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MeshPL
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Disposal of hexavalent chromium
Hello everybody!
Assume I will do an experiment with a minute amount of hexavalent chromium in form of chromic anhydride (no more than 1g). I will actually likely test
it's influence on plants.
The only problem is I MUST dispose the waste SUPER properly.
I know adding a waste to a bucket of acidified reducer will get rid of Cr(VI) to form much less harmful Cr(III) which can be flushed down the drain.
In terms of reagents, I'm slightly limited. I mean if it is necessary I can order something, but anyway:
Will phosphoric acid in form of a 25% rust remover be ok to acidify reducer solution? Or just plain vinegar?
Can I use sulphur + NaOH reaction products (polysulphides + thiosulphate) as a reducer? Or just some sugar/glucose?
Thanks for help!
[Edited on 6-10-2015 by MeshPL]
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woelen
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Some phosphoric acid with glucose added works fine as reductor to convert the hexavalent chromium to chromium(III). Just gently heat the solution or
allow it to stand for a day or so and then you can flush it down the drain. For a gram of chromic anhydride you could take 50 ml or so of your 25%
acid and a few grams of glucose.
Plain sugar works as well, but it reacts much more slowly. Denatured ethanol can also be used as a reductor.
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MeshPL
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Thank's for the response!
The only thing is I haveto do it SUPER properly, like 100% according to law so that no one can think it could harm enviroment (part of "research" I
may have to do for competition). So we can assume all Cr(VI) will be reduced to Cr(III).
Now I'll just need to find out if vague term "waters" used in law here also covers "canalization"  . Cause strict norms of Cr content apply to "sewage" which is dumped into the ground or into "waters".
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DalisAndy
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When in doubt with chornium ions, call hazmat since chornium ions are carcinogenic. And flushing them could be a legal violation
Elements Collected: 19/81 (Excluding all radioactive, using placecard for those)
Any tips or good sources are welcome.
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gdflp
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Quote: Originally posted by DalisAndy  | | When in doubt with chornium ions, call hazmat since chornium ions are carcinogenic. And flushing them could be a legal violation
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For 1 gram? That's completely ridiculous. Chromium(VI) ions in solution are not that dangerous, they are
toxic, but it has only been shown to be a carcinogen on repeated exposures to airborne dust(which you can't get from a solution) or chronic ingestion
of solutions of it. Wearing nitrile gloves is a simple precaution which prevents skin contact, mitigating essentially all risk with such small
amounts.
Slightly acidified sodium metabisulfite renders solutions harmless very quickly by reducing them to chromium(III) which is not carcinogenic and not
significantly more toxic than other transition metal ions such as iron or copper.
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Little_Ghost_again
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| Quote: Originally posted by MeshPL | Hello everybody!
Assume I will do an experiment with a minute amount of hexavalent chromium in form of chromic anhydride (no more than 1g). I will actually likely test
it's influence on plants.
The only problem is I MUST dispose the waste SUPER properly.
I know adding a waste to a bucket of acidified reducer will get rid of Cr(VI) to form much less harmful Cr(III) which can be flushed down the drain.
In terms of reagents, I'm slightly limited. I mean if it is necessary I can order something, but anyway:
Will phosphoric acid in form of a 25% rust remover be ok to acidify reducer solution? Or just plain vinegar?
Can I use sulphur + NaOH reaction products (polysulphides + thiosulphate) as a reducer? Or just some sugar/glucose?
Thanks for help!
[Edited on 6-10-2015 by MeshPL] |
Its a good plant killer! chromic anhydride is normally used to quantify the organic carbon content of plant material using the Turin method of Chromic
Anhydride in sulphuric acid and titration.
I havnt seen or read of anything about using it as an additive of some sort but hey I could be wrong.
I dont have the reference handy but if your trying to get the Organic C then the Tyurin 1975 method has been superseded by a better more accurate
method, I will look it up if that what your doing. I have also been messing with plants on the quiet  but keep in mind alot of tomatoes have died in my endeavors
[Edited on 6-10-2015 by Little_Ghost_again]
Dont ask me, I only know enough to be dangerous
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MeshPL
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I mean I want to test Cr(VI) influence on plants at different concentrations. Not that I want to titrate poor plants, they wouldn't survive it.
My current plan is to plant some garden cress, on a cellulose soaked in Cr (VI) solution. I'll test several concentrations, from control test, to
visibly yellow-ish (or higher if it turns out to be very dilute still), including safe to drink and safe to dump. And after some time compare the
plants and their amount.
Why do I want to use chromic anhydride? It turns out it was the cheapest source of Cr(VI) available for me. And I still have some hanging around.
