# Filtering techniques?



## autumnwillow (May 1, 2016)

I am really having problem filtering gold chloride even after dilution, its taking hours for a 6 troy oz on a 125mm buchner funnel w/ #3 Whatman Filter paper assisted by vacuum. I tried turning up the vacuum really high and I ended up with a hole in the filter. :| 

My primary contaminant is iridium and silver chloride.

What are your filtering techniques? What funnel size and what volume of liquid do you filter? 

Would stacking a Whatman #3 and a #2 filter work?


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## Topher_osAUrus (May 1, 2016)

autumnwillow said:


> I am really having problem filtering gold chloride even after dilution, its taking hours for a 6 troy oz on a 125mm buchner funnel w/ #3 Whatman Filter paper assisted by vacuum. I tried turning up the vacuum really high and I ended up with a hole in the filter. :|
> 
> My primary contaminant is iridium and silver chloride.
> 
> ...



Hoke tells us to let the silver chloride settle well, sometimes "for days" she says.
Then either-
-carefully pour, VERY carefully pour off, as to not disturb the sediment. Then filter once you reach the bottom.
-try a charmin plug (some use fiberglass)
-try a suction bulb (after settling) to not disturb the AgCl
-try a syphon (tubing and gravity)

What is your solution in right now? A beaker? A bucket?

I will sometimes tilt it, let it sit an hour...let it sit back upright for an hour... Tilt it again (like a 45 degree angle) let it sit an hour again. Then SLOWLY roll it to one side about 90 degrees....THEN sit it back upright again... REPEAT over n over (last "roll" session, i roll it the opposite way, so the powder is in the middle) 

After doing that, (depending on what kind of solution/sediment i have) I either slowwwewwly pour off, or use a suction bulb.

That last technique is hard to explain. But, I can maybe post a video if my description is too vague to help.

-topher


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## autumnwillow (May 1, 2016)

As much as I would like to follow your technique, I don't have that much time. Its either I get a bigger buchner funnel and filters or something is wrong with the way I am filtering.


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## acpeacemaker (May 1, 2016)

Do you stick anything under your filter. One of the mods several years ago (I believe it was GSP) told me to use some fiberglass screen like in windows and doors. My subject was with using glass frit.


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## Topher_osAUrus (May 1, 2016)

Yes, i remember reading that thread. 

Just a little fiberglass mesh (like window screen) will help from clogging up.

But, in this case i believe its a double edge sword, where it may allow the AgCl to flow through it.

What you could do.. Is just filter it quick, drop the gold, act like this is a first recovery. Then be very meticulous with the "second refining"

Lou gave that tidbit of wisdom to someone in another thread (im pretty sure it was lou)-if your crunched for time, that may be the best bet. As the 2nd refine usually has MUCH less solution since its significantly easier to dissolve powder pms


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## Smack (May 1, 2016)

Don't know why you think you have to filter your precipitated gold. If your following Harold's or Lou's washing technique (and it's clear your not) I don't see why you would be having a problem. What test have you done to determine you have those contaminants?


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## Palladium (May 1, 2016)

Your not going to beat the system! Procedures are in place for a reason. I filter thru a diaphragm pump with filter socks that are rated at 100psi plus and i still let solutions settle so the trash falls out before filtering. When filter papers clog the depth of the filter (Funnel) or the amount of solution the filter (Funnel) holds is not important. What's important is filter paper surface area exposed to the solution. The bigger the surface area the more area their is to filter before it clogs, but it will still clog. It is a double edge sword. Let it settle and decant.


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## nickvc (May 1, 2016)

I had filters from 6 inches to 24 inches and they still would clog up.
My best suggestion is to use a wick system for ŷour first filter.
Look up GSP thread on using a wick, it works. And then you use a proper filter to finish.


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## goldsilverpro (May 1, 2016)

Silver chloride, especially when it's been sitting around, is slow to filter. Sometimes it goes faster with a gravity filter than a vac filter - a vac filter can tend to pack it. At one place I worked I did about 100 oz at a time in a big porcelain buchner. Slow as molasses. It might take hours, a drip at a time. I discovered that about a 1/2" layer of freshly made silver chloride as an underlayer in the filter made it go 10 times faster (believe it or not). I kept a bucket of fairly strong silver nitrate near the filter. I dipped out a liter or so into another bucket, added enough HCl to drop all the silver and immediately filtered it. When most of the liquid was out, I put the AgCl I was working with on top. Big time saver, especially with large jobs. Rinsed fast also.


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## autumnwillow (May 1, 2016)

Smack said:


> Don't know why you think you have to filter your precipitated gold. If your following Harold's or Lou's washing technique (and it's clear your not) I don't see why you would be having a problem. What test have you done to determine you have those contaminants?



_I am really having problem filtering gold chloride even after dilution_
What I mean is 6 troy oz of gold chloride diluted in 3000ml. Not precipitated gold.
I know my contaminants because I made these alloys. They are karat gold.
You have been replying in my posts but it seems that you do not read the entire context very well, this might confuse other members reading.
Or maybe its just my English?

GSP's technique makes sense. I'll try that. If not, I'm off to a bigger buchner funnel and filters.


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## Smack (May 2, 2016)

Guess I read that too fast.


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## Anonymous (May 2, 2016)

The correct answer to your issue is to change your filter papers to number 1. 

They work perfectly. Enjoy.

Edit: Also get yourself a 375ml buchner funnel that takes 90mm papers- - more surface area.

Jon


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## autumnwillow (May 2, 2016)

spaceships said:


> The correct answer to your issue is to change your filter papers to number 1.
> 
> They work perfectly. Enjoy.
> 
> ...



