lodcomm Posted August 20, 2009 Posted August 20, 2009 Hey All, I will shortly be treating a batch of Mg using a solution of potassium dichromate in water. My question is - what is the best way to treat the left over dichromate solution so it can be safely disposed of. -thanks
WSM Posted August 20, 2009 Posted August 20, 2009 Hey All, I will shortly be treating a batch of Mg using a solution of potassium dichromate in water. My question is - what is the best way to treat the left over dichromate solution so it can be safely disposed of. -thanks I believe the residual material is potassium chromate which could be converted from chromium (VI) to chromium (III) but I haven't studied a process to do so yet. What I have done is concentrate the filtered potassium chromate solution by heating to drive off surplus water then added copper sulfate solution which dropped out (medium brown) copper chromate. I washed, vacuum filtered and dried the copper chromate but discarded the potassium sulfate solution. I plan to use the copper chomate (powdered) as a catalyst in perchlorate rockets or put it in a crucible and roast it into black copper chromites for a superior AP/HTPB propellant catalyst.
Mumbles Posted August 21, 2009 Posted August 21, 2009 There is really no way to "Safely" dispose of it at home. No matter what you do to it, it can't be flushed down the drain or put on the lawn or anything like that. You might want to do the following manipulation, and save the solid in a jar. Collect it, and all other heavy metals for a while, and see if the city/county offers any heavy metal waste disposal. As you may know, chromium (VI) is the bad stuff, so we want to get it to chromium (III). Whether it be dichromate (orange) or chromate (yellow), they are essentially just as bad for you. They both treat Mg the same, so you really could filter it, and evaporate the water. If you want to keep things consitent, and you do have chromate, it can easily be converted to dichromate by acidifying the solution with vinegar or HCl. Most of the OTC chromium reductions have some side effect. For a while I was promoting reduction with oxalic acid. It produces a black potassium chromium oxalate complex that precipitates out of the water. I'm still looking into how safe that is. I've also recomended acidifying, and mixing with dextrose to allow that to serve as the sacraficial reductant. The other suggestion is good too though. Copper Chromite has many uses, and is a powerful catalyst. I have a stockpile of special copper chromate right now I've been meaning to convert. By inclusion of ammonia into the chromate stock, it produces many micropores in the final product. It's better for the chemistry catalytic activity, and I was advised it may also be better for rocket compositions.
lodcomm Posted August 26, 2009 Author Posted August 26, 2009 (edited) There is really no way to "Safely" dispose of it at home. No matter what you do to it, it can't be flushed down the drain or put on the lawn or anything like that. You might want to do the following manipulation, and save the solid in a jar. Collect it, and all other heavy metals for a while, and see if the city/county offers....... Thanks for the input.. I'm not Ewell Gibbons or the like, but the Dichromate is particularly ugly stuff, and simply dumping it would be a fairly lameass manouver by anyones standards. Is there any reson why I could not simply evaporate the h20 from the left over solution and reclaim the dichromate for use another time - say using it in Velines super prime or the like? Which begs another question: In Velines super prime (and other various compositions), I see the addition of Dichromate. I am assuming that this is simply screened or milled dry into the composition. In these formlations, is the dichromate being added for its protective properites on one of the other components (say the MgAl in the super prime) or rather contributing somehow to the reaction? - I would imagine I could simply dispose of (burn up) my reclaimed Dichromate in one of these compositions. (Thus allowing Mr Gibbons to rest in peace -t Edited August 26, 2009 by lodcomm
Mumbles Posted August 26, 2009 Posted August 26, 2009 You can absolutely evaporate it, and reuse it. It might be partially converted to the chromate, but I can't think of a situation where that would really be a problem. Dichromate is added to those kind of mixes as a catalyst. It speeds up the burn rate, and gets it a bit hotter. I suppose it can't hurt as far as protection, but I can't think of anything in those primes that would attack it. Maybe the water used to wet it. MgAl is actually fairly resilient toward attack. Thats not a bad use of reclaimed dichromate actually.
mercyfulfate Posted October 3, 2014 Posted October 3, 2014 Addition of sodium metabisulfate will convert hexavalent chromium into safer trivalent chromium.
pyrojig Posted October 3, 2014 Posted October 3, 2014 That method sounds about right , and even a further treatment with a iron salt( I believe it was iron sulfate ) but dont quote me on it. that makes it a disposable safe chem at that point . WSM was sharing that with me a year ago, when I asked him the very same Q. Ill have to re-check my notes , but a PM to him may get you a very simple method and safe way to dispose of that toxic material.
schroedinger Posted October 3, 2014 Posted October 3, 2014 Also it would be able to add a barium compound to precipate solid barium chromate. But like mumbles said, the best way to dispose this stuff is local hazardous waste disposal of the solution.If you boil it for concentration do it outside, i would be concerned about tiny ammounts getting airborne due to spitzes ormthe like.
taiwanluthiers Posted October 3, 2014 Posted October 3, 2014 Question is, how is burning dichromate in the form of veline superprime any better than dumping it in the lawn? Does burning it render the dichromate safe?
schroedinger Posted October 3, 2014 Posted October 3, 2014 Well i would assume that chromate will be converted to Cr2O3 in the temperatures of the hot flame of a star which is much better, but still just leave ut out that prime works without too
marks265 Posted October 6, 2014 Posted October 6, 2014 Put 1Kg of Mg in a tub. Boil 300 grams of distilled water (or microwave) in a container. I use a dedicated coffee cup. When boiling and removed from heat add 50g of dichromate. Stir and it will dissolve rapidly. Quickly add this to the tub of Mg and stir quickly again. You'll be in for a treat at this point but don't chicken out. Because it will pop and spit. Once well mixed spread it out on paper to dry. There won't be a lot of liquid and you can burn the paper. Done! Reminds me I gotta make a batch again myself! Mark
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