# the amazing impossible to filter clean solution!



## cnbarr (Jan 8, 2014)

I have a gold solution that no matter what I've done, wont filter clean, I've never seen anything like it. I started with spring pins (unfortunately don't have a picture available) from a custom built testing board, ran them through a nitric digestion. Then I filter the nitric off and collected all the foils and solids, they were still a bit dirty, possibly some Cut, Fe, Ni still in the mix, but I digested in AR and let settle overnight.

The first round of filtering captured the small amount of solids left, now is where the nightmare begins! I can't figure out what is finely suspended in the solution that keeps slipping through the filters, it runs right through like there's no filter there at all.

I've tried vacuum filtering, gravity, medium filters with and without fiberglass plug and charmin plug, it just won't filter clean, the solution runs right through like clean water. My last attempt at it I put seven filters in my buchner funnel and tried vacuum filtering that way, I ran it through 12 times and it is no cleaner then when I started, and I've filtered over 25 times with many different techniques. (see pics). 




Any help or thoughts on why this is happening is greatly appreciated, I've never experienced a solution that wouldn't eventually filter clean, this is a new beast for me.


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## goldsilverpro (Jan 8, 2014)

Doesn't look like much gold in the solution. Why it happened isn't important. Don't waste a lot of time trying to filter it. I would just drop out the gold from the cloudy solution. You probably will have to re-dissolve the powder and drop it again. No big deal.


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## Palladium (Jan 8, 2014)

Yep! that's exactly what i do. The particles will form neculation sites for the precipitant to trap and bring down with the gold. Once that is done you can redissolve it and it will almost always filter just fine.


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## cnbarr (Jan 8, 2014)

Hey GSP,

That's my intent to just drop it dirty and start over, but I'd really like to know what it is in the solution that slips through the filters so easily.?


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## Palladium (Jan 8, 2014)

I've had gold powder that was so fine it would do that!


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## cnbarr (Jan 8, 2014)

Palladium said:


> Yep! that's exactly what i do. The particles will form neculation sites for the precipitant to trap and bring down with the gold. Once that is done you can redissolve it and it will almost always filter just fine.



I've had more then my fair share of dirty solutions and have done just what you've done, but again never had one this cloudy that wouldn't clear up a bit with filtering!


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## goldsilverpro (Jan 8, 2014)

Palladium said:


> I've had gold powder that was so fine it would do that!



In this case, I don't think the cloudiness is gold.


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## cnbarr (Jan 8, 2014)

Palladium said:


> I've had gold powder that was so fine it would do that!



Don't you love it when that happens, I just decant it then let it settle in another beaker overnight, then redissolve.


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## cnbarr (Jan 8, 2014)

goldsilverpro said:


> Palladium said:
> 
> 
> > I've had gold powder that was so fine it would do that!
> ...



I don't think its all gold, but I know some of it is. I think it's a suspension due to impurities.


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## Palladium (Jan 8, 2014)

No i don't think it's gold either. I was referring to how fine some particulate can be.


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## Palladium (Jan 8, 2014)

Like you i ask questions to but sometimes the what works is more important than the whys. 
One day you will find the answer you seek grasshopper!


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## cnbarr (Jan 8, 2014)

Palladium said:


> I've had gold powder that was so fine it would do that!



I thought you were referring to a fine suspension after a gold drop that takes quite a bit of time to settle.


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## goldsilverpro (Jan 8, 2014)

By the color, I don't think the suspension contains any gold - no brown. Why would it? You just used AR. By the color of the solution, no yellow that I can see, I would expect little or no gold.


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## Palladium (Jan 8, 2014)

cnbarr said:


> Palladium said:
> 
> 
> > I've had gold powder that was so fine it would do that!
> ...



I was. On a side note. I have taken half a bounty paper towel and boiled it in solution until it totally pulps. Then filter that through your buchner funnel twice and it will clear things up sometimes. I've also used a sponge cut to the size of a buchner funnel and squeezed in to fit. You can pour from the top through the whole sponge and filter paper. I've tried lots of tricks for different problems.


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## cnbarr (Jan 8, 2014)

goldsilverpro said:


> By the color, I don't think the suspension contains any gold - no brown. Why would it? You just used AR. By the color of the solution, no yellow at all, I would doubt if there's any gold in there at all.



In the case of my solution, I know the suspension contains no gold at all, I was referring to Ralph's comment assuming he was speaking of a fine suspension after dropping gold.

But I do know my solution holds gold, it was just the product of a dirty AR digestion. I just dropped it with FeSO4, it should be close to 15g based on my calculations from previous batches of the same material.



Edit : to add picture


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## cnbarr (Jan 8, 2014)

Palladium said:


> cnbarr said:
> 
> 
> > Palladium said:
> ...



I've heard that before, probably from you actually now that I think about, but I've never tried it. I'll have to make note for future reference.


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## Palladium (Jan 8, 2014)

Please forward my cut to the save a cat foundation. :mrgreen: 
Did you add it dry or dissolved?


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## cnbarr (Jan 8, 2014)

LOL, nice Ralph, save the cats!

I'm lazy I added dry, I've never noticed a real difference between dissolving ferrous sulfate or adding it dry.