_its taking hours for a 6 troy oz on a 125mm buchner funnel_

What is up with you guys? Hehe
I'll try the #1 filter paper. Then filter on the #3 after.


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## Anonymous (May 3, 2016)

ahh 125 mM my mistake. It was past midnight here when I was typing out advice on a forum.


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## 4metals (May 3, 2016)

> Just a little fiberglass mesh (like window screen) will help from clogging up.
> 
> But, in this case i believe its a double edge sword, where it may allow the AgCl to flow through it.



Almost right. On a porcelain buchner with paper on it the problem is the entire filtering area is limited to the sum of the area of all of those little holes so it's actual filtering area is not close to a 125 mm diameter filter. What the screen does is lift the paper just a hair so each little hole can draw from a greater area. When the paper sits flat on the funnel, the only suction comes directly through those holes. By lifting it just a smidge, that area is much larger. Just be sure to cut the screen so it is less than the area of the perforated section and not extending out onto the flat border. The flat border is where the paper seals to the plate and if the paper doesn't make a good seal particulates seep past the bad seal.


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## Anonymous (May 3, 2016)

Willow- Number 1 is perfectly adequate for removing silver chloride.


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## autumnwillow (May 7, 2016)

The fiberglass mesh makes a lot of sense. Since I usually just see the holes of the funnel clogging up, not the entire filter paper. It should help, but I still think that I need a larger buchner funnel as this is all a matter of surface area. What do the big guys use for filtration?


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## Anonymous (May 7, 2016)

I've never had to use a mesh. I use hot liquors where possible and the number one papers I mentioned. For extremely filthy solutions I sometimes pre filter using very rough paper such as coffee filters but it's rare that this is required.


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## autumnwillow (Dec 10, 2019)

Hi guys

Its been a long time since I've posted in this forum.

So I've bought this 300mm buchner funnel. For years I was doing it by gravity. But now that I've built a stand for it with the drain hole attached to a filtering flask. It works but holes get punctured when I increase the vacuum.

With gravity filtering I was not able to wash the chlorides/silver well. We used a 125mm buchner funnel before doing it by batches and we were able to wash the chlorides and silver well. With gravity filtering we end up with a fuming silver smelling like SO2 when melting.

So I was hoping somebody could suggest a good filter media for this?
I was thinking I could just buy a polypropylene cloth rated at 15um more or less then just cut it to size covering the funnel in excess so I could just easily pull out the filter media along with the filtered material but I couldn't find any online.


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## Shark (Dec 10, 2019)

I have put a filter paper in the bucher funnel then added about an inch of clean sand on top of it then add another filter over the sand of a slightly larger size. The sand allows for a larger area of the filter to work while allowing the filtrate to pass through. Now I usually just set the vacuum to a safe level and let it work, or try the rope idea, it works pretty well on large or stubborn solutions.


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## autumnwillow (Dec 10, 2019)

Shark,

Rope? Is that GSP's wick technique? Already applied it. 

I think the filter paper is just too thin. 
There's this thick whatman filter paper but I find it too expensive for just filtering AgCl


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## kernels (Dec 10, 2019)

You could try something like this -> https://www.youtube.com/watch?v=i3jYu61eLEo but it might be a pain to separate your AgCl after filtering ?


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## Deano (Dec 10, 2019)

There are a lot of filter cloth suppliers on line, just type in "filter cloth".

You need a woven form of polypropylene with a thickness and weave similar to canvas, filter cloths are usually rated by volume of air passing through a fixed area of cloth.

When you cut the cloth to fit in the funnel the best way is to cut 80% of the circle and then make a tail from the other 20% so that the tail can lead up over the wall of the funnel and down most of the outer side of the wall.

This allows you to easily remove the cloth when required.

Make sure that you spend time to get the cloth circle cut so that it fits snugly against the walls of the funnel.

Cloth is usually sold by the square metre, it is fairly cheap and a square metre will last you many years.

I use them on pressure filters and get around 10 years per individual cloth when running both strong acids and alkalis through them.

Deano


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## snoman701 (Dec 11, 2019)

Deano said:


> When you cut the cloth to fit in the funnel the best way is to cut 80% of the circle and then make a tail from the other 20% so that the tail can lead up over the wall of the funnel and down most of the outer side of the wall.
> 
> This allows you to easily remove the cloth when required.
> 
> Make sure that you spend time to get the cloth circle cut so that it fits snugly against the walls of the funnel.



Is there a trick to getting them to lay flat in a buchner? 

I bought the filter cloth, but never could get it to lay flat, without tape.


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## autumnwillow (Dec 11, 2019)

Deano said:


> There are a lot of filter cloth suppliers on line, just type in "filter cloth".
> 
> You need a woven form of polypropylene with a thickness and weave similar to canvas, filter cloths are usually rated by volume of air passing through a fixed area of cloth.
> 
> ...



I used a filter bag today and it worked well. I think I'm gonna sell this big buchner funnel and just go for pressure filtering in a filter bag.

Put all chlorides in the bag, squeeze the liquid out. Put the bag in a clean water, squeeze the liquid out until I get the same or close TDS reading as the clean water. Its more work than this buchner funnel but it can get the job done in 30 minutes. Buchner funnel with a filter paper is taking about 8 hours just to finish a 5 gallon bucket.

Where can I shop for pressure filters? I think a 10L one will serve me well.


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## Deano (Dec 11, 2019)

There are many forms of filter cloth which can be used as a base for filter papers.

What you are looking for is a soft cloth with a weave and thickness similar to coarse soft canvas, this type will lay flat in the funnel without needing taping down.

Do not try the smooth sided calendered cloths, they are too stiff to lay flat properly.

Deano


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