Waste hydrochloric acid from the pickling/descaling of carbon steel is typically reused by regenerating the acid through a chemical reaction with subsequent absorption/scrubbing/separating steps. The most common process is performed with high-temperature hydrolysis and absorption of hydrogen chloride in water and is based on the following chemical reactions:
4FeCl2 + 4H2O + O2 → 2Fe2O3 + 8HCl
2FeCl3 + 3H2O → Fe2O3 + 6HCl
Downstream of the roaster/reactor, the resulting products are fed into a separator that can include a VORSOMAX® cyclone mist eliminator. Next, an absorber column with INTALOX® ULTRA random packing and associated internals will remove residual chlorides from the gas, and final scrubber columns will trap any trace chlorides and iron before exhausting to the atmosphere. A DEMISTER® mist eliminator in the absorber and final scrubber columns are recommended to maintain water balance and keep liquids from emitting in the exhaust stream.