# Filtering



## kroutonz (Feb 4, 2011)

I have a Buchner vacuum filter that I use, but the pgm powder was quite hard to get off the filter after it dried. I was able to get maybe 80% of the material, but that was alot of paper too. I decided to just throw the filters in the AR, but I'm wondering if theres a better way to get the powder off? Plus I know I'll have the same problem with the pt/pd salts.


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## Anonymous (Feb 4, 2011)

kroutonz said:


> I'm wondering if theres a better way to get the powder off?


You can incinerate the filters in one of steves melting furnaces.But if you decide to incinerate them make sure you place a lid on your melting vessel so you don't blow your values away.


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## lasereyes (Feb 4, 2011)

kroutonz said:


> I have a Buchner vacuum filter that I use, but the pgm powder was quite hard to get off the filter after it dried. I was able to get maybe 80% of the material, but that was alot of paper too. I decided to just throw the filters in the AR, but I'm wondering if theres a better way to get the powder off? Plus I know I'll have the same problem with the pt/pd salts.



Perhaps you should try decanting the liquid from the precipitates instead of filtering it?


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## kroutonz (Feb 4, 2011)

hm perhaps I'll try building a siphon rig and doing that next time. Does that mean I basically was suctioning too much and it got stuck in the filter, and that gravity filtering would be better after I decant?


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## Barren Realms 007 (Feb 4, 2011)

Pretty much most of the time you try to filter your solutions with PM solids residue in your solution you will get some in your filter and when you wash your filter it is unlikely that you will get all of them out of your filter. Letting your solids settle to the bottom of your container and siphoning the solution off with out disturbing your solids on the bottom is the best action to take. IMHO...


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## 4metals (Feb 4, 2011)

Your best bet is a combination of decanting to recover the majority of the solids followed by filtering in ashless filter paper. Ashless paper burns off leaving little residue and the material in the paper can be processed with your next lot.


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## HAuCl4 (Feb 5, 2011)

For platinum black obtained after ammonium formate reduction, which produces very fine powders, a cheap and easy solution is decanting most of the liquid, as previous posters have suggested, and passing the supernatant liquid through a "charmin plug" filter. After all is done and the filter is dry, I burned the paper with concentrated sulphuric acid to retrieve the little Pt particles that were stuck to the filter.
http://en.wikipedia.org/wiki/File:Sulfuric_acid_burning_tissue_paper.jpg


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## goldsilverpro (Feb 5, 2011)

Two new secrets from my repertoire.

You can put the gold, filter paper and all, in hot aqua regia. The paper pulps up, acts as a filter-aid, and the solution filters rapidly. Use several small rinses to get the yellow color out of the filtered garbage. Re-drop. This time, rinse the gold in the beaker. Gold refined twice settles much better and can easily be rinsed many times without pouring any gold off. As we speak, I am doing 20 oz using this exact method, with the addition of Harold's HCl leach, of course. I'm thinking of switching to 50/50 nitric, though. With the proper precautions, of course. I really think it's a better solvent than HCl. 

Although it can be very dangerous, I used to "wet ash" the gold, paper, and all, with very hot concentrated sulfuric and an occasional drop of nitric. When the nitric hits the hot sulfuric, little explosions occur - it's quite exciting. The gold comes out in basically one or two spongy pieces that are very easy to rinse. I would also imagine that this improved the purity of the gold. The more acid you are using, the more (geometrically) dangerous this is. I limited it to about 300-400 ml, which was enough to make a couple of filter papers or a good sized grasshopper disappear. I used it when a lot of dirty or fine gold was stuck to the paper. Don't try this without explicit instructions. There's more to it than I wrote.

For gold assaying purposes, I used to "wet ash" samples of ion-exchange resin. Works great. 

