Red Solution - what did I do?

[didit]

So to start I'll say this is only my 2nd refine so forgive my ignorance on some topics as I am new to the hobby.

The material being refined are a collection of gold dental crowns that I have accumulated over the past year.

I had tested them and had 20.82 grams of 14K, 33.14 grams 16K, and 7.53 grams of 18K gold crowns. All non-gold materials such as teeth removed.

I decided to process them as karat gold and inquarted them with approximately 117.82 grams of marked and tested 925 Sterling silver.

***I did have an issue when dropping inquarted material into shot and over heated the crucible which definitely caused a contamination problem.

I proceeded with the standard Nitric boils until I had no red fumes.

I rinsed the remaining gold and did AR. (I noticed a fine black residue that would not go into solution) - Stannous was just heavy Black.

I denoxed with Sulfamic Acid, iced, and filtered.

The resulting solution was a very dirty avocado green.

I filtered about three times. The first a very heavy layer of debris probably from the crucible mishap and the other two had very fine black/grey powder.

At this point I decided it best to just drop the gold and deal with contaminates in the re-refine.

I had a PH of 1 so I wanted to raise it to a PH of 2-4 before adding SMB.

So I added Sodium Hydroxide.....................at this point the solution turned blood red and now there is a light brown precipitate at the bottom of the beaker.

Advice? Suggestions? Help?

What kind of mess have I made and is it fixable?

 

[Yggdrasil]

So to start I'll say this is only my 2nd refine so forgive my ignorance on some topics as I am new to the hobby.

The material being refined are a collection of gold dental crowns that I have accumulated over the past year.

I had tested them and had 20.82 grams of 14K, 33.14 grams 16K, and 7.53 grams of 18K gold crowns. All non-gold materials such as teeth removed. How did you test?

I decided to process them as karat gold and inquarted them with approximately 117.82 grams of marked and tested 925 Sterling silver.

***I did have an issue when dropping inquarted material into shot and over heated the crucible which definitely caused a contamination problem.

I proceeded with the standard Nitric boils until I had no red fumes.

I rinsed the remaining gold and did AR. (I noticed a fine black residue that would not go into solution) - Stannous was just heavy Black.

I denoxed with Sulfamic Acid, iced, and filtered.

The resulting solution was a very dirty avocado green.

I filtered about three times. The first a very heavy layer of debris probably from the crucible mishap and the other two had very fine black/grey powder.

At this point I decided it best to just drop the gold and deal with contaminates in the re-refine.

I had a PH of 1 so I wanted to raise it to a PH of 2-4 before adding SMB.
Why change the pH?

So I added Sodium Hydroxide.....................at this point the solution turned blood red and now there is a light brown precipitate at the bottom of the beaker.
How did you add the NaOH? Solid dissolved?

Advice? Suggestions? Help?
You have probably added too much NaOH and created some Hydroxide.
Have you tried to re acidify with HCl?

What kind of mess have I made and is it fixable?

I will comment in bold inside the quote.
Next time ask first before you start.
Then we can correct your plan before you make mistakes.
It is much easier to avoid mistakes than fixing them.
And you need much more studies.

 

[didit]

I will comment in bold inside the quote.
Next time ask first before you start.
Then we can correct your plan before you make mistakes.
It is much easier to avoid mistakes than fixing them.
And you need much more studies.

Thank you for your response Yggdrasil. Your advice helped a great deal previously.

How did you test? I tested the crowns with acid scratch and file test and also a Kee Gold Tester. They were all non-magnetic and only gold colored. No silver colored crowns.

Why change the pH? I was following the advice I received here on the forum during my first refine that it is best to have a PH of 2-4 for dropping the gold with SMB.

How did you add the NaOH? Solid dissolved? I added the NaOH by dissolving in a small beaker with distilled water until there was a saturation then poured it into the solution.

You have probably added too much NaOH and created some Hydroxide.
Have you tried to re acidify with HCl? I have not tried to re acidify with HCl. Would that cause the precipitate to go back into solution whatever it is?

 

[Yggdrasil]

Thank you for your response Yggdrasil. Your advice helped a great deal previously.

How did you test? I tested the crowns with acid scratch and file test and also a Kee Gold Tester. They were all non-magnetic and only gold colored. No silver colored crowns.

Why change the pH? I was following the advice I received here on the forum during my first refine that it is best to have a PH of 2-4 for dropping the gold with SMB.

How did you add the NaOH? Solid dissolved? I added the NaOH by dissolving in a small beaker with distilled water until there was a saturation then poured it into the solution.

You have probably added too much NaOH and created some Hydroxide.
Have you tried to re acidify with HCl? I have not tried to re acidify with HCl. Would that cause the precipitate to go back into solution whatever it is?

The advice for dropping Gold is that it should NOT be higher than 4 so the SO₂ can evolve. Anything ftom 4 ish to 0 or even -1 will be good.
The testing you did will notbreveal any Pd or similar which is relatively common in dental alloys.

You should have added Silver (inquarted it) and parted it to remove the Silver and potential Pd, Pt and Copper.
Then dissolved and dropped the Gold.

 

[Yggdrasil]

Thank you for your response Yggdrasil. Your advice helped a great deal previously.

How did you test? I tested the crowns with acid scratch and file test and also a Kee Gold Tester. They were all non-magnetic and only gold colored. No silver colored crowns.

Why change the pH? I was following the advice I received here on the forum during my first refine that it is best to have a PH of 2-4 for dropping the gold with SMB.

How did you add the NaOH? Solid dissolved? I added the NaOH by dissolving in a small beaker with distilled water until there was a saturation then poured it into the solution.

You have probably added too much NaOH and created some Hydroxide.
Have you tried to re acidify with HCl? I have not tried to re acidify with HCl. Would that cause the precipitate to go back into solution whatever it is?

Did you test with Stannous?

 

[didit]

The advice for dropping Gold is that it should NOT be higher than 4 so the SO₂ can evolve. Anything ftom 4 ish to 0 or even -1 will be good.
The testing you did will notbreveal any Pd or similar which is relatively common in dental alloys.

You should have added Silver (inquarted it) and parted it to remove the Silver and potential Pd, Pt and Copper.
Then dissolved and dropped the Gold.

I assumed I had removed all of the silver and palladium during my Nitric boils to remove the base metals.

Below is a photo of my sliver jar which is dark green. During my first refine which was also a dental grade gold I successfully separated the palladium from the sliver as yellow salt using DMG but have not gone further with it yet as it is a small amount of palladium in that first refine and I want to study up some more before processing the palladium. I am fully aware of the extra steps needed and also the inherent safety/danger risks involved with palladium.

I wanted to have more to work with when I do that which is why I chose this particular batch of gold because I suspected there would be a fairly large percentage of palladium to add to my previous refine when I feel confident enough to do that.

 

[didit]

Did you test with Stannous?

Yes. Stannous was very black. Some hints of purple.

 

[Yggdrasil]

I assumed I had removed all of the silver and palladium during my Nitric boils to remove the base metals.

Below is a photo of my sliver jar which is dark green. During my first refine which was also a dental grade gold I successfully separated the palladium from the sliver as yellow salt using DMG but have not gone further with it yet as it is a small amount of palladium in that first refine and I want to study up some more before processing the palladium. I am fully aware of the extra steps needed and also the inherent safety/danger risks involved with palladium.

I wanted to have more to work with when I do that which is why I chose this particular batch of gold because I suspected there would be a fairly large percentage of palladium to add to my previous refine when I feel confident enough to do that.

Sorry did not notice the inquart with Sterling.
Depending on the amount of Pd, DMG might be impractical or expensive due to the amount of DMG salts produced.
Anyway since you have already dissolved in Nitric it should be free from Pd and Ag depending on achieving a good homogeneous melt.
Did you test with Stannous before and after the pH adjustment?
What pH is it now?

 

[4metals]

Ruthenium is often used in dental alloys as a grain refiner I suspect that was the black powder you saw.

 

[didit]

Sorry did not notice the inquart with Sterling.
Depending on the amount of Pd, DMG might be impractical or expensive due to the amount of DMG salts produced.
Anyway since you have already dissolved in Nitric it should be free from Pd and Ag depending on achieving a good homogeneous melt.
Did you test with Stannous before and after the pH adjustment?
What pH is it now?

Yes. I did Stannous test before and after. Stannous has remained unchanged although in the first test I noticed a bit of purple (somewhere in the sweeps bin and can't find it).

The current pH is around 3 (at least I think, the red solution seems to obscure the reading a bit. The original pH was between 0 and 1.

The photo is of the pH and Stannous I just went and took.

 

[didit]

Another piece of the puzzle that might help.

So I poured off the last Nitric boil to use in the future and not waste it. It has since degraded somewhat and turned a bit yellow (it was clear before) but there is a curious red powder at the bottom. ????

 

[Alondro]

Another piece of the puzzle that might help.

So I poured off the last Nitric boil to use in the future and not waste it. It has since degraded somewhat and turned a bit yellow (it was clear before) but there is a curious red powder at the bottom. ????

If the crowns were in contact with old fillings that came along for the ride... could be mercury compounds!

 

[didit]

If the crowns were in contact with old fillings that came along for the ride... could be mercury compounds!

As I recall one did have filling that I could not remove but I thought it was relatively small. I have to work tomorrow so decided at this point it best to filter my solutions again and bottle them up for another day because I don't like having open acids in the shop even if in the hood. The AR solution filtered rather easily but left me with this strange sediment in the filter.

I took a photo in the sunlight. It's very orange, shiny, almost metallic. Thoughts anyone?

Do you guys think I should just continue with SMB and drop the gold now that solution is filtered or should I be afraid...very afraid.