How to dissolve the precious metals after cuppelation

G

Gydo

New Member
#1
Dear,

We just started to use the fire assay method at our company and we have a problem dissolving the gold/silver after cuppelation. We want to use a ICP-OES or FAAS finish for gold but when we dissolve it with aqua regia the little ball of gold/silver turns black and doesn't dissolve completely and a too low concentration of gold is found.

Any tips on dissolving the gold?

Thanks in advance!
 
fireguy

fireguy

Supermoderator
#2
Dear,

We just started to use the fire assay method at our company and we have a problem dissolving the gold/silver after cuppelation. We want to use a ICP-OES or FAAS finish for gold but when we dissolve it with aqua regia the little ball of gold/silver turns black and doesn't dissolve completely and a too low concentration of gold is found.

Any tips on dissolving the gold?

Thanks in advance!
Several things to consider:
1) You must have 4X as much silver in your bead as gold. If you don't, add high purity inquart silver.
2) First, dissolve the silver in nitric acid, then add the HCl to make the aqua-regia.
3) You will probably form silver chloride after adding the HCl. You will need to wait for this to settle, or centrifuge.
 
fireguy

fireguy

Supermoderator
#3
Several things to consider:
1) You must have 4X as much silver in your bead as gold. If you don't, add high purity inquart silver.
2) First, dissolve the silver in nitric acid, then add the HCl to make the aqua-regia.
3) You will probably form silver chloride after adding the HCl. You will need to wait for this to settle, or centrifuge.
Further to this, the nitric should not be full strength. The strength used varies, but 50% would not be uncommon. If you have a 2-4mg dore bead, you might use 3 ml of the 50% nitric, 2 ml of concentrated HCl, and bring to a 10ml volume with DI or distilled water. Use a vortexer or other mixing method.
 
A

AuExplorer

New Member
#4
There is another specific to consider. Other metal impurities that may also be alloyed in the bead. An example would be Pt grp elements to just name one little nasty.
 
D

devan

New Member
#5
There is another specific to consider. Other metal impurities that may also be alloyed in the bead. An example would be Pt grp elements to just name one little nasty.
Pt and Rh do not dissolve in Nitric acid, and can remain alloyed with your gold sponge. Sometimes you have to reinquart with proof silver (3:1) and re-part to get those Pt Group Metals out. Rh is a little more difficult.
 
B

Brandon Sheley

Administrator
Staff member
#6
Great thread, I'd like to learn more about recovering precious metals like silver and gold from scrap computer parts.
 
fireguy

fireguy

Supermoderator
#7
Great thread, I'd like to learn more about recovering precious metals like silver and gold from scrap computer parts.
Scrap computer parts can be tough. They can contain a lot of plastic, bakelite, base metals, as well as precious metal. The general procedure might be: 1) roast to remove/char any organics and break down other compounds, then a crucible fusion with a flux to make a metallic button. This will contain your precious metals, but will also have some of your base metals (some of the base metals will report to the slag). A couple of pretty good low cost books dealing with this:
Refining Precious Metal Wastes
Small Scale Refining of Jewelers Waste

Your flux could be either:
Borax
Or Chapman Flux is popular
 
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