Gold and tin mishap

I have been reading these forums for awhile — incredible amount of info! I have ran into a unique problem that I wanted your expert advise in.

Recently I was experimenting with my placer gold (naturally about 93% gold and 7% silver with a fractional amount of copper). I melted it down using a home made furnace and was trying to create gold “shot” by pouring it into what I thought was a steel cup... I Realized something was wrong when the gold started to melt threw the cup. I realized after that I accidentally used a pewter cup. and the gold quickly melted and “fused” (not sure the correct terminology) with the pewter (which is predominantly tin). I was able to remove most of the gold from the pewter cup but a lot of it has a tin “plating” on it if you will. Any advice on how to get this tin off the gold? It’s nearly an ounce of gold...

Part of me wants to learn how to fix the issue. Another part of me is not sure if it’s worth it and should I just sell it to a refiner and Call it a day. Would love your expert opinion.

While I don't consider myself an expert you can put it in hydrochloric acid. Unless it is cold, it shouldn't take long. If it is cold, put it on a hotplate just warm enough to not boil. On my hotplate the medium mark is about right. If it is tin/pewter it should go fast as long as it is just on the outside and not mixed with your gold.

You can melt that with borax and a little nitre and it should get rid of most of it. In abscence of nitre, a strong oxidizing flame and good mixing will work.

Ok interesting, two different methods. so Nitre - (Potassium Nitrate) plus Borax. So is the goal is to oxidize the tin and then the borax will help separate the oxidized tin from the gold? Would anyone be willing to provide a chemical reaction? (I was a chemistry major so it is important for me to understand what reactions are taking place).

For the HCL - would OTC Muriatic acid work or do I need a stronger concentration? Looks like this type of reactions can take some time but heat will speed things up a bit.

Thank you!!

It's just forming tin oxide which is then soluble in the flux.

You honestly probably don't even need the nitre if you are using a cutting torch and the gold is only plated with the tin.

Thank you again! Will let you know how it worked out =)

To answer your question about the chemistry, two things are happening.

One, in extreme oxidizing conditions, Tin oxide will actually heave the melt as vapor. Hence the reason good ventilation is of paramount importance. You can also lose silver this way, but on a 6% of 1 oz basis, it's a negligible loss.

Two, the tin oxide is soluble in alkali, the tin will form a complex with the sodium from the borax.

Thank you again. I usually do all my smelting activities well down wind from my house - and far from any other houses as well. How long do you think I need to keep the gold molten in the furnace for the reaction to finish?

As for the Hcl. 32% that you can get from home depot, lowes or menards is what most here use. If you cant get 32% than a lower concentration will work but of course it will take longer and more. If you can only get lower that 20% you can distill it (I believe it forms an azeotrope at 20-21%)

I get my hydrochloric at Home Depot. It is listed as a pool and concrete cleaner. 2 gallons here runs about $12. I have used several brands and have not had a problem so long as it isn't some of the "green" stuff.