Sciencemadness Discussion Board

Mercury(II) Nitrate to Mercury Sulfide

DocX - 14-6-2022 at 11:49

So if one has mercury nitrate in solution, how would one go about converting it to mercury sulfide for safe disposal?
It's cheerily advised in the wiki on mercury nitrate, but without a described reaction.
I see reactions using H2S, but that doesn't feel very safe now does it?

[Edited on 20222222/6/14 by DocX]

PirateDocBrown - 14-6-2022 at 12:57

Sulfide isn't the only safe disposal, you could also do chloride. That's easy, just precipitate.

But if you're deadset on getting sulfide, try thioacetamide.

Texium - 14-6-2022 at 13:05

Or sodium sulfide

Rainwater - 14-6-2022 at 16:09

Page 301. Hazardous laboratory chemicals disposal guide 3rd edition
https://gprivate.com/5zj6o

Bettor world books is where i got my copy. $10 bucks

Says dissolve mercury salts(10g) as much as possible in water (100ml)
Use NaOH to bring the ph to 10
Add sodium sulfide solution until percipitate stops forming
Hg2+ + Na2S -> HgS + 2Na+
Nilered has a video showing the process

[Edited on 15-6-2022 by Rainwater]

woelen - 14-6-2022 at 23:01

I would proceed by first adding NaOH, such that the liquid is neutral or just slightly acidic. No precipitate should be formed with the mercury salt.
Next, carefully add an excess amount of solution of Na2S or NaHS. Do that outside or in a fume hood, due to formation of H2S. All mercury will settle as HgS.
The liquid can be disposed of in the drain. Just rinse it with a lot of water to get rid of the sulfide. Sulfide is very quickly oxidized in the environment, so this can be flushed down the drain without longterm environmental consequences.

B(a)P - 15-6-2022 at 17:31

Quote: Originally posted by woelen  
I would proceed by first adding NaOH, such that the liquid is neutral or just slightly acidic. No precipitate should be formed with the mercury salt.
Next, carefully add an excess amount of solution of Na2S or NaHS. Do that outside or in a fume hood, due to formation of H2S. All mercury will settle as HgS.
The liquid can be disposed of in the drain. Just rinse it with a lot of water to get rid of the sulfide. Sulfide is very quickly oxidized in the environment, so this can be flushed down the drain without longterm environmental consequences.


Just clarifying that you are suggesting only the liquid is to be disposed of via the sewer? The solid HgS would need to be taken to a suitably licensed waste facility.

woelen - 15-6-2022 at 22:42

Yes, only the liquid can go down the drain.

Tsjerk - 16-6-2022 at 02:39

HgS can go down the drain. In a liter of saturated solution there will be about 10 atoms of mercury. You can safely eat HgS, it takes quite some effort to get HgS in solution.

B(a)P - 16-6-2022 at 03:07

Quote: Originally posted by Tsjerk  
You can safely eat HgS.

While it is one of the least toxic forms of mercury, I am not sure it is quite safe to eat. The jury is still out on an LD50 for mercury sulfide, but it is thought to be 10 to 30 times higher than mercury chloride. Not something I would add to my diet. Interestingly though, it has been for a long time and still is a component of a number of traditional Chinese medicines.

Tsjerk - 17-6-2022 at 00:23

Although I wouldn't recommend to actually eat HgS, as there is absolutely no reason to do so. It was only used to illustrate a bit of HgS going down the drain won't harm anything.

woelen - 17-6-2022 at 00:37

I do not fully agree with Tsjerk that having a bit of HgS down the drain is not harmful. I agree with the statement that it is extremely insoluble and that it does not pose a severe health risk if you are exposed to it. It just exists as solid matter in your body.

However, having finely dispersed mercury-containing material in the environment is not good. If it is flushed down the drain, then it will be spread as fine particles and finally it will settle somewhere in the sludge at water purification stations or just somewhere in nature in water or soil. Once it is there it cannot be separated anymore. What will be the long term effect? I can imagine that HgS will be oxidized slowly over the years, when it is finely dispersed in water and soil. Oxygen may get in contact with it and the sulfide may be oxidized to sulfate and/or a mix of sulfate and oxide. In the long run, the mercury may become more mobile again.

