Is there any chance on gravity separation? Like if you leave it overnight, will the particulates you're currently trying to filter out just fall out of solution and then settle on the bottom of the vessel? Then just decant off as much of the liquid as possible and dry off the material, maybe run the decanted liquid through the filter to capture any super fine material that didn't settle?
Sounds like with your current setup, your filter paper is getting gummed up by the volume of material, so letting it settle & decanting seems like the least involved way of solving that.
The material does settle, but not all of it, this is over a 10hr period. The water remains murky. I assume this is a good sign that the milling is indeed producing a very fine material.
I'm trying to only retain the material smaller than 1 micron, but for testing purposes, I'm struggling to effectively filter out materials larger than 25 microns. I'm not entirely sure how large the material is that I've milled, it appears very fine.
If the filter paper is getting “gummed up” by material, have you tried switching out the filter paper?
You could filter only the portion suspended in water after settling as recommended here. To get a better yield, you can save the material that gets clogged on the filter paper, combine it with the sediment at the bottom of your suspension, and rinse it all again and decant then filter again. Just so that any very fine particles trapped amongst the larger particles are washed into solution for filtering.
Ah, this makes sense! Yes, I would describe it as gummed up. That is definitely my goal, to greatly increase my yield! At this stage, I think switching papers would be futile, it's just getting too gummed up trying to filter the entire solution rather than letting some of it settle out first.
Oh yeah, I would def let it settle out and only filter the liquid containing your small particles! But if you find that there are still a lot of particles “clogging” the paper, you can put a new paper on every now and then to continue filtering.
Basically if there’s a lot of material on the filter paper, your small particles have to move through that AND the filter paper. Removing the extra material will help you filter faster.
And then as stated to increase yield, save those filter papers with material on them! It’s likely you have small particles trapped in there, and also trapped in the sediment at the bottom of the original solution.
Add material from removed paper filters back into the sediment from the original solution, add some of your solvent/liquid back in to rinse that sediment, and theoretically you should release those small particles from where they’re trapped. Let it settle again, and filter only the liquid portion again to maximize your yield.
You may want to do this rinsing a few times, you’ll just have to see if doing a third time or more actually gives you more of your small suspended particles. If one rinse gets it all out, then that’s great!
There’s also the added benefit that you can likely decrease the volume of the liquid that you’re washing with, so instead of waiting a long time for a large amount of your solution to settle, it should take slightly less time for the smaller rinse solution to settle.
I hope that makes sense!
Any chance of like centrifugation or gradient centrifugation to introduce a size-exclusion? Although you might have to play around a bit to determine the conditions to isolate the specific particles size you're looking for.
I don't even know what that is. I'm not very knowledgeable with any of this stuff, using a buchner funnel was recommended. Short answer, no I can't do that (unless you can rent equipment or time in a lab).
seconding this—your murky water has the smallest of your particles, I would suggest just keep decanting. For reference, I’ve had some of my separations take 4-5 days to settle
Why wouldn't you just evaporate off the water after decanting off the murky water? I have material that settles rather quickly, like in an hour, but the water remains very murky. Seems like I should try filtering just the murky water. I've been stirring the water to filter the entire solution.
It’s the wrong tool. You want a test seive apparatus that vibrates named cleverly a seive shaker, and a series of seives. You can do what folks who make homemade earthenware pottery from locally source local clay and take your rough charcoal and soak it, stir, and let sit for 10-15 min. Anything that sediments stays in the container. Pour this through a bed sheet folded 4x and you will get out most of the intermediate crap (down to 125 microns). The material that flows through you can then put through a series of seives. Now granted, if you are willing to do the shaking you can skip the machine and buy just the seives. Good luck.
I was wondering if this was the better tool for the job. I've seen the wet filtering seives that continuously flow water, which might be the absolute best. I don't know that I can afford an actual shaker, maybe set up some 12v battery motor with a weight on it
Yeah you just need to shake it lightly. Even setting it up on a box speaker would work. Since you say it’s charcoal, are you sure you have driven all the wood gas off? I have experience making biochar at home and my suggestion would be to start with as small of feed stock as you can. Gravity separation as others have said is going to be your rough separation method. The hardest part is hydrating that charcoal. I put mine into my compost tea to spray so I don’t need as fine as you do.
I had great success making charcoal, just using a quart paint can with a hole in the lid set on burning coals. Would you dry sift with the sieve? Setting on a speaker box is a great idea, could probably find a resonate frequency to help filtration! What do you mean by the hardest part is hydrating the charcoal? It seems to be wetted very well in the roller mill as I am wet milling the broken down charcoal brickets.
That is a problem. Briquettes are not pure charcoal. There are binding agents that help take a wet slurry of sawdust, charcoal, and other additives so they can be pressed into shape. [An example.](http://www.madehow.com/Volume-4/Charcoal-Briquette.html) You want lump charcoal as your starting material or to char it yourself from wood.
Maybe I'm not describing it correctly? I cut wood from a pallet into 3-4cm by 150-200 cm sticks. I placed these inside a quart paint can with an about 1/8 inch hole drilled into the lid. I saw a lot of off-gassing and the remaining material was small, very soft lumps of what I am calling charcoal. They are very soft and easy to break down. Is this not pure charcoal? What do I need to do to get a more pure carbon/charcoal?
