The old jewelry scrap with stones is weighed in.

Nitric acid (NHO3) is added. 

Hydrochloric acid (HCL) is added.  These two acids together are called aqua regia in which gold is soluble.  This means the acid will eat away at the gold and it will dissolve into the solution.

The aqua regia starts to attack the jewelry producing quite a strong reaction, bright colors and a fairly substantial amount of fumes that are processed through pollution control equipment to render them harmless.

As the reaction continues the color changes.  The beaker is stirred to promote the reaction.  You will also note that it is sitting on a hotplate.  The elevated temperature from the hotplate also helps promote the reaction.

The jewelry is dissolving with most of the metal going into the solution leaving a small amount of un-dissolved residue.

Once the acid has dissolved the metal to the point that all the diamonds have been freed from the jewelry, the acid is decanted into another beaker.  In larger scale refining where there is no concern about recovering stones, the reaction will be allowed to continue until all the metal has dissolved.  Here, however, the object is to recover the diamonds as quickly and efficiently as possible.  Hence as soon as all the diamonds are freed from what they were in, the acid is decanted allowing for a speedier recovery.

The acid is in the beaker on the right.  Dissolved in the acid, invisible to the eye, is the gold and other metals, such as copper, zinc and silver.  

The un-dissolved metals in the other beaker are washed with aqua regia removing any residue containing gold from the un-dissolved material.  

It is then added to the acid in the other beaker.  The green color is an indication that copper is present

After the material has been washed a few times and the water added to the beaker containing aqua regia; the stones and the un-dissolved pieces are relatively clean. 

They are then put through a couple other washes with different chemicals as a final cleaning

The diamonds, other stones and un-dissolved metals are completely cleaned and ready for sorting. 

The diamonds and other stones being sorted from the un-dissolved metal pieces. Since the un-dissolved pieces no longer have any stones in them, it is most efficient to melt them, run an assay and add the fine gold content so determined to the gold recovered from the direct acid refining to determine to total fine gold due the client.

Here the sorting process in almost complete with the metal pieces in the beaker.  Since the un-dissolved pieces no longer have any stones in them, it is most efficient to melt them, run an assay and add them to a non-diamond-removal lot.

The un-dissolved metal completely separated ready to be melted.

The diamonds and other stones completely separated and ready to be weighed, packaged and returned to the client.

As the reaction develops, gold starts accumulating in the bottom of the beaker.

The reaction is nearing completion with a thick layer of gold accumulating in the bottom of the beaker.

A piece of paper towel is dunked into to the solution.

And then tested with a chemical to make sure all the gold has been precipitated out of the solution.  The fact that there is no color change means all the gold has been precipitated.

Here is an example of what the test strip can look like when the test chemical has been applied and there is still gold and other precious metals contained.

The solution is then decanted through a filter paper to catch to gold.

The gold precipitate is scraped into the filter paper

The beaker is thoroughly washed to make sure all the gold is removed.

The filter paper with the gold after all the solution has passed through it.

The filter paper with the gold is then removed.

The filter paper with the gold is spread out on a ceramic dish and then placed on a hotplate to dry out.

The gold as it is drying out.

The completely dried out gold.

The gold is removed from the filter paper.

The gold is chopped up to make sure it is completely dry.

The gold in final refined form.  At this point it is a powder that is called "sponge".  When this is melted, it turns into the sun-yellow metal that most people recognize as gold. View our Melting Gold Sponge -From Refined Powder to Recognizable Gold.