Problem with dissolving inquarted gold

[stefano]

Hello the forum.

For the first time i inquarted jewelry gold. I melted five buttons. Each one of them with different karat gold and adding a bit more of the calculated amount of silver. The silver contained around of 20% of copper. The buttons after the inquartation melt weight around of 38 grams each one.

Then i began to dissolve the buttons in hot nitric /water ( seven parts of 53% nitric / three parts of distilled water). The reaction was very strong, and after some hours when the bubbles stopped i added more nitric/water until nearly all buttons where dissolved.

At this point at the bottom of the beaker was a lot of gold powder and a lot of hard pieces with a diameter of around 3-5 mm, which where brittle and could be crushed in the beaker with a glass rod.
But there are too two pieces of not completely dissolved buttons. They are sheets of the bottom of the original buttons, with the original diameter of the button. The thickness is around of one mm ( the original button had a thickness of around seven mm ). The colour is the colour of silver.

I siphoned the green silver/copper - nitrate -solution and added fresh nitric/water to the beaker and let it stay on hot plate over night. There was no bubbling reaction and only a few NO2-gas. The undissolved buttons remained undissolved.

Now my question.
Can i try to dissolve the mix of rinsed gold powder / crushed pieces / undissolved buttons in AR, or had i to inquart for a second time the remained powder or the undissolved buttons ?

Or how had i to proceed to refine the gold without creating a lot of silver chloride ?

 

[nickvc]

Stephano my advice is to wash the gold powder out and remove the solid pieces from your beaker, weigh them and estimate the gold content and then add enough silver to inquart them, the part you may have missed is to stir the melt well to make sure the silver is combined with all the gold alloy. The button then can be dissolved back in nitric to remove silver and base metals and then combined with the other powder to dissolve in AR.
You could try to dissolve what’s left straight in AR but you will get some silver chloride so if you wish to avoid as much as possible the remelt route is best, do not forget to chill your AR solution prior to filtering, adding ice is good, as this precipitates most of the silver chloride so you can filter it out.

 

[stefano]

Hello nickvc,

thank you very much for your reply. You are right, i didn't stir the melt because i melted for the first time, and i had no idea with which rod to stir it.
What is the material of the rod and how had i to preparate it before stirring the hot melt ? ( cleaning ? heating up ? )

 

[nickvc]

I believe I used quartz rods but you can buy them easily from jewellery tool and supply shops, you could try putting the silver at the bottom and the gold should merge into the silver as it melts as it’s denser than the silver or simply swirl the molten metal around using tongs and gloves and been careful as molten metals are very dangerous.

 

[FrugalRefiner]

I would also suggest granulating / cornflaking the metal instead of letting it cool as a button. Get a large pot, like a 5 gallon stainless steel cooking pot, and fill it with cool water. When your gold is molten, give the water a good stir to get it swirling in the pot, then pour the gold slowly into the pot. It creates what looks a lot like cornflakes. It provides a lot more surface area for the acid to contact the metal, so the dissolution goes a lot faster, and you're less likely to end up with a core where the base metals are protected by the gold and aren't fully dissolved.

Dave

 

[stefano]

Thank you for your advices. I considered them all and decided to pick out the undissolved metal parts for remelting and inquarting.
Because i couldn't see what type of metals remained in the solids, i went with them straight to AR. All dissolved well and i saw only very few of silver chloride left over.

But after the melting and inquarting in my crucible ( ceramic, 58 mm diameter, parabolic form, all glazed with borax before melting with mapp-gas burner ) i noted on the sides of the crucible hundreds of very tiny balls of metal. The color of the balls varies from silver to gold.

I let the cooled crucible soaked in boiling water for two hours and the borax with the larger ones of the tiny balls fall on the bottom. But many of them are always sticking very strong to the sides of the crucible. I tried to scrap them of with a tool, but they are very hard to scrap off.

How can i recover these tiny balls which are sticking to the sides of the crucible ?
How can i prevent that they go and stick to the walls of the crucible while the melting ?