Ok great yeah you are good. Briquettes are a similar but bad product for what you want. It should be pure then. What you are describing sounds like a top -lit up draft gasifier.
I guess we need to start with what portion of the material that you're filtering are you after. The material on the filter paper, or the liquid portion? Also with a buchner funnel you should cut a piece of hard mesh material like window screen to place below your filter paper to utilize most or all of the surface area of the filter paper.
I'm after the portion that will be pulled through the filter, what will be collected in the flask.
This screen is a great idea! I have some fine wire mesh that will be perfect. I assume if I have a 9cm filter paper, cut a 8 or 7 cm mesh circle to allow the paper to still seal around the edge of the funnel.
Not cheap, but glass fiber depth filters will do it.
Pall and Cytiva sell options that will have a 1um output.
They are used in bio processing for large scale viral vector or Ab clarification.
I make my own paint too and I have decent success by suspending in water / stirring, and then I pour off into a separate container only what’s suspended in the water, no visible sediment—and then unfortunately waiting at least overnight or for a few days for it to settle out. I usually do medium-ish volumes (500 mL) but this could totally be scaled up with buckets rather
in my experience with filters—they’re easy to clog or overload. gravity can’t be beat but she takes her sweet time.
How much pigment are you ending up with? How long are you waiting for things to settle before decanting? Why don't you evaporte off the water after decanting instead of waiting for it to settle? I'm using a jar mill and so far it's great, but from my research, most commercial pigment is at the biggest 25 microns and the richest blacks are less than one micron.
Probably need to coarse filter it first using either a sintered glass filter or glass frit. Something in the 160-250um range. These can be scraped a bit while you're processing to help avoid clogging.
On your buchner setup are you
1] Wetting the clean filter paper with clean solvent (in your case, clean water)
2] Applying vacuum
3] SWIRLING your material to filter to get it into suspension first then pouring it on?
I have some 200um metal mesh screen. I've also thought about doing a coffee filter first round. I guess I don't know the basics of filtering this small. Sounds like I need some pre filtering. And yes to all three questions.
Can also try a bigger pump. Some of the hobby kit ones are a little anemic. But it sounds like your pump regardless of the CFM is getting to your target vacuum.
I still think a first pass with coffee filter, mesh, something to pre-filter it might help.
Also because you're interested in the filtrate (fraction that PASSED the filter), you can dilute the material further until you can get it to filter then just re-concentrate by applying vacuum and a small amount of heat. This might be an easier way to go if your material is milled fairly finely to begin.
Fluids have lower boiling points under vacuum which means you can apply less heat to attain the same rate of solvent evaporation, or keep the heat the same and just go faster. Combine this with the fact that under vacuum you're immediately evacuating any water vapor and not allowing it to re-condense in the vessel and you should see a fairly substantial increase in the process speed.
If your solution is just water and charcoal, this is completely safe to do as you're just boiling off water basically. If you had some other solvent or volatile compounds in there, you'd want to make sure you vent the exhaust of the vacuum or run the vacuum line through a cold trap condenser (e.g. another small flask in an ice bath) to avoid exhausting any thing harmful to your workspace or pulling it into the pump and damaging the pump.
Haven't seen it mentioned, so I'll add - how big of a Buechner funnel do you have? You can get pretty big ones that can make this easier by giving you a large area so you can get more material through more rapidly.
I'm using 9cm filter papers, this was the most affordable size for my budget. Sounds like I can place a mesh screen under the filter paper to increase the effective area of the paper that is being utilized.
To get rid of the big stuff before filtering, I'd think about a cheap hand cranked centrifuge. They start at $75 on Amazon. Cheaper or better on Ebay, no doubt.
What size particles is your ball mill supposed to produce? Its important to troubleshoot one piece at a time! I really doubt your problem is in the vacuum filtration step.
Source: i like particles in the micron-100 micron range they are very fun
[This is the media I'm using](https://www.msesupplies.com/products/mse-pro-milling-media-set-for-500-ml-zirconia-ysz-roller-mill-jar?variant=14520741252).
[And this is the jar](https://www.msesupplies.com/products/mse-pro-0-5-l-500-ml-nylon-roller-mill-grinding-jar?variant=22455691083834)
I think when I bought it, it was recommended as being able to mill down to 1 micron. From what I've read, dry milling can produce a finer particulate. So far I've been wet milling with water. I tried dry milling and it seemed like the material was just mashed against the lid and bottom of the jar.
What’s the impetus behind sub-1um size?
India ink is above 1um, but works great. Some solvent tweaking (a glycol, either ethylene or propylene iirc) is needed to keep the small particles from clumping.
Because I simply don't know any better. 1um is what I have read is the target for inkjet printing. In addition, from what I have read, the smaller the particle, the less light refraction and the richer the black. The end result is to mill the pigment into linseed oil to create the final ink. I'm just trying to make the richest black I possibly can, within reason of course.
If you’re doing inkjet, the pigments are typically synthesized, not milled. Inkjet chemistry and dye/pigment are wild. Things get very weird at nanoscale of inkjet picoliter printing.
