# Filtering



## goldsilverpro (Apr 9, 2007)

*An excellent, simple filtering setup.* Buy a standard plastic filtering funnel from Walmart's auto department. I prefer about a 6" dia. one that I can use for everything. For good refining filter papers, my favorite (and fairly cheap) is S&S 596. They may not make them any more. If they do, you'll have to order them from the factory. Second best and, the cheapest paper around, is S&S Sharkskin. Don't buy Whatman #42 or another company's equivalent. They're OK but, are expensive and, slow as molasses. A perfect size paper is twice the depth of the top part of the funnel. If you use coffee filters, you can buy big ones cheap from a restaurant supply. You can also buy big stainless spoons, for things like stirring stuff while burning small amounts or, for uses while working around nitric acid. Leave most of your money at home when going to a restaurant supply.

Get a very clean or new bucket. I don't like using soap to clean buckets, except to remove oils or grease. I use a Scotch Brite pad and water. Soap residue can generate much foam when doing reactions that foam even without using soap. One time, I filled 7, 7 gallon plastic trays with foam from 2 gallons of aqua regia. To get those heavy gold powder residues off of the inside of a bucket and into the filter, first cut about a 3/4" square of Scotch Brite. Put a squirt of water in the bucket and scrub the bucket with the wet pad. Rinse the pad and fingers into the bucket with water. Using a lab type squirt bottle - all others are worthless - tilt the bucket towards you and rinse down the inside of the bucket. Still maintaining the tilt, move it to the filter and rinse the gold from the bucket, into the filter. It doesn't all come out easily. 

Get a square piece of 1/2" or 3/4" plywood, sized to cover a bucket. In the middle, cut a hole so that the funnel will sit in it with an inch or two sticking out the top of the board. Most of the funnel will stick out the bottom. Instead of plywood, you can cut a hole in the top of a bucket lid. If you're using coffee filters, open them up flat. Fold the circle in half. Fold it again but, this time, don't fold it all the way - stop about 1/2" short on a regular size coffee filter. Open up the paper so that it's cone shaped and place it in the hole in the bucket. Put it all on the bucket. 

Before filtering, wet down the paper, slightly, with the squirt bottle. Pour in whatever you are filtering to near the top of the paper. Keep it filled.

When filtering most things with a lot of volume, like aqua regia solutions, it's much easier and faster to let it settle, siphon off as much clear solution as you can, and then filter only the remaining residues. When you learn how to do it, siphoning can eliminate 90% of your filtering time. Filtering is always the bottleneck in refining operations. There are many tricks to speed things up.

When you first start filtering things like aqua regia solutions or gold mud, some of the solids will almost always pass though the paper. After a while, the paper will start clogging and the solution coming through will run clear of solids. You can tell when it runs clear by observing the drips at the tip of the funnel. When the drips are running clear, transfer the board and funnel to another clean bucket and re-filter the stuff in the first bucket. If you don't do this while filtering aqua regia, your final gold will be off purity. It's a good habit to get into, no matter what you're filtering.

I always have 6 or 8 of these bucket/funnel setups going, for the various things that always seem to require filtering. They're cheap and are easy to make.

I've owned several vacuum filters in my lifetime but, for most things, I prefer the filtering setup like I've described above. Vacuum filters are expensive and are a pain to use. They pull the solids down tight on the paper and seem to clog fast, especially with things like solver chloride. With certain plastic vacuum funnel designs (Bel-Art comes to mind), it's almost impossible to get the paper to seal. But, when you're filtering very large volumes of unsettled solutions, vacuum filters can speed things up. 

A friend of mine had a unique way of filtering large volumes. He put about 15 restaurant coffee filter papers into a plastic kitchen colander. When the top filter paper became clogged, he would carefully remove it, exposing a fresh paper. It was messy but, it worked pretty good.


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## lazersteve (Apr 9, 2007)

I started out with the large automotive funnel type originally, but they are really slow near the end of the filtration process.

Now I use a jumbo plastic food strainer from Wall Mart. It fits exactly in the mouth of a 5 gallon bucket edge to edge as seen here:







I bought some 12"+ diameter coffee filters to line it with:






*That's a quarter in the center of the filter.*

Typically 4-5 does the trick on keeping the fine particles out of the solution. I also reuse the lower filters until they get clogged. The one drawback is that as the filter fluid level receeds, the drip slows. To compensate for this I gently tilt the filter to one side of the bucket lip so as not to cause a spill over the top of the filter. This allows the solution to filter thru the less clogged side of the filter.

