Fantasma4500 - 1-7-2021 at 13:02
very long ago, maybe 5 years+ i was prompted by a youtube with a method for turning stainless steel into sodium chromate- at the time being for
whatever reason i failed it, and i deemed the method not working
it was essentially a way of isolating/purifying chromate.
first up the SS is dissolved in HCl
then its ppt'd with Na2CO3 or NaOH
then the chromium hydroxide is oxidized using NaClO, bleach- but using electrolysis of NaCl for this
chromate is formed. now at this stage you need to seperate out the NaCl and chromate
you do this by adding copper salts, i used copper acetate just recently
how youre supposed to do this broke my head for quite some days, i knew it was possible. then i found an ancient note regarding exactly this from that
youtuber, it was ingenious and it works.
copper chromate can be reacted with NaOH to form Cu(OH)2, and with heating- CuO. infact the granules of NaOH was already forming CuO on contact with
the sludge after it first formed a very beautiful blue colour
i can confirm that it also does generate sodium chromate, as the 200mL of solution has now settled down leaving a strongly yellow colored solution
along this process i also figured a method (with help of others) to produce ammonium dichromate.
Cu2Cr2O7 + (NH4)3PO4 = (NH4)2Cr2O7 + Cu3(PO4)2 (ppt)
the thing is, i was trying to abuse the fact that copper chromate is insoluble in water, where copper dichromate is soluble- so acidifying copper
chromate should yield water soluble copper dichromate, which could then be seperated into ammonium dichromate- one can then abuse the ammonium salt by
reacting it with NaOH to form NH4OH (which can then easily leave solution) to acquire sodium dichromate
with this very doable method, with a working electrolysis setup one could really produce some nice bulk of chromate from stainless steel- the
stainless steel could also be dissolved using electrolysis of NaCl.
macckone - 1-7-2021 at 20:46
Original youtube from extraction and ire. He is a member here.
https://www.youtube.com/watch?v=F_W-IyUTM5M
https://www.youtube.com/watch?v=3uzTNjuUyyk
Fantasma4500 - 2-7-2021 at 06:36
he didnt get to do copper chromate but went into calcium chromate to calcium dichromate into ammonium dichromate
i believe using phosphate on copper dichromate, or could probably work with calcium dichromate as well would work better
but with calcium dichromate you would have other impurities, and thats why copper chromate is really interesting
clearly_not_atara - 2-7-2021 at 08:26
The monohydrogen phosphate <> dihydrogen phosphate pKa is 7.2 but the dichromate <> chromate pKa is about 6 at low-ish concentrations. So
phosphates will be quite protonated and possibly soluble under this condition. Oxalate might work (pKa2 4.14) as long as you don't get complex
formation (an issue with oxalates).
But maybe you could precipitate potassium dichromate with K ions and acid?
macckone - 2-7-2021 at 11:01
Antiswat,
He used the chromate waste in his copper chromite synthesis in another video.
https://youtu.be/3KrjbIp-Za0
Doug and NileRed also have videos.
Amos - 3-7-2021 at 08:03
I don't know why you're bothering with copper; just extract the mixed oxides with bleach, reduce pH with sulfuric acid and add potassium sulfate
solution; potassium dichromate will readily crystallize out. You can even use the potassium bisulfate byproduct of nitric acid distillations.
Fantasma4500 - 5-7-2021 at 02:49
@macckone
i dont see him using copper chromate, he does make ammonium copper chromate which he then decomposes into copper chromite
one drawback of copper chromate is that it hydrolyses and doesnt sink very well to the bottom of a liquid so you need to filter it
i found out that if theres not much ppt you wanna add some NaOH and the copper chromate will come out, not sure how that was required, pH wasnt acidic
to start with.
im not so happy about potassium dichromate, i got a bunch of it in a PTFE lid glass bottle, it forms chlorochromate with too much HCl which forms
chlorine gas, also.. H2SO4 in something with bleach? wouldnt that generate chlorine gas? theres surely some chlorates in there which should form Cl2 /
ClOx
my method could be done without fumehood, and thats a major plus