Al, Your concern is well-placed. In many instances, the procedure you describe would not cause any dire consequences. BUT! There is always the exception (Murphy's Law) operating in the background. As you know, conc HNO3 is a pretty d____ good oxidizer and it WILL oxidize any poor,unfortunate reducing agent in an eager, not to say voracious, manner. When, one day, somebody uses the procedure described, the reducing agent will acquiesce a bit too readily and the resulting exotherm could very well be catastrophic. Jay A. Young ****************************** ----- Original Message ----- From:To: Sent: Tuesday, September 04, 2007 9:49 AM Subject: [DCHAS-L] nitric acid mixture with aqueous IPA Has anyone heard of the practice of mixing concentrated nitric acid (70%) waste contaminated by small amounts of organic polymer with aqueous isopropyl alcohol as a means to "passivate" the waste so it can be safely mixed with aqueous mildly acidic waste streams? One of my scientists recently described this "passivation" practice as routine during his experience, but I am sceptical about mixing the oxidizer with a flammable organic, even if the IPA is in aqueous solution. The procedure does not seem prudent to me, even under controlled conditions, and I have recommended against implementation. Here is the written procedure he provided: "The procedure for passivation of HNO3 is as follows. 600 ? 800 mL of 50% (weight) isopropanol in water is prepared in a 1-L beaker. The 50 ? 60 mL of depleted HNO3 is added slowly to avoid any sudden temperature rise. This addition is accompanied by an evolution of gas, and the contents of the beaker change color from a deep orange to a lemon yellow. Upon completion of the addition, the beaker is stirred or swirled gently to degas, then capped with a watch glass and allowed to stand and complete passivating and degassing overnight (at least 12 hours). In the morning, the mixture is again stirred to remove any traces of gas, and then is commingled with the normal laboratory waste stream." What are your thoughts regarding the safety of the proposed procedure, and do you have recommendations for the best nitric acid waste handling practices. Kind regards, Al Muehlhausen CIBA Vision Corporation Chemist/Certified Industrial Hygienist Health, Safety, and Environmental Officer JCE/JCA/BTI Office 678-415-4217 Cell 678-644-7026
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