They work great and I've been using them for over a year now. 

Great post! There are so many topics the forum hasn't even scratched. It would be great if more members posted information on how they are doing things (filtering, melting, etc.).

Steve


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## MacMasterMike (Apr 9, 2007)

Hate to pull a TLR (too long didnt read) on another one of your awesome posts but what do you think of a filter flask with buchner funnel and vac, goldsilverpro? Im new to the hobby and I met someone at back yard metal casting.com who is helping me out and learning me and he led me down the path of using chemistry glassware. Having only used this the one time I played with silver it ran well except for the small quantites i was using always getting stuck on the filter paper. Also either i need practice or a better was bottle but getting stuff from one container or another is needlessly time consuming at times it seems.


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## Harold_V (Apr 10, 2007)

goldsilverpro said:


> For good refining filter papers, my favorite (and fairly cheap) is S&S 596. They may not make them any more. If they do, you'll have to order them from the factory. Second best and, the cheapest paper around, is S&S Sharkskin. Don't buy Whatman #42 or another company's equivalent. They're OK but, are expensive and, slow as molasses.



I ran the full course of filter papers over the years, and narrowed down my choices to a very small few. I used, exclusively, Whatman 32 cm #2 for filtering my gold chloride for the first refining, and never anything but a Whatman 32 cm #5 for a second refining. I was paying around $50 for a pack of the #5's back in the early 90's, but in my opinion they were worth the money. The reasons are obvious when you filter regularly. Particularly using Sharkskin, which I used for filtering polishing wastes, too much gets through the filter, and allowing solutions to settle isn't always a faster way. If they are inclined to filter poorly, they are correspondingly difficult to settle. It's far better to address the problem than to try to live with it. How you process your material initially dictates how well it will filter. There are washes one can do before dissolving gold that insure filtration. It took me a while to come to terms with that, but I had no problems filtering solutions once I did my homework. Remember, I had filters running continually----24/7/365-----with rare time off. You learn to do it properly, or your work never gets done. 



> Get a very clean or new bucket.



This is one area where you and I differ totally. In my opinion, plastic has no place in the gold process-----aside from dealing with solutions of base metals or the use of proper lab funnels, often made of plastic. Never for precipitation. I don't even recommend beakers be used that have scratches when it comes to precipitating gold. It has an affinity for surface defects and often adheres doggedly to such imperfections. Plastic would be a real nightmare under such circumstances, and anything you did to it would only encourage the problem for future use. When scraping down the sides of a beaker, a plastic policeman should be the tool of choice, to avoid damaging the beaker. You can then deal with the small area of the policeman that gets gold encrusted. 

While I realize that most guys do this for fun (that was my objective at first), there's still money in it, and the cost and convenience of proper lab ware is one of the bargains as compared to values of extracted metals. I strongly encourage readers to buy proper labware-----beakers (and proper watch glasses) in keeping with volumes you intend to process. Use an unscratched beaker for precipitation. Don't even use glass stirring rods in it---they leave miniscule scratches that are trouble. 



> Get a square piece of 1/2" or 3/4" plywood, sized to cover a bucket.



If you choose this system of filtration, be certain to NOT discard the plywood, which, over time, will become heavily contaminated with values. Incineration and processing of the ash will make an almost complete recovery. Learn to always recycle anything that comes in contact with precious metals. It's an amazing savings plan. 



> When you first start filtering things like aqua regia solutions or gold mud, some of the solids will almost always pass though the paper. After a while, the paper will start clogging and the solution coming through will run clear of solids. You can tell when it runs clear by observing the drips at the tip of the funnel. When the drips are running clear, transfer the board and funnel to another clean bucket and re-filter the stuff in the first bucket. If you don't do this while filtering aqua regia, your final gold will be off purity. It's a good habit to get into, no matter what you're filtering.



Yep-----I did that even though I used Whatman #2 paper. It is very good at filtration, however, so if your preliminary work has been done properly, flow is usually not a problem. 



> Vacuum filters are expensive and are a pain to use.



Agreed, but there are applications where they are the best choice, and by a wide margin. I used a large one for washing silver crystal from the silver cell. It made that job much easier, and allowing the filter paper to dry released all but the tiniest of silver bits. The paper, naturally, was recycled, so there was no loss. 

