RogueRose
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Filtering speed - same filter but poor results with vacuum pump
I've been filtering a number of things, one being leached K2CO3 from ash, and when I gravity filter with a VERY tightly packed 2" long roll of cotton
(flat swabs rolled into a cylinder in a layered manner) I get a very light brown, translucent filtrate that looks like super watered down Ice'd tea.
If I add a vacuum pump with the same setup, I get almost no filtration at all. The big stuff comes out, but no light passes through 1/2" of liquid
where with the gravity filter I would say the filtrate would need many feet (4-5+) to block light - so that is a huge difference.
Everything has been pre-filtered with a paper coffee filter which has a layer built up, making it remove more than a standard filter but the super
fine (ash I guess) passes through.
Is there something I can do to make the filtering faster but still get good quality?
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JJay
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The usual answers would be to use sand or diatomaceous earth (you already tried filtering through the filter cake, right?). You might try filtering
through a pad of cotton with more area for the solution to percolate.
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Sulaiman
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You could try operating with less suction/vacuum,
e.g. using filter papers in a Buchner funnel
I have completely stopped filtrate flow using a rotary where my little partial-vacuum pump did a good job and just gravity was waaay toooo slooow.
I do not know why,
but I noticed that my rotary left very distinct small dark spots, one per hole in the Buchner plate,
whereas gravity or moderate vacuum left none or 'fuzzy' larger spots respectively.
CAUTION : Hobby Chemist, not Professional or even Amateur
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PirateDocBrown
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Whenever possible I always put paper on top of a frit. Help keep the frit clean. Obviously, it doesn't work if the paper also gets clogged.
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JJay
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I've been having problems with strong oxidizers eating holes in the filter paper and letting unwanted particulate matter through... I wonder if filter
paper would keep calcium sulfate from clogging a frit....
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Magpie
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I suggest you put down a 1/8" bed of diatomaceous earth, such as Celite. This is put down in a slurry.
[Edited on 20-5-2017 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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PirateDocBrown
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Quote: Originally posted by Magpie  | I suggest you put down a 1/8" bed of diatomaceous earth, such as Celite. This is put down in a slurry.
[Edited on 20-5-2017 by Magpie] |
Especially if your product is in solution, and not the precipitate.
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RogueRose
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I have some diatomaceous earth (DE) (it says "dust" on the package) from a garden supply store, I assume this is adequate for the filtration? I know
there is different sizes and they can vary from 3um to 1mm in size but I think the dust will be more fine.
I've never used this before to filter and I don't know how I can make sure the 3um - 20um (or larger) particles from passing through the filter that
holds it in place. Any recommendations for what I should use to hold the DE in place? my funnel has a 3" fine SS mesh filter screen and i've put
different cloths and papers on that before, but IDK if anything different needs to be done while using DE or not.
For anyone who doesn't know how to use DE in filtering, I found this short video - 80 seconds long..
https://www.youtube.com/watch?v=fBl4ZCowynY
It says "Celite" which is a brand name for DE I believe.
Does anyone know if there is a technical term for what happens when a filter collects particles on it and allows for finer filtration that what the
filter is rated? Like when you use a coffee filter and the first 500ml filtered the liquid may be cloudy but it removed a lot of particles - from
then on it filters the finer material giving a clear/translucent liquid. I figured there would probably be some technical term for it or a way to
describe it or it's action..
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PirateDocBrown
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Garden grade DE can be quite impure. Give it several wash/dry cycles before using it in earnest.
You can get a better grade from a pool supply store.
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RogueRose
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| Quote: Originally posted by PirateDocBrown | Garden grade DE can be quite impure. Give it several wash/dry cycles before using it in earnest.
You can get a better grade from a pool supply store. |
Thanks for the suggestion! the stuff I have was pretty expensive comparatively to the normal stuff they sell in bigger bags - this was "ultra pure
Organic" and is pretty darn white. I'll have to see if it says it is marine or lake sourced.
I'm washing some now with a mild HCl wash and thought I'd do that a few times - IDK if that is the best acid to try. I thought I'd finish with a few
washes of either baking soda or washing soda - unless NaOH would be a better option..
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PirateDocBrown
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No, definitely not with NaOH. 2NaOH +SiO2 = Na2SiO3, which is soluble.
HCl, OTOH, is the usual way for cleaning up silica by acid wash. Just rinse it with water after.
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Praxichys
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You might have some luck adding a small amount of a flocculating agent and allowing things to settle. Potassium alum might be an option for clarifying
but I'm not sure how well it will work in a K2CO3 solution. Assuming there is some KOH in the leachate, it might just ppt. aluminum hydroxides.
Gelatin is another option. I use gelatin to clarify beer since the yeast cells are only around 5 microns across and are very difficult to filter. I
add 5g of gelatin dissolved in about 100ml near-boiling water per 5 gallons of beer as cold as you can get it without freezing. Add without stirring.
The effect is a jelly mat that forms a layer on the bottom of the bucket and over the course of several days the yeast will "stick" to the mat and be
absorbed by it. The clarified supernatant liquid is then decanted off.
There's no telling what might happen to gelatin in the fairly strongly basic K2CO3 solution but the materials are cheap enough to give it a try.
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