My mate and I are neutralizing (what we think is) a 2.5 gallon carboy of 10% HNO3 and 1% HF solution. Reason: We want to pour this stuff down the drain and be done with it. We use calcium hydroxide because we didn't want to create any sodium fluoride (nasty stuff that it is) from using soda or Na-hydroxide and also because calcium carbonate is very insoluble (and too damn slow). Initially we slaked the lime in water and added it ever so slowly. Nothing happened. I wanted to at least get the satisfying fizz I get when I neutralize diluted nitric acid with soda; so I started dropping the lime powder in by the scoopful. I had my lab coat on - carboy in the fume hood, what could possibly go wrong? Still, no heat, no fizz (no carbon dioxide evolved I guess), nothing. We had to stir it up a bit to allow the solid powder to react but once pH was around 7 we called it good and started pouring it down the sink (with lots of excess water). It took 250 g of 95% calcium hydroxide to do the job. I think the reaction is this: 2HNO3 + Ca(OH)2 -> Ca(NO3)2 + 2H2O 2HF + Ca(OH)2 -> CaF2 + 2H2O Something doesn't feel right. I feel like we had a very uneventful reaction and, at least in theory, that we were "blessed" with fairly benign products. Is there a byproduct we are overlooking? Could the CaF and (dilute) calcium nitrate solution damage our plumbing? Probably our solution was more dilute than we thought (who can keep track of these things - details!). So many questions... EDIT *I did a stoichiometry and I guess the solution was more like 3-4% acid. Still - am I overlooking something that is going to cause my lab to explode?