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Little_Ghost_again
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| Quote: Originally posted by MeshPL | I mean I want to test Cr(VI) influence on plants at different concentrations. Not that I want to titrate poor plants, they wouldn't survive it.
My current plan is to plant some garden cress, on a cellulose soaked in Cr (VI) solution. I'll test several concentrations, from control test, to
visibly yellow-ish (or higher if it turns out to be very dilute still), including safe to drink and safe to dump. And after some time compare the
plants and their amount.
Why do I want to use chromic anhydride? It turns out it was the cheapest source of Cr(VI) available for me. And I still have some hanging around.
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I would look up the method I mentioned, even in tiny amounts it wont do the plant much good.
Dont ask me, I only know enough to be dangerous
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MeshPL
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It may not do anything good, but what and how much bad it will do is the other thing. Also I assume the safe for drinking concentration and safe for
dumping concentration will not be too harmful.
I may not do that experiments in near future or at all, but I'll try to post the results once I'll do them.
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Amos
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How about you reduce it(for small amounts I like to use a piece of vitamin C tablet, I bet citric acid will also work albeit more slowly) and then add
baking soda or sodium carbonate solution to precipitate the hydroxide, filter it out, and put it in the trash?
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MeshPL
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I bet that chromium hydroxide would contaminate landfill. Slightl, but still. So it wouldn't be much better. But not worse either.
But if I would roast it a bit, chromium (III) oxide will be formed which is so inert it would definitely be safe to dump.
[Edited on 9-10-2015 by MeshPL]
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Little_Ghost_again
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Are you growing the plants soil based or soiless? I do alot of plant experiments and if poss go with soil less. If you have a micro scope take a slice
of a control sample root tip and one with Chromium, take a good look at the meristem cells. Also look at the leaf guard cells (look at shape).
Dont ask me, I only know enough to be dangerous
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MeshPL
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Thanks for the microscope tip! Although I don't have an actual microscope, I have an acces to.
I was planning to go with soilless anyway. That's why I opted to chose garden cress. It grows well soiless and it does it fast and in large amounts.
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MeshPL
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Actually I've found out I may not be allowed to use any mutagenic, dangerous or
enviromentally dangerous substances.
But if I did l I would have to dispose them properly anyway. Nevertheless, in that case, I would break rules, causr I used them. Sounds strange but is
true.
And the more stupid thing is the fact that thins like FeCl3 or CuSO4, KMnO4 fit these definitions. Solvents too. Even things like mortar, nail polish
remover, window cleaner and most detergents.
Theoretically, if I prove anyrhing is harmful for the plants, I'm breaking the rules, cause I've proven something is harmful towards plants and thus
enviroment.
I have a kind of stupid, yet intrresting idea: test effects of glucose/fructose/sacharose (I think I may chose glucose) on garden cress... results MAY
be interesting, although the idea of giving plants some sugar sounds stupid. Plants grown in sugar containing enviroment may grow better (more energy
available), but may also grow worse (less need to make own energy, harder osmosis). And sugar shouldn't be considered anykind of dangerous.
Will consult my mentor (his not chemist, but biologist, hence I asked you guys about Cr(VI))
[Edited on 11-10-2015 by MeshPL]
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Tsjerk
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Plants love glucose, the trick is to do it sterile otherwise everything overgrows with fungus in no-time.
I know you can sterilize arabidopsis seeds with bleach and then grow them in a sterile 50ml falcon tube partly filled with liquid medium. Just place
them on a shaker (I know, sounds strange to grow plants in liquid medium on a shaker, but it works fine).
The medium you have to filter sterilize because in an autoclave the glucose will caramelize.
Afterwards you could dry them and weigh the mass.
[Edited on 11-10-2015 by Tsjerk]
[Edited on 11-10-2015 by Tsjerk]
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jackchem2001
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I've recently been spending some time in an academic lab. Today me and a PhD student were working with chromium trioxide in water. While the bulk
solution was put into a waste container, all of the glassware cleaning was done in the sink. The PhD student said it was okay to be released in small
quantities (maybe half a gram total of CrO3 down the drain). Lab manager said the same thing
I am obviously not going to go and tell some university how to run their lab but this does feel a bit negligent, especially when the Cr6+ can be
neutralised cheap, fast, and easy (adding reducing solution)
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j_sum1
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Thread Moved
12-8-2025 at 02:06 |
Sulaiman
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a safe way to dispose of all of the chromium may be to electroplate objects that need a chromium plated finish.
CAUTION : Hobby Chemist, not Professional or even Amateur
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j_sum1
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CrO3 used to be routinely used to clean glassware. I am sure it was dumped down the drain.
As a minimum I reduce to Cr(III). (Very) small quantities can be flushed IMO.
I store and recycle larger amounts most of the time.
If I must dispose of it and it is more than a gram or two, I reduce to Cr(III) and then precipitate. I then mix with cement and sand and make a solid
inert block that I don't mind throwing in the trash.
Cr(III) is released into the environment via corroding tapware and plated objects. Cr2O3 is routinely used as a colorant for concrete and in pottery
glazes and other similar applications. I figure that if my activities are comparable in scale and kind, then I am not causing excessive harm.
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teodor
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Flush or not to flush Cr(VI), that is the question!
Some people say Cr(VI) kills those gems they use for water treatment on sewage plants. This is the explanation I have heard why Cr(VI) is no good to
put down the drain.
But any chemist who is familiar with the topic will tell you that any soluble Cr(VI) compound will be reduced on the first contact with organic matter
which will occur far before the sewage can rich the plant.
So, depending on your experience with organic oxidation by Cr(VI) ions and glassware cleaning you can follow those who tell you not to flush it
without reducing or flash it as it is. Both sides have their arguments. If somebody was really interested and the topic is so serious economicwise I
expect there should be some publicaion on ResearchGate about the life of Cr(VI) ions in sewage.
Based on my experience I don't care about reducing it when it is hard to do (like glassware cleaning) but if I need to get rid of 1L solution I spent
a minute to do neutralization. Basically I don't think it is required. The sewage itself has the same reducing properties as any other compound you
can use for that. And, for example Cu ions are not less deadly for gems in the water as well as zillion other compounds. I believe Cr(VI) polution is
far from the top 100 problems of sewage plant operation.
So, this topic has a sense only as an instrument to divide amateur chemists into 2 camps - those who flush and those who don't. This makes much less
sense than discuss any chemistry of Cr(VI) which fits both camps.
P.S. I expect some day when people will try to know "flush or not to flush" AI will suggest the solution based on my answer here. 2 days ago I asked
google what is the solubility of lithium acetate in methanol. Their AI presented me the answer based on my own post here. I know that because I was
not lazy to check the source. But really, do you think flushing Cr(VI) is a bigger problem than that?
P.P.S. The image as a chemist as an evil and the nature and people around as a victim is the achivement of the latest time. Try to kill all slugs in
your garden or educate orhters and you can understand who is a real victim. Home science today requires more protection from us than that nice world
around.
[Edited on 12-8-2025 by teodor]
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Eithern
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| Quote: Originally posted by j_sum1 |
If I must dispose of it and it is more than a gram or two, I reduce to Cr(III) and then precipitate. |
Do you use NaOH to form the hydroxide?
For the reduction I normally use citric acid, is cheap and very effective.
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teodor
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Na2SO3 works great for soluble chromates. Insoluble chromates coule be also reduced, but I am not sure that with any reducer. I had 2 incindents with
dichromate mixtures, once I had it on walls (and myself) and second time on a carpet. That one on a carpet I was failed to redice, so just covered the
place with a tape. It was removed later together with a carpet.
So, basically cheap Na2SO3 can work except in cases I just described.
Also, still alive.
P.S. There are some procedures of getting dichromate from stainless steel published in different places including youtube. Most of them are not
accurate enough and can produce more insoluble chromates than soluble ones in form of e.g. ferric chromate. I believe nobody cared pouring off that
rusty residue. So, as you see, the question of better understanding chemistry and what we are doing is the most important one.
The world Health Organization's limit for drinking water of 50 μg of Cr(VI) per liter. If I understand it correctly that means 140 ug for K2Cr2O7
compound. The typical waterflow in sewage as google AI suggests is 200 l/day. That means if you pour 10g per day and nothing is reduced the seawage
water should be no more than 1/360th part of your drinking water - it's like 2.5 ml to liter. If I would add sewage to my soup at this quantity I
would no bother about Cr (VI). Actually, it would make the soup more healthy. So, I don't think it can be a real problem. Except probably for sewage
plant operation.
[Edited on 27-8-2025 by teodor]
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chloric1
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| Quote: Originally posted by Amos | | How about you reduce it(for small amounts I like to use a piece of vitamin C tablet, I bet citric acid will also work albeit more slowly) and then add
baking soda or sodium carbonate solution to precipitate the hydroxide, filter it out, and put it in the trash? |
If you go to the trouble of precipitating the chromium(III)hydroxide you mind as well keep it in a vial or glass jar for later use. Just oxidize
with sodium hypochlorite and you get your Cr(VI) back and you can convert it to potassium dichromate by potassium chloride and acidification with
acetic acid
Fellow molecular manipulator
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teodor
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.. actually chromium (III) hydroxide in alkaline conditions is partially converted to Cr(VI) by air very fast (practically on filtering stage) which
is kind of chromium - hydroxide - chromate and if your concern is safety all insoluble compounds of Cr(VI) are much more dangerous than solible ones
because they are not reduced on contact with tissues, so they can penetrate cell walls and cause mutations in much bigger proportion than K2Cr2O7
which will be reduced by body fluids. But you know, I am sceptical on the attempts to study safety BEFORE chemistry, so you can ignore my posts in
case, for example, if your attitude is different 
... in some old book I have read that CrO3 has acrid taste which is mostly released on chawing, but not so strong as I don't remember what, but that
second (reference) compound was some really nasty stuff, I am sure it was. This type of analysis is not recommended for home chemistry though ...
Update
Seriously, those safety discussions are not substitute for discussing of experiments and sharing their results. But because it looks like today
nothing happening in our laboratories (well, I have cleaned volumetric glass with KOH/ethanol and now try to recallibrate), I took the book "Standard
methods for the Examination of Water, Sewage, and Industrial wastes" 1955 and have read the chapter about chromium.
There is almost no Cr(III) in water, especially in sewage which is alkaline. By the same process as I mentioned for chromium (III) hydroxide all
chromium is converted to Cr(VI) by air. So, it doesn't mater
DO YOU reduce Cr(VI) or YOU DON'T reduce it
The chemical process in water will convert everything to Cr(VI).
Most of Cr(VI) in water is from minerals, not from home chemists.
So, I was not right that everything will be reduced to Cr(III), but still, it doesn't matter.
[Edited on 27-8-2025 by teodor]
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chloric1
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Holy crap teodor that’s terrifying! I have a glass jar with 1 KG of pure CrO3 crystals I’ll use to make ammonium dichromate and other chromates
with and I can only describe the odor as evil metallic smell. It may be a solid but next time I get into the jar, I’m wearing a respirator! Well
at least until I get it fully dissolved in water and no mist is over the solution! You’d be surprised how many solid reagents produce mist! Alkali
hydroxides and sulfamic acid are two I experience irritating mist from.
Stuff can be handled safely just have to avoid spills or at least have a containment contingency and prevent accidental absorption into the body with
prudent hygiene protocols.
Fellow molecular manipulator
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teodor
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So, chloric1, you also noticed that. I also try to work with CrO3 in a fume hood because otherwise it acts as a pepper on my nose. I unable to explain
that. The same with chromic acid solution, that one which is based on HNO3 is particularly volatile and irritating as fumes, not as HNO3 but much
worse. Mist/dust? Probably, still I am not sure. But may be if we would taste the "reference stuff" for the acrid taste on a daily basis we can better
tolerate those things.
That case with spill was exactly during ammonium dichromate preparation. You know, "volcano", some people like it. The accident happened because the
beaker I put on my shelf with the mixture was cracked without any visible reason (most probably defect in manufacturing) and I noticed that after
several weeks or monthes. It was a big spill under the bed (I didn't have a dedicated laboratory space, bedroom, work cabinet, musical studio and
chemistry laboratory in the same room). But that CrO3 was "for synthesis", so 90% or less of purity, I expect there were some other metals which gave
insoluble staff.
If you need to reduce some insoluble staff you can try H2O2 or oxalic acid, that what I tried for barium chromate in my experiments with insoluble
chromates, probably it was my first publication here.
What I am disappointed about is that some shop cells such pieces of volumetric glassware that even hot chromic acid unable to degreese that.
If you have developed a normal laboratory habbits I doubt you can have dangerous contact with Cr(VI) except if you do experiments with insoluble
chromates - when dry this staff is like a dust. For example, I always put gloves when I touch glass because the grease from hands go to outer side of
glass and then it spread itself and goes inside then. I don't like when I see drops inside a flask or beaker, that means that the surface is greased.
So, respect to glassware pays you back and you are more safe when you are careful with glassware operations. But some lessons must be learned first.
Oh, I see, you have mentioned sulfamic acid! Did you try to warm it to ~ 200C ? At this temperature it produce mist which is not possible to adsorb by
water, it goes through it without reaction into your room. Old school of german chemists would definitely identify SO3 by its property. Because they
had, I would say, the first-tooth experience. By this reason when they built sulfuric acid plants they didn't try to adsorb SO3 by water, it doesn't
work. But this strange penetrating SO3 through H2O is completely different story than we discussing now. If I will not poison myself some day probably
I will tell you. It goes to water not directly but through pyrosulfate ion.
[Edited on 27-8-2025 by teodor]
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