# Filtration - Process Bottle Neck



## Macgiver (Aug 4, 2011)

Greetings list,

Thank you in advance for your time and consideration. I have searched the site and not found an answer to my issue.

I am dropping various salts out of solution and then vacuum filtering them off. I am using a five liter vacuum flask with a 500ml Buckner funnel and standard filter paper. My pump tops out at 21 inches of vacuum. Once full, the filtration slows to a drip and then it is all day and night to complete and dry the filter cake. I have ordered a larger B.funnel and more vac flasks but think there may be a better way.

Any suggestions? Does anyone know of a faster way to do this? Maybe a centrifuge type of system or??? I need to filter pounds of sludge from my syrup like AR and this is also slow. Every step is restricted because of this filtration bottle neck.

Thank you again.

CW :shock:


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## goldenchild (Aug 4, 2011)

Sounds like you are using a fine filtration as your primary (and possibly only) filtration. If you have that much salt that the filter clogs then do coarse filtrations working your way down to fine filtration. Or is it up to? Ex #1 paper to #2 paper to #5. You will have very little salt in the #2 paper and even less in the #5. Although they can be calcined you would probably be better off rinsing them into the stock pot.


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## Noxx (Aug 4, 2011)

Filter Press ?


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## goldenchild (Aug 4, 2011)

Yeah that too :lol:


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## 4metals (Aug 4, 2011)

Filter presses are very costly and if your chemistry is harsh, like AR is, you can ruin one quickly. 

Since you have a buchner and a decent vacuum, try a superfilter. Place a circle of fiberglass window screening on the plate of the buchner funnel, cut the circle so it is the same size as the hole pattern and when placing it make sure it stays centered. This functions to lift the paper just a hair off the filter plate and allow more of the paper to work. This is good practice whenever filtering. 

Next add a sheet of coarse filter paper and wet it to help it stay in place, next add a slurry of diatomaceous earth (yup, like they use in swimming pool filters) which is prepared by saturating a few scoops of the DE and quickly pouring it over the filter paper, level the layer so it is about 3/4" deep uniformly across the funnel. Finally place a sheet of coarse paper on top of the smooth DE layer. 

When pouring liquids into the funnel be careful not to erode a hole in the earth layer. I do this by putting a small cereal bowl on the top paper and pouring into that, it overflows and gently flows on to the paper. 

I have used this for some pretty nasty acids in need of filtering, sometimes it works great and other times it doesn't. worth a try.


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## goldenchild (Aug 4, 2011)

4metals,

Any diagrams or pictures of this setup? It's kind of hard to envision.


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## 4metals (Aug 4, 2011)

It's pretty simple actually


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## Macgiver (Aug 5, 2011)

Wow! You guys are all awesome. Thank you for taking the time to help me out. 

I will try the super filter as suggested. I will also try the various grade filters. I just returned after 3 days in the lab and literally 36 hours of filtration, and then more filtration and drying.

The filter press we have is a MONSTER and way to much for the stage we are at now. Also worried about frying it with the AR.

I have not tested the material with stannous as of yet but will read up on it. I believe I have Ir and I will be sending it out for official testing after converting it from salts to sponge. Other than a hydrogen/ox torch anyone have any ideas (or links) on how to do this in bulk? Torching so much may take days.

Thank you again very much.

CW


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## Harold_V (Aug 5, 2011)

Macgiver said:


> The filter press we have is a MONSTER and way to much for the stage we are at now. Also worried about frying it with the AR.


As you should be. Common filter presses _can not be used_ to filter solutions that contain precious metals unless the solution is basic (think cyanide). Otherwise the values are cemented by the metallic portions of the filter press, to which solutions have access. That destroys the press quickly, and will be the source of lost values. That's true even of gasketed filter presses, so don't assume you can use a different design without issues. The only way you can is if 100% of the elements that contact the solution are inert. Possible, but not likely to be found without having one built for the purpose. 

