Neutralizing mercury salts

[MadHatter]

So you've made some interesting reaction using toxic mercury salts like mercury nitrate or mercury chloride? And you washed it out into a separate beaker, and being a responsible, reasonable and nice person you're NOT going to pour that into the drain or into nature. Because only assholes and idiots do that.

But at the same time, you're not up to going to some waste disposal place and leave a big jar of suspicious shit.
Ok, let's do chemistry:

Reagents needed:
Sodium Hydroxide
Sodium Sulfide

Procedure:
Do this reaction outside or in a fume hood. Even better to wear a respirator.

1. Wash your glassware with boiling water. Mercury salts are highly soluble in water, and even more so in boiling water. Pour the water into any container.

2. To the solution of toxic mercury salt in water, add sodium hydroxide to pH around 10.

3. To the basic solution, start adding sodium sulfide. There will probably be fumes produced: do not breathe these in! They are toxic hydrogen sulphide, H2S, which is corrosive to lung tissue. Meantime, a black precipitate is formed in the vessel. Continue adding sulfide and venting off fumes until no more precipitate is formed.

This is the reaction: Hg2+ + Na2S -> HgS + 2Na+

The precipitate is mercury sulfide, which is totally harmless and can be discarded in any way you please. Pour it down the drain if you want.

 

[ACAB]

How much H2S gas are we talking about here, assuming about 1g of mercury salt dissolved in water?
Is there no way to suck the gas out and put it down in a water jet pump or neutralize it in a wash bottle?

 

[MadHatter]

Probably not a lot. And probably yes.
If one has, say, 500 ml of water/mercury salt one could very well do it in a necked flask and just lead the vapors wherever one pleases. But an alternative is to just put it in a plastic bucket, carry that bucket to any secluded place and dump in sodium sulfate, and then just pour the resulting black mixture out. Cinnabar is a common enough mineral, no harm is done to the environment by dumping it in it.

 

[MadHatter]

The reaction is taken from here, page 352:

https://molchem.science.ru.nl/images/hazardous-laboratory-chemicals-disposal-guide-2003.pdf

Great book. Sorry for the typo. SULFIDE.

 

[ACAB]

If one owns land or which has in the proximity, I can imagine that also well, but dispose once unnoticed a bucket with black broth, which smells also still badly after rotten eggs in a large city, where not even dogs find a piece of meadow to shit. That will be a great challenge

H2S is not exactly harmless and can mean death with a single breath at the right concentration, so the amount of gas would be relevant, at least for me. The question now is, how is H2S produced during the neutralization of the mercury salts? There is nothing about that in the book. Can you also please explain?

 

[MadHatter]

It's a good question. I think it happens in the reaction between sodium SULFIDE and water. I know sodium sulfide gives off H2S when damp or wetted. I also know that sodium sulfide produces a lot of that toxic crap when treated with an acid. Now, this reaction takes place in a strongly basic solution, so I guess the production of H2S would be minimal.

 

[ACAB]

hmm you guess, so you have never carried out these instructions yourself, that you do not know more precisely whether gas is produced or not?!
But I could also imagine that only the Na2S solution smells of H2S and no more is produced.

I'll have to figure out where to get sodium sulfide, not easy, but as far as I've investigated now I can make it by reacting sodium with sulfur, that should be doable, you don't need that much to neutralize a few grams of mercury salts.
Theory:
2Na+S-> Na2S
2*22.98g Na + 32.06g S --> 78.02g Na2S
neutralize 324.60g mercury(II) nitrate
or 271.50g mercury(II) chloride

I have seen two different ways to start the reaction, one is to sprinkle the sodium with water, or to ignite the sulfur . In any case, you have to cut the sodium well into small pieces and you need a fireproof base.

 

[MadHatter]

No, unfortunately I haven't had the opportunity to try the reaction myself yet, but it is thoroughly documented. And as you can see I posted the source.
I found sodium sulfide on Ebay though, from Germany, UK and ... Ulraine. Pretty cheap actually.

 

[MadHatter]

Oh, and I found this: the ever-so-boyscouty NileRed has done a video on this. As usual, it's very good.
In it, he recommends bringing the solution to a NEUTRAL pH, and he doesn't seem to be the least bit concerned about H2S.