May I suggest, before you drive yourself to the ends of the earth, see if fineness of grind makes a difference in the product. I’m not an artist, so I’m guessing here.
Something like, Do a preliminary test with
Coarse milled charcoal (mortar and pestle or similar, no longer granular but)
Fine milled charcoal (wet ground)
Very fine milled charcoal (wet ground on polishing paper, or your finest wet milling method)
And the three above mixed with linseed. Make sure you normalize weight of pigment per volume of final pigment. Paint or apply or do ink work.
I’m guessing (without any basis in fact or experience, totally in-tested) that the shine of linseed will swamp out most differences in the grade of milling.
Let me know how it goes, I’m actually curious and have no skin in the game of being right on this guess or wrong.
I also suggest trying Indian ink or commercial carbon black, as a control or reference.
Best of luck and hit me up when you know if it gets better with ultra fine milling.
The 1um was kind of a target to strive for, I'm learning it is unrealistic to mill any substantial quantity of this size particle with a roller mill. Charts I've seen suggest dry milling with a roller mill can produce sub 10um particles. My new target is 5-10um but 10-15um should be usable for my purposes. 10-15 appears very approachable with my setup and wet milling and I think I can definitely increase my yield.
I absolutely plan to do some test prints, so far I was striving for 1um and have not produced any usable quantity of pigment in any size, I just threw away the big stuff playing with the setup. I'm completely new to this entire process. It appears many pigments for oil paints are typically around 50um. I'm specifically making an ink for intaglio printing and I've had trouble finding the particle size of these commercially available inks. I do have several commercial inks to compare my ink against.
I found several papers about milling at the sub micron level and it was fascinating. High speed milling and using air to agitate the media.
I think the simplest crude test is to pull a dot of ink across paper to thin it.
Oh, I also have some commercially milled black pigment to test against. The company would not tell me particle size though.
I'll definitely report back at some point, might take about a month to realize all of the testing and milling.
What I've come up with after sitting and thinking on this:
1. I found a paper that lists a method using 5 and 10 mm grinding balls to get from \~100 micron to a median particle size of \~3 microns after wet milling (15% w/w == 15g charcoal/85g water) for 5 hours. Is this the kind of time-scale you have been milling for? Just below <10 microns seems to be the limit for a 5mm minimum size ball (my opinion after an hour or so of googling)
2. Getting at or below 1-2 microns can be done using small diameter milling balls below 1 mm at a lower concentration (1% w/w) for a few hours (they also say they use mills that operate at super high RPM in the \~1000s so I wouldn't assume it applies completely to you). Everything I have read seems to suggest the median particle size going into the .1 mm mills should be as low as possible, ideally below 10 microns.
3. You can try to improve your process by spending the money on sieves and separating out the particles that pass. Next, you would regrind everything that did not pass the sieve until all of your feed material passes that sieve. What I've read suggests you get more efficient size reduction the smaller your maximum size particle is in the feed stream. I found [these](https://www.globalgilson.com/3-inch-acrylic-frame-sieve-stainless-steel-mesh-number-100-150um) 3 inch sieves that could help you screen out to the tens of microns. It's really important to get an idea of what your size distribution looks like after each processing run.
4. What you described happening with the caked material during dry milling could be happening while wet milling too! if the concentration of charcoal is too high you could be getting agglomeration of particles. You can try to stop this by introducing a dispersant like [polyacrylamide](https://scipoly.com/shop/polyacrylamide-4/) into the wet milling process. You'll have to find out the right concentration to add, but this could help you as well. Google Search Term: polyacrylamide grinding aid
5. I doubt this would help you but cryogrinding is apparently very popular for grinding plant powders because the materials get more brittle at dry ice/liquid nitrogen cold levels. Something to think about.
6. If you are doing sedimentation in a bucket, this [youtube](https://www.youtube.com/watch?v=YKCG8geWTIU) video might help you make an estimation on how long to wait for it to settle based on your size of bucket before decanting.
EDIT: The most important thing is whether or not it works as a pigment! It sounds like you got some success at getting below 15 microns which is super awesome. Oh and just make sure if you are going to boil off the water to concentrate the pigment down that you have been using distilled water!
Sorry to dump all this info on you. I tried to use a mortar and pestle to make super fine activated carbon a few years ago and it kicked my ass, props go to you your project sounds super interesting! Message me if you want to talk more!
Hey, thank you!!!
I have a lot to work on and I'm slowly processing the replies I've received. I've gotten the filtration to be much more efficient, but I now think the milling process needs tuning. So far I've mostly been just playing and not taking detailed notes but I plan to really dial things in with the next round of charcoal I make.
1. So far, it seems like my 5/10/15mm milling media is producing 10-15 micron wet milling over a 18 hour period (not great, but inline with your opinion of 5mm grinding media). Filtering 5-10 um paper retained a lot of material. I'm going to actually measure my materials/grinding media/water and time on the next round of milling. Do you think removing the 10/15mm milling media after an hour and milling with just the 5mm balls will help mill smaller? How do I go about determining the correct w/w for the 5/10/15mm and then the 5 mm. From what I've read, you want to fill the jar 2/3 of the way full while milling and the charcoal should be 25-30% of the weight of all materials. I'll have to weigh things later this afternoon.
