# Need help regarding filter paper...



## sugush01 (Dec 21, 2008)

What type of filter paper is good for gold refining? Grade? Size?






Edited for clarity.


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## Lou (Dec 21, 2008)

This relies upon your reducing agent and on which metal you're precipitating. Moreover, it depends on what you consider an acceptable loss. Additionally, it also depends on your skill and understanding of thermodynamics--there is a right way and a wrong way to precipitate materials.

As for filter paper, generally speaking, Whatman Grade 1 is good. You want a medium filter paper that will retain precipitates over ~30 micron, qualitative is fine. Finer precipitates can require some very slow filters. 

Also depends on if you're doing quantitative or qualitative work.


What I use for filtration is a separable fritted glass funnel and each are labeled specifically for which metal I'm doing and which purity it ought to be. This means that one is used exclusively for platinum, one for palladium, one for rhodium, etc and reduces risk of cross contamination. This requires some investment, but it is well worth it. It allows for rapid throughput, no worries about fibre contamination, and allows you to maximize your yield of precipitates because of easy removal. Also, they are easy to clean (boil in aqua regia and then bake out at 400*C ). Millipore makes these. 

[img:370:424]http://www.textbookofbacteriology.net/Millipore.jpg[/img]


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## butcher (Dec 23, 2008)

I have not got that fancy yet.
I like to let solutions settle well sometimes day or more, then decanting (can pour off liquid), but I have a suction bulb like a turkey baster except smaller tip and larger bulb, to remove solutions not disturbing powders in bottom, then filter last potion through coffee filters pre wet with water).


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## goldsilverpro (Dec 25, 2008)

The best general purpose filter paper I've ever used for refinery operations is S&S 596. I used it for about 20 years, until the manufacturer, Schleicher and Schuell, stopped making it. I see some references to it on the internet, so maybe they're making it again. It was cheap, strong, medium retentive, fast, and quite acid resistant. When they stopped making it I tried everything, but could never find a substitute. About 15 years ago, I could buy 400, 50cm circles for less than $100, including shipping. I had to order it directly from the factory. I used it mainly in a large vacuum filter and in large funnels. I fluted them for the funnels and actually got pretty fast at it.


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## Harold_V (Dec 25, 2008)

goldsilverpro said:


> The best general purpose filter paper I've ever used for refinery operations is S&S 596.


Is that the Sharkskin paper? If so, I used it routinely for filtering values from polishing wastes. I agree---it was a paper I couldn't get along without. I didn't prefer it otherwise, concluding that it allowed too much to pass through the filter. 

I preferred Whatman #2 for filtering my solutions after evaporation. The only exception was in re-refining my gold----at which time I changed to a Whatman #5. 

With my limited experience, I never found a paper that served better than Whatman. Their quality appeared to be the best in the industry. 

Harold


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## goldsilverpro (Dec 25, 2008)

No, it's not S&S Sharkskin. It's much thicker. In a pinch, I've used a lot of Sharkskin but never really liked it. I started with Whatman 42. It's very retentive, slow as molasses, and quite expensive. When I discovered S&S 596, it was like a breath of fresh air. I have used many of the Whatman papers, but never liked their prices. I used a lot of large papers, 50cm and larger, and the Whatman price on those is out of sight.


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## qst42know (Dec 25, 2008)

Whatman bought S&S, Reeve Angel, and then General Electric bio science bought them all. Some of there best lines are still available though they are all one company now.


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## Harold_V (Dec 25, 2008)

goldsilverpro said:


> No, it's not S&S Sharkskin. It's much thicker. In a pinch, I've used a lot of Sharkskin but never really liked it.


I agree-----it allowed far too much to pass through, but when separating solutions from polishing waste, it had no equal. It was the only place I used Sharkskin, and found other papers would fail miserably. The strength of Sharkskin placed it well above anything else I ever encountered. 



> I started with Whatman 42. It's very retentive, slow as molasses, and quite expensive.


My experience parallels yours. I used 42 only with a Buchner. Virtually all of my filtration was done by gravity, using Nalgene funnels that accepted 32cm circles. 



> I have used many of the Whatman papers, but never liked their prices.


I agree, they were not cheap. I paid in excess of $50 for a box of 100 32cm circles when purchasing the Whatman #5. Whatman #2 was less expensive, around $30 for 100 circles. Considering the cost for filtering what was often several thousand dollars worth of gold, I wasn't the least bit concerned with the price. What did concern me was the end result, and I was never disappointed with Whatman. Assuming their formation remains unchanged with the change of ownership, I'd recommend them today.

