# Vacuum Filter



## dmarth10 (Sep 24, 2008)

Hey Guys,
I was boiling my cats in AR for 2.5 hrs. Now comes filtering time. I started slowly poring my pot into the coffee filter inside a funnel, into a flask. Wow, that takes forever. Almost like its sealing any holes. I heard about the vacuum setup for filtering. I just cant find it anywhere when I search. Its always giving me the wrong results. Can anyone recomend where to find these setups or how to possibly construct one?

I appreciate it,
David


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## Noxx (Sep 24, 2008)

You need a filtering flask, a stopper, a buchner funnel and a vacuum source. Look on eBay.


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## Harold_V (Sep 25, 2008)

dmarth10 said:


> Hey Guys,
> I was boiling my cats in AR for 2.5 hrs. Now comes filtering time. I started slowly poring my pot into the coffee filter inside a funnel, into a flask. Wow, that takes forever. Almost like its sealing any holes.



That's what you can expect from the process. Vacuum filtering isn't the answer. It, too, will slow to a stop. That very problem is why I never messed with cats, although that was many years ago and I had adequate refining business so I could afford to ignore them. 

Have you given any thought to simply allowing contents to settle by gravity? It's slow, too, but effective. 

Harold


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## Lou (Sep 25, 2008)

This is a case when a filter press does magic.

Filter press removes initial sediment.

Then vacuum filter with good paper or frit to get a clear solution.


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## lazersteve (Sep 25, 2008)

David,

If the material is crushed filtering is going to be difficult no matter how you try it. 

Harolds advice is dead on for using gravity and siphoning the solution off of the crushed cats. Several washes (3-4) will be required to get the extracted solution out of the crushed material. This will increase the volume of your solution considerably. 

If you are processing whole honeycombs the problem is typically the black carbon sludge that floats in the solution as the pgms are extracted. For this situation it pays to follow a two step filtering process. This is still slow, but not as slow as a single stage filtering. It has the advantage that it will benefit from a vacuum setup.

Step one is to filter out the bulk of the carbon sludge. This is best accomplished with a setup of two large coffee filters. The two filters only catch part of the sludge and allow the very fine residues to pass through. vacuum assist will speed this process. Be sure to throughly rinse your carbon sludge to free any trapped pregnant solution.

Step two involves a second filtering through a packed neck funnel to catch the very fine material that passed through the first filtering stage. The packing can be made from unscented charmin toilet paper or glass wool. The technique is known among garage chemists as a 'charmin plug' for obvious reasons. The trick to the packed neck funnel is that the plug must not be too tight so as to slow the process tremendously. Yet the plug must be tight enough not to allow the fine particulate to pass through.

Here's how I pack a 1 quart plastic funnel neck:


Tear off 4 sheets of the tissue and fold them so that the long outside edges of the paper are brought halfway towards the centerline of the strip. 
Fold the ends in about a half inch to hide the rough edge.
Fold the strip in half lengthwise.
Loosely roll the folded strip into a cylinder with all the folds towards the inside of the roll.
Fold the top third of the plug over to form an upside down 'J' shape with the cylinder. The J shape prevents the plug from being pulled through the funnel and also prevents fine particulate from migrating through air spaces in the plug.
Push the plug into the large opening of the funnel and slide it into the neck of the funnel. Be sure the 'J' shape does not unfold and the curl of the J is towards the large part of the funnel.
Use a glass rod to seat the plug gently into the neck of the funnel until the tip of the plug just exits the bottom of the funnel where the drip comes out. Be sure the neck of the funnel is filled with the plug and no large air spaces exist in the top area of the plug.
Test the flow by adding a few (20-30) mL of water into the funnel. Enough to saturate the plug and produce dripping from the exit end. The drip rate without vacuum assist should be between 1-2 drops per second. 
Test the wet plug with vacuum assist and confirm that, when the top of the funnel is covered with your hand, the plug does not get pulled out of the end of the funnel. 
Pour any remaining water out of the funnel and begin the filtering process.
The filtered solution should come through 100% free of particulate and transparent. If particulate makes it through you will need to repack the funnel tighter and filter again.
Rinse the plug with several mL of clean water after the last of the solution filters through.

With a little practice this procedure will become second nature and will improve the quality of your precipitates. Glass wool will simplify the procedure as it will not require any special folds, just pack the neck, test the flow rate and filter. Glass wool may not resist some acids, maybe Lou will comment on this as I have not used it.

For smaller funnels a single sheet of toilet paper will produce a good plug.

The above procedure works extremely well for me on a daily basis.

Steve


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## goldsilverpro (Sep 25, 2008)

*(A)* Here's a method a friend of mine used for difficult-to-filter material. I used it a few times and it worked pretty well. He used a plastic colander for the funnel and put about 10-20 large restaurant sized coffee filters in it, to start with. When the filter started clogging, he lifted the top paper slightly, carefully punched a small hole or two in the bottom of it, raised it carefully and allowed the liquid to drain into the second paper. Most of the solids stay in the first paper. He then removed the first paper and repeated with the second paper. Fresh unfiltered solution was added as needed. Eventually, everything gets filtered.

