Nitric acid pickling of metals - where nitrogen oxide fumes are converted to nitric acid in an enclosed scrubbing system

摘要

Metals are pickled with nitric acid or its solns., and the NO and NO2 gases evolved are fed to a scrubbing liq. and converted to HNO3 in the presence of O2. The novelty is that the nitrous gases travel in a closed circuit contg. the scrubbing liq. and also supplied with an adjustable dose of O2 or a gas contg. O2 so that the NOx are removed. The O2 is pref. supplied as air, and the scrubbing liq. is pref. water or dil. HNO3, possibly with the addn. of absorbents or adsorbents for removing NOx. The pref. plant consists of a closed chamber contg. two pickling tanks and two rinsing tanks, and fitted with a fume extn. channel leading to the scrubbing liq. which is also located in the chamber. The chamber also has an air removal duct which causes air to be drawn into the chamber where it is used to aid the conversion of NOx into HNO3. Method is used e.g. for pickling brass or stainless steel. A simple and inexpensive pickling plant is obtd. which avoids environmental pollution.