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Gold.refinery

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I tested with XRF some graphite powder after melting, from the bottom of the crucible.
I did a few tests from different places. In some places, XRF gave an error, but in some places it showed some base metals. Most of all showed Fe.
The pollution seems to be from here.

Some also suggested immersing the hot ingot in dilute nitric acid solution after Vaccum Furnace to remove white deposits on the ingot surface. Do you think with them?

Do you suggest a better way to melt a gold sponge than to melt it with graphite crucible in an induction furnace?

Is the conversion of pure gold into shots (granules) effective in the appearance quality of the ingot?
 
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FrugalRefiner

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My first thought would be to test a new crucible, if you have one, but I don't know enough about XRF to know if the result is reliable in this case.

Dave
 

4metals

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Did you XRF the dry gold sponge before you melted it to see the purity from the refining process? Are you using graphite molds or iron molds? We discussed making shot before casting ingots so you can weigh exactly to cast your bars. What does the XRF tell you about the purity of this shot before the bars are cast? First you have to determine when the iron came into the picture.
 

Gold.refinery

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Did you XRF the dry gold sponge before you melted it to see the purity from the refining process? Are you using graphite molds or iron molds? We discussed making shot before casting ingots so you can weigh exactly to cast your bars. What does the XRF tell you about the purity of this shot before the bars are cast? First you have to determine when the iron came into the picture.
We use graphite crucibles to melt.
We also use graphite molds for casting in vaccum furnace.
I tested more than 12 points of gold sponge with xrf. None showed Fe.
Is iron used in the structure of crucible graphite?
 

Durdane

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I tested with XRF some graphite powder after melting, from the bottom of the crucible.
I did a few tests from different places. In some places, XRF gave an error, but in some places it showed some base metals. Most of all showed Fe.
The pollution seems to be from here.

Some also suggested immersing the hot ingot in dilute nitric acid solution after Vaccum Furnace to remove white deposits on the ingot surface. Do you think with them?

Do you suggest a better way to melt a gold sponge than to melt it with graphite crucible in an induction furnace?

Is the conversion of pure gold into shots (granules) effective in the appearance quality of the ingot?
I recommend using a ceramic crucible instead.
 

4metals

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I have never heard complaints of refined gold being contaminated in a graphite crucible. I googled “iron contaminated graphite” and found articles on using iron contaminated graphite to clean up polluted water from both arsenic and chromium.
This begs the question of the source of the graphite used in your crucibles.
If you melt the gold sponge in a crucible and test the bar, then melt some sponge in your vacuum casting machine do they test the same for iron? I doubt both your graphite crucibles and graphite boats are similarly contaminated.
 

Gold.refinery

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I have never heard complaints of refined gold being contaminated in a graphite crucible. I googled “iron contaminated graphite” and found articles on using iron contaminated graphite to clean up polluted water from both arsenic and chromium.
This begs the question of the source of the graphite used in your crucibles.
If you melt the gold sponge in a crucible and test the bar, then melt some sponge in your vacuum casting machine do they test the same for iron? I doubt both your graphite crucibles and graphite boats are similarly contaminated.
On the advice of you and other members, we do not add any additives to pure gold sponges when melting.
Therefore, cricibles oxidize after melting and begin to pulverize.
(To melt the scrap, we cover the crucibles with boric acid)

I think like you, the type of graphite molds used in vaccum furnace is different and they do not oxidize because it is not oxygen.
I will test, I guess there is no problem with Fe in graphite molds.
What is the solution then?
Change crucibles
Or
Melting with gas and ceramic crucible
Or what?

What is the best way for a refiner to face this problem every day?
 

Palladium

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Pic of furnace and crucibles?
Who manufactures the crucibles and is there a data sheet for the crucibles or a website?
 

AMS-Pro

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Ceramic crucible with gas, not induction furnace
What kind of Gas/fuel are you using?

Petcoke, Oil, Natural, MAPP, Prop, etc.

We also use graphite molds for casting in vaccum furnace.
,
Possible contamination in the hot zone of your vacuum furnace?

Maybe from process induced contaminations such as carbon in the form of soot or tar, fluxes, air leaks, outgassing, or you have oil soaked insulation, etc. Something random and not detected in the Gold with the XRF but is a contamination of the hot zone could set off a chain reaction of sorts, resulting in a reading/reaction of Fe particles coming from parts in the furnace itself because of degradation maybe.

Do you regularly do leak tests, clean up cycles, or hot zone maintenance of your Vacuum furnace?



This sentence is the last edit after a couple edits. What I'm wanting to type is a little jumbled. I'm tired, with a lack of coffee, and about to go to sleep. I hope what I typed above makes some sense in what I am asking, or that what I'm attempting to convey is a reasonable enough explanation/insight to what may be a possible issue that needs to be addressed.
 
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Gold.refinery

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Maybe from process induced contaminations such as carbon in the form of soot or tar, fluxes, air leaks, outgassing, or you have oil soaked insulation, etc. Something random and not detected in the Gold with the XRF but is a contamination of the hot zone could set off a chain reaction of sorts, resulting in a reading/reaction of Fe particles coming from parts in the furnace itself because of degradation maybe.
I made a standard gold ingot and re-melted it in a vacuum induction furnace. There was no problem. Its surface became like a mirror.
 

Palladium

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Why do i get the feeling this guy just picks and chooses which questions to answer?
If you want help how about answering the questions we ask also. Information is a two way street. We are here to help as well as educate others. If all you want is to get the benefit that best serves your needs then you can hire someone for that, but wait.... that's what has you here asking for our FREE help! This is starting to piss me off.
 
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4metals

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What Ralph is trying to say, in his ever so subtle way, is you are the eyes seeing the problems first hand. We are not there and we can only rely on what you say and what you show us. We can only help you if we have a more complete picture of your issues. That means if someone asks for specifics or a photo it is in your best interest to answer. And if something is working for you after suggested changes it is something you should comment about. You have been given a lot of good advice here and should come out of this much more proficient at your job. But by you not taking an issue to completion and commenting about the changes, it gets frustrating for those trying to help you. If the people trying to help you get the idea it’s a one way street, with them giving but you only taking, they may very well just stop trying to help you. And where will that leave you? The guy who sold you the equipment wasn’t much help was he?
 

Palladium

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Telling it like it is has gotten me banned more times than i can count now. 🤣
Come to think of it it didn't work out for Howard to well with ABC in the end either!
:unsure::unsure::unsure:
 

AMS-Pro

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I made a standard gold ingot and re-melted it in a vacuum induction furnace. There was no problem. Its surface became like a mirror.
So because your "standard gold ingots surface became like a mirror after re-melt".
I have a few questions:
- Was this a one off happenstance, or are you now having to "re-melt" every ingot?
- If it was a one off happenstance, are you able to replicate the issue by choice or purposely?

I also of course would like clarification on if you're using gas, what kind if you are, and for what purpose?

The reason I ask is because some gas sources can cause contaminates, even if they're supposedly very clean burning.

For example, let's say you're using natural gas.
Natural gas:
- Is supposed to be a very clean burning gas.
- On occasion, it is possible to get dirty gas due to improper filtering, improper treatment before distribution, lack of pigging the distribution lines after a compressor station, and several other scenarios.
- There should be a filter in your facility that is routinely serviced, before gas would be distributed to any of your equipment that uses it.
- If you're running with a dirty filter, or no filter at all, there's a good chance that you would be sourced gas that will still have some particulate or liquid. It doesn't take much for the little bit of particulate, or liquid to get through and wreak havoc in some ways, or make you chase a contaminate problem that may only happen occasionally.

Edit: Spelling.
 
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