I had a viewer on YouTube leave me a comment about the dangers of Hexavalent Chromium in the waste water of my Hydroxy experiments. This made me concerned about what it was I was doing, but the warning only told me to watch the movie "Erin Brokovich" to see how bad it was. Oh, and don't throw away the water.
Well, rather than rely on a movie I decide to find out what OSHA had to say about it. Essientially Hexevalent Chromium, Cr(VI) is a known carcinogen which causes cancer over long periods of exposure. It also causes cell necropsy in the lungs when inhaled. Woah! More reading indicates that the acceptable levels of exposure are set pretty low. This is unlike Trivalent Chromium, Cr(III) which is an essiential trace element.
Now that I know what kind of problem I'm dealing with, I decided to see if there is an industry solution out there. Thus the digging begins and about 2 days later the result I'm looking for pops out at me and the rest can be pieced together pretty quickly. namely, that Fe(II) can be used to reduce Cr(VI) to CR(III). Way cool! Now what does that mean to me?
More digging reveals this adobe file.Tertiary Treatment Chemical Treatment. The third paragraph, titled "Removal of Hexavalent Chromium" contained everything I needed to know about the subject, namely to reduce Cr(VI) I need to add Ferrous Sulfate and Lime to the water and let it sit awhile. It also recommended making sure 5 or 6 atoms of Fe(II) to one atom of Cr(VI) will allow the reduction to occur in timely fashion.
The chemical process is described thus:
Cr6+ + 3Fe2+ → Cr3+ + 3Fe3+
Cr3+ + 3 OH → Cr(OH)3
Fe3+ + 3 OH → Fe(OH)3
So in reading this I see that for every Chromium atom I need 6 Ferrous atoms, and I need three lime molecules for each Fe & Cr. The rough recipe then is 1Cr + 6FeSO4 + 21CaOH. This means for each 1/4 teaspoon of FeSO4 I also need to estimate about 1 teaspoon of lime for the mix. This is a slightly more lime than needed, but that should be fine. The estimate doesn't take into account any side reactions with the electrolyte itself.
From knowledge comes planning and from planning comes action. More to my line of thinking. So I know what the problem is (Cr(VI) is bad), and I know what the plan is(reduce it to Cr(III)). What's left? I need to buy the Ferrous Sulfate and Calcium Hydroxide and begin treating my waste water with it.
To solve this problem, I did some more digging and found The San Jose Scientific web site which sells lab grade ferrus sulfate in 100 gram and 500 gram increments for $8.95 or $21.50 plus shipping.
And here's a site to get the lime: hvchemical.com.
Lastly the MSDS sheet for the lime sold at hvchemical.com.
I've begun Cr(VI reduction studies on my waste water and subsequent articles record what I've done to date.
Hexavalent Chromium Articles
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