Question about Gold and Mercury in AR?

[Yukon99669]

I have a batch of AR that has Placer Gold and Mercury in solution. I’ve denoxed the AR w/ Sulfamic Acid and diluted w/ 3x Water by volume to precipitate and filter any silver.
My game plan is to drop AU w/ SMB as usual. After filtering to recover AU my understanding is that I can precipitate Mercury w/ Lye (Sodium Hydroxide) to Mercury Oxide. Then dry and use strong heat to drive off the oxygen and re-claim my liquid Mercury.

Does that sound like an accurate scenario for pulling this off?

I have a retort, but am not really a fan of dealing with Mercury like that and this was a mixed bag of various material that I wanted to deal with in one process (more or less)….and figured I could pull it off this way.

 

[Lino1406]

The silver precipitated should be checked for mercury, it may join silver (as well as lead)

 

[goldshark]

Retorting can be done safely, if done properly. If retorting, make sure you have a good seal on your pot, and use plenty of cold water on your condensate tube, and under a fume hood in case of any lead or other heavy metal fumes not condensed. A good seal on the pot is super critical to eliminate any seepage from pot. Clay is sometimes used as "luting" to create a gasket. A little clay or bone ash on the bottom of crucible/pot will keep material from sticking to it in the event of turning the metal(s) liquid. Also tieing a fabric tail piece around the exhaust pipe will further help Mercury condense. Do not put tail submerged into water. Let fabric wick some moisture up, but do not let tail submerge into water catch basin.Upon removal of heat, water will get sucked into tail, and cause an explosion via steam. Let pot cool completely before opening. Very rarely does all Mercury go through condenser, so be prepared to deal with a little Mercury condensate stuck to various points of pot/ tubes. Opening the retort should be done in a plastic container to contain any errant blobs knocked loose during pot opening. Do it safe and clean, and you won't have any problems.
Others may chime in and add any steps I may have forgotten to mention.

 

[Stibnut]

Mercuric oxide decomposes to metallic mercury at 500 C, but metallic mercury has a boiling point of just 357 C. The result is that heating mercuric oxide will produce mercury as a vapor initially, not a liquid. If you want to recover it that way, you'll have to use a retort.

 

[kurtak]

The silver precipitated should be checked for mercury, it may join silver (as well as lead)

Correct - just like the silver chloride should fall out after dilution so should the mercury as mercury chloride

Silver chloride - lead chloride & mercury chloride are all made by the addition of HCl to a nitrate solution of those metals

At least according to Wiki --- "Mercuric chloride is obtained by the action of chlorine on mercury or on mercury(I) chloride. --- It can also be produced by the addition of hydrochloric acid to a hot, concentrated solution of mercury(I) compounds such as the nitrate"

https://en.wikipedia.org/wiki/Mercury(II)_chloride
However - this is an assumption on my part - as there are any (many) other factors to consider in this situation (as I am not an actual chemist)

What we know - HCl will precipitate both AgCl & PbCl from a nitrate solution with both Ag & Pb dissolved in it

We also know that AgCl will not dissolve in cold water or hot water --- on the other hand PbCl does not dissolve (well) in cold water - but dissolves in hot water --- therefore we can separate PbCl from AgCl with hot water washes

I am not sure about the (water) solubility of HgCl - (therefore my "assumption" of HgCl falling out by dilution)

Another thing we know - lead in an AR solution stays dissolved - even diluted - which is why we drop the lead out as lead sulfate by the addition of sulfuric acid

So - in an AR solution will Hg - like Pb - stay in solution - or drop out (upon dilution) like Ag (as a chloride)

Then there is another possibility - due to the low vaporization temp of Hg - it is (theoretically) possible that the heat from the reaction of dissolving the gold could/may cause the Hg to gas off & out of solution

So - ???? --- it would be good to hear from our more "chemistry" oriented members (Lou, 4metals, Lino, Orvi, Deano etc.) on this mater

IMO - when dealing with placer gold that has mercury on it you are better served retorting it to remove the Hg before dissolving both the gold & Hg in AR

Kurt

 

[nitrous]

Retorting can be done safely, if done properly. If retorting, make sure you have a good seal on your pot, and use plenty of cold water on your condensate tube, and under a fume hood in case of any lead or other heavy metal fumes not condensed. A good seal on the pot is super critical to eliminate any seepage from pot. Clay is sometimes used as "luting" to create a gasket. A little clay or bone ash on the bottom of crucible/pot will keep material from sticking to it in the event of turning the metal(s) liquid. Also tieing a fabric tail piece around the exhaust pipe will further help Mercury condense. Do not put tail submerged into water. Let fabric wick some moisture up, but do not let tail submerge into water catch basin.Upon removal of heat, water will get sucked into tail, and cause an explosion via steam. Let pot cool completely before opening. Very rarely does all Mercury go through condenser, so be prepared to deal with a little Mercury condensate stuck to various points of pot/ tubes. Opening the retort should be done in a plastic container to contain any errant blobs knocked loose during pot opening. Do it safe and clean, and you won't have any problems.
Others may chime in and add any steps I may have forgotten to mention.

Just one suggestion based on my life as a chemist and medical doc.... once you have your best (read "safest") system in place, get a mercury level done. and then get one yearly. Minamata disease is preventable but not curable. Personally, I wouldn't want to add a mercury still to my life... and I've done a few dodgy syntheses in my day Good luck!