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Hi everybody
In this video I will demonstrate the refining of gold from old karat jewelry.
Here's our scrap gold, 36.12 grams of 18 karat and 33.05 grams of 14 karat.
The first step in this process is to calculate the amount of silver that should be added
in order to make the alloy into a 6 karat,
meaning, one quarter of the alloy is gold and the rest is silver or copper or other
elements that are soluble in nitric acid.
For inquarting, I always use scrap sterling silver. This basically gives the opportunity
to hit two birds with one stone as I also
get to refine the silver from the scrap sterling.
For the amount of 18 karat scrap i have here, I'll need to add 72.24 grams of sterling silver
and for the amount of 14 karat scrap I'll add 44.03 grams.
All in all, the result is 185.44 grams of 6 karat gold alloy.
You can calculate it yourself... Or you can simply use the calculator on my website...
it's pretty self-explanatory... here's the link. I'll leave it here in the corner for
a while..
Alright... The next step is to melt everything together.
Keep in mind that the alloy needs to be homogenous... so that means to stir the liquid metals thoroughly.
Of course, if you are melting the scrap with an induction furnace, stirring is not necessary.
To granulate the metal, I will pour the molten metal into a bucket filled with water from
a height of about a foot and a half. The water depth is about 14 inches.
OK... here we go...
Pouring the molten metal from this height produces shot which has large surface area,
quite similar to corn flakes.
The metal granules are placed in a reaction vessel and placed on a hot plate. Here you
can see the addition of the 50/50 nitric acid solution.
That means half of the solution is 70% nitric and the other half is distilled water.
The nitric leach usually takes about 2 to 3 hours at near boiling temperature.
The acid will dissolve all of the silver and other base metals such as Copper, Nickel and
Zinc into the solution.
Here, I have decanted the solution which reveals the gold sponge.
As you can see, the structure of the corn flakes is still intact. This is exactly what
we want because it is easier to wash this way. Keep it intact as it is very brittle.
By the way, some refiners would choose to perform another Nitric leach at this point
using a slightly more concentrated acid, meaning 1 part distilled water and 2 parts 70% Nitric.
I find it useful as well.
The next step is to clean the gold sponge from the silver and base metals solution.
To do that, we will wash the sponge several times with boiling hot distilled water.
Repeating these washes three to five times would be enough. The wash water is kept separate
so it could be re-used on the next batch.
Time to dissolve the gold with a hot Aqua-Regia.
Two things happen immediately as the Hydrochloric acid is added: first - Some Silver Chloride
forms and re-dissolves, we will deal with it later on in the process.
Second - Some gold starts to dissolve and give color to the solution.
As the solution heats up, you can clearly see the gold being dissolved before any Nitric
acid addition.
I have time-lapsed the gold dissolution, though even at this speed you can clearly see whenever
a small increment of nitric acid is added. Every addition is allowed to react until it
is exhausted.
The point is, to add just enough nitric acid to dissolve the metals. That's it.
Please, do NOT follow recipes that calls for pre-mixing the Aqua-Regia.
Just in case you are wondering, here's a little behind the scenes snapshot of the setup. If
you have any question about it, just leave it on the comment section below.
When the dissolution of the gold is done, the solution is diluted three times over with
water to precipitate the traces of Silver chloride that was previously dissolved.
Again, I forgot to film it, but a few milliliters of Sulfuric acid were added carefully to the
dilute gold solution to precipitate traces of Lead just in case there was any in the
solution.
The gold solution is left to stand overnight to cool down and precipitate Silver chloride
and Lead sulfate.