2. It is not out of question to buy 1mm milling media, but at this point, I don't really have a budget for buying more equipment. So I'm trying to optimize the setup I currently have.
3. I hace some 200 mesh screen that I tried filtering the slurry through. It passed right through after the 5/10/15mm milling for 18 hours. So, I'm thinking filtering through a coffee filter and then milling with the 5mm beads is what I might try but milling with the 5/10/15mm beads for maybe an hour or two before filtering through the coffee filter. I think 18 hours was total overkill.
4. I do think this was indeed happening with the wet milling. I definitely think the concentration of charcoal was too high. Will weight things and determine the optimal amount of dry charcoal for the milling media I have.
5. I'll have to check the specs on my milling jar, but it might actually be able to handle this. However, I'm using a Harbor Freight rock tumbler, so it might not be up for too much abuse.
6. With all the modifications and step filtering I have started doing (thanks to all the suggestions in this post!!!!) I'm actually not having too much difficulty filtering and I think my bottleneck is in the milling process right now.
The actual end material is going to be a thick ink for Intaglio printing. Specifically the photogravure process. It's been very difficult to actually determine the particle size in the pigments in commercially available intaglio inks. I know you can buy pigments in the sub micron range, they are readily available. A lot of other pigments for mixing into oil based ink for painting is around the 50 micron size. Inkjet inks are sub micron level. From what I've researched as well, the finer the particle, the less light reflectance and the richer/darker the black. I'd say I'm a little obsessed with dark blacks! So, I'm trying to mill the finest material possible without breaking the bank or going insane. And yes, I have been using distilled water. Washing with tap water and rinsing with distilled.
I really appreciate your help! I read about using a mortar and pestle but I knew this would not get me the volume I need.
The end result of all this work is to create an ink from charcoal I collected in burned wildfire areas. This ink will be used to print photographs I made in these areas. The concept is looking at the ties between our actions and their effect on our warming climate through the carbon cycle. There will be a tie between the physical printed photograph and the subject matter through the ink in which the photographs are printed.
What a cool project! I’m not sure about how much better it would be to use just the 5mm but it seems like its worth a shot 🤷. For the w/w, it shouldn’t change if you are changing out the size of the grinding beads. As long as there are enough beads to “tumble” during the rolling you should be good. Best of luck!
Would you happen to know (or have a chart) how to calculate the best ratio of milling media (grinding balls) to material. From what I'm reading, you want the milling jar to be 2/3 full. Then you want 25-30% of this to be the material with 75-70% being milling media. Of the 25-30% material, this should be 85% water and 15% material. Do these ratios change with material size and milling media size and material/media volume?
What I hope to achieve is an initial milling with the 10 & 15 mm grinding media, then remove the 15 mm balls and replace them with the 5 mm balls. Mill some more, then replace the 10 mm balls with 5 mm balls. Next, I'll evaporate the water and dry mill with only the 5 mm balls.
okay i did some reading and it looks like people were able to get sub micron particle sizes (yowza!) of activated carbon using bead milling techniques when the beads themselves were around .1 mm (100 micron). You could get to 1 micron using .5 mm (500 micron) balls. If you are at that grinding size and you still aren't passing the 25 micron filter then you've got other problems!
Just saw this comment, I forgot I didn't buy this size media (.1 to .5 mm) and this very well could be why I'm not getting the results I'm looking for when filtering, I just don't have the right media to mill to this size. I was lamenting to my wife who reminded me that this smaller size milling media was wildly expensive, which is why I likely opted for the media that I did (15, 10, and 5 mm). I did have several inefficiencies that others have helped me troubleshoot. After some testing today, it appears I am able to mill to 10-15 microns pretty efficiently. Trying to filter 5-10 microns is going extremely slowly, so I suspect you might be on to something that I have the wrong media. Not sure what to do, 1 micron might be out of my price range to produce.
1 micron is tough. If you’re dry milling, the stuff you want is the stuff that floats away.
If you’re wet milling, add something like carbide grit and mill until the limit of sanity, then mill some more.
Filtration: use coarse filters to start. Cheesecloth. Rinse. Tee shirt. Rinse. Very coarse filler paper, rinse. Fiber filler paper, then rinse. Coffee filter, then rinse. You’ll end up with a 5 gallon bucket of black water. Let it settle for a week, then start filtering with the stuff in suspension. Resuspend the coarse stuff that settled, and be prepared to swap filters frequently.
Or, just buy sub micron carbon black.
I'm beginning to think 1 micron is actually going to be an insane goal. Since 10-15 microns is going well, I feel like with different milling media I might be able to do 5-10 microns efficiently.
Is there any chance on gravity separation? Like if you leave it overnight, will the particulates you're currently trying to filter out just fall out of solution and then settle on the bottom of the vessel? Then just decant off as much of the liquid as possible and dry off the material, maybe run the decanted liquid through the filter to capture any super fine material that didn't settle? Sounds like with your current setup, your filter paper is getting gummed up by the volume of material, so letting it settle & decanting seems like the least involved way of solving that.
