Sciencemadness Discussion Board

Disposal of hexavalent chromium

MeshPL - 6-10-2015 at 07:21

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]

woelen - 6-10-2015 at 09:21

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.

MeshPL - 6-10-2015 at 09:48

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" :mad:. Cause strict norms of Cr content apply to "sewage" which is dumped into the ground or into "waters".

DalisAndy - 6-10-2015 at 10:27

When in doubt with chornium ions, call hazmat since chornium ions are carcinogenic. And flushing them could be a legal violation

gdflp - 6-10-2015 at 11:11

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
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.

Little_Ghost_again - 6-10-2015 at 14:24

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 :D but keep in mind alot of tomatoes have died in my endeavors

[Edited on 6-10-2015 by Little_Ghost_again]

MeshPL - 8-10-2015 at 08:02

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.

Little_Ghost_again - 8-10-2015 at 09:57

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.


I would look up the method I mentioned, even in tiny amounts it wont do the plant much good.

MeshPL - 8-10-2015 at 10:45

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.

Amos - 8-10-2015 at 10:49

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?

MeshPL - 8-10-2015 at 22:18

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]

Little_Ghost_again - 9-10-2015 at 01:04

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).

MeshPL - 10-10-2015 at 09:21

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.

MeshPL - 11-10-2015 at 00:36

:mad: Actually I've found out I may not be allowed to use any mutagenic, dangerous or enviromentally dangerous substances.:mad:

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]

Tsjerk - 11-10-2015 at 02:34

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]