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## Palladium (Jan 8, 2014)

It's the small things you have to pay attention to that gives you the clues to answer your questions. I was just wondering how you did it for the sake of asking. If you add it dry you wind up with the precipitation occurring at the surface of the FeSo4 or in the liquid region around the FeSo4. If it's dissolved in the liquid you add to the solution it changes the reaction kinetics considerably. The neculation process is much faster for instance. Now this might not mean anything right now or for the particular situation, but what it will show you is the attention to detail and the difference in reactions that you can use to answer some of your questions or helping you solve certain problems.


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## cnbarr (Jan 8, 2014)

Your right I never really realized it till I read your post, but the precipitation does react quicker when when the FeSO4 is predissolved before adding it to the solution.

Another observation, after dropping this solution as the gold settles, the solution is just as cloudy as the picture I posted above. I figured as the gold settled, it would pull down some of those impurities with it and clear up the solution a little. But I've never precipitated from a solution this cloudy so it was just a theory.


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## Palladium (Jan 8, 2014)

That may be because the gold didn't use the particulate as a neculation site because it occurred at the FeSo4 surface instead as an overall reaction in the solution. The trash would act as a seed crystal for the formation of gold clusters to occur on the surface.


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## cnbarr (Jan 8, 2014)

That makes sense in way, but I still don't understand what's in the solution that made it so cloudy and why it wouldn't. Filter clean? Sometimes you just gotta roll with punches I guess!


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## Lou (Jan 8, 2014)

I'd be shocked if you get 15 g, but perhaps the color was stronger before all the filtration/dilution...


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## nickvc (Jan 9, 2014)

My guess as to the cloudiness is that you may have some tin in the mix, not much but some. If that's possible I'd suggest incinerating your gold powder and a good hydrochloric acid soak to remove any traces before redissolving.


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## g_axelsson (Jan 9, 2014)

I had a similar experience with what I believe was saturated lead chloride. It went straight through the filter and never cleared up. Then I remembered to add a few drops of H2SO4, a lot of white salt precipitated and suddenly I could filter it without problem.

Göran


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## cnbarr (Jan 9, 2014)

, all the pins were pressed into the board, clean no solder on any them. I always incinerate as a pretreatment just incase there are any oils or organics.

I processed 15lbs of the same pins a few days prior, with no issues at all, and I always add a bit of H2SO4 to help clear up any possible lead.

@Lou, yes my original volume was much lower, about 500ml, it increased to almost 2000ml after 30+ filterings.


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## Geo (Jan 9, 2014)

looks like an insoluble chloride. actually, it looks like AgCl. is there the possibility of some cross contamination with silver? maybe the pins had a component that was silver or was plated with silver. once the silver goes through the AR solution, the AgCl will be so fine that it will pass through the finest filters until you get down to lab filters made to filter 1 micron or less.


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## moose7802 (Jan 9, 2014)

I see that some people are guessing if there is Au in solution just by the color. I'm curious as to how that works when a lot of times doing ewaste we are working with very dirty solutions? I have a picture of a solution I literally just dropped and am waiting for it to settle so I wanted to see what everyone thinks about this solution. I know it's a little off topic but wanted to post the pic to this thread to see if the people who have commented on this would comment on my picture.


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## cnbarr (Jan 9, 2014)

Moose, to be honest I absolutely never judge gold content by the color, unless it is a very clean solution, but by that point I already know what I have!

Hey Geo, you were right! I took a 100ml sample to work today, and filtered it through a glass fiber filter, then digested the solids, and had it and the filtrate tested on the icp-oes. The digested solids were 285ppm silver and the solution held 122ppm silver!

The question is were did the silver come from and why didn't I see with the other two batches of the same pins I ran? 
I don't know where it came from but it was there, the only thing I can figure is if there were some other pins mixed in with them that I overlooked.


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## Geo (Jan 9, 2014)

well, it sounds like something residual. check the nitric bath that you digested the pins in. there may be a recoverable amount of silver in it.


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## freechemist (Jan 14, 2014)

> I see that some people are guessing if there is Au in solution just by the color.



To me, this is the key-sentence in this whole long thread, the most important word being "guessing". But I see no notion, like testing, SnCl2 and the like. Testing will show you, if there still are really values in the pictured remaining "amazing solution", and if it makes sense, therefore to continue working with it.


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## goldsilverpro (Jan 14, 2014)

Even with a lot of dissolved base metals, the presence of gold (yellow) in the solution can usually be seen, if you look at it in the right way. With good lighting, the yellow color of dissolved gold can sometimes be seen at the very edges, where the surface of the solution meets the glass. In a clear glass beaker or white plastic bucket, I draw some solution up on the plastic or glass an inch or two with a stir rod. With good lighting, if gold is present, you will momentarily see a yellow streak that is fairly slow to drain back into the solution. Assuming no PGM's are present, about the only other common thing in solution that will be yellow is iron. However, iron in solution doesn't produce a yellow streak on the glass or plastic. 

Believe it or not. It's always worked for me, but only as a quicky gross indicator, especially while I'm dropping gold. You still need stannous chloride testing to determine whether all the gold is 100% dropped.


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## moose7802 (Jan 14, 2014)

Thanks for the info Chris. It's always good to have those little tricks in the bag. I have noticed what you said though especially at the top of the solution where the AR meets the glass before dropping there is yellow and after it has faded to more of a green color. This is in AR solutions from ceramic cpus, not a clean AR solution. 

Tyler


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