Sodium dichromate wastewater treatment?
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This post was last edited by cdpulin on 2012-2-17 at 11:29. In industry, sodium dichromate is used for oxidation; after the reaction, washing is carried out to remove the chromium-containing inorganic salts. I would like to ask everyone, how should this kind of wastewater be treated? The wastewater is green in color; it seems that sodium dichromate has been reduced to trivalent chromium. However, I’m not sure whether this trivalent chromium exists as Cr3+ or as CrO2-. If it’s Cr3+, should liquid alkali be added to precipitate it? What if it’s CrO2-?
This post was last edited by The sea is my home on 2012-2-10 09:18. Thank you to the moderator for the answer; we use acetic acid as a solvent, and sodium dichromate is used to oxidize naphthene into naphthalic anhydride. Is Cr3+ produced as a result of the reaction?
In alkaline solutions, Cr(III) has strong reducibility. Therefore, in alkaline solutions, chromite can be oxidized by H2O2 or Na2O2 to form chromate(VI). 2CrO2 + 3H2O2 + 2OH- → 2CrO42- + 4H2O. 2CrO2 + 3Na2O2 + 2H2O → 2CrO42- + 6Na+ + 4OH-. In industrial applications, hydrogen peroxide is used; sodium peroxide is completely unsuitable for this purpose. It’s worth considering whether ozone can be used to carry out this reaction, so that chromium(VI) is formed and precipitates immediately. The prerequisite is to adjust the pH to an alkaline level using lime. I’m not sure if this approach can be used
I’m still interested in the moderator’s questions and am keeping a close eye on them
To correct the moderator: I’m not using acetic acid to reduce hexavalent chromium. The situation is as follows: We use acetic acid as a solvent in our products to oxidize naphthene to naphthalic anhydride using sodium dichromate; the sodium dichromate is partially reduced to trivalent chromium by the naphthalene. I have now found that sodium dichromate is reduced to Cr3+, as supported by textbooks.
If it’s trivalent chromium, then it’s simple: add an alkali to cause precipitation, forming a hydroxide precipitate, just like in the treatment of electroplating wastewater.
This should result in the formation of trivalent chromium ions, which can be precipitated by adjusting the pH value. However, both trivalent and hexavalent chromium are harmful substances; therefore, proper handling is necessary for both the water and the residue resulting from precipitation, to avoid environmental contamination.