So my advice would be to separate the HgS from the liquid and dispose of the HgS in a proper way. The remaining liquid, freed from HgS particles, can go down the drain.

[Edited on 17-6-22 by woelen]

B(a)P - 17-6-2022 at 02:16

Trace mercury in biosolids restricts the opportunity for a beneficial reuse of the sludge produced at sewage treatment plants (in the Australian context). This means that instead of being able to be used as fertiliser it goes to landfill.

Tsjerk - 17-6-2022 at 03:16

You guys are absolutely right, a couple grams going down the drain in a big city might not do anything, but larger amounts in less densely populated areas could very well.

DocX - 18-6-2022 at 11:53

Great answers, thank you all!
Although, I won’t be eating any mercury sulfide. I’m thinking about the gastric acid which is basically concentrated HCl.

[Edited on 20222222/6/19 by DocX]

DocX - 21-6-2022 at 09:15

BTW, anyone knows what amounts of H2S one can expect? It's a really nasty nasty gas after all.

woelen - 21-6-2022 at 23:06

Depends on amount of mercury to be precipitated. You can use quite dilute solutions, the mercury sulfide is extremely insoluble. By using dilute solutions, you probably will not even see any bubbles of H2S, but you'll definitely smell it.

If you do this outside, then you'll be safe. The gas, expelled from the dilute solutions, will be blown away quickly. You can also mix the solutions and immediately step away and just let it settle. I would not worry too much about the H2S, unless you really have to do this in a closed room with little ventilation.

If the quantity of mercury to be precipitated is just a gram or so, then you'll be safe anyway, even in a closed room. In that case you only need a gram or so of Na2S and that will not produce sufficient H2S to be a direct danger, unless you stick you nose directly into the flask with the solutions and inhale from that.

DocX - 22-6-2022 at 05:40

Quote: Originally posted by woelen  

If the quantity of mercury to be precipitated is just a gram or so, then you'll be safe anyway, even in a closed room. In that case you only need a gram or so of Na2S and that will not produce sufficient H2S to be a direct danger, unless you stick you nose directly into the flask with the solutions and inhale from that.


But where in this reaction is H2S produced?
Isn't it just in the reaction between water and sodium sulphide? And isn't that reaction avoided if the solution is neutral or slightly basic?

clearly_not_atara - 22-6-2022 at 06:30

Practically any cup of water exposed to the atmosphere on Earth contains dissolved carbon dioxide, which will react with sodium sulfide to release H2S and produce bicarbonate. You can probably avoid this by basifying a little, but I think we want to ensure all of the mercury is trapped as the sulfide and none becomes an intermediate like HgO.

DocX - 22-6-2022 at 11:05

Quote: Originally posted by clearly_not_atara  
Practically any cup of water exposed to the atmosphere on Earth contains dissolved carbon dioxide, which will react with sodium sulfide to release H2S and produce bicarbonate. You can probably avoid this by basifying a little, but I think we want to ensure all of the mercury is trapped as the sulfide and none becomes an intermediate like HgO.


Yes, I understand that, and still the protocol described in the book posted earlier in this thread (with the description on page 352, not 301. I had half a mind retorting Rainwater with a condescending LMGTFY link about page numbering. But the tip was excellent, so I didn't) calls for bringing the mercury salt solution to pH 10. Wouldn't that risk creation of mercury hydroxide?

woelen - 22-6-2022 at 12:31

That's exactly why I suggest to keep the solution slightly acidic at all times, you don't any mercury in another form than the sulfide, when it is precipitated. With sulfide, you certainly will get some H2S in the air, but if the solutions are just slightly acidic, then you will not have strong bubbling of H2S gas. Probably you won't see any gas formation at all, the liquid simply emits some H2S without bubbling.