Using activated carbon to remove dyes

[Sonny Jim]

My H2SO4 is dyed black. Today, I bought some activated carbon to remove the dye. I added the activated C to the H2SO4 and after a few hours nothing has happened. Is this alright? Anyone done this before? I'm a little concerned as to how long this should take, so I can guage how well it's working.

[Mumble]

Due to the Sulfuric being black, as well as the carbon, it may be a bit difficult to judge when any of the dye is removed. Filtering would probably reveal quite a bit. With sulfuric it's advisable to use a glass filter. Agitation of the mix will greatly improve the removal of the dye. I haven't actually done it before, but it is in the future. Mine has a mixture of dye and particulate matter. I already filtered out the solid matter at least. It would leave little brown specs in whatever I used it for.

[grandyOse]

Where are you guys getting your dirty acid? Hi-Yield brand "IONATE" soil acidifier?

I bought a bag of this stuff, thinking I could distill HNO3 from it. WRONG! Well, maybe after purifying it quite a bit. This stuff is pelletised and contains "free sulfuric acid physically held by a gel of silicic acid in combination with soluble sulfate of iron, zinc, and copper". Yeechhh, what a mess.

Is this stuff good for anything besides making the roses bloom?

[megalomania]

You did filter the mixture after you added the carbon didn't you, Sonny? It doesn't just doscolor upon adding the carbon, only after filtering would you get a discolored liquid. I am also not certain activated carbon is going to work. Decolorizing charcoal is made from animal bones exclusively. You can make your own by burning down chicken/pig/cow bones just like you would make charcoal for black powder (look it up).

[Sonny Jim]

I havnt filtered it yet. I had a niggling feeling that I should do that, but I wans't about to do it until I was sure it was nescessary. Thank you for that.

The charcoal I bought was obtained as 'filter carbon' from a pet shop. It's used in aquarium filters methinks. I assumed it would have decolourising properties because of this. I guess I will be able to tell you if it does upon filtering the H2SO4. Which brings me onto my next problem.

I can think of nothing to effectively filter fine particles from the H2SO4 that would not get eaten in the process. My usual filters, kitchen paper and somethimes fabric would be a gonner for sure. Would one have to construct ones own filter out of powdery inert material in a container for the acid to seep through or something like that?

[Anthony]

Would glass-fibre matting for GRP work be fine enough?

[Sonny Jim]

You are a genious :D

EDIT: But unfortunately my carbon did sweet diddly shit with my acid. I had it sitting there for 24 hours, and nothing happened at all after filtering. I think meg was right about needing to prepare my own. I am very disappointed, and I can't stand the sight of that acid, so I intend to use it up as it is but leave a little sample that I can try my animal bone carbon on.

[Mumble]

Activated charcoal is not the same as decolorising. Decolorising is made from animal bones, and activated is washed with phosporic acid or something to create a huge number of small pores to collect things. I think for an aquarium it would mainly filter out suspended particles. Perhaps try a water filter. I think those maily take out particles too. Ours does make the water taste less chlorine like though.

Also, heres a way to filter it out. I suppose you could probably use sand instead of the finely crushed glass. Its a modified apparatus we used in school to remove the Charcoal from water we were purifying. http://www.angelfire.com/empire/megapyro6/images/Acid_proof_filter.jpg My container is a HDPE container from a can of bubbles, very well washed of course.

[Chade]

As far as I was aware, activated charcoal was simply charcoal that had been treated so it had a large surface area and therefore improved adsorbtion qualities. Everything I can find about using activated carbon or activated charcoal to remove impurities, including dyes and coloured impurities only seems to back this up. The fact that it is charcoal and not pure carbon isn't a massive issue, as it's only the carbon that adsorbs the particles. Different starting materials should only affect the physical properties such as the softness/hardness, and pore size distribution. So it should discolorise, not matter what type of activated charcoal it is.

I've got a fair bit of activated carbon, as I use it for low pressure experiments. It you have a vacuum pump, you can get close to a vacuum, but you can't remove those last few particles. If you use activated carbon, the huge surface area, along with the tendancy for carbon to adsorb things onto its surface, means that it traps most of the remaining particles and much better vacuum. This was mentioned in one of those old amateur scientist pages on low pressure experiments from scientific american. (which I sadly don't have any more)

This page:
http://www.deltrex.com.au/products/s005.htm
contains safety data for activated carbon. Ignoring the frankly laughable safety requirements (activated charcoal is one of the safest things I can think of) it does use Decolourising charcoal as a synonym for it.

A very good Activated carbon page can be found here:
http://www.snowblack.com/carbon/carbon.htm
This explains everything better than I can, and it's quite readable. The two links at the bottom of that page give further info.

Some points to remember.
1/ Your activated carbon may not be able to adsorb your desired particle size efficiently
The structure of the activated charcoal is carefully selected (in store bought product) to adsorb a given range of particles. The charcoal is 'activated' generally by wet etching or pumping an oxidising gas through it at high temperatures, so a network of pores run through it giving a really, really, really big surface area (0.5 to 1 million metres squared per kilo). If it's designed to adsorb small particles, like nitrogen from air, the pore sizes will be on the scale of N2 molecules, and large molecules like proteins will be more poorly adsorbed. Most store bought activated carbon will be geared to adsorbing large organic molecules, rather than smaller molecules or atoms. There's a hefty range usually, so it'll still work, it just won't be optimised for that substance.

2/ Your activated carbon may not be as activated as you think.
How long has it been around? Has it been in a sealed container? If left out, it'll adsorb nitrogen and oxygen from air in significant amounts, and reduce the amount it can still adsorb. Funnell a cupful into a 2L plastic pop bottle (if you've that much to spare) and leave it a day or too. It should suck in the walls of the container a noticable amount.

Heating the carbon by baking it in the oven releases a significant amount of the adsorbed particles. If possible (read: 'if I can be bothered'), I bake the activated charcoal in the oven for an hour on high before use. This doesn't work forever though, and it you're looking to keep re-using the same activated carbon, you're out of luck. It'll help it last longer, but eventually it'll get choked with contminants that you can't get out.

I have activated carbon as a powder, and as pellets (cylinders about 1mm long). The powder is better for removing gases, as the pores are more easily exposed and it can adsorb quicker. The pellets are designed for use in liquids as the won't block liquid filters, like those for aquariums. The liquid can still make its way around the pellets.

If I was trying to remove impurities from H2SO4, I'd use the pellets in the acid, and leave it overnight. Then I'd pour it through a funnel of sand with a thin layer of pellets underneath to stop the sand being washed through. In fact, having written all this has inspired me to try this with my own acid. It only has a faint purple tinge, but I'll try it anyway to see if this works. Stirring would help, but sod that. I'll just give it a swirl every so often. (Note to self: build that automatic stirrer!)

Sonny Jim, do you have home brew stores by you? If you do, they sell activated charcoal optimised for decoloring wines and beers that should work great.

[edit: added following]
Found out about animal charcoal, also known as bone black. according to Wikipedia it's 10% carbon and the rest is phosphates. That means it'll just turn your H2SO4 into phosphoric acid.

There's an old high school science practical I used to do in my teaching days, which involved taking two bones. You put one in the oven for a while, and leave the other in H2SO4 overnight. The one in the oven can be crushed with light blows from a hammer as the fibres holding it together have been destroyed, leaving only the phosphates (mostly calcium phosphate) and carbon. The one in the acid has had the phosphates destroyed leaving the fibres making it bendy. You can literally tie a femur in a knot.

I really should have remembered that in the first place. I hope my students remember my lessons better than I obviously did. Anyway, activated charcoal will remove color, just don't use the charred bones. Unless you want phosphoric acid, that is.

[Sonny Jim]

That's interesting. I think I shall still attempt to decolorise a small sample my H2SO4 with the animal bones though, since they are easy to prepare. All the other hints and tips are greatfully receiced!

I've just whacked all hell out of one of the dogs bones (cow I think) and shattered it into small pieces, and have set about turning it into charcoal. I can tell you, nothing smells more disgusting. I shall test it's decolourising properties and report back here.

[grandyOse]

If I may veer off topic slightly; Activiated charcoal seems like a good way to incorporate KNO3 for black powder. If you can get the right sized filter charcoal, it should fill up nicely with microscopic nitrate crystals, which could then be crushed and dried, (or dried and crushed) for your black powder. Simple before and after weighing should reveal the proportions which can then be adjusted. Too bad I can't think of some way to incorporate the sulfer as well.

[Sonny Jim]

Well anyway, I have succeeded in preparing at least what looks like 'animal charcoal' The bones were heated without O2, and lots of stinking smoke was made. When this was about stopped, I discontinued heating just like I would when making regular charcoal.

A couple of differences were observed though.

The overall process took a lot longer before the smoke began to subside.

Although blackened all way through, it was nowhere near as fragile as regular charcoal, but much less tough than the bone.

Right. I then added the animal charcoal to the only thing I have about that I think could be de-colourised - blue antifreeze. Streams of very fine bubbles were produced eminating from the charcoal. That's it for now. I'll see if the antifreeze goes clear by tomorrow.

[Arkangel]

If I may veer off topic slightly; Activiated charcoal seems like a good way to incorporate KNO3 for black powder
One of the best sources for pyro charcoal is in filters from respirators etc. If you can get a boxful of them before they have been used you can get some REALLY high quality BP

[Mumble]

Activated charcoal wont work well for BP, well at least as good as some other kinds. It has been discussed elsewhere, but I doubt you've came across it. The problem, while it does have a large number of pores, is that it lack the naturally occuring volitile oils that seperate good BP from great BP. The bp made will by no means be bad at all, it will be suitable for most purposes. Perhaps a mix of willow and the activated filter charcoal would work well. You get your oils, and you get the micropores.

[Edit] Errors. This is just reports from others I've heard. I've never actually tried it personally. I stick to my homemade willow because it works well.

[Arkangel]

Actually that does make sense. I've only used it in limited amounts, but maybe the improvement I saw was because my normal charcoal is so shitty:)

[Sonny Jim]

Right, a couple of test results. The antifreeze didnt do much, but when I added the charcoal to methylated spirits the liquid went red and a thin blue layer formed on the top of the redness. Not clear though, but something is happening. :confused:

I did have another thought though. If calcium phosphate is present in these bones, would they be a viable source of P when heated in a furnace, releasing P vapour which goes through water? I read a thread here on it.