Chris


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## samuel-a (Feb 5, 2011)

goldsilverpro said:


> Two new secrets from my repertoire.
> 
> You can put the gold, filter paper and all, in hot aqua regia. The paper pulps up, acts as a filter-aid, and the solution filters rapidly. Use several small rinses to get the yellow color out of the filtered garbage. Re-drop. This time, rinse the gold in the beaker. Gold refined twice settles much better and can easily be rinsed many times without pouring any gold off. As we speak, I am doing 20 oz using this exact method, with the addition of Harold's HCl leach, of course. I'm thinking of switching to 50/50 nitric, though. With the proper precautions, of course. I really think it's a better solvent than HCl.
> 
> ...



Those are very useful process for filters treatment.
I'm using AR for filters regularly, and discovered that, if you will leave it for a week or so, the papers will disintegrate and settle at the bottom as fluffy white solids.

Although never tried wet ashing filters with PM's in it, i have done so when needed to remove stuck toilet paper out of some test tubes i was cleaning and it's working great, Hot sulfuric always scars me though...
I'm wondering, if there is the possibility to create nitrocellulose using the method you described? (Although flammable only when dry)


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## goldsilverpro (Feb 5, 2011)

If the AR is concentrated and hot, as it usually should be, the paper will "pulp" in an hour, or less. Paper towels don't "pulp" as easily. Every filter paper I've used does.


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## kroutonz (Feb 6, 2011)

Sounds good goldsilverpro, I'll see how my AR does on Tuesday with the paper pulp. I'm gonna try decanting and just use a small glass funnel for the last pt salts. Probably be getting some ashless filters as well soon. 

Also got some alumina crucibles coming in Monday for calcining/melting, so hopefully I'll have something to show soon.


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## goldsilverpro (Feb 6, 2011)

> I'm wondering, if there is the possibility to create nitrocellulose using the method you described? (Although flammable only when dry)



I think the sulfuric breaks down the paper, or other organic materials, to it's elements. The solution immediately turns black, which is the carbon in the paper. After awhile, the carbon is consumed and the solution clears. It essentially is like incineration. Thus, the term, "wet ashing". You are "ashing" it but there is no residue, at least with filter paper.

We've discussed this several times.
http://www.goldrefiningforum.com/phpBB3/search.php?keywords=wet+ashing&terms=all&author=&sv=0&sc=1&sf=all&sk=t&sd=d&sr=posts&st=0&ch=300&t=0&submit=Search

Concerning the cellulose, here's a quote from Lou in one of these discussions.


> Well let me say this then, when you put hot sulfuric acid and do the wet ashing like Chris suggested (indeed a very, very dangerous procedure), you're not dissolving the cellulose--it is being destroyed.



In the plating industry, the standard wet and gravimetric way of analyzing gold in cyanide solutions, is to wet ash a 5 ml sample in 100 ml of sulfuric in a 250 ml erlenmeyer flask - under the fume hood, of course. I guess I've done this so many times I am a little blase about it. It is a very dangerous process. The boiling point of concentrated H2SO4 is about 600F. Therefore, the solution keeps getting hotter and hotter and progressively more dangerous. When you get that hot, beakers are more prone to breakage. I always heat the sulfuric by placing the flask or beaker in a Pyroceram (or Vision) Corning Ware dish - there is no substitute for these dishes that I know of or would trust for this procedure.


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## wrecker45 (Feb 6, 2011)

grasshoppers have pm,s in them? :lol:


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## goldsilverpro (Feb 6, 2011)

wrecker45 said:


> grasshoppers have pm,s in them? :lol:



Of course not. It was a joke. I haven't done grasshoppers, but I have done dead flies, just to see what would happen. They just disappear and you end up with a clear solution. In Pulp Fiction, they supposedly got rid of a body with a few jugs of sulfuric, at room temp. In reality, it would probably take a large vat of very hot sulfuric to do that.


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## wrecker45 (Feb 6, 2011)

i was also joking. i have been told i have a twisted sence of humer. :mrgreen:


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## samuel-a (Feb 6, 2011)

wreker45, 
It was funny !


Chris, thanks for the insight.

Btw. Check your pm box


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