the amazing impossible to filter clean solution!

[cnbarr]

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.

 

[goldsilverpro]

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.

 

[Palladium]

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.

 

[cnbarr]

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.?

 

[Palladium]

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

 

[cnbarr]

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!

 

[goldsilverpro]

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

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

 

[cnbarr]

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.

 

[cnbarr]

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

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

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

 

[Palladium]

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

 

[Palladium]

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!

 

[cnbarr]

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.

 

[goldsilverpro]

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.

 

[Palladium]

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.

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.

 

[cnbarr]

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

 

[cnbarr]

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.

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.

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.

 

[Palladium]

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

 

[cnbarr]

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.

 

[Palladium]

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.

 

[cnbarr]

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.