i need a lot of reagent that I don't have to make it (aka, metallic sodium and THF)
Is there a clear advantage of using a sulphide ? My guess is that you get a good leaving group, yielding some stable sodium nitrate and thus facilitating the reaction, but the thing seems to be a PITA to get... Well, anyway, thanks for the advice.


The reaction is driven forward by the precipitation of the very insoluble HgS. This is the advantage of sulphide - the resulting mercury sulphide is very insoluble, so one of the safest forms of the element, and will remove almost all of it from solution. However, given how difficult mercury is to get hold of, I recommend trying to reduce it to the metal, and treat the waste with sulphide, rather than your "stock" solution of Hg2+.

I've had success with making potassium sulphide by burning a slightly super-stoichiometric mixture of potassium nitrate and sulphur (excess sulphur), leaving potassium sulphide as the sole product. Definitely a reaction to do outside though.

Vanry - 2-11-2019 at 04:22

Okay quick update: I've done 2 recristalization I now got a Cristal-white solid with superb needle in my RBF (I'll post photo if I can)
On the other side I've got ~0,5L of yellowish solution wich, I assume, contains my mercury.
I tried to basify it with sodium bicarbonate and it took a Lot of it. When the bubbling started to be less violent on addition, I added some zinc (not really sure it was Zinc to be fair, it was scrap from an old gutter. Grey, non-ferric, don't look like aluminum, I assumed it was zinc... Anyway its cheap) it started bubbling gently, I was thinking of an acidic attack releasing H2? I didn't tried with a flame, don't wanted to put flame/explosion anywhere near mercury salts.
Anyway, I stored it in a safe ventilated area and get some rest.
When I came this morning to check for news, nothing had happened. No solid mercury, the zinc is still there maybe it was passivated? :/

So now I wonder what to do. I've started some test with aluminium foil, but I'm not sure what will come from this, because I'm pretty certain it will be passivated...
I'm trying to find some iron, we'll see.
Don't hesitate to give some advices :)

unionised - 2-11-2019 at 05:02

Shake the solution with some wire wool- which is cheap.
That will reduce the mercury to the metal and strip it out of solution (apart from the rather small solubility of mercury in water). It will fall to the bottom of the flask.
You can then flush the solution of iron, zinc and other rubbish down the drain.

All the mercury will be in the solid metal sludge. You can rinse the soluble rubbish off it.
You can either dispose of that solid as it is-- as toxic waste.
Or react it with a large excess of sulphur which will render it pretty much inert.
Or you can dissolve the excess iron + zinc with HCl or dilute H2SO4 (which won't attack metallic mercury)
Then extract the mercury from the residue.

Personally, I d add a bunch of sulphur, leave it to react and then dump it.

Sulaiman - 2-11-2019 at 05:35

I've not tried or researched this.
but I know that zinc and aluminium form amalgams with mercury whereas iron does not,
so I guess that your zinc and aluminium are now contaminated with mercury :(

S.C. Wack - 2-11-2019 at 06:32

You realize of course bases tend to precipitate mercury salts...BTW sulfide, oxide, and other Hg salts might be very insoluble in water, yet soluble in salts...there are a number of strong reducing agents from which to choose and I question whether any Hg was released at all; shiny copper would have tested this simply (after removing the acid).

[Edited on 2-11-2019 by S.C. Wack]

Vanry - 2-11-2019 at 06:44

Quote: Originally posted by S.C. Wack  
You realize of course bases tend to precipitate mercury salts...BTW sulfide, oxide, and other Hg salts might be very insoluble in water, yet soluble in salts...there are a number of strong reducing agents from which to choose and I question whether any Hg was released at all; shiny copper would have tested this simply (after removing the acid).

[Edited on 2-11-2019 by S.C. Wack]


Shiny copper? You mean transmetallation with copper instead of Zn/Fe? (edit: I just realized transmetalation is a concept of OC, but you get my point)

As reducing agent I've got sodium metabisulfire, and therefore SO2, could it be of any use?


Edit: if an amalgam has formed I'll just distill the metallic mercury off with other impure mercury I have lying around. My real problem here is getting that mercury back from its oxydation state

[Edited on 2-11-2019 by Vanry]

[Edited on 2-11-2019 by Vanry]

S.C. Wack - 2-11-2019 at 07:56

Mercury on copper such as a US penny tends to be obvious. Zn or Al should be fine but Mg and Sn are too. Acids dissolve excesses of these as said before. I would think that the easiest sulfide to make is sulfur dissolved in NH4OH and AFAIK HgS is not soluble in excess of this, but it's too late if Zn is also in solution. Dissolve the ?zinc in sulfuric acid and see if there is dark heavy residue. (if the Hg wasn't already precipitated in some form by base) (I would give ample time for metals to reduce Hg in solution)

[Edited on 2-11-2019 by S.C. Wack]

Vanry - 3-11-2019 at 07:33

Quote: Originally posted by S.C. Wack  
Mercury on copper such as a US penny tends to be obvious. Zn or Al should be fine but Mg and Sn are too. Acids dissolve excesses of these as said before. I would think that the easiest sulfide to make is sulfur dissolved in NH4OH and AFAIK HgS is not soluble in excess of this, but it's too late if Zn is also in solution. Dissolve the ?zinc in sulfuric acid and see if there is dark heavy residue. (if the Hg wasn't already precipitated in some form by base) (I would give ample time for metals to reduce Hg in solution)

[Edited on 2-11-2019 by S.C. Wack]


Quick and last update for the 2 weeks to come.
1- the solution is insanely dirty, but this look much more like zink oxyde to me

2- mercury is reducing slowly (that's good knews) but formed amalgam, at least with Al
I noticed some Aluminium oxyde string formation after letting the Al foil that had been put into the flask exposed to air. So it seems like am is reducing my mercury.
I will put a lot of Al foil into this and leave it for the 2 weeks to come (I won't be able to access it anymore, so if you got any last advice, it's now or never xP)

Fluorite - 17-12-2020 at 02:33

Quote: Originally posted by DavidJR  
I would distill off most of the nitric acid before treating the residue - no need to waste it all.


are you sure the distillation doesn't carry droplets/mist with mercury compounds?
like can you drink distilled mercury contaminated water? sorry i ask stupid questions but how good is distillation
nurdrage said distilled water isn't completely pure h2o