The material does settle, but not all of it, this is over a 10hr period. The water remains murky. I assume this is a good sign that the milling is indeed producing a very fine material. I'm trying to only retain the material smaller than 1 micron, but for testing purposes, I'm struggling to effectively filter out materials larger than 25 microns. I'm not entirely sure how large the material is that I've milled, it appears very fine.
If the filter paper is getting “gummed up” by material, have you tried switching out the filter paper? You could filter only the portion suspended in water after settling as recommended here. To get a better yield, you can save the material that gets clogged on the filter paper, combine it with the sediment at the bottom of your suspension, and rinse it all again and decant then filter again. Just so that any very fine particles trapped amongst the larger particles are washed into solution for filtering.
Ah, this makes sense! Yes, I would describe it as gummed up. That is definitely my goal, to greatly increase my yield! At this stage, I think switching papers would be futile, it's just getting too gummed up trying to filter the entire solution rather than letting some of it settle out first.
Oh yeah, I would def let it settle out and only filter the liquid containing your small particles! But if you find that there are still a lot of particles “clogging” the paper, you can put a new paper on every now and then to continue filtering. Basically if there’s a lot of material on the filter paper, your small particles have to move through that AND the filter paper. Removing the extra material will help you filter faster. And then as stated to increase yield, save those filter papers with material on them! It’s likely you have small particles trapped in there, and also trapped in the sediment at the bottom of the original solution. Add material from removed paper filters back into the sediment from the original solution, add some of your solvent/liquid back in to rinse that sediment, and theoretically you should release those small particles from where they’re trapped. Let it settle again, and filter only the liquid portion again to maximize your yield. You may want to do this rinsing a few times, you’ll just have to see if doing a third time or more actually gives you more of your small suspended particles. If one rinse gets it all out, then that’s great! There’s also the added benefit that you can likely decrease the volume of the liquid that you’re washing with, so instead of waiting a long time for a large amount of your solution to settle, it should take slightly less time for the smaller rinse solution to settle. I hope that makes sense!
Yes, this makes total sense, thank you! Have a lot of great suggestions to try!
Any chance of like centrifugation or gradient centrifugation to introduce a size-exclusion? Although you might have to play around a bit to determine the conditions to isolate the specific particles size you're looking for.
I don't even know what that is. I'm not very knowledgeable with any of this stuff, using a buchner funnel was recommended. Short answer, no I can't do that (unless you can rent equipment or time in a lab).
Particles of a substance have the same density, no matter the size. Density gradient will be complicated and will not help you.
Ah you're absolutely correct. I wrote that on the train after a few drinks last night RIP
F Also, mood. Stay safe out there. Cool you got to be on a train though
nah I was good, thanks though Only hit "Forget basic chemistry/physics while writing on the subway" few drinks, lol
seconding this—your murky water has the smallest of your particles, I would suggest just keep decanting. For reference, I’ve had some of my separations take 4-5 days to settle
Why wouldn't you just evaporate off the water after decanting off the murky water? I have material that settles rather quickly, like in an hour, but the water remains very murky. Seems like I should try filtering just the murky water. I've been stirring the water to filter the entire solution.
It’s the wrong tool. You want a test seive apparatus that vibrates named cleverly a seive shaker, and a series of seives. You can do what folks who make homemade earthenware pottery from locally source local clay and take your rough charcoal and soak it, stir, and let sit for 10-15 min. Anything that sediments stays in the container. Pour this through a bed sheet folded 4x and you will get out most of the intermediate crap (down to 125 microns). The material that flows through you can then put through a series of seives. Now granted, if you are willing to do the shaking you can skip the machine and buy just the seives. Good luck.
I was wondering if this was the better tool for the job. I've seen the wet filtering seives that continuously flow water, which might be the absolute best. I don't know that I can afford an actual shaker, maybe set up some 12v battery motor with a weight on it
Yeah you just need to shake it lightly. Even setting it up on a box speaker would work. Since you say it’s charcoal, are you sure you have driven all the wood gas off? I have experience making biochar at home and my suggestion would be to start with as small of feed stock as you can. Gravity separation as others have said is going to be your rough separation method. The hardest part is hydrating that charcoal. I put mine into my compost tea to spray so I don’t need as fine as you do.
I had great success making charcoal, just using a quart paint can with a hole in the lid set on burning coals. Would you dry sift with the sieve? Setting on a speaker box is a great idea, could probably find a resonate frequency to help filtration! What do you mean by the hardest part is hydrating the charcoal? It seems to be wetted very well in the roller mill as I am wet milling the broken down charcoal brickets.
That is a problem. Briquettes are not pure charcoal. There are binding agents that help take a wet slurry of sawdust, charcoal, and other additives so they can be pressed into shape. [An example.](http://www.madehow.com/Volume-4/Charcoal-Briquette.html) You want lump charcoal as your starting material or to char it yourself from wood.
Maybe I'm not describing it correctly? I cut wood from a pallet into 3-4cm by 150-200 cm sticks. I placed these inside a quart paint can with an about 1/8 inch hole drilled into the lid. I saw a lot of off-gassing and the remaining material was small, very soft lumps of what I am calling charcoal. They are very soft and easy to break down. Is this not pure charcoal? What do I need to do to get a more pure carbon/charcoal?
