Determining the contaminant.

[anachronism]

Sure, but that willow pattern on the button above is a sign of contaminants too, no pun intended of course!

Edit- from what I've been told that's possibly PGMs

 

[autumnwillow]

Sure, but that willow pattern on the button above is a sign of contaminants too, no pun intended of course!

Edit- from what I've been told that's possibly PGMs

True, that could have been Pt/Ir. That was my very first refine. I only have 2 pictures of gold that I have refined before. How about the 2nd picture of my first post? Judging it by the way it looks does it seem to have any contaminants?

I can't really assay my gold properly though, can't find a proper assay lab in my country that can perform a fire assay/ICP/etc. I also don't have the equipment to perform a fire assay.

 

[autumnwillow]

I scanned my phone and this is another picture of a bar I used to make:

 

[Topher_osAUrus]

A second dissolve will help give clues to what the contaminant is. From the color of the solution after precipitation.

The excess smb could have caused contaminants to drop with the gold, or they could have got dragged down mechanically.

When gold is in powder form, a redissolve and precipitation can be done within a day.

I cannot say for sure that it is your problem, but, a single refine is sometimes considered to just be "recovery"

The first bars you produced could have ended up more pure because it may not have had the same contaminant, may not have been overdosed with smb, or you may have just got lucky. Not sure :lol:

 

[anachronism]

The second pic of the first post looks fine to me to be honest. You say you poured that into a mold?

I think you're worrying over things you don't need to worry about because none of it looks badly contaminated.

By the way over dosing with SMB doesn't really cause that many issues. You're cleaning your gold with HCl and water washes anyway.

 

[allenp]

You may have a bit of silver left which can cause the effect. After you add the sulfamic acid you should triple the volume with very cold water to cause silver chloride to precipitate.

 

[anachronism]

I do not sell gold at the moment as we are in need of it. We are actually buying.
I own a jewelry shop and we only want to use the finest gold possible and If ever I decide to sell gold I can ask for a premium since most of the gold traders here supply about .990 - .995 gold purity at 24k market price.

Hi Willow I see where you say that you can ask a premium but if that's the case you're going to need a way to know that your gold is above this. It's entirely possible that it's over 99.9 right now, but then again it might not be. What it looks like doesn't really cut the mustard at the high end of purities.

Jon

 

[Lou]

Follow the wash procedure and be sure to remove lead. Do not over use reducing agent and you will make high purity gold.

A final sonication with 70% hot sulfuric acid can be used to clean up the gold markedly in purity.


You can remove the ugly appearance with ammonium chloride sprinkle when the gold is hot. It is a very fumey process.


Feathering in your gold is due to Pt.

Oxidation color can be due to most likely copper or iron. My suggestion is to wash your gold powder much better as most impurities are by physically absorbed processes rather than included/co-reduced with the gold.

 

[autumnwillow]

Solved.

The 2nd refine was due to clay crucible contaminants as what Goran have mentioned.
We only changed crucible and followed the same process using the same chemicals.
Also my previous posts regarding steel mold contamination is ruled out as we also poured this in the same steel mold.
HCl is the contaminant in our process, supply is from a swimming pool chemical store. Must be not that pure, everytime we use this we get a very strange AR color (cloudy and greenish).
We used the HCl from a drug store supply instead.

Results:

 

[anachronism]

Sorry but that gold is no purer than the previous pics. The surface visibly shows this. For reference look at my profile picture. I don't get how impure HCl was the issue when your precipitant is selective and your wash process further takes more impurities out.

Can you share how you came to this conclusion please?

Jon

 

[goldsilverpro]

Sorry but that gold is no purer than the previous pics. The surface visibly shows this. For reference look at my profile picture. I don't get how impure HCl was the issue when your precipitant is selective and your wash process further takes more impurities out.

Can you share how you came to this conclusion please?

Jon

I would agree with Jon. Doesn't look too pure to me either - dull color, no crystal, no pipe. I would try to clean it up in the melt (simplest way) by alternating a pinch of niter (2 or 3 BBs) with a pinch of borax. Do this until the molten gold forms a mirror-like surface, with no white film. Shouldn't take more than 2 or 3 applications. If it doesn't clean up, re-dissolve in AR and re-purify it.

 

[4metals]

A final sonication with 70% hot sulfuric acid can be used to clean up the gold markedly in purity.

Lou mentioned this above but it seems nobody bit on it so maybe I should explain the process and the value of the technique in cleaning up gold that isn't quite up to standards.

About 5 or 6 years ago there was a discussion amongst the moderators about getting high purity gold in a single pass. Lots of suggestions were discussed but most involved chelation and that always throws a monkey wrench into waste treatment so, for me, it isn't worth the effort. Especially if there is something simpler.