Harold


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## Lou (Dec 25, 2008)

This is why I use the fritted glass disks--they're expensive, several hundred dollars depending on the specifications, but it is a one time expense. Harold, I too have a set of 32 cm Buchner funnels but I find myself using the frit filters (only 12 cm across) because they are far more convenient in removing the precipitate, no worries about contamination, and much cheaper in the long run. 


I don't process in anywhere near the quantity you two did, so for my purposes, I have found nothing better. Unfortunately, a 50 cm frit would probably cost several thousand dollars.


I have somewhere on one of my computers a PDF of all the various different filter papers Whatman makes. If I can find it, I will be sure to attach it to this thread.

Lou


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## Harold_V (Dec 26, 2008)

Lou said:


> This is why I use the fritted glass disks--they're expensive, several hundred dollars depending on the specifications, but it is a one time expense. Harold, I too have a set of 32 cm Buchner funnels but I find myself using the frit filters (only 12 cm across) because they are far more convenient in removing the precipitate, no worries about contamination, and much cheaper in the long run.


Heh! I folded my papers and used gravity with a Nalgene 60° funnel. I should have made that clear. My largest Buchner was something like 24cm, and I'm trusting to memory here. I found that *if* I did the proper preliminary work on my wastes (incineration accompanied by a wash with HCl), I had no difficulties filtering solutions. I could filter a huge volume of gold chloride (as much as 75 ounces in solution) easily in a day, usually far less. That's using a Whatman #5, which was dreadfully slow and retentive. 

I must admit, Lou, I am not familiar in the least with the fritted discs. Never seen one, but I have heard of them. Didn't even know what they were for.

I do have a question, however. You mentioned removing precipitate. While that was my practice with palladium and platinum, I never separated gold from solutions by filtering. I simply decanted via a small vinyl hose, then did my washing procedures. Once the gold consolidated nicely, the solution could be poured off with no risk of losing any of the gold. That, of course, works only when the gold is quite pure. It it's heavily contaminated it rarely clumps up. Gold precipitated from filings was usually far too dirty to do so. My re-refined gold was so eager to become a solid that it was difficult to keep it in a powdered configuration. 



> I have somewhere on one of my computers a PDF of all the various different filter papers Whatman makes. If I can find it, I will be sure to attach it to this thread.


That might be interesting for readers to see. I know it holds my interest. I experimented more than enough before landing on my choices--and am secure in the idea that Whatman provided the best filter papers, at least for what I was doing. 

Harold


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## mhmmd1375 (Jul 31, 2018)

Hello my friends.
What filter is suitable for filtration of precipitated gold chloride with sodium methabi sulfite?


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## nickvc (Jul 31, 2018)

You should try and avoid filtering your gold precipitate and simply decant the acid and wash in the beaker with water and a hot Hcl wash followed by more hot water rinses, this should help clump together your gold and you should be able to dry it in the beaker on your hot plate but use a watchglass in case it spits.


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## RickRag (Nov 20, 2018)

Hi Nick,

I screwed up and filterd my last refinement into a Buchner for washing etc. Now I have the gold powder agglomeratated on the filter. What's the best way to proceed? I intend to re-refine the gold to get a higher purity as the scrap from which it came (and the solution) was quite dirty. Shoukd I incinerate it, burning up the filter and melt melt the powder into an impure ingot and re-shot it? Or can I add some sulfuric and dissolve the paper, then pour that off and rinse in a beaker as I should have.

Rick


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## butcher (Nov 20, 2018)

Why not just dissolve the gold (putting the filter in solution), then filter this decanted solution, pouring the old filter and insoluble salts in the last stages of this new filter.

Sometimes adding shredded filter paper to a filter can improve difficult to filter solutions.

You can handle these several different ways.


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## Shark (Nov 20, 2018)

When I was using coffee filters I would pour the pulp from the old filter in first to help clog the pores of the coffee filter so it would hold some of the finer materials first. With a bit of practice, you can learn when to pour the pulp, first or last. butchers advice to run the whole filter has worked well for me for several years, even now that I use better grades of filters.


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## anachronism (Nov 20, 2018)

butcher said:


> Why not just dissolve the gold (putting the filter in solution), then filter this decanted solution, pouring the old filter and insoluble salts in the last stages of this new filter.
> 
> Sometimes adding shredded filter paper to a filter can improve difficult to filter solutions.



100% bang on great advice. 8) 8) 

Jon


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