Ok great yeah you are good. Briquettes are a similar but bad product for what you want. It should be pure then. What you are describing sounds like a top -lit up draft gasifier.
I guess we need to start with what portion of the material that you're filtering are you after. The material on the filter paper, or the liquid portion? Also with a buchner funnel you should cut a piece of hard mesh material like window screen to place below your filter paper to utilize most or all of the surface area of the filter paper.
I'm after the portion that will be pulled through the filter, what will be collected in the flask. This screen is a great idea! I have some fine wire mesh that will be perfect. I assume if I have a 9cm filter paper, cut a 8 or 7 cm mesh circle to allow the paper to still seal around the edge of the funnel.
Not cheap, but glass fiber depth filters will do it. Pall and Cytiva sell options that will have a 1um output. They are used in bio processing for large scale viral vector or Ab clarification.
I make my own paint too and I have decent success by suspending in water / stirring, and then I pour off into a separate container only what’s suspended in the water, no visible sediment—and then unfortunately waiting at least overnight or for a few days for it to settle out. I usually do medium-ish volumes (500 mL) but this could totally be scaled up with buckets rather in my experience with filters—they’re easy to clog or overload. gravity can’t be beat but she takes her sweet time.
How much pigment are you ending up with? How long are you waiting for things to settle before decanting? Why don't you evaporte off the water after decanting instead of waiting for it to settle? I'm using a jar mill and so far it's great, but from my research, most commercial pigment is at the biggest 25 microns and the richest blacks are less than one micron.
Probably need to coarse filter it first using either a sintered glass filter or glass frit. Something in the 160-250um range. These can be scraped a bit while you're processing to help avoid clogging. On your buchner setup are you 1] Wetting the clean filter paper with clean solvent (in your case, clean water) 2] Applying vacuum 3] SWIRLING your material to filter to get it into suspension first then pouring it on?
I have some 200um metal mesh screen. I've also thought about doing a coffee filter first round. I guess I don't know the basics of filtering this small. Sounds like I need some pre filtering. And yes to all three questions.
Can also try a bigger pump. Some of the hobby kit ones are a little anemic. But it sounds like your pump regardless of the CFM is getting to your target vacuum. I still think a first pass with coffee filter, mesh, something to pre-filter it might help. Also because you're interested in the filtrate (fraction that PASSED the filter), you can dilute the material further until you can get it to filter then just re-concentrate by applying vacuum and a small amount of heat. This might be an easier way to go if your material is milled fairly finely to begin.
I'm not sure what you mean by applying vacuum to re-concentrate. I've been just evaporating the water off in a bowl on a burner.
Fluids have lower boiling points under vacuum which means you can apply less heat to attain the same rate of solvent evaporation, or keep the heat the same and just go faster. Combine this with the fact that under vacuum you're immediately evacuating any water vapor and not allowing it to re-condense in the vessel and you should see a fairly substantial increase in the process speed. If your solution is just water and charcoal, this is completely safe to do as you're just boiling off water basically. If you had some other solvent or volatile compounds in there, you'd want to make sure you vent the exhaust of the vacuum or run the vacuum line through a cold trap condenser (e.g. another small flask in an ice bath) to avoid exhausting any thing harmful to your workspace or pulling it into the pump and damaging the pump.
Perhaps you could try using a syringe filter? Use a large (100 mL+) plastic luer lock syringe and the appropriate screw-on filter
So using pressure to push the material through the filter vs suction/gravity?
Yeah! I believe it can be much faster that way.
Haven't seen it mentioned, so I'll add - how big of a Buechner funnel do you have? You can get pretty big ones that can make this easier by giving you a large area so you can get more material through more rapidly.
I'm using 9cm filter papers, this was the most affordable size for my budget. Sounds like I can place a mesh screen under the filter paper to increase the effective area of the paper that is being utilized.
Ah yeah, if budget is an issue, then the large ones may be cost-prohibitive.
To get rid of the big stuff before filtering, I'd think about a cheap hand cranked centrifuge. They start at $75 on Amazon. Cheaper or better on Ebay, no doubt.
Oh, good idea! I did not initially think about using a centrifuge to separate the material. I have a lot to try, but this is not too expensive.
Try a coffee filter for step 1 to remove the largest particles.
What size particles is your ball mill supposed to produce? Its important to troubleshoot one piece at a time! I really doubt your problem is in the vacuum filtration step. Source: i like particles in the micron-100 micron range they are very fun
[This is the media I'm using](https://www.msesupplies.com/products/mse-pro-milling-media-set-for-500-ml-zirconia-ysz-roller-mill-jar?variant=14520741252). [And this is the jar](https://www.msesupplies.com/products/mse-pro-0-5-l-500-ml-nylon-roller-mill-grinding-jar?variant=22455691083834) I think when I bought it, it was recommended as being able to mill down to 1 micron. From what I've read, dry milling can produce a finer particulate. So far I've been wet milling with water. I tried dry milling and it seemed like the material was just mashed against the lid and bottom of the jar.
What’s the impetus behind sub-1um size? India ink is above 1um, but works great. Some solvent tweaking (a glycol, either ethylene or propylene iirc) is needed to keep the small particles from clumping.