I mentioned a method I had used which I called pulping. Basically it involves tumbling in a violently agitated tumbler, gold sponge and adding 25% concentrated sulfuric acid to 75% hot distilled water. I was working on a large project and looking to gas gold in a single pass from direct aqua regia digestions and get a purity of .9999. The way I was doing it was to gas the solution with SO₂ and stop before the drop was complete. The gold that drops first is cleaner and the gold assayed high first drop. The balance of the gold in solution was filtered off and the gassing was completed, resulting in the balance of the gold which required a second pass or re-refine. I put this gold aside and continued work on the first drop high purity process I was hired to implement. I have worked with gold all my adult life and because of that I have a sizeable mental block assigning value to piles of in process gold. So while I was blissfully playing with the single drop process, a pile of gold was accumulating which was worth well over a million dollars, probably closer to 2 million. The boss was apparently watching and noticed, after all it was his money. He came to me and asked me to please make that gold sale-able. Like yesterday if possible!

I took a sample of the sponge before treatment and then used the pulping process in a large oblique barrel with a blade mixer and did the sulfuric water thing and ran it for 15 minutes. Filtered, rinsed, and resampled the gold. The gold before the process was .999+ and the gold after the process was .99999. This was run in an ICP by difference. I had used the process before and knew it worked but never actually quantified how effective it was in the lab. Although the first few runs came out 5 nines, I would be satisfied claiming 4 nines which we consistently hit in production.

Since this was the gold dropped at the end of a SO₂ drop it was the dirtiest of the gold dropped. I realized we could drop it all with gas, forget the extra filtration step, and use the pulping to process the entire lot and bring up the purity. This process was effective at bringing .999 gold up to .9999 gold easily without major waste treatment ramifications.

Lou had never heard of this before and since he has a well equipped lab with all of the big boys toys he gave it a try. The thing is he didn't have the oblique barrel and he didn't have the gold quantity to require the big barrel anyway so he used ultrasonics to provide the agitation. He used the ultrasonic to process lots up to 2 kilo's or so in size of sponge if I remember correctly. And his testing also verified the usefulness of the process.

So now, with a more detailed description of sonification as Lou called it, a good rinse protocol, followed by the sonication process, this may be the answer to cleaning up your gold sponge before you melt it. You need to do this in a beaker because most ultrasonic cleaners will not withstand the hot sulfuric. And I think the time requirements go up with an ultrasonic as well, maybe Lou can refresh my memory on that detail.

 

[autumnwillow]

SMB is not selective.
Hcl was clearly the contaminant as this is the only thing we changed. It required more than 4:1 ratio. If I recall correctly we used about 12:1 hcl nitric ratio for digestion to complete when using the contaminated hcl.

Gold has no pipe due to slow cooling.
This gold was very shiny. As very pure gold is prone to scratches even with just a plastic brush it resulted in a dull color. Crystals are visible if you zoom in.
Pipe did attempted to form as shown in the bottom of the bar.

I will try sonification with sulfuric acid on the next lot and see if there is any improvement. Anyone reading this thread should be aware of the danger of using sulfuric acid at that concentration.

 

[anachronism]

Given that you don't get all the metals out when you use SMB it is therefore by definition selective. Yes you can get some drag down using it however it's still selective.

I appreciate that you think your HCl is causing the problems however I would respectfully have to beg to differ.

I've had exactly the same contaminated "look" on gold myself and it's turned out to be PGM contamination as has already been mentioned in this thread. Using a different precipitant on the second refine usually works for me to get the gold pure.

Jon

 

[autumnwillow]

I'm not asking for any appreciation.
We alloy the gold ourselves and know when there is PGM present in the lot. Most of what we processed that resulted in gold surface tarnishing did not have any PGM present.

Again. Only hcl was changed in the chemicals used and we got a better result.

 

[anachronism]

I believe something has got lost in translation here.

That given, it's apparent that my help is not wanted, which is fair enough so I'll bow out.

 

[autumnwillow]

My bad. Must've read it the wrong way. Driving and reading isn't good.

 

[salman1122]

how much smb should be added to AR?

 

[upcyclist]

how much smb should be added to AR?

Until gold stops precipitating out when you add it. Waiting for the last addition of SMB to settle out, having clean glassware, and having good lighting all help in this respect.

 

[autumnwillow]

Bump this topic.

The problem was filter paper grade. Used a #1 filter paper and moved to a #2.

I'll try to order a #5 next and might as well go for a larger buchner funnel as this is really our current bottleneck in the process. Any tips on the size that we need? We are currently using a 125mm.