Determining the contaminant.

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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
 
anachronism said:
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
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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.
 
A final sonication with 70% hot sulfuric acid can be used to clean up the gold markedly in purity.
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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.
 
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.
 
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
 
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.
 
salman1122 said:
how much smb should be added to AR?
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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.
 
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.
 
As Lou said Belart makes nice tabletop buchner funnels, but they are available with a perforated plate and a Fritware porous plate. Make sure you get the perforated plate. That is the plate with the drilled holes. The fritware porous plate does not have visible holes and as they age and you get sloppy, the pores get clogged and are tough (if even possible) to clean out.

You can choose either plate fixed (welded in) or removable. I have always had good luck with a welded in plate but some refiners swear by the removable plates as well, so it is a personal preference.

Belart claims the removable plates are for precious metals recovery but if you are accumulating values that have gone through your filter media (or under the edge of your filter media) you need to work on your technique.

The holes in the perforated plates are available in two sizes. If you choose the larger hole size you may need to back your filter paper with cloth sheet material to prevent the vacuum from blowing a hole in your paper (if filtering hot this is a bigger issue).

https://www.belart.com/buchner-table-top-funnels.html

Another nice tool if you are using a tabletop buchner is a vacuum plate. It is basically a rigid piece of polypro that covers the top of the funnel and is sealed with a gasket. In the center is a fitting to connect to a suction hose which allows you to pull a vacuum on the filter and put the hose in the liquid you want to filter. The suction will pull the liquid through the hose and into the funnel and you will not have to lift and pour. iShor makes one of these systems but they are super simple and easy to make your own for substantially less money.

https://www.ishor.com/shor-buchner-vacuum-plates-and-gaskets
 
I hope justin sees this reply.
Brilliant stuff.
He was just talking about something identical to the polypropylene cap and hose design recently on another thread.
 
Topher_osAUrus said:
I hope justin sees this reply.
Brilliant stuff.
He was just talking about something identical to the polypropylene cap and hose design recently on another thread.
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Yes that is perfect.
I have bid on tabletop buchner funnels but had not thought about simply using a plate and four threaded bars to form a vacuum.
Much thanks.
 
The 300$ 26cm inside diameter is similar to a 240mm 130$ Buchner funnel?
I guess I'll stick with the funnel type first not unless we process heavier lots. Silver can wait. Heh. I'll go buy the 36" when our lot sizes increases. Hopefully the 240mm will speed things up. Thanks for the advice guys!

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Would a #4 filter paper for silver chloride and silver powder filtration then a #5 for any gold solution/precipitate filtration suffice?

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autumnwillow said:
Would a #4 filter paper for silver chloride and silver powder filtration then a #5 for any gold solution/precipitate filtration suffice?

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I think I've seen that combo used willow. But then again if the solution is still not Crystal clear there will still be contaminates. I'm still poor as far as equipment goes and still use coffee filters. Yea I know guys. But anyways I filter until the contaminates fill the pores in the filter paper and then I'll continue filtering until my AuCl is clear. Even with coffee filters via a lot of filtering you can still get a really pure product. The clarity of your solution will tell you a whole lot.
 
Just noticed that silver chlorides bypasses a #1 filter. Proceeding with a #4 filter will not be good. I think a #5 will be enough for aucl. We used to use a #42 and a #2. This #1 whatman filter is the worse filter that I have used. Very slow, clogs easily and some precipitate bypasses the filter.

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