gold mixed with stainless steel and steel.

[goldnugget77]

Someone asked me for help
He is a jeweler and he has gold mixed with stainless steel and steel.
He wants to remove the steel and have only the gold so he can use it again for jewelery.
I said he should boil in HCL but I dont know if I said the right thing
Can anyone help
Thanks

 

[goldenchild]

Maybe he should melt it down.

 

[4metals]

Boiling in HCl may take a long time with stainless.

Dissolve the mess in aqua regia, make sure there is enough acid to test positive with stannous. With a lot of base metals the gold will dissolve and drop out if the acid becomes saturated with base metals. You didn't say how much steel, stainless and gold so it is difficult to predict how much acid will be needed. If it were me, I'd digest it in AR until there is nothing on the bottom but silver chloride, then and add copper until there is no more gold as indicated by stannous chloride. Then filter off the liquid and rinse the mud.

If there was karat gold, not just gold, you will have some silver chloride in the residues. A rinse in ammonium hydroxide will clean that up leaving only gold (assuming no Pt in the gold)

The remaining impure gold sponge can be digested in a small amount of aqua regia and dropped normally producing a very pure button.

 

[goldnugget77]

Hi 4 metals
Thanks for your help
That makes sense but I cant picture exactly how the reaction will be.

and add copper until there is no more gold as indicated by stannous chloride.

Do I drop a piece of copper in the AR solution.
Thanks

 

[martyn111]

Cement the values from solution using copper until a test with stannous chloride is negative for gold

 

[goldnugget77]

Hi martyn111
Thanks
That makes sense I didnt think of it that way.
Can SMB used as usual for cementing or is there a reason why not

 

[eeTHr]

Can SMB used as usual for cementing or is there a reason why not

Because there are probably too many contaminants in solution for SMB to work well.

Suspend solid copper (not tubing or multistrand wire) in the solution, to bring out just the PMs, then refine the sediment in the usual way.

Search "cementing with copper," in the forum search feature.

 

[Harold_V]

You do have a second option---one whereby you use less than the amount of AR required to dissolve the entire lot. When the acid is consumed, some of the base metal will remain un-dissolved. It, in turn, will cement the gold, further dissolving the stainless. When the solution tests barren with stannous chloride, you then allow it to settle well, then decant.

This reduces the amount of impurities considerably. A second iteration will serve to remove even more, but you must be careful to use AR sparingly, so you don't dissolve all of the base metals, which you will rely upon to cement the values. When you have reduced the base metals to a bare minimum, you can then dissolve everything, evaporate, then filter for recovery with SMB, or even ferrous sulfate. This method will yield quite respectable quality gold.

Harold

 

[qst42know]

You do have a second option---one whereby you use less than the amount of AR required to dissolve the entire lot. When the acid is consumed, some of the base metal will remain un-dissolved. It, in turn, will cement the gold, further dissolving the stainless. When the solution tests barren with stannous chloride, you then allow it to settle well, then decant.

This reduces the amount of impurities considerably. A second iteration will serve to remove even more, but you must be careful to use AR sparingly, so you don't dissolve all of the base metals, which you will rely upon to cement the values. When you have reduced the base metals to a bare minimum, you can then dissolve everything, evaporate, then filter for recovery with SMB, or even ferrous sulfate. This method will yield quite respectable quality gold.

Harold

I do like the idea of incremental digestion slowly cornering your values. 8)

I will give this a try when I've accumulated enough magnetic gold filled.

 

[Harold_V]

I do like the idea of incremental digestion slowly cornering your values. 8)

I will give this a try when I've accumulated enough magnetic gold filled.

I contrived this method of recovery when I received a large batch of dental material, much of which was no value high temp alloy. To sort each by hand would have taken way too much time, so I gave the idea a go. Turned out to be a great way to sort. You can closely judge the solution by color alone--brown with values, blue/green when barren. Needless to say, one must test with stannous chloride, but color monitoring helps you decide when it's time to begin testing.

Harold

 

[goldenchild]

I discovered this very thing when digesting the foils from GF material that had not been stripped of enough base metal. At first in the AR digestion there is a nice bright yellow to yellow-green as you would expect. But then as Harold says it turns to greens and blues when the AR is all used up and the values have cemented out. Cool, test, decant, filter and add fresh AR. Don't forget to put copper in your filtered solutions.

 

[Palladium]

Funny how copper can both be your friend as well as you enemy. :mrgreen: