Refining Assistance please

[michael1311]

Hi All,

After assistance from reading tutorials here and watching streetip youtube video's I successfully completed my first refine with approximately 100 grams of 25% gold using the inquarting method and nitric acid only and achieved 99.00% pure gold.

Last night I did round 2 with more gold this time 400g 25% alloy gold, I used the formula of 2.5ml of Nitric for the 300grams base metal which came to a total of 750ML of nitric to mix 1 to 1.

Today with the furnace I melted the refined brown gold and only achieved a result of 88% purity. I also noticed little bits of zinc/copper/silver balls stuck on top of the bar and not mixed into the 88% alloy. Which I have never experienced before, I XRF'd the little balls on top and it was 50% gold 50% base.

Can anyone please assist in where I have gone wrong?

Thanks guys

 

[FrugalRefiner]

There's much in your post I don't understand, so I have some questions.

After assistance from reading tutorials here and watching streetip youtube video's I successfully completed my first 99.0% refine with approximately 100 grams using the inquarting method and nitric acid only.

What do you mean by your first "99.0% refine"? Are you saying you are expecting the remaining gold after inquartation and a nitric leach to be about 99% pure?

So you started with 100 grams of inquarted material, right? What did you start with? Are you working with karat gold, or something different? To help figure out why your yield didn't match your expectations, we need an accurate idea of what you started with.

After this first nitric leach, did you have the 25 grams of 99% gold you were expecting?

Last night I did round 2 with more gold this time 400g of gold 25% alloy, I used the formula of 2.5ml of Nitric of base metal which came to a total of 750ML of nitric to mix 1 to 1.

Again, what was the weight of your final gold after the nitric leach?

You say you used a 2.5 ml of nitric per gram of base metal. That may or may not be enough depending on the base metals involved.

Today I melted the gold and only achieved a result of 88%.

88% what? 88% of the weight you expected? 88% purity? If purity, how did you determine it was 88% pure? If 88% of expected weight, how did this weight compare to the weights of the gold from the first two steps? I'm confused by what you mean.

I also noticed little bits of zinc, copper, silver impurities stuck together on top of the bar and not mixed into the 88% alloy.

Zinc, copper, and silver should all alloy with the gold if it is fully melted. Did you use a lot of flux? Was there flux covering the melt?

Again, you mention an 88% alloy. How was this determined?

Sorry I have nothing but questions, but I really can't understand quite what you're dealing with.

Dave

 

[michael1311]

Hi Dave

I have access to XRF at work. I melted a 500g alloy, The composition was roughly AU 25%, AG 45%, CU 25%, 5% other (mostly ZN with some PD, FE, PB)

The first refine to test I used 100g of this composition which came out at 99.00%

The second refine I used 400g, the weight after the Nitric leach was 132g.

After melting the gold sludge it yielded a 88% pure bar with those small round bits on top of the bar, no i didn't use borax as I expected it to be pure. Can I guess that perhaps those 'bits' were wet and didn't mix in correctly?

After melting Refine 1 & refine 2 together I got a perfect alloy of 92% with everything mixed in together. Technically it took 2 melts to melt those small bits on the top...

I also edited my original post for you

 

[Martijn]

Welcome to the forum michael1311.
You are recovering, not refining imo.
XRF reads the surface composition of a bar. The top layer of atoms. No deeper.
Having 50% Au drops on your gold bar is an indication you are not achieving a homogenous alloy, which should tell you an XRF mesurement is a rough indication at best in that case.
Drlling a small hole in a bar to measure inside the bar eliminates any surface contaminants being measured.
The difference of 4 percent purity between 92 and 88. Its a guess.
Drill a hole on each side, measure each, compare and that will give you an idea of the purity and how well the metals are actually mixed.

I dont think the little balls were wet in a 1100 degree C melting bath. That would have turned into steam really fast.
Water also stop the temp. from going over 100degr. C until all is evaporated.

Martijn.

 

[michael1311]

Hi Martin,

Cheers, but, I'm talking about nitric acid not melting and XRF.

 

[Martijn]

Yes, I understand your point of view.
But, you are basing your conclusions on an XRF surface measurement after smelting your recovered gold, correct?
So your conclusion can be off, the 92% bar could actually be only 89% and the 88% bar could actually be 91%.... something to think about..

Where you gone wrong, I don't know for sure, maybe too little HNO3 to start with, so not all base metals were digested? Did you add a little more HNO3 after first digestion was done and waited for a reaction?

Maybe an initial melt bath that was not homogenous enough causing areas in the initial gold lower than 75% base metals in it? That could have resulted in the alloy not being digested properly. Refining with AR would reveal that. You could have a blob of undigested PM after AR.

Dirty Crucible? (don't mean to insult you but these things do happen) with flux remains and base metals?

Melting your recovered gold is almost never a good idea if you want to refine it further. Small and spongy material has more surface are for the acid (HNO3) to work on.

I hope this helps you a bit.

Martijn.
(edited for correct percentages and silver to base metals change)

 

[FrugalRefiner]

I have access to XRF at work. I melted a 500g alloy, The composition was roughly AU 25%, AG 45%, CU 25%, 5% other (mostly ZN with some PD, FE, PB)

The first refine to test I used 100g of this composition which came out at 99.00%

The second refine I used 400g, the weight after the Nitric leach was 132g.

Assuming your XRF on the feed material was correct, doesn't it seem odd to have ended up with 132 grams of gold from the 400 grams of feed material in your second batch? Whether it was too little nitric in your nitric leach, or as Martijn has suggested you had some areas in your material where the gold shielded some of the base metals from being digested by the nitric, it sounds like you still had base metals left in your second batch. That would explain your final purity problem.

As Martijn has mentioned, following your nitric digestion of the base metals, the best practice would have been to dissolve the remaining material in AR, then selectively drop the gold with your choice of reducing agent.

Dave

 

[michael1311]

Hey Martin,

No I didn't add more Nitric in the 1st digestion. I did 2 digestions, on the 2nd one I waited for the reaction/red fumes to stop and steam come out from under the watch glass then decanted it and washed it.

Maybe I have done my nitric digestions procedures wrong? What would be best practice?

I am pretty confident the 25% alloy was homogeneous

 

[Martijn]

Your best option would be refine your recovered gold bar in Aqua Regia.
Dont use too much nitric.
To have more surface for the acid to work on you could pour shot and then digest.

Cool your Auric Chloride with ice cubes and filter cold.

Drop with SMB and follow Harold's washing procedure step by step.
https://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=325

Melt your washed powder in a brand new crucible with a cleaned torch tip or in a furnace in a (a closed with a lid?) clsan crucible.

Please share the XRF results and some pictures here.

I would love to see that shiny gold bar with crystals and a nice pipe :G

Have fun. Martijn.

 

[michael1311]

Thanks Martin, I am trying to avoid AR for now until my skills are better. I am happy to achieve 99.00%

I've been told by other members here only using the nitric should achieve this?

 

[nickvc]

When using just nitric you need to give the acid plenty of time and heat for it to do its work, lack of obvious fumes isn’t always a true indication of no dissolution, if your solution is boiling remove it from the heat and watch to see if bubbles still come from the material if so the acid is still working, if you use this method correctly you can achieve very good results , 995 can be obtainable.

 

[Martijn]

Make sure the base metal content is (lower?!?> wrong sorry!!) higher then 75% and stirr well before pouring (shot) this should ensure all base metals are digested properly in HNO3. So less then 25% gold should ensure complete digestion.

But why stay away from AR, yet digesting with Nitric? A nitric bath also creates dangerous fumes that need comparable attention. Then put the gold aside and learn how to do a nitric base metal digestion safe.
I believe you may have a false sense of safety with nitric.

Martijn.
(edited to correct lower to higher, and gold content remark... it was toooo early..sorry)

 

[g_axelsson]

Michael, as Dave pointed out, 400g alloy that only dissolves to 2/3 have an issue. Either there is too much gold and then the nitric isn't able to reach all the base metal as the gold is protecting it or all the base metal wasn't dissolved. The thickness of the material, uneven alloy or even problematic metals could be the problem.
Did you pour shots of the alloy so there were no thick pieces?

And as Nick pointed out, it can be hard to see if the acid is still working at the end. I usually pour off the acid and fill up with fresh acid and look for any changes in the color of the fresh acid. Silver doesn't give any color but copper and palladium does. I save the last batch of nitric and use it in the beginning the next time I inquart or for silver work.

Göran

 

[michael1311]

Guys thank you for the tips. Today I made sure I poured in shots of the 25% alloy as last time there were thicker pieces as suggested. The granules are smaller and not stuck together like last time.

I am going to try another batch tomorrow and have noted the tips with boiling/ bubbles. Do you guys recommend using the water/acid 1/1 or 2/1 (2 parts water, 1 part acid) ? Also for my acid calculations, lets say for example 750ml of Acid is required to dissolve the base metal. would I split it over 3 washes of 250ml each? Followed by a 4th wash to make sure to clear to then save and re-use?

Cheers

 

[nickvc]

In my opinion don’t worry about exactly how much acid you need just use the amount needed to complete the process, I would start with distilled water heated to almost boiling, enough to cover your shot and slowly add the acid and cover the beaker with a watchglass, after each reaction has slowed add more water as you reach the 50/50 point, when after an addition of acid very little reaction occurs cool and pour off the solution and start again with the same process.
Keep in mind no visible fumes doesn’t mean the reaction has stopped, once you reach that point boil the solution for a few minutes to see if it kicks off again.

 

[michael1311]

Hi Guys,

With your assistance and tips i'm now managing to successfully produce 99.5% gold with the Nitric acid from Jewellery scrap via the inquartation method.

I just wanted some pointers and guidance with the silver recovery. Currently i am just putting copper into the solution waiting a few days for the solution to turn blue with silver mud at the bottom of the beaker, then pouring and washing it through a vaccum filtration flask. The process is pretty slow and tedious and the silver mud is a pain to work with. Any pointers or tips for me to research to improve this part of the recovery process?

Cheers

Michael

 

[nickvc]

The hardest part in dealing with cemented silver is washing the acid off your recovered silver, for that use the largest vacuum funnel you have and do not overload the silver, bear in mind that with this process of inquarting you will also carry over small amounts of gold and any PGMs with the silver that were in the mix you can normally see a color change overtime as it becomes more grey, with the high price of Pd in particular recovering it should be a priority and a small silver cell should be easy to build and run to do it.