Q&A for How to Refine Gold

The muriatic acid, when added to the nitric acid, is what enables the mixture to melt the gold... Neither Nitric nor muriatic,(Hydrochloric) by themselves are capable of liquefying gold. The metabisulfite will separate (precipitate) the gold from the Aqua Regia solution (once the solution has had the Nitric neutralized with Urea), "dropping" the actual purified gold into the mud like substance that will sink to the bottom.

If your gold is unrefined, your best option may be to ship it to a refiner. These processes may be challenging and cost-prohibitive for you. Another issue is that if you try to refine your own scrap, you may only recover the gold and not the other precious metals that may be present, such as silver and platinum. One great refiner that has been doing this for over 100 years is Pease & Curren.

In some cases, you are correct. If gold is mixed evenly in the alloy and at a low enough concentration, you can use plain nitric acid to dissolve away impurities. However, if the gold is more pure (or is an external plating), what actually happens is that the nitric acid tries to dissolve everything, but the gold blocks it from coming through. In that case, you purify an outer layer, but the internal layers are not pure because they are protected by an insoluble layer of gold. To fix this, we can add hydrochloric acid to the nitric acid (so the gold is also dissolved) and then selectively precipitate out the gold.

Sodium carbonate can be used instead of urea to neutrialize the remaining nitric acid by introducing it into the solution in the same way the urea was used. The excess nitrates can also be simply dissipated by gently heating the solution and reducing it's volume considerably, but use caution while heating --"gentle" is not boiling. This method works best only when minimal amounts of excess nitrates remain, so if you really over used the nitric acid you should neutralize as stated above.

Nitric acid dissolves the other metals commonly found alongside gold. Nitric acid doesn't dissolve gold, however, so after the acid dissolves all the other metals, only gold is left over.

Yes, if the urea you added did not neutralize the nitric acid, your gold will not come out of solution. There are several steps you can take from this point, but the easiest is to reheat and add more urea. The nitric acid must be completely gone.

No, by itself, gold is not attracted to the magnetic fields that we come across in our regular lives. It would take a massive magnetic field for the gold to be attracted. However, it is safe to say that for practical purposes, gold is not magnetic.

Putting a coffee filter over a jar and slowly pouring the acid and gold mixture through it seems to work. Safety measures are a MUST however.

Yes. You're not going to 'damage' the gold by re-melting it. Granted, you may get a tiny bit of an oxide layer, but just wait for it to cool down and wipe it away.

To strengthen it; pure gold is too soft for many applications.

Place a small magnet inside a plastic film canister or similar size plastic container and pass it over the black sand. It should stick to the bottom of the container and then you just shake it to make the magnetite sand fall off.