*(B)* Here's one that I invented. It worked great for most anything, but especially sludges. Get a piece of cloth that is impervious to the solution you're filtering. I found that heavy polyester worked the best. I got it at Wal-Mart. You'll need a strip about 1" wide and 3 or 4 feet long. 
(1) Place an empty 5 gal. bucket on the floor. 
(2) Wet and squeeze out the strip of cloth with water. In a second bucket, run the strip of cloth across the inside bottom, up the side, and over the edge. It should hang over the edge about 2', or so. 
(3) Add the sludge that you want to filter to the second bucket. Be careful not the disturb the strip of cloth. Don't fill it more than about 40% full.
(4) Place a clean third bucket on the floor, next to the first bucket.
(5) Place the second bucket in the first bucket, at an angle, so it stays on top of the first bucket. Adjust the angle of the second bucket so that the sludge is near the lip. You may have to wiggle the second bucket carefully, side to side, to make the sludge sit smoothly.
(6) The end of the strip of cloth should hang into the third bucket. The end of the strip must be lower than the bottom of the first bucket. Clear filtered solution will soon start dripping off the tip of the cloth into the third bucket.

The most difficult thing I've ever filtered was the black gelatin sludge off of x-ray film. I once loaded about 2 gallons of this sludge in the above filter system. By morning, the sludge was nearly bone dry - very slightly damp. For a rinse, I could have added water to the sludge, mixed it well, and then repeated the filtering.

The cloth never clogs. Instead of catching the particles, it removes the liquid through the cells of the cloth. It uses the principles of capillary action and it also siphons the solution through the cells.

This is only one of the many arrangements of the "wick" filter that I came up with. It might go faster if, instead of a strip of cloth, one used a piece of cloth about a foot wide. The cloth hanging over the edge could be cut in 12 strips an inch wide. In my experiments, I found that, if the numbers of drip points was increased, it went faster.

Since I wanted to filter aqua regia with this, the first cloth I bought was polyester. After "wick" filtering, the AR solution was faintly cloudy. This could possibly have been remedied by using cloth of a higher thread count.

*(C)* Another way is to blend a filter aid with the sludge before filtering. Diatomaceous Earth (DE) is commonly used. Or, you make a slurry with some DE, filter it, and then place the sludge on top of it. These methods sometimes work and sometimes don't work. I never cared much for it. 

*(D)* There are also chemicals that, when added, will improve settling. I think they are called agglomerating agents. One of the alums is an common example. There are many of these and the success of most is dependent on the solution composition. When you can find one that works, it can work quite well.


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## lazersteve (Sep 25, 2008)

GSP,

I love the wick filter, I'm going to try it on my next filtration.

Steve


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## goldsilverpro (Sep 25, 2008)

Steve,

Keep me posted on it. I only worked with it for a couple of months - at the tail end of the last refinery I had. 

I started playing with it when I watched the solution climb up the filter paper, while filtering. I did quite a few experiments with various things such as widths of cloth, distance between the top solution level and the drip point, number of drip points, temperature, how high it would climb etc. I think I still have the data some where. I didn't get a chance to work with other types of cloth or wicking media. The first cloth I happen to pick worked great.

Since then, I've learned that there are special wicking materials made of plastics, ceramics, and other materials. These might be interesting.

I have always thought that this has potential. I can visualize a setup of a much faster application of it being used on a commercial scale - a sort of one stage filter press. I successfully made a small version of it and filtered another extremely hard-to-filter material with it, with no problems - metal hydroxides. It would work great on silver chloride. Also, I came up with a portable filter for prospectors. 

I have a list of about a dozen projects like this that I never followed through on. Too many ideas - too little time.


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## dmarth10 (Sep 25, 2008)

Wow,
Lots of response. Ok, Harold said allow the junk to settle. Now, once settled, Im still going to need to filter just to separate the clean solution from the junk at the bottom. Also to get all the liquid out from the sediment. Do you think I should use a large pipette to suck off the liquid? Then filter the little remainder?


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## Harold_V (Sep 26, 2008)

Simply siphon off the settled solution, using a small (3/8" works well) vinyl hose that is primed with clean water. When you near the bottom, adjust the level of the discharge end of the hose so it's just barely below the intake, which is held near the bottom, but above the crud. That slows down the transfer to a dead crawl, so it won't pick up the undesirable material. When you have transferred the majority of the values, the small amount remaining can then be filtered easily. Simply wash all the sediment to a filter and give it a day or so. 

If you have a lot of trouble getting the solution clean, one of the tricks you can use is to precipitate everything with zinc, then give the entire lot a good boil in dilute HCl. You'd decant the bulk of the solution before the HCl boil, by the way. That will re-dissolve all the things you don't want, which can then be siphoned off after settling once again. A trick that can yield excellent results is to incinerate the precipitate before the HCl boil. You may be surprised at the amount of crud that will be eliminated. Incineration is a very important step in processing. 

