i don't know if i need to add more smb
- Thread starter Atrash
- Start date
-
- Tags
- aqua regia polishing smb
Help Support Gold Refining Forum:
- Joined
- Apr 3, 2024
- Messages
- 29
have you tried a stannous test? it will let you know if you still have PMs in solution, or if they have all been precipitated out.
As Master Nater says, you need to test with Stannous.
But first describe your process in more detail.
i have tried the stannous test but i don't know exactly the gold amount in the solution my question is if i add more SMB then needed what will happen when i put the gold for melting ? this is my first time doing this process. does the smb effect the gold ?
i have about 2.5kg of gold dust from polishing machine the gold is 18k i dissolve the gold with aqua regia immediately and add SMB for recover the gold i get the gold back but i don't now how much i need to add more SMB because when i tried stannous test i still get a postive indcation of gold in solution my question how i can get the right amount of smb to add and if i dissolve the 18k gold immidatly with aqua regia is this right or i need to dissolve the copper first with nitric then i put the gold in solution with aqua regia.
You need to be sure you have no free nitric acid in solution before you add metabisulfite. You can kill off the free nitric with sulfamic acid or a small amount of copper. If you choose copper stop adding when the solution stops making red fumes and take out the copper.
Did your solution produce red fumes when you added the metabisulfite? If it did this means you still have free nitric in solution and the acid is redissolving the gold that is dropped with metabisulfite.
When you dissolve polishing sweeps you need to incinerate the polishing dust to burn off the oils in the rouge or the acid will not effectively dissolve the gold because the oils in the dust keep the acid from wetting the sweeps completely. Also when testing burnt sweeps, place a drop of the solution you are testing on a piece of filter paper and allow the acid to travel outward from the spot. This is because dirty acid is hard to test. If you let the solution separate from the point where you dropped it on the paper, you can test the clean solution by adding a drop of stannous so it too bleeds out from the center, and where the 2 solutions meet, you will have an easy to identify color change.
Too much metabisulfite will bring down base metals so your gold will not. be as pure. What you should do is make a small amount of solution which tests positive for gold with stannous, maybe 1/2 or 1/4 of a gram in aqua regia diluted to fill a small dropping bottle. Then whenever you doubt your stannous test, you can test your stannous with a solution you know contains gold.
no my solution did not produce red fumes when i add metabisulfite i talked with chemist he told me to check the ph of the solution but i didn't got what he exactly want me to check is he refer to check if my soultion have no excess nitric and what is the pH i should get in this case?
pH is the acidity of the solution.
You really need to study more!
- Joined
- Nov 26, 2010
- Messages
- 13
Not only be free of residual nitric acid, but also have enough residual HCl to react with SMB. It is this reaction that produces SO2 gas which is the actual reducing agent.
There is no specific pH but is should not get higher than 4.
After dissolving the metals it usually are in the 1-2 range.
Just make sure there is no surplus of Nitric.