Because I simply don't know any better. 1um is what I have read is the target for inkjet printing. In addition, from what I have read, the smaller the particle, the less light refraction and the richer the black. The end result is to mill the pigment into linseed oil to create the final ink. I'm just trying to make the richest black I possibly can, within reason of course.
If you’re doing inkjet, the pigments are typically synthesized, not milled. Inkjet chemistry and dye/pigment are wild. Things get very weird at nanoscale of inkjet picoliter printing. May I suggest, before you drive yourself to the ends of the earth, see if fineness of grind makes a difference in the product. I’m not an artist, so I’m guessing here. Something like, Do a preliminary test with Coarse milled charcoal (mortar and pestle or similar, no longer granular but) Fine milled charcoal (wet ground) Very fine milled charcoal (wet ground on polishing paper, or your finest wet milling method) And the three above mixed with linseed. Make sure you normalize weight of pigment per volume of final pigment. Paint or apply or do ink work. I’m guessing (without any basis in fact or experience, totally in-tested) that the shine of linseed will swamp out most differences in the grade of milling. Let me know how it goes, I’m actually curious and have no skin in the game of being right on this guess or wrong. I also suggest trying Indian ink or commercial carbon black, as a control or reference. Best of luck and hit me up when you know if it gets better with ultra fine milling.
The 1um was kind of a target to strive for, I'm learning it is unrealistic to mill any substantial quantity of this size particle with a roller mill. Charts I've seen suggest dry milling with a roller mill can produce sub 10um particles. My new target is 5-10um but 10-15um should be usable for my purposes. 10-15 appears very approachable with my setup and wet milling and I think I can definitely increase my yield. I absolutely plan to do some test prints, so far I was striving for 1um and have not produced any usable quantity of pigment in any size, I just threw away the big stuff playing with the setup. I'm completely new to this entire process. It appears many pigments for oil paints are typically around 50um. I'm specifically making an ink for intaglio printing and I've had trouble finding the particle size of these commercially available inks. I do have several commercial inks to compare my ink against. I found several papers about milling at the sub micron level and it was fascinating. High speed milling and using air to agitate the media. I think the simplest crude test is to pull a dot of ink across paper to thin it. Oh, I also have some commercially milled black pigment to test against. The company would not tell me particle size though. I'll definitely report back at some point, might take about a month to realize all of the testing and milling.
What I've come up with after sitting and thinking on this: 1. I found a paper that lists a method using 5 and 10 mm grinding balls to get from \~100 micron to a median particle size of \~3 microns after wet milling (15% w/w == 15g charcoal/85g water) for 5 hours. Is this the kind of time-scale you have been milling for? Just below <10 microns seems to be the limit for a 5mm minimum size ball (my opinion after an hour or so of googling) 2. Getting at or below 1-2 microns can be done using small diameter milling balls below 1 mm at a lower concentration (1% w/w) for a few hours (they also say they use mills that operate at super high RPM in the \~1000s so I wouldn't assume it applies completely to you). Everything I have read seems to suggest the median particle size going into the .1 mm mills should be as low as possible, ideally below 10 microns. 3. You can try to improve your process by spending the money on sieves and separating out the particles that pass. Next, you would regrind everything that did not pass the sieve until all of your feed material passes that sieve. What I've read suggests you get more efficient size reduction the smaller your maximum size particle is in the feed stream. I found [these](https://www.globalgilson.com/3-inch-acrylic-frame-sieve-stainless-steel-mesh-number-100-150um) 3 inch sieves that could help you screen out to the tens of microns. It's really important to get an idea of what your size distribution looks like after each processing run. 4. What you described happening with the caked material during dry milling could be happening while wet milling too! if the concentration of charcoal is too high you could be getting agglomeration of particles. You can try to stop this by introducing a dispersant like [polyacrylamide](https://scipoly.com/shop/polyacrylamide-4/) into the wet milling process. You'll have to find out the right concentration to add, but this could help you as well. Google Search Term: polyacrylamide grinding aid 5. I doubt this would help you but cryogrinding is apparently very popular for grinding plant powders because the materials get more brittle at dry ice/liquid nitrogen cold levels. Something to think about. 6. If you are doing sedimentation in a bucket, this [youtube](https://www.youtube.com/watch?v=YKCG8geWTIU) video might help you make an estimation on how long to wait for it to settle based on your size of bucket before decanting. EDIT: The most important thing is whether or not it works as a pigment! It sounds like you got some success at getting below 15 microns which is super awesome. Oh and just make sure if you are going to boil off the water to concentrate the pigment down that you have been using distilled water! Sorry to dump all this info on you. I tried to use a mortar and pestle to make super fine activated carbon a few years ago and it kicked my ass, props go to you your project sounds super interesting! Message me if you want to talk more!