A Buchner is almost mandatory for filtering palladium that has been precipitated from solution using sodium chlorate. It's eager to go back into solution, so I filtered it almost immediately after precipitation, first cooling the beaker slightly by submerging it in cool water. I found it to be the best possible way to handle the precipitate. 

Nice report, Chris!

Harold


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## goldsilverpro (Apr 10, 2007)

Man, nobody is agreeing with me today.



> Remember, I had filters running continually----24/7/365-----with rare time off. You learn to do it properly, or your work never gets done.


Me, too



> This is one area where you and I differ totally. In my opinion, plastic has no place in the gold process


I'll argue till our dying days about the merits of *white* plastic buckets. They're cheap, unbreakable, and safer to handle. You can even heat their contents (aqua regia) hot enough to dissolve karat gold, if you put them in a hot water bath.

My first 10 years in the business, the companies I worked for all used Pyrex. After that, in my first refinery, we used Pyrex. In all these cases, we found the biggest beakers available, the 4 liter size, too small, so we used big Pyrex 5 gallon and 7.5 gallon battery jars. These cost, at the time, about $100 each. The glass thicknesses on their bottoms was very uneven and, therefore, they would break easily and often, especially with direct heat. The first company put the jars into a tray made of 1/4" sheet lead, to catch the solution when the jars broke. They heated the aqua regia with a titanium steam table. In my refinery, we heated the jars on a 6' gas restaurant grill. We put a very heavy asbestos cloth between the jars and the grill to distribute the heat. Still, there was breakage. I can't tell you how much gold solution I have seen on the floor.

The last place I worked, during my first 10 years, found a local glass fabricator, who made us up about 20, 3.5 gallon Pyrex jars that were actually very hard to break. These took the heat, were easier to handle than the bigger battery jars, and were generally terrific.

In 1980, I found enlightenment, when I was the technical guy for Labash metals in Newbury Park, CA. Louie, the owner, was the best refiner I have ever known. I credit him with much of my knowledge. He ran a lot of karat gold and had at least 12, 4 liter aqua regia beakers set up, on individual hot plates. Each beaker had a lid with tubing running out of it and the fumes ultimately went through a fume scrubber. All dropping of gold was done in white plastic buckets. The operation was smooth, efficient, and produced an amazing amount of very pure gold. Don't forget, 1980 was the year of the giant gold and silver boom. We always had people waiting in line, to sell us scrap, when we opened up in the mornings. Louie was also the world's champ when it came to cleaning dirty gold in the furnace. He also had big rolling mills to roll out the karat gold bars very thin. This made the aqua regia operation go very fast. We rarely had to shot the gold. We had 12 silver cells that produced a total of about 5,000 ozs. per day. Even with all this, we had enough scrap to keep the cells going for several months. Before the boom, we charged $0.25 to refine an oz. of silver. During the boom, we got $7.50 per oz. The good old days. White plastic buckets and de-lidded plastic drums were the mainstays of Louie's operation. I'll never refine without them. Different strokes for different folks. There's more than one way to skin a cat. And, of course, you should always look before you leap.


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## aflacglobal (Feb 9, 2010)

8)


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## Irons (Feb 9, 2010)

MacMasterMike said:


> Hate to pull a TLR (too long didnt read) on another one of your awesome posts but what do you think of a filter flask with buchner funnel and vac, goldsilverpro? Im new to the hobby and I met someone at back yard metal casting.com who is helping me out and learning me and he led me down the path of using chemistry glassware. Having only used this the one time I played with silver it ran well except for the small quantites i was using always getting stuck on the filter paper. Also either i need practice or a better was bottle but getting stuff from one container or another is needlessly time consuming at times it seems.



I like the Buchner funnels. I have several sizes of glass frit,up to 600 ml. I use borosilicate glass filters inside the funnel to act as a prefilter to keep from contaminating the frit. the Whatman 934 AH is rated at 1.5 micron with retention down to .3 and they are very fast, and also expensive. A box of 90 mm filters is around $100 but they are reusable and very little sticks to them, even PGMs.. The problem is the volume of solution that can be filtered without constant attention.

The ceramic Buchner funnels work but the perforated plate doesn't pass liquids as well as a glass frit. The coarse frit works best with the glass filters.


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## aflacglobal (Feb 9, 2010)

That gives me an idea. I have some 5 gallon 5 micon polypropylene water filters. I wonder if i can put this in my 5 gallon ap buckets and then drop the other bucket with the holes into it. Like bagging an anode but a bucket instead. That way instead of all the filtering i can just move the top bucket and pick the filter up with all the gold flakes inside drop the bucket back in and keep on processing without having to stop and filter the whole solution. 