Harold


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## goldsilverpro (Aug 5, 2011)

Polypro filter press plates are common and I've seen them made from gray PVC also.


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## 4metals (Aug 5, 2011)

That takes care of the plates, but what are you using in the double diaphragm pump to withstand aqua regia. With the internal pressures needed to successfully run a filter press, especially at the end when the press is full, I don't trust the pump components to stand up long term. I've always used Wilden pumps, and found them to be pretty good but never for aqua regia.


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## goldsilverpro (Aug 5, 2011)

Have you ever used these for anything, 4metals? They had one in a place I consulted, but I never saw it used. Spendy! 
http://www.ishor.com/refining.htm

At the bottom of the page.


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## 4metals (Aug 5, 2011)

I do know of a refiner who uses their vacuum pump, it is a mechanical pump and it needs O rings replaced from time to time from wear and tear of normal operation. This particular guy used ammonia rinses to clean up his fine gold and the ammonium chloride fumes (that thick white cloud we all know and love) made short work of the O rings, requiring a laborious rebuild sooner than expected. 

They also make a flat plate with a hose nipple in the center of it. You pull a vacuum into a tabletop buchner with this thing on top and stick the hose in the liquid you want filtered and it sucks it right out of the bucket. This thing will work with any vacuum source, not just their pricey pump.




They get $725 for a plate for a 18" buchner!

A lot of cash for threaded rod, plexyglass, and sheet rubber.


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## Barren Realms 007 (Aug 5, 2011)

4metals said:


> That takes care of the plates, but what are you using in the double diaphragm pump to withstand aqua regia. With the internal pressures needed to successfully run a filter press, especially at the end when the press is full, I don't trust the pump components to stand up long term. I've always used Wilden pumps, and found them to be pretty good but never for aqua regia.



The Wilden diaphram pump's we use to use did a good job of transfering fluids from tank to tank or from sump drain to tank. They were pretty durable pumps. They stood up well to the use of HCL, HBR, Zinc chloride, Zinc bromide, highly concentrated peroxide and other chemicals they we used. I would not use one on a large filter press, but on a small one they might do ok. As far as a metal impellar pump, I can't remember an impeller that would hold up to the acid's we used much less to AR. I would be interested in hearing from one of the desighners on the forum what is used for pumping AR or what is used in a commercial facility that handles AR.


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## Macgiver (Aug 6, 2011)

Thanks again for all the input.

One thing to note is all of the nitric seems to be consumed out of the AR at about day three of the digesting stage. In fact there is very little if zero smell of HCL or Nitric. I have refrained from sticking my head in directly in the drum, as tempting as it is, but the STRONG smell and fumes of the fresh AR is completely gone. I have also tested it to see if it brings small bubbles to the surface a silver spoon. My thinking is that if the nitric has been consumed, then we are left with HCl which may not be as hard on a diaphragm pump. 

CW


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## Macgiver (Aug 6, 2011)

I think I have it sorted, taking advice from Goldenchild, I have ordered a prefilter set up which consists of filters which sit atop a drum, 600, 200, and 50 micron. This should remove much of the bulk. I will then filter through the "super filter" set up suggested by 4metals. I have found 10.5" buchners and if that does not work then I will try the 18 inch buchner.

Boy I hate waiting for the shipping!

Thank you all again.

CW


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## Barren Realms 007 (Aug 6, 2011)

Macgiver said:


> Thanks again for all the input.
> 
> One thing to note is all of the nitric seems to be consumed out of the AR at about day three of the digesting stage. In fact there is very little if zero smell of HCL or Nitric. I have refrained from sticking my head in directly in the drum, as tempting as it is, but the STRONG smell and fumes of the fresh AR is completely gone. I have also tested it to see if it brings small bubbles to the surface a silver spoon. My thinking is that if the nitric has been consumed, then we are left with HCl which may not be as hard on a diaphragm pump.
> 
> CW



Heat will be your friend when it comes to nitric, if you get the temp raised in your solution it can show you still have nitric and allow you to eliminate it. 