If you choose this route, after boiling, fill your beaker with tap water and stir well, so you dilute the acid solution. It will likely settle almost instantly, but allow enough time for the fines to hit the bottom. Be certain to check the solution with stannous chloride, to insure that you have not lost any values. If you have, pour the solution to a stock pot for recovery. 

Harold


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## skippy (May 9, 2011)

Just thought I'd give this thread a little bump, as I have found the cloth wicking works extremely well for separating the last water from the sludgy muck in some of my cat leaching solutions. The polyester is brilliant - the sludge doesn't stick to the material or plug it up and it just keeps dripping nice and constantly. It's a simple gem of a technique.


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## goldsilverpro (May 9, 2011)

skippy said:


> Just thought I'd give this thread a little bump, as I have found the cloth wicking works extremely well for separating the last water from the sludgy muck in some of my cat leaching solutions. The polyester is brilliant - the sludge doesn't stick to the material or plug it up and it just keeps dripping nice and constantly. It's a simple gem of a technique.



I'm glad that someone got some good use out of it. It's not for everything but, for hard to filter sludges, it works great. Just set it and forget it.


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## Shaul (May 9, 2011)

There's a type of Polyester material that's been found to be highly effective in wicking water for use in 'Earthbox'-type (self-watering) container gardening.

This same material might be just as useful here.

It's called: Pellon Thermolam Plus #TP971F (Fusible Fleece).
Available at hobby and craft stores, also maybe Target, Lowes, etc.


Shaul


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## Joeforbes (May 14, 2011)

Is there a way to just wash the cat material before processing it with out washing away values as well?


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## skippy (May 14, 2011)

Sure Joe, some people have suggested using a hose or a pressure washer to blast away carbon on the surface of whole combs. There may be some values washed off the surface that you can recover by letting any solids settle out of the water.
There shouldn't be any water soluble pgms unless someone has sold you something which has been leached already. 

Shaul, thanks, I bought a bit of that pellon material and it works quite well as a wicking material. My first attempt at the wick idea I used a polyester hawaiian style t-shirt, but the pellon is better. 8)


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## samuel-a (May 15, 2011)

did i get it right chris ?


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## goldsilverpro (May 15, 2011)

samuel-a said:


> did i get it right chris ?



Perfect, Sam. The lower the end of the strip on the left, the faster it will tend to drip, but there is a limit. You might set the 2 right hand buckets on a low table (or on a 4th bucket with a lid on it and some water in it for weight) and the other one on the floor.


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## samuel-a (May 15, 2011)

This is geniusly simple idea !

I'll defiantly give it a try next time a large sludge will need filtration. I already have a candidate in mind.

Thanks for bumping this thread.


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## goldsilverpro (May 15, 2011)

The first time I tested it I made a slurry of very fine clay and water. I figured that would be a pretty good test. Worked great

After doing this a couple of times, you'll think of a lot of different ways to set this up. For example, I found that the more drip points, the faster it goes. You could use a wide cloth covering the bottom and up the side and slit it several times on the exit end.


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## samuel-a (May 16, 2011)

Hi Chris

I just introduced this idea to a slurry of filter papers/wiping tissues treated with very dilute hot AR (I hate burning stuff).
So far seems to be working just fine with polyester wick, tomorrow morning I'll see the end results hopefully.

Thanks again, i was shivering from the idea of vacuum filter it.


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## qst42know (May 17, 2011)

Filter paper pulp vacuum filters better than you might imagine. It no longer has a structure that clogs.


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## rusty (May 5, 2012)

Wicking works.


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## goldsilverpro (May 5, 2012)

Gill,

Thanks for posting the photo. It's great to see the wicking filter used with different setups. It really does work, especially for hard to filter sludges. Recently, I used it for x-ray film emulsion, which quickly clogs in normal filtration, and it worked great. The wick can be slow, but it never clogs or stops.


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## rusty (May 5, 2012)

goldsilverpro said:


> Gill,
> 
> Thanks for posting the photo. It's great to see the wicking filter used with different setups. It really does work, especially for hard to filter sludges. Recently, I used it for x-ray film emulsion, which quickly clogs in normal filtration, and it worked great. The wick can be slow, but it never clogs or stops.



The wick is actually fairly quick if your not standing there in anticipation, the wick in the picture siphoned out 5 gallons in two days, I've already added a fresh rise to the pulp.

The beauty is that wicking leaves fine slimes behind. I also learned that of you leave cemented PGM blacks for a month you need a chisel to break it loose from the bottom of the pail.

I do have a question though, the pulp I'm working with is milled cat combs leached with AR for over a year. From what I gather home recovery is not 100 percent there's going to be some platinum group salts left behind.

What if I added some iron to cement any values left behind in the pulp then incinerate, I'm thinking that I should add the incinerated pulp to the virgin pulp I have milled that I plan to ship out for refining.

I've also thought an assay of the spent pulp would be a good idea, this could save me from unnecessarily contaminating the virgin pulp. Thoughts anyone.


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