Recovery of hydrofluoric acid and nitric acid from air vented from metal pickling plants

摘要

In a first stage hydrofluoric acid (HF) is removed from air by washing first with dilute HF solution and then with clean water. In a second stage, nitrogen oxide (NOx) is removed by treatment with an aqueous solution of nitric acid (HNO3) and hydrogen peroxide (H2O2). In the first washing in dilute HF, the dwell time of the air stream in the active zone is ca. 2.5 seconds. When washing with water the dwell time is ca. 1.5 seconds. The H2O2 is added to the liquid in the NOx washer immediately before the HNO3 enters the packed column. The amount added is about 1.8 times the stoichiometric requirement. The mean dwell time of the H2O2 in the absorption zone of the NOx washer is a maximum of 120 seconds.