Determining the contaminant.

[autumnwillow]

From my previous refining compared to now I have been getting poor results.

This was a gold refined previously.


This is the gold that I am getting now.


I have ruled out the following so far:
Steel mold contamination - I am now using clay crucibles until I get a nice surface finish

HCl not pure enough - I switched suppliers and the hcl that was provided was not fuming. So I assumed it to be contaminated or not pure. But this does not seem to be the problem as I have tried to HCl from another supplier. Although I did get better result now.

Filter paper - I had to switch to a #1 filter due to supply of #2 was not available. I was able to get my hands on a #2 though. Same result.

Come to think of it I was using a #42 filter paper. Maybe that's the problem?

Or maybe because I switched to propane/oxygen? Which I doubt could be causing the problem.

 

[Geo]

The bottom button doesn't look like it was in a liquid state very good before it cooled. It may not be enough heat.

 

[autumnwillow]

No the bottom one was a good refine. It was poured in a mold. The first picture is the problem. It has an orange stain.

Edit to add. Pictures mixed up in tapatalk.
The button/disc is the problem.
The other one was poured in a mold which is better. No surface stains (signs of oxidiation).

 

[anachronism]

How do you know it's not as pure please? Are you just judging it by its look or have you got a proper test result?

 

[autumnwillow]

How do you know it's not as pure please? Are you just judging it by its look or have you got a proper test result?

Just by the way it looks.
Pure gold will not have any form oxidation on its surface.

 

[autumnwillow]

Here's a higher resolution picture.

 

[g_axelsson]

Show us a picture of the melting dish/crucible used.

Göran

 

[autumnwillow]

This type:


I let the gold cool off there, smash it and retrieve the gold. I'm using a new one every time just to properly rule out whats causing the problem.
So far this is the 2nd button produced. Could it be the clay crucible? Maybe I should use silica?

I didn't dilute the solution to twice its volume, could it be this one? I didn't do it to save space for wastes processing as most of the washings will most likely double the volume. I'll try to dilute it on the next refine.

Water quality? Could a water with 3ppm reading from a TDS meter from an RO system cause the problem?

SMB used was at 62g, gold refined was only 49g, will 13 grams of excess SMB cause problems? This was processed in nitric first then AR.

 

[autumnwillow]

Oh wait, you wanted to see the flux color/stain. I'll check on that tomorrow but if I remember it right I think it was clear, not purple.

 

[g_axelsson]

Yes, pictures of the molten borax in the clay crucible would have been good, if it is clear or slightly purple it shows a low level of contamination. Dark borax is usually a lot of oxides.

What was the starting material?

Since you said the borax was clear, I wonder if it might be a slight palladium contamination. I don't know if it would show up as a slight discoloration on the surface. Maybe someone else can pitch in on that.

Göran

 

[anachronism]

As Goran said what's the starting material please.

Too many variables in here until we get more relevant data. By the way your crucibles don't look bad at all.

Edit: Goran is he's melted it properly there would be hardly any borax to show. The red tinge looks like collodial gold which is fine.

 

[autumnwillow]

Starting material was jeweler's bench sweep. I had a similar result from karat scrap.

Those crucibles are cheap but they are porous. I still prefer the silica crucibles but I won't be using one until I get a proper finish. I usually only use this type of crucible when I have soda ash in the flux.

Let me try to enumerate my process:
1) Inquart then shots.
2) Digest in nitric until no red fumes (2:1 water/nitric, then 1:1 nitric)
3) Wash 3x with hot water
4) Add HCL, add nitric
5) Sulfamic while hot
6) Cool the solution to precipitate contaminants
7) Filter
8) Add SMB in a cold environment (I put the flask in a bowl filled with ice)
9) Wash 2x hot water, cold water, cold HCL, cold water, hot water, cold water, cold ammonia, cold water, 2x hot water.

 

[g_axelsson]

As Goran said what's the starting material please.

Too many variables in here until we get more relevant data. By the way your crucibles don't look bad at all.

Edit: Goran is he's melted it properly there would be hardly any borax to show. The red tinge looks like collodial gold which is fine.

If I'm not mistaken the picture of the crucible is a similar one and has not been in use.

He wrote that he had to smash the crucible to get the gold out.

Göran

 

[autumnwillow]

Could small stains in a flask cause such? I'm also thinking it could be this one, I'll try to clean all the flask tomorrow before proceeding with the next lot.

Borax color is black, I just checked the button now and it was visible at the bottom of the disc.

 

[g_axelsson]

Inquarting should remove palladium, I don't think it might be palladium any longer.

Small stains in flasks and beakers shouldn't be a problem either. Just keep the beaker where you precipitate the gold and clean it spotless. But it never hurts to have clean glass ware.

Black borax in the crucible points to a lot of oxides in the final melt. Try to just melt borax without gold and see if it also turns black, then there is probably contaminants coming off the clay crucible.

I'm just throwing out a wild idea, I don't know even if this is possible...
Maybe contamination from the crucible. Are you using an oxidizing or reducing flame when you melt your gold? The red color of the crucible looks like iron staining. If some iron oxides are dissolved in the borax it might be reduced into iron and contaminate the button, showing up again when the surface is cooling down with oxygen from the air around it.
If this is the problem then it would be easy to just use more oxygen in the torch. Any iron oxide will stay in the borax.

If you pluck the button from the crucible while the borax is still fluid then you don't need to crush your crucible every time.

You can compare the color of your borax with the melting dish I'm using to melt fine gold. This was a first melt and the small prills were collected in the next melt. When a dish gets too contaminated I use it for inquarting or other melting to collect any remaining gold.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=61&t=19622&p=235911#p235911

Göran

 

[autumnwillow]

Ahhh. Come to think of it your crucible idea could be right. I may have solved the problem by replacing my Hcl supplier but if the crucible that I was using is contaminated I would probably not ever solve this problem. I use an oxidizing flame but there may be not enough borax used as I usually only use a pinch for 24k gold melts on a silica crucible. Ill try to use a lot of borax on the next process.

 

[anachronism]

I think you're over complicating this gents if you don't mind me suggesting that.

Willow what was the base material please?

 

[g_axelsson]

I think you're over complicating this gents if you don't mind me suggesting that.

Willow what was the base material please?

Starting material was jeweler's bench sweep. I had a similar result from karat scrap.

At... http://goldrefiningforum.com/phpBB3/viewtopic.php?p=268387#p268388

Göran

 

[Topher_osAUrus]

Maybe another dissolution of the gold powder would solve your problem. After the washes, of course.

 

[autumnwillow]

Maybe another dissolution of the gold powder would solve your problem. After the washes, of course.

I was able to produce buttons like this before:


Using the same process. No 2nd refines. Some of the materials that I am using have changed so it has something to do with them. The feedstock is also the same.

Edit to add:
The orange tint is just from a light source. That button is pure yellow. The button/bars produced now is clearly off from the buttons that I used to produce before.