Re: I have a question
I think formaldehyde is not the only chemical that needs attention in disposal among what's used in cyanotype and gum dichromate. If formaldehyde is for hardening gelatin, glutaraldehyde has easier regulatory standard and it is less harmful. Much smaller quantity of glutaraldehyde is required, meaning you can work with more dilute solution just as effectively, reducing potential hazard to the user. Disposal is also simple with glutaraldehyde. If the amount of formaldehyde is small, and the waste doesn't contain much of other compounds, I'd mix the waste solution with sodium percarbonate or oxiclean and let the mixture sit overnight at room temperature, and then dump it down the drain. Alternative is to mix the waste solution with sodium metabisulfite and dump it down the drain. The former treatment irreversibly breaks down the formaldehyde by oxidation, while the latter makes sulfite adduct of formaldehyde (which is reversible and can form formaldehyde again later upon dilution). Another option is to react aldehydes with a primary amino alcohol or something at pH around 10. Again, with formaldehyde the reaction is reversible. (But irreversible with glut.) Dichromate should be disposed after letting it go "stale" with the gum-mixed solution (either by light or dark reaction), or by mixing with metabisulfite. Better yet, give it to a licensed chemical hauler. Ferricyanide/ferrocyanide should be given to a licensed chemical hauler. Can't think of an easy way to deactivate their toxicity. -- Ryuji Suzuki Q. What is your real message? A. Keep a good head and always carry a light bulb. (Bob Dylan, Don't Look Back, 1965)
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