A diaphram pump will hold up fine for use with HCL. I have used the big commercial one and the small one's like you use on an RV for pumping water with no problem.


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## Lou (Aug 6, 2011)

Goldenchild gave very good advice about using tiered filtration.


I.e. filter component one 50 cfm polypropylene, filter component two is 25 cfm polypropylene, filter component three is 12 cfm and so on until the filtrate is sediment free. 


4metals suggestion of using diatomaceous earth is a great one. I use that on many tricky filtrations, especially those for metal blacks and other fine particles that would require multiple filtrations to get all out of suspension. Very good advice from him. 


Wilden makes a PTFE internal polypropylene external diaphragm pump that really rocks. You can in fact pump aqua regia with it.


At Impala Platinum in South Africa, they use centrifuges to get the precipitate out.


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## HAuCl4 (Aug 7, 2011)

Barren Realms 007 said:


> 4metals said:
> 
> 
> > I would be interested in hearing from one of the desighners on the forum what is used for pumping AR or what is used in a commercial facility that handles AR.



Gravity and a hose maybe?. 

Almost anything that can be achieved with a pump can be achieved with gravity or with vaccuum or both. Without expensive pumps. :idea:


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## Barren Realms 007 (Aug 7, 2011)

HAuCl4 said:


> Barren Realms 007 said:
> 
> 
> > 4metals said:
> ...



I agree on a small scale operation.

Have you ever tried to siphon 55 gallons of solution, much less 5,000-20,000 gallons?


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## HAuCl4 (Aug 7, 2011)

I don't think there is a single 5,000 Gallon AR installation on this planet, but sure, use a bigger hose and gravity, or several hoses/pipes. :shock: 

55 gallon?. Sure, with a 6 inch pipe it will empty in a few minutes. Probably need to tilt/ decant the last portion.


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## Barren Realms 007 (Aug 7, 2011)

HAuCl4 said:


> I don't think there is a single 5,000 Gallon AR installation on this planet, but sure, use a bigger hose and gravity, or several hoses/pipes. :shock:
> 
> 55 gallon?. Sure, with a 6 inch pipe it will empty in a few minutes. Probably need to tilt/ decant the last portion.



ROFL, not of AR just acids and fluids in general. 8)


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## pesco (Aug 27, 2011)

Once my vacuum died while I was doing some filtering. As it would take few days to obtain replacement and I wanted to finish the process ASAP I built very simple replacement.
Legend to (crude) diagram below:
- bottle - I used bottle, so the cylinder could rest on it, could be anything really if cylinder is properly secured
- hole - 2mm hole below the buchner
- shelf - perplex circle with a hole in the centre for buchner filter, hole has small rubber seal
- filter - buchner originally, could be any filter really
- cylinder, 150mm diameter perspex cylinder
- air pump connector, thats where hose from air pump is attached

This little quick fix diy forced filter worked much better than vacuum. I didn't need to clean vaccum bottle every time I needed to filter something, instead I could use any container. Originally it was a bottle, but later when I built a stand for the cylinder I could filter to any beaker. The cylinder itself was a leftover from construction of a anti-nitrate aquarium filter, 150mm diameter, bigger diameter would be easier to handle. I didn't put that on a drawing, but the cylinder has 2 sections with rubber seal and 3 clip-on locks - the type you get on tool cases. On top glued in small connector for hose from aquarium pump. Below the filter little hole which lets the pressure out.

Pressure in a cylinder above the shelf is higher than below. That's why is important that the shelf itself is glued on the outer rim and has good seal where the filter goes in.

As the air is pushed in no corrosive gases are going through the pump. To prevent diffusion of gases the hose was only 4mm and around 2m long - popular silicone air hose for aquarium.

It is easy to control the pressure by fitting standard aquarium hose T-connector - one from air pump, one to the filter, one to the room :mrgreen: The branch going to the room has a valve.

I never got replacement for the vacuum - wasn't needed anymore :mrgreen:


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