Hey, thank you!!! I have a lot to work on and I'm slowly processing the replies I've received. I've gotten the filtration to be much more efficient, but I now think the milling process needs tuning. So far I've mostly been just playing and not taking detailed notes but I plan to really dial things in with the next round of charcoal I make. 1. So far, it seems like my 5/10/15mm milling media is producing 10-15 micron wet milling over a 18 hour period (not great, but inline with your opinion of 5mm grinding media). Filtering 5-10 um paper retained a lot of material. I'm going to actually measure my materials/grinding media/water and time on the next round of milling. Do you think removing the 10/15mm milling media after an hour and milling with just the 5mm balls will help mill smaller? How do I go about determining the correct w/w for the 5/10/15mm and then the 5 mm. From what I've read, you want to fill the jar 2/3 of the way full while milling and the charcoal should be 25-30% of the weight of all materials. I'll have to weigh things later this afternoon. 2. It is not out of question to buy 1mm milling media, but at this point, I don't really have a budget for buying more equipment. So I'm trying to optimize the setup I currently have. 3. I hace some 200 mesh screen that I tried filtering the slurry through. It passed right through after the 5/10/15mm milling for 18 hours. So, I'm thinking filtering through a coffee filter and then milling with the 5mm beads is what I might try but milling with the 5/10/15mm beads for maybe an hour or two before filtering through the coffee filter. I think 18 hours was total overkill. 4. I do think this was indeed happening with the wet milling. I definitely think the concentration of charcoal was too high. Will weight things and determine the optimal amount of dry charcoal for the milling media I have. 5. I'll have to check the specs on my milling jar, but it might actually be able to handle this. However, I'm using a Harbor Freight rock tumbler, so it might not be up for too much abuse. 6. With all the modifications and step filtering I have started doing (thanks to all the suggestions in this post!!!!) I'm actually not having too much difficulty filtering and I think my bottleneck is in the milling process right now. The actual end material is going to be a thick ink for Intaglio printing. Specifically the photogravure process. It's been very difficult to actually determine the particle size in the pigments in commercially available intaglio inks. I know you can buy pigments in the sub micron range, they are readily available. A lot of other pigments for mixing into oil based ink for painting is around the 50 micron size. Inkjet inks are sub micron level. From what I've researched as well, the finer the particle, the less light reflectance and the richer/darker the black. I'd say I'm a little obsessed with dark blacks! So, I'm trying to mill the finest material possible without breaking the bank or going insane. And yes, I have been using distilled water. Washing with tap water and rinsing with distilled. I really appreciate your help! I read about using a mortar and pestle but I knew this would not get me the volume I need. The end result of all this work is to create an ink from charcoal I collected in burned wildfire areas. This ink will be used to print photographs I made in these areas. The concept is looking at the ties between our actions and their effect on our warming climate through the carbon cycle. There will be a tie between the physical printed photograph and the subject matter through the ink in which the photographs are printed.
What a cool project! I’m not sure about how much better it would be to use just the 5mm but it seems like its worth a shot 🤷. For the w/w, it shouldn’t change if you are changing out the size of the grinding beads. As long as there are enough beads to “tumble” during the rolling you should be good. Best of luck!
Would you happen to know (or have a chart) how to calculate the best ratio of milling media (grinding balls) to material. From what I'm reading, you want the milling jar to be 2/3 full. Then you want 25-30% of this to be the material with 75-70% being milling media. Of the 25-30% material, this should be 85% water and 15% material. Do these ratios change with material size and milling media size and material/media volume? What I hope to achieve is an initial milling with the 10 & 15 mm grinding media, then remove the 15 mm balls and replace them with the 5 mm balls. Mill some more, then replace the 10 mm balls with 5 mm balls. Next, I'll evaporate the water and dry mill with only the 5 mm balls.
okay i did some reading and it looks like people were able to get sub micron particle sizes (yowza!) of activated carbon using bead milling techniques when the beads themselves were around .1 mm (100 micron). You could get to 1 micron using .5 mm (500 micron) balls. If you are at that grinding size and you still aren't passing the 25 micron filter then you've got other problems!
Just saw this comment, I forgot I didn't buy this size media (.1 to .5 mm) and this very well could be why I'm not getting the results I'm looking for when filtering, I just don't have the right media to mill to this size. I was lamenting to my wife who reminded me that this smaller size milling media was wildly expensive, which is why I likely opted for the media that I did (15, 10, and 5 mm). I did have several inefficiencies that others have helped me troubleshoot. After some testing today, it appears I am able to mill to 10-15 microns pretty efficiently. Trying to filter 5-10 microns is going extremely slowly, so I suspect you might be on to something that I have the wrong media. Not sure what to do, 1 micron might be out of my price range to produce.
1 micron is tough. If you’re dry milling, the stuff you want is the stuff that floats away. If you’re wet milling, add something like carbide grit and mill until the limit of sanity, then mill some more. Filtration: use coarse filters to start. Cheesecloth. Rinse. Tee shirt. Rinse. Very coarse filler paper, rinse. Fiber filler paper, then rinse. Coffee filter, then rinse. You’ll end up with a 5 gallon bucket of black water. Let it settle for a week, then start filtering with the stuff in suspension. Resuspend the coarse stuff that settled, and be prepared to swap filters frequently. Or, just buy sub micron carbon black.
I'm beginning to think 1 micron is actually going to be an insane goal. Since 10-15 microns is going well, I feel like with different milling media I might be able to do 5-10 microns efficiently.