Sciencemadness Discussion Board

A stirring exception

Sulaiman - 22-5-2024 at 01:33

I'm currently planning and testing some purification procedures for mercury.
The first stage is 'washing' the mercury in dilute (c1M) nitric acid.
Agitation (air bubbler, strong stirring) is required to dissolve any base metals, oxygen from the air helps with oxidation of some base metals.

Now the odd part;
The mercury/acid mixture must be agitated continuously,
if not nitrous acid builds up in the vicinity of the mercury and starts to dissolve it!
Mercury consumption by the acid is over 100x slower with agitation!
So stirring/agitation is required to REDUCE the reaction rate.

charley1957 - 22-5-2024 at 03:23

What an exceptional observation!:D

Sulaiman - 22-5-2024 at 05:23

Not my own observation,
I'm just repeating what I read, and have tried a little;


V H Veley, 1890, "The conditions of chemical change between nitric acid and certain metals"

Attachment: nitric-acid-and-certain-metals.pdf (7.5MB)
This file has been downloaded 140 times

I'm just researching methods of mercury purification that minimise toxic waste generation.

Mentioned just because it's anomalous and probably not commonly known.

[Edited on 22-5-2024 by Sulaiman]

Precipitates - 22-5-2024 at 05:44

Please let us know how you get on.

I've got a pound of mercury I would love to clean up at some point (ideally without generating a load of toxic waste!).

I love having it, but the joy is somewhat ruined by how dirty it is.

Sulaiman - 22-5-2024 at 06:09

It seems that there are well recognised stages to 'cleaning' mercury;

1) to your mercury add about 1/2 the mercury volume of c1.5M nitric acid (1 part Az. nitric : 9 parts water) in a glass or plastic container.
Agitate/shake violently until you are exhausted,
(your mercury will now be 'shiny')
(the full procedure involves vigorously bubbling air for 24 hours per acid wash, and a few hours per water rinse)
pour off the acid that now contains most of the base metals (toxic),
rinse with water a couple of times.
Repeat the acid wash, rinse with water a few times.
Your mercury will now be beautifully 'shiny', fluid, and leave no 'tails' .

2) rinse with a little acetone to remove moisture and oils/grease etc.
3) mechanical filtering, fritted funnel with vacuum (gravity alone will not force mercury through)
or any other method you like.


Remaining Silver and PGMs can be removed by distillation.
I've not got to this stage yet.

Any PGMs in trace ammounts do not significantly effect the properties of mercury,
and do not oxidise to form 'scum' on the surface of the mercury.
Store dry with as little air/head space as practical.

Apparently if your mercury is completely 'shiny' after months of storage, the base metals contamination is measured in 10's of ppb, not in ppm.

I have c100g Hg heading to me in the post at the moment.
This batch I will try to measure how much base metals contamination there is.
Then add it to the rest of my mercury.
I intend to do a video of the cleaning process of my entire stock (c120ml), including distillation, within a few months.

PS I've read that adding a little peroxide to the acid removes any sulphides.
I've not tried.

[Edited on 22-5-2024 by Sulaiman]

Precipitates - 22-5-2024 at 06:45

Quote: Originally posted by Sulaiman  

I intend to do a video of the cleaning process of my entire stock (c120ml), including distillation, within a few months.


That would be great!

Quote: Originally posted by Sulaiman  

'scum' on the surface of the mercury..


That's exactly what I've got on my mercury right now sigh :(

charley1957 - 23-5-2024 at 04:42

I have several pounds of mercury I got from a dentist who was retiring. To that I added some mercury I’d had for years which had a nasty scummy layer on top, some rust and dirt. I finally decided to clean it all up somewhat so I forced it through a cotton ball in the bottom of a syringe. It took a couple of days to do it all that way. It was beautifully shiny after that, and I just stored it under some distilled water in a glass jar, which is inside of a plastic jar. Years later it is still just as pretty as it was back then. Don’t know what metals may be dissolved in it if any, but I’m content with it the way it is. If I need really pure mercury I guess I can distill the amount I need.

chornedsnorkack - 23-5-2024 at 12:31

Quote: Originally posted by Sulaiman  


Remaining Silver and PGMs can be removed by distillation.
I've not got to this stage yet.

Any PGMs in trace ammounts do not significantly effect the properties of mercury,
and do not oxidise to form 'scum' on the surface of the mercury.

For platinum group metals, see solubility data series 25:
https://iupac.github.io/SolubilityDataSeries/volumes/SDS-25....
Pages 258-267 mysteriously missing in pdf. Anyway, platinum group is:
Ru: 308-of work, 318 of pdf. Below all detection limits.
Os: 309 of work. Below all detection limits.
Rh: 314-315 of work. Below detection limits at rt - but forms solid amalgam, unlike Ru and Os
Ir: 316 of work. Below all detection limits, no solid amalgam either
Pd: 326-330 of work. At 25 C, about 50 ppm at; solid PdHg4
Pt: 330-334 of work. At 25 C, about 5 ppm at; solid PtHg4. Vast scatter of experimental data due to slow equilibration.
So as you see, Ru, Os, Rh and Ir can be excluded...
Ag: 357-368 of work. Around 800 ppm at 25 C. Solid is gamma phase, without a simple announced stoichiometry.
You are omitting just one noble metal. Which, however, could also be removed by distillation.
Pages 369-384.
Solubility about 1100 ppm at at 25 C. Solid phase called delta.
The example of platinum equilibration makes me wonder: how readily does Au2Hg nucleate from supersaturated solutions? How are Hg properties affected by modest supersaturation with noble metals Au and Ag?


Sulaiman - 24-5-2024 at 00:21

Quote: Originally posted by Sulaiman  
I have c100g Hg heading to me in the post at the moment.
This batch I will try to measure how much base metals contamination there is.
Then add it to the rest of my mercury.
I intend to do a video of the cleaning process of my entire stock (c120ml), including distillation, within a few months.

It seems that the mercury that I received has very little base metal contamination,
about 0.03% weight loss after 'cleaning'.
Next is the video....

PS that 0.03% made a huge difference to the look and flow of the mercury.

chornedsnorkack - 24-5-2024 at 00:55

Quote: Originally posted by Sulaiman  
Quote: Originally posted by Sulaiman  
I have c100g Hg heading to me in the post at the moment.
This batch I will try to measure how much base metals contamination there is.
Then add it to the rest of my mercury.
I intend to do a video of the cleaning process of my entire stock (c120ml), including distillation, within a few months.

It seems that the mercury that I received has very little base metal contamination,
about 0.03% weight loss after 'cleaning'.
Next is the video....

PS that 0.03% made a huge difference to the look and flow of the mercury.

In other units, about 300 ppm mass.
Does your mercury have a significant precious metal contamination?
At room temperature saturation, the under 800 ppm at of Ag binary solubility would be about 400 ppm mass. Au binary solubility is quoted as about 1300 ppm mass. (As established, other precious metals, i. e. platinum group, are well below 100 ppm).

Sulaiman - 24-5-2024 at 01:27

Quote: Originally posted by chornedsnorkack  
Does your mercury have a significant precious metal contamination?
I do not know, I'll find out when I distill it.
Relative weight loss measurements are fairly simple and quite accurate
(220g x 0.1mg balance)