Pure Gold Refined From Jewelry And Dental Scrap

I'll bet it was exactly that: pure gold dissolved in aqua regia or other oxidizing chlorine solution, then precipitated with sodium nitrite or other reducing agent. Sodium sulfite or metabisulfite will work for that, as well as many other chemicals.

I'll further guess that the gold sponge was a convenient way to portion out the gold to create alloys for casting crowns or other dental appliances. Much easier to weigh an exact amount of soft sponge than to cut gold metal into specific weights! Another possibility would be that gold sponge would be used to mix with mercury to form an amalgam. Mercury/silver amalgams are used to fill cavities (although they seem to have dropped out of favor). A gold amalgam would work just as well; maybe in some cases gold would be superior to silver for that purpose.




Buddy, I just made a pile of sponge on a flat slab of stainless steel and gently applied the flame; the sponge sintered together easily. I then used steel tongs to turn the gold mass, flaming each side to round the edges. The gold showed no tendency to stick to the steel and since it is chemically very inert it does not tarnish when heated to the melting point in air. Easy to handle, really!

Nice! Cheaper than using a refiner I suppose? How much did the chemicals cost you?

I bought $3 worth of concentrated bleach from the Dollar Tree. Swimming pool acid from Home Depot was about $6/gallon as I recall. The sodium nitrite was maybe $5/pound, although I bought that a long time ago. I probably used less than 4 ounces of it for this project.

I bought 100 ml of 50% nitric acid on Amazon which cost about $30 shipped. It came all the way from Turkey and took a month to arrive. I only needed about 10 ml of it to prepare the dilute nitric for my final round of sponge purification.

This process will NOT work for silver. Any silver that dissolves in the bleach/HCl mix will form insoluble silver chloride. Recovery would be difficult. If you want to process silver you would likely need to use nitric acid exclusively and another reducing agent, like hydrazine. Large-scale silver reclaim (like getting silver out of old X-ray film) often employed toxic cyanide solution and is totally impractical (and dangerous) for a home chemist.

Very nice. You should consider prepping your nugget in the final step by dropping the molten metal into a beaker of water. This will give a "natural" porosity to the nugget that looks really nice. It may even purify it slightly as it any remaining water solubles may stay in the beaker. A little dangerous handling the molten metal, but then the whole thing is dangerous to begin with. I'd never do this at home.

I actually consider this process to be pretty safe. I set up on my back porch which is covered but open on three sides. Fumes of chlorine and nitrogen dioxide generated during the process were quickly dispersed and no extra ventilation was needed. I'm not concerned about minor contact with bleach or swimming-pool-grade HCl, and sodium nitrite is practically non-toxic. The biggest hazard I faced was getting impatient about picking up the gold nuggets before they were cooled; I might have singed a finger!

Great work.
You'll have to change your handle to "Walter White"!

Final report on this thread:
I took my brick to our local coin shop where they have an XRF machine used to measure precious metal content of jewelry and other items they buy from the public. The brick tested at 24 karat / 99.99 gold which is the highest purity the device can measure.

As I shaped my brick the edges became thin and sharp. I used my torch to touch up the edges, heating the brick just enough so those edges would liquefy and become rounded. A glowing gold brick is a lovely thing!

Sure is
I like your process