Will it work. I have a plastic drum full of ap. Hummmm.


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## Irons (Feb 9, 2010)

aflacglobal said:


> That gives me an idea. I have some 5 gallon 5 micon polypropylene water filters. I wonder if i can put this in my 5 gallon ap buckets and then drop the other bucket with the holes into it. Like bagging an anode but a bucket instead. That way instead of all the filtering i can just move the top bucket and pick the filter up with all the gold flakes inside drop the bucket back in and keep on processing without having to stop and filter the whole solution.
> 
> Will it work. I have a plastic drum full of ap. Hummmm.



I saw some big ones for sale on Ebay for $10 ea. It works well. You can prefilter a lot of solution in a short time. I'm sure GSP is familiar with them, since they were made for the Plating industry.

http://tinyurl.com/yjpyz6j


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## aflacglobal (Feb 9, 2010)

I bought 10 for $20 off ebay last year.


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## Irons (Feb 11, 2010)

aflacglobal said:


> I bought 10 for $20 off ebay last year.



La vida me chinga!


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## Barren Realms 007 (Feb 11, 2010)

Irons said:


> aflacglobal said:
> 
> 
> > I bought 10 for $20 off ebay last year.
> ...



Hey English please, remember what the higher ups said a few days ago. We don't want you getting kicked off.


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## rewalston (Jun 10, 2010)

Harold_V said:


> This is one area where you and I differ totally. In my opinion, plastic has no place in the gold process-----aside from dealing with solutions of base metals or the use of proper lab funnels, often made of plastic. Never for precipitation. I don't even recommend beakers be used that have scratches when it comes to precipitating gold. It has an affinity for surface defects and often adheres doggedly to such imperfections. Plastic would be a real nightmare under such circumstances, and anything you did to it would only encourage the problem for future use. When scraping down the sides of a beaker, *a plastic policeman* should be the tool of choice, to avoid damaging the beaker. You can then deal with the small area of the policeman that gets gold encrusted.
> 
> 
> 
> Harold



ok I admit I'm having a major brainfart here....Harold I've seen you mention the use of a plastic policeman before but for the life of me I have no idea what you are talking about...can you please explain..


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## Barren Realms 007 (Jun 10, 2010)

rewalston said:


> Harold_V said:
> 
> 
> > This is one area where you and I differ totally. In my opinion, plastic has no place in the gold process-----aside from dealing with solutions of base metals or the use of proper lab funnels, often made of plastic. Never for precipitation. I don't even recommend beakers be used that have scratches when it comes to precipitating gold. It has an affinity for surface defects and often adheres doggedly to such imperfections. Plastic would be a real nightmare under such circumstances, and anything you did to it would only encourage the problem for future use. When scraping down the sides of a beaker, *a plastic policeman* should be the tool of choice, to avoid damaging the beaker. You can then deal with the small area of the policeman that gets gold encrusted.
> ...



A plastic spatula.


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## rewalston (Jun 10, 2010)

ah a plastic spatula make a lot more sense than what was going through my mind.....


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## Harold_V (Jun 11, 2010)

rewalston said:


> ok I admit I'm having a major brainfart here....Harold I've seen you mention the use of a plastic policeman before but for the life of me I have no idea what you are talking about...can you please explain..


As has already been suggested, they're just a plastic spatula, but a specific one. I used to find them in chemical supply catalogs, listed as policemen, when I was actively refining. Those I used were ¼" in diameter, about ten inches in length, and had a triangular blade on one end, maybe 3/8" wide, with a square one on the other end, maybe ½" wide, with small corner radii. They allowed for scraping down the sides of beakers when gold grew there. 

In spite of scrupulously clean glass, when you precipitate large volumes of gold, using SO2, there's a serious growth of gold near the discharge tube, and upwards. It often comes off in a sheet. Rarely does it adhere strongly, but if the surface is abraded, it can lodge very securely. I had to use AR to remove traces of gold when I'd inadvertently use a scratched beaker. For that reason, I always used new beakers for precipitation only, never for any of the preliminary operations. When I lost one of the well used beakers, I'd demote one of those in use for precipitation, replacing it with another new one. 

Harold


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## joem (Nov 13, 2010)

Has anyone used a hepa filter to filter smb drop?


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