Safe Dichromate Use

Dichromates are potentially hazardous substances. Care should be taken in handling them and the disposal of solutions containing dichromates. Ingestion and inhalation of dichromate dust is toxic and should be avoided. Putting bare skin in dichromate solutions can contribute to the development of an allergic sensitivity and should be avoided. The following are two methods of disposing of dichromate solutions. Chemically, the following procedure should work. Add used developer, or even better, a strong alkaline (baking soda, lye [sodium hydroxide], etc) to the dichromate solution until it becomes alkaline. Determine this by using litmus paper, which should be available from many sources, including Edmund Scientific, if you are in the US. Then filter the solution to remove the chromium III sludge. I was told that double layers of coffee filters should work, though lab grade filter paper would be best. (Do I need to say that you *don't* use you coffee maker for this step?). At that point, you should be able to dispose of the liquid which should be chromium free and give the filtered sludge to a place that handles hazardous waste. The trivalent chromium is less toxic (according to my sources) but I still wouldn't just toss it down the drain. - If the dichromate has been used in conjunction with a silver process (not an issue with gun printing, but with bleach and intensification processes it is) then you need to go the extra step of adding table salt (sodium chloride) after neutralizing the acidity but before filtering. Unfortunately, I don't have any information about how much sodium chloride to add. - Several people warned not to use thiosulate to neutralize the acidity of the dichromate solution as any silver in the dichromate won't then precipitate easily.

Information provided by: http://duke.usask.ca/~holtsg/photo/dichromate_disp_faq.html