Mercuric Chloride is a great salt of mercury for amalgam reductions because of it's high solubility in polar solvents. It can be easily prepared from mercury metal, which is in turn converted to the intermediate HgSO4, and HgO to charge the mercury ion to its +2 oxidative state(since it has a neutral charge of 0) for it's final double displacement rxn into HgCl2...and also to purify the salt throughout the workup.


Note: Elemental mercury is *fairly* poisonous, HgSO4 is *a bit less poisonous*, HgO is *decently poisonous* and HgCl2 is *very* poisonous. Be careful and make sure you vent outside or work outside. Also make damn sure your vac adapter tubing is connected well if you're venting outside. Mine fell off towards the end which could've been potential very bad. Worst case scenario it falls off and you get blasted with SO2 gas and volitile Hg vapors. Seriously, be extra careful.

Prepare a ratio of Hg:H2SO4 to 1:3. Make sure the HgSO4 is concentrated. This reaction can be scaled up or down with ease. Add the mercury to the sulfuric acid in a suitable flask, preferably flat-bottom, attach the flask to a stoppered bent vac. adapter, and connect a tube to the nipple and lead outside, or just use a similer setup. The heavy mercury metal will just sit on the bottom and stare back at you after you add it to the flask...so much for a rxn.


The rxn needs a lot of heat to get started so crank up the hotplate to +200C. You'll know the rxn has begun when the mercury starts to twitch and convulse. It will then start to change the color of the H2SO4 to a darker color, usually a yellow or brown depending on the grade of H2SO4 you're using. This is because of the interaction between the Hg and SO4 ions. Eventually you'll see the mercury start to effervesce and immediately upon hitting air those bubbles will form SO2 gas...Kinda reminds me of the end of Terminator 2.

You want to keep the SO2 gas evolution at a vigorous pace otherwise it's *possible* Hg2SO4 can form instead of HgSO4...possible, but unlikely. The whole rxn should take between 30-60 minutes if you're keeping it vigorous. The rxn is complete when no more mercury metal is present, and no more SO2 evolution is visible. Allow the rxn to cool and decant most of the remaining H2SO4 while being careful not to pour off the HgSO4 crystals that have precipitated on the bottom. They should be very white.

Since most sulfate salts, especially mercury ones, are very soluable in water, SLOWLY add enough hot(not boiling! slightly volitile!) dH2O into the flask to dissolve all the HgSO4. This was the first time I got a big wiff of H2SO4...wow, I'm not going to forget that scent anytime soon. If you're using 5g Hg metal to start with, then use ~200ml hot dH2O. Swirl the whole mix for a bit to make sure everything is dissolved and let settle. You should now see a yellow-ish precipitate on the bottom, which is trashy sulfate decomp. salt. Don't worry about it. The water also now contains H2SO4 in it again from the decomposition of HgSO4 in the water, and also Hg+2 ions.

When yellow precipitate stops forming filter the whole solution through a buchner and keep the filtrate.

Now, when Hg+2 ions in an aqueous solution are treated with a saturated alkali solution HgO is formed, and thus will precipitate out of the solution due to its high insolubility in water.

Create a saturated solution of either sodium bicarbonate or sodium carbonate. I have yet to test this on other alkalis so I can't speak from experience but feel free to experiment! Slowly pour your carbonate solution into the filtrate and continue to add until effervescence stops. The bubbles forming are actually CO2 bubbles so all is well...probably one of the only non-poisonous products in the whole workup.


As the solution is being added a yellow/orange/red mercuric oxide will precipitate out. A great indication of when the alkali is done reacting is if you carefully put your ear to the flask and listen for any fizzing...if you don't hear any fizzing similer to soda fizz then the rxn is done. Dump the whole solution into a buchner and vac. filter. Since the oxide is insoluable in water(just like that yellow sulfate crud earlier) it will be your filter cake. Wash the filtrand with dH2O. Now, your cake is fairly pure orange-ish mercuric oxide.

Now, prepare a wide-mouth glass piece(a beaker or pyrex measuring cup is fine) and prepare a 15% con. HCl solution. After that, remove the filter cake from the buchner with the HgO on it and carefully place it into the wide-mouth glass piece. Pour enough dH2O onto the cake to wash off the mercuric oxide. This saves a lot of time trying to scrape the HgO off, then remove the wet filter paper with tongs being extra careful not to tear it up(paper=bad).

Finally slowly titrate in your 15% HCl solution and stir occasionally. The orange/yellow HgO will quickly transform into a white salt. This white salt is your mercuric chloride. Keep adding the HCl until all the HgO has disappeared. If for some reason the solution is saturated with HgCl2 and still some HgO remains on the bottom add more water(because you didn't add enough). Pour the HgCl2/water solution into a flask and wash the rxn piece with dH2O that you titrated the HCl into to remove any remaining HgCl2. All you have to do now is gently boil(rotavap,ect..) off the water, and air dry the remaining crystals.

Yield 90%


-PStain.

Nice Poison,
 As for what to do with the Hg... I just thought of something a few days ago. Im an artist, I do sculptures and alot of kiln work. There are some older formulas of glazes that use HgO to generate ... red I think it is. Anyway where as your not suppose to eat out of them they are safe to handle. A mixture such as this could solve peoples mercury sluge problems because it could be dryed in a piece of disposible earthenware mixed into some sand and aluminum oxide or possibly just mixed with clay. And thrown in a fire. As long as the fire is 1100 degrees C the shit will fuse and you will be able to bury the formed rock some where far away later on with almost no worrys. Id chuck it in my kiln but a strong fire should work as well.

very interesting idea sedit, sounds a bit hard for most of us though. Isn't their some sort of free thing that takes away are toxic stuff? I know their must be a place for light bulbs to go since they contain Hg compounds, right?

I should also probably mention that both mercury metal and HgCl2 are *slightly* volitile at room temp...so unless you're working in a closed space for less than 5 minutes I recommend you try to keep air exposure to a minimum between you and the compounds(i'm assuming most other mercury salts are somewhat volitile too). A little won't hurt, it's not like cyanide poisonous.

Also, in the final step to remove the water a rotavap would be best or even stripping off the water under vaccum would be fine. Short path distillation also works but make sure you don't disassemble everything until the rig is completely back to room temp.

An interesting side-note mercury vapors can be seen only under blacklight.

Haha, I was actually looking for a blacklight today for that same reason.

I couldn't find one  ...but you could probably find a thermostat mercury bulb and shine the blacklight up to it just to test it in theory. The literature on the subject says it's true but I haven't actually tried it from experience.

I'd imagine the vapors can be seen at room temp or slightly above. That's just an educated guess though.

If I understand correctly, then yes...it is possible to seperate HgO from Hg if both are in a solution.

HgO is the incest cousin of HgCl2, it's only a throw away as far as oxidative states are concerned.

Oh, this is important and I just found this out...HgCl2 IS WAY MORE VOLITILE than you may think, at least I thought so.

Like I said earlier the best way to increase yields once the chloride is formed is to rotavap or vac distil...I STRONGLY urge against straight distilling without a vac source.

I can say from experience that even at 100C a fair number of HgCl2 crystals will sublime and your yields will go down a lot. I didn't even notice it at first, but after multiple runs I arrived at this conclusion.

Honestly, I think for most people's needs simply getting the HgCl2 after it's formed, throwing it in the freezer for 20 minutes or so to decrease the solubility of some of the chloride, and then running it through a buchner is enough. Then just carefully scrape the dry filter cake.

Here is a video of it, oh boy do I want to spill mercury in my carpet!
http://www.youtube.com/watch?v=_QC6F9Pu0dE

according to this site http://acc6.its.brooklyn.cuny.edu/~scintech/mercury/WhatBigDeal.htm

..the mercury evaporation rate, is the rate of mercury vaporization per unit area of mercury. This is a constant value of 7 ug/cm^2/hour at 20*C.

I wonder how compounds like mercury chloride compare in sublimation. If they sublimate similarly they could be much more dangerous since their surface area is so much greater considering they are a powder. What dictates sublimation of solids? It seems like mercury chloride wouldn't have any problems sublimating since both Hg and chlorine sublimate easily at room temperature. Well, in chlorine's gas, is already a gas. I know that the properties of both the elements that make up the compound has little or nothing to do with the properties of the compound. I know at least in some cases it seems to matter/correlate though such as with ammonium salts.

Aha! I was doing some poking around and found some fantastic information.

HgSO4 and HgO are entirely nonvolitile, BUT HgO is *very slightly* soluable in water at 20C so you should freeze your HgO solution for awhile before decanting to obtain a somewhat higher yield when you form the chloride.

This would explain why my highest losses(which were small to begin with) were when the oxide was formed from the sulfate.

Actually, that's nothing compared to if you distill it without a vaccum like I was saying earlier. You lose so much HgCl2 at 100C from stripping off the water it's ridiculous.

So I have to add these few tidbits to my writeup:

-freeze the HgO/alkali solution before decanting the HgO
-do not strip off the excess water from the HgCl2/HCl solution unless under vaccum
-if vac if unavailable freeze HgCl2 solution and decant excess water.

...this should increase yield ~5% give or take.

I never saw the vapors and I tried it.  I have a feeling the UV wavelength of a black light wont do it, you need a higher wavelength.

Yeah, if you look in the video, they use a short wavelength and a fluorescent background, so the mercury forms a shadow by not responding to the black light.

If you put something white behind it